University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Soft drink

Classification: Beverage -> non alcoholic -> soft drink

Citations 49

"Non-spectrophotometric Methods For The Determination Of Vitamin C"
Anal. Chim. Acta 2000 Volume 417, Issue 1 Pages 1-14
S. P. Arya, M. Mahajan and P. Jain

Abstract: In view of the widespread use of Vitamin C, a large number of methods have been developed for quantifying Vitamin C contents in natural and fortified food samples and pharmaceuticals. It is therefore essential to assess these methods. Accordingly, this paper reviews non-spectrophotometric methods. 277 references.
Ascorbic acid Fluorescence LC Polarography Titrations Review

"Micro-scale Determination Of Glucose By Capillary Flow Injection With An Immobilized Enzyme Reactor"
Anal. Chim. Acta 1999 Volume 381, Issue 2-3 Pages 165-173
Yi Shi and Stanley R. Crouch

Abstract: Capillary flow injection was combined with an immobilized enzyme reactor to determine glucose in various juice and soft drink samples. Glucose oxidase was successfully immobilized onto open tubular capillary reactors by covalent bonding. The glucose oxidase catalyzed oxidation of glucose to gluconic acid and hydrogen peroxide was coupled with the Trinder reaction in which the hydrogen peroxide reacts to form a quinoneimine dye. The dye produce was monitored spectrophotometrically. Quantitative determinations showed improved sensitivity and reproducibility over determinations using conventional flow injection and glucose oxidase immobilized in a single bead string reactor. The use of capillary flow injection reduced reagent consumption to 320 µl/h, only 1.4% of that consumed with conventional flow injection.
Glucose Spectrophotometry Capillary Immobilized enzyme Reactor Manifold comparison Reagent consumption

"Flow Injection Analysis Capillary Electrophoresis System With Hydrodynamic Injection"
Anal. Chim. Acta 1999 Volume 378, Issue 1-3 Pages 55-62
Petr Kuban, Reza Pirmohammadi and Bo Karlberg

Abstract: A flow injection analysis-capillary electrophoresis (FIA-CE) system with hydrodynamic injection has been developed. Sample is injected in an electrolyte carrier solution pumped continuously in the FIA part of the system. The interface, connecting the FIA and the CE system moieties, accommodates one end of the separation capillary and a platinum electrode. The other capillary end and the second platinum electrode are immersed in a separate vial containing electrolyte solution. Carrier outflow from the interface is provided by a pinch valve. When the sample plug in the carrier passes the capillary end in the interface, the pinch valve is closed and a fraction of the sample is forced into the capillary. The high voltage supply, shut off during this sample introduction cycle, is then resumed and separation takes place in the capillary. Repeated sample injections in one electrophoretic run are facilitated. The overall repeatability, expressed as relative standard deviation for eight consecutive injections of 50 mg L-1, was about 3%. Quantitative analyzes can be accomplished ~5 times faster than that obtained using conventional CE instrumentation. The developed instrument was used to determine common inorganic cations (Na+, K+, Ca2+, Mg2+) in water and soft drink samples.
Sodium Potassium Calcium Magnesium Electrophoresis Hydrodynamic injection Interface

"Sheath-flow Fourier Transform Infrared Spectrometry For The Simultaneous Determination Of Citric, Malic And Tartaric Acids In Soft Drinks"
Anal. Chim. Acta 2000 Volume 417, Issue 1 Pages 41-50
María José Ayora-Cañada and Bernhard Lendl

Abstract: A new approach for the determination of organic acids in soft drinks based on pH modulation and Fourier transform infrared spectroscopic detection is presented. The analytical readout was taken from the spectral changes induced by the pH change of the sample. The pH modulation was carried out in a novel sheath-flow cell which was connected to a sequential injection analysis system. The sheath-flow cell comprised three stream lines flowing adjacent to each other in a strongly laminar fashion, The sample (pH similar to 9) was introduced in the central channel whereas reagent (hydrochloric acid) was introduced in the outer channels. As a consequence of the laminar flow profile, hardly any mixing between the stream lines was observed while maintaining the flow, hence allowing the measurement of the sample spectrum at alkaline pH (similar to 9). Upon stopping the flow, diffusion of protons from the outer stream lines into the central line occurred resulting in a complete protonation of the analyte (pH similar to 2). The spectral changes were calculated and the region between 1400 and 1180 cm-1 used to set-up a partial least squares (PLS) calibration model. For the PLS model only standards containing the analytes but no matrix molecules were used. By evaluation of the spectral changes induced by the pH modulation the PLS model could successfully be applied to test samples containing sugars as well as to natural soft drinks.
Citric acid l-Malic acid Tartaric acid Spectrophotometry Sequential injection Sheath flow Partial least squares Stopped-flow

"Sequential Injection Fourier Transform Infrared Spectroscopy For The Simultaneous Determination Of Organic Acids And Sugars In Soft Drinks Employing Automated Solid Phase Extraction"
Anal. Chim. Acta 2000 Volume 422, Issue 1 Pages 63-69
Hai LeThanh and Bernhard Lendl

Abstract: A fully automated method for the rapid determination of organic acids (citric-, malic- and tartaric acid) and sugars (glucose, fructose, and sucrose) in soft drinks by sequential injection Fourier transform infrared (FTIR) spectroscopy is presented. A convective interaction media (CIM) disc carrying quaternary amino moieties was added as a solid phase extraction column to the flow system. Upon injection of a sample the organic acids were completely retained on the CIM disc whereas sugars passed to the flow cell. The organic acids were subsequently eluted by injection of an alkaline (pH 8.5) 1 M sodium chloride solution and recorded in their fully deprotonated form as a second flow injection peak. In both cases, the FTIR spectra corresponding to the peak maxima were selected for data evaluation. Two partial least squares models, one for sugars and the other for organic acids, were constructed based on the analysis of standards containing all six analytes. The developed method was applied to natural samples yielding results which were in good agreement with those obtained by an external reference method (enzymatic test kits). Deviations in the results were 3.4. and 4.1% for citric and malic acid and ranged from 4.7-5.1% for the sugars. The developed method is characterized by its short analysis time, experimental simplicity and its potential applications in routine analysis and process control.
Citric acid l-Malic acid Tartaric acid Glucose Fructose Sucrose Spectrophotometry Sequential injection Preconcentration Method comparison Solid phase extraction

"Dual Electrode Signal-subtracted Biosensor For Simultaneous Flow Injection Determination Of Sucrose And Glucose"
Anal. Chim. Acta 1999 Volume 380, Issue 1 Pages 7-15
Werasak Surareungchai, Supinda Worasing, Pornpimol Sritongkum, Morakot Tanticharoen and Krissanapong Kirtikara

Abstract: A multi-enzyme electrode obtained by a two-step immobilization of the enzymes glucose oxidase, mutarotase and invertase was developed for the determination of sucrose. Glucose oxidase was entrapped in a poly-1,3-diaminobenzene film on a platinum electrode by electrochemical polymerization and a combination of mutarotase and invertase was cross-linked over the electrode via bovine serum albumin and glutaraldehyde. The sucrose concentration was determined from hydrogen peroxide oxidation at +0.7 V vs. Ag/AgCl. This immobilization method minimized interference from ascorbic acid. A second electrode, for glucose only, was constructed containing inactive invertase. This gave an almost identical glucose response to the sucrose sensor and hence could be used for signal subtraction. In this manner, sucrose could be determined in the presence of glucose at higher concentrations. The influence of enzyme content, pH, temperature, and optimum operational conditions for use in a flow injection analysis (FIA) system were determined. When used in FIA, the sensor responded to sucrose in the range 1-300 mmol l-1. The sensor was stable for 15 h of continuous use (150 assays) and retained 70% activity after 30 days. When used to analyze the sucrose and glucose contents in a number of different soft drinks, the sensor showed good agreement with the standard liquid chromatography (LC) method.
Sucrose Glucose Amperometry Immobilized enzyme Optimization Method comparison Interferences

"Amperometric Determination Of Glucose In Undiluted Food Samples"
Anal. Chim. Acta 1991 Volume 242, Issue 1 Pages 91-98
A. Amine and G. J. Patriarche, G. Marrazza and M. Mascini

Abstract: A sensor is described for determination of glucose. It involves glucose oxidase immobilized on to a cellulose acetate membrane through glutaraldehyde bonding. The membrane is placed over the Pt electrode of a H2O2 sensor. By placing a silanized polycarbonate membrane over the enzyme layer, the rectilinear range of the calibration graph was extended to higher concentration. The variation in response was studied as a function of pore size of the polycarbonate membrane. Response was approximately even from pH 4 to 8. The sensor was used in a flow injection system to determine 1 M glucose in soft drinks at a sampling rate of 60 h-1, and without the need for sample dilution. The coefficient of variation was 1.8% (n = 16) for 0.4 M glucose.
Glucose Amperometry Electrode Electrode Immobilized enzyme pH Cellulose acetate

"Flow Injection System For The Fluorimetric Determination Of Fructose With An Immobilized Mannitol Dehydrogenase Reactor"
Anal. Chim. Acta 1991 Volume 243, Issue 2 Pages 183-186
Nobutoshi Kiba, Yukari Inoue and Motohisa Furusawa

Abstract: Sample solution was injected into a carrier stream of water (0.5 mL min-1), which was merged with 10, 100 or 200 µM-NADH in 0.2 M phosphate buffer (pH 7.0; 0.5 mL min-1) for reaction in a reaction column (5 cm x 4 mm) of mannitol dehydrogenase immobilized on poly(vinyl alcohol) beads (prep. described) at 40°C. The decrease in NADH was monitored fluorimetrically at 465 nm (excitation at 340 nm). Calibration graphs were rectilinear for 3 to 30, 15 to 150 or 60 to 600 µM-fructose (I) for 10, 50 and 200 µM-NADH, respectively; the detection limit was 1 µM-I for 10 µM-NADH. Seventeen carbohydrates did not interfere; D-mannitol did interfere. The sampling rate was 30 h-1. The column retained >80% of its activity after continuous use over 2 months. The method was applied in the determination of I in fruit juice, wine and cola.
Fructose Fluorescence Buffer Column Heated reaction Immobilized enzyme Interferences

"Monitoring Of Reducing Sugars By Flow Injection Analysis Using P-hydroxybenzoic Acid Hydrazide"
Anal. Chim. Acta 1994 Volume 285, Issue 1 Pages 1-8
Peter Hartmann, Stephen J. Haswell*, Manfred Grasserbauer

Abstract: Wine, beer, Lucozade and cola drinks were diluted with or without decolorization and banana, apple and kiwi fruit were homogenized, sonicated and filtered and injected into a water carrier stream. The solution merged with a pre-mixed stream of NaOH and p-hydroxybenzoic acid hydrazide (PAHBAH), passed through a reaction coil at 90-95°C and the absorbance measured at 410 nm. The concentrations and flow rates of NaOH and PAHBAH (listed) were optimized for three systems investigated: System A, non-catalyzed for glucose at high concentrations (0.025-1.5 g/l); System B, Bi(III) catalyzed for glucose at low concentration (4-40 mg/l); and System C, non-catalyzed for glucose and fructose (0.08-0.6 g/l). Standard calibration graphs (peak height) were linear (r = 0.9999) for the above concentration ranges and linear for fruit and beverages over the calibration range for System C with a RSD of 2%. Interference due to Ca(II) increased dramatically above 2 mM for System C and above 10 mM for System A and 20 ppm of glucose standard.
Fructose Glucose Spectrophotometry Interferences

"Flow Injection Chemiluminometric Determination Of Ascorbic Acid Based On Its Sensitized Photo-oxidation"
Anal. Chim. Acta 1995 Volume 308, Issue 1-3 Pages 299-307
Tomás Pérez-Ruíz*, Carmen Martínez-Lozano and Antonio Sanz

Abstract: The chemiluminescent reaction between lucigenin and the photo-oxidation products of ascorbic acid was utilized for the determination of ascorbic acid. The FIA system allowed 275 µL sample solution and 215 µL 1 mM toluidine blue (as photosensitizer) to be injected simultaneously into two phosphate buffer streams (both at 1.1 ml/min) at pH 3. The streams were merged before passing through a photoreactor equipped with a reaction coil (2 m x 0.5 mm i.d.) and a W halogen lamp. The stream was merged with streams of 0.1 mM lucigenin (1.1 ml/min) and 0.7 M KOH (4.1 ml/min). The three merged zones travelled 6 cm (0.5 mm i.d.) to the detector cell were the chemiluminescence was measured with a photomultiplier tube. The calibration graph was linear for 1.1 nM-0.3 mM ascorbic acid and the detection limit was 0.2 nM. The RSD (n = 11) for the determination of 0.2 mM, 20 µM and 0.7 µM-ascorbic acid were 0.43, 1.65 and 1.22%, respectively. The sampling frequency was 80 samples/h. The method can be applied to the determination of ascorbic acid in pharmaceutical preparations, fruit juices, soft drinks and blood serum.
Ascorbic acid Chemiluminescence Photochemistry

"Determination Of Sucrose Using Sucrose Phosphorylase In A Flow Injection System"
Anal. Chim. Acta 1997 Volume 337, Issue 1 Pages 107-111
Mamie Kogure, Hisakazu Mori*, Hisano Ariki, Chika Kojima and Haruhiko Yamamoto

Abstract: The fluorimetric determination of sucrose was accomplished using a single-channel flow manifold incorporating an enzyme reactor (8 cm x 2 mm i.d.) prepared by immobilizing 5 iu sucrose phosphorylase/11 iu phosphoglucomutase/4 iu glucose 6-phosphate dehydrogenase on to 0.4 g aminopropyl glass beads (200-400 mesh, 500 angstrom pore size). The determination was carried out by injecting a sample (50 µL) into a carrier stream at a flow rate of 0.4 ml/min containing 30 mM KH2PO4/3 mM MgCl2/1 mM NADP+/0.05 mM glucose 1,6-diphosphate in 200 mM PIPES buffer of pH 7.5. The stream was propelled through the enzyme reactor at 30°C and into the detection cell (12 µL volume); detection was at 460 nm (excitation at 340 nm). The calibration graph was linear from 0.1-200 µM sucrose; the detection limit was 0.1 µM. The method was applied to the determination of sucrose in soft drinks. The samples were diluted 1000-fold prior to analysis and the phosphate concentration in the carrier stream was increased to 100 mM to reduce the inhibiting effects of fructose. The detection limit was 0.2 µM sucrose. RSD was 1.06% (n = 5) for 50 µM-sucrose.
Sucrose Fluorescence Immobilized enzyme Glass beads Heated reaction

"Determination Of Ascorbic Acid In Soft Drinks, Preserved Fruit Juices And Pharmaceuticals By Flow Injection Spectrophotometry: Matrix Absorbance Correction By Treatment With Sodium Hydroxide"
Talanta 1995 Volume 42, Issue 6 Pages 779-787
Archana Jain, Anupama Chaurasia and Krishna K. Verma*

Abstract: Schematic diagrams of two flow injection systems for the spectrophotometric determination of ascorbic acid at 245 nm are presented. On treatment with NaOH, a fraction of the ascorbic acid was decomposed into substances which do not absorb in the UV region, and the decrease in signal, which was directly related to the amount of ascorbic acid present, was measured. The calibration graph was linear from 1-25 and 1-50 µg/ml using the two methods. Corresponding detection limits were 0.5 and 0.2 µg/ml, respectively. RSD for 1 µg/ml were 2.5 and 1.8%, respectively, (n = 6) and the sampling throughput was 30/h. The methods permitted the use of 6 µg/ml of 2-mercaptoethanol as an anti-oxidant and stabilizer for ascorbic acid. Recoveries were 101%. Results compared well with those from standard methods.
Ascorbic acid Spectrophotometry Method comparison Standard method

"Online Coupling Of Gas Diffusion To Capillary Electrophoresis"
Talanta 1998 Volume 45, Issue 3 Pages 477-484
Petr Kuban and Bo Karlberg*

Abstract: Online gas diffusion has been coupled to a capillary electrophoresis system (CE) via a specially designed interface. The sample is merged with a modifying solution, e.g., a strong acid, in a flow system to transform the analytes of interest into their respective gaseous forms. These transformed, gaseous analytes permeate through a PTFE membrane into an acceptor stream comprising of a tris-buffer. The continuously flowing acceptor stream is led into an injector forming an integrated part of a flow injection analysis (FIA) system. The sample receiving carrier stream in the FIA system, a chromate buffer, brings the sample, 50 µl, to the FIA-CE interface into which one end of a separation capillary has been inserted. A small portion of the injected sample enters the capillary (electrokinetic injection) and separation takes place. A UV detector is placed at the other capillary end and a run potential of 25 kV is applied to two platinum electrodes positioned in the flow system. Multiple sample injections can be performed in one uninterrupted electrophoretic run. A typical sampling frequency is 15 h-1; each run may result in quantitation of at least five anions. The overall repeatability is in the range 1.8-3.6% (RSD). The technique has been applied to the analysis of real samples such as soft drinks, vinegar and wine. Selective discrimination of anions which are unable to form volatile species is accomplished. No off-line sample pre-treatment is needed.
Anions Electrophoresis Gas diffusion Interface Teflon membrane Volatile generation

"Indirect Determination Of Cyclamate By An Online Continuous Precipitation-dissolution Flow System"
Talanta 1998 Volume 45, Issue 6 Pages 1115-1122
M. C. Yebra* and P. Bermejo

Abstract: A continuous-flow procedure is proposed for the indirect determination of sodium cyclamate by an atomic absorption spectrometric method in artificial sweeteners mixtures and soft drinks. Sulfamic group is oxidized to sulfate and it is continuously pptd. with lead ion in a flow manifold. The lead sulfate formed is retained on a filter, washed with diluted ethanol and dissolved in ammonium acetate for online atomic absorption determination of lead, the amt. of which in the ppt. is proportional to that of cyclamate in the sample. The proposed method allows the determination of sodium cyclamate in the range 1-90 µg mL-1 with a relative standard deviation of 3.1% at a rate of ~35 samples per h. The 3s detection limit is 0.25 µg mL-1. The method is very selective, no compounds normally found in the analyzed samples and other artificial sweeteners had any effect on the determination of cyclamate.
Cyclamate Spectrophotometry Precipitation Indirect Interferences

"Graphite Paste Based Enzymatic Glucose Electrode For Flow Injection Analysis"
Analyst 1988 Volume 113, Issue 5 Pages 735-738
Wojciech Matuszewski and Marek Trojanowicz

Abstract: The electrode was prepared from a mixture of graphite powder, silicone oil and glucose oxidase, and was used with a wall-jet flow-through cell at +0.9 V vs. Ag - AgCl. Response was rectilinear up to 30 mM glucose (40 µL injection) with a detection limit, for 750 µL injections, of 20 µM in 0.1 M phosphate buffer (pH 6.5) at 1 mL min-1. In the analysis of soft drinks, recoveries of glucose added at the 2 to 20 mM level were between 91.8 and 105.1%. Up to 120 samples h-1 could be analyzed.
Glucose Amperometry Electrode Electrode Calibration Optimization

"Flow Injection Chemiluminometric Determination Of Citrate Based On A Photochemical Reaction"
Analyst 1995 Volume 120, Issue 2 Pages 471-475
Tomás Pérez-Ruiz, Carmen Martínez-Lozano, Virginia Tomás and Otilia Val

Abstract: Sample (235 µL) was injected into a stream of 0.5 mM Fe(III) in 0.01 M H2SO4 and 0.01% poly(vinyl alcohol) and transported to a coiled photochemical reactor (250 cm x 0.5 mm i.d.). When the sample zone reached the reactor, the flow was stopped and irradiation was carried out for 60 s. The flow was then resumed and the solution was merged with a buffered luminol stream, produced by previously mixing a stream of 1 M borate buffer of pH 11 with a stream of 0.5 mM luminol. The chemiluminescence generated was measured. A diagram of the manifold used is given. The total flow rate was 12 ml/min. The calibration graph was linear from 0.2-100 µM-citrate. The RSD (n = 10) for 5.5 and 0.55 µM-citrate were 0.45% and 1.5%, respectively. The throughput was 30 samples/h. Possible interferences were investigated. The method was applied to pharmaceuticals and soft drinks. The results agreed with those obtained by an enzymatic method.
Citrate Chemiluminescence Photochemistry Stopped-flow Interferences

"Flow Injection Spectrophotometric Determination Of Cyclamate In Low Calorie Soft Drinks And Sweeteners"
Analyst 1995 Volume 120, Issue 7 Pages 2009-2012
Sandro Thomaz Gouveia, Orlando Fatibello-Filho and Joaquim de Araújo Nóbrega

Abstract: The soft drink was agitated for 15 min to remove CO2. Ascorbic acid, if present, was oxidized by passing air through the drink for 20 min. A portion (5-7 ml) of the soft drink was then diluted to 25 mL with water and adjusted to 0.1 M H3PO4. Liquid sweetener (0.5 ml) was diluted to 500 mL with 0.1 M H3PO4. The sample was passed through an alumina column (5 cm x 3.5 mm i.d.) before injection into carrier stream (2.11 ml/min) of 0.1 M H3PO4. The solution was merged with a reagent stream (1.14 ml/min) of 45 µM-nitrite and then passed through a tubular reactor (360 cm) before merging with a colorimetric reagent stream (1.14 ml/min) of 1% sulfanilamide and 0.05% N-1-naphthylethylenediamine dichloride in 0.5 M H3PO4. The mixture passed through a second tubular reactor (100 cm), then through a de-bubbler to remove N2 after which the absorbance was measured at 535 nm. A diagram of the manifold used is given. The detection limit was 30 µM of cyclamate, the RSD (n = 12) was 0.5% and recoveries were 97-102.2%. The throughput was 24 samples/h. The results agreed with those obtained by bi-amperometric titration.
Cyclamate Spectrophotometry Alumina Method comparison

"Biamperometric Titration And Flow Injection Determination Of Cyclamate In Low-calorie Products"
Analyst 1995 Volume 120, Issue 9 Pages 2407-2412
Orlando Fatibello-Filho, Milton Duffles Capelato and Silvana Aparecida Calafatti

Abstract: Two methods for cyclamate (I) determination are described. In the titrimetric method, a portion (5 ml) of the sample in 1 M H3PO4 was titrated with 0.1 M NaNO2, with biamperometric detection at two Pt electrodes polarized at +0.7 V vs. Ag/AgCl. In the flow injection (FI) method, a portion (0.25 ml) of the sample in 1 M H3PO4 was injected into a carrier stream (2.96 ml/min) of 1 M H3PO4 containing 0.001% Triton X-100. The sample/carrier stream was merged with a reagent stream (0.77 ml/min) of 0.1 M NaNO2. The mixture was passed through a 50 cm coiled reactor before biamperometric detection of two Pt electrodes polarized at +0.7 V vs. Ag/AgCl. For the titrimetric method, the calibration graph was linear from 10 to 60 mM I, the detection limit was 1.3 mM and the RSD (n = 9) was 1%. Recoveries of I were 97.6-102.5%. For the FI method, the calibration graph was linear from 5 to 40 mM I, the detection limit was 2.5 mM and the RSD (n = 10) was 1.2%. Recoveries of I were 97.8-102.4%. The throughput was 90 samples/h. The methods were applied to various low-calorie products, viz., sweeteners, puddings, jellies and soft drinks.
Cyclamate Biamperometry Electrode Surfactant Triton X Titrations

"Flow Injection Fluorimetric Determination Of Ascorbic Acid Based On Its Photooxidation By Thionine Blue"
Analyst 1997 Volume 122, Issue 2 Pages 115-118
Tomás Pérez-Ruiz, Carmen Martínez-Lozano, Virginia Tomás and Ciriaco Sidrach

Abstract: The photooxidation of ascorbic acid sensitized by Thionine Blue was studied. The Leucothionine Blue formed during the reaction is highly fluorescent. A flow injection method using merging zones is proposed for the determination of ascorbic acid over a concentration range from 8 x 10^-7 to 5 x 10^-5 mol L-1 with a throughout of 80 samples per h. The method was used for the simple and rapid determination of ascorbic acid in pharmaceuticals, fruit juices and soft drinks. A sample (250 µL) and 150 µL 80 µM-Thionine blue were simultaneously injected into two carrier streams (each flowing at 0.6 ml/min) of 0.2 M phosphate buffer of pH 3 then synchronously merged. The mixture was passed through a 200 cm PTFE reactor where it was irradiated for 20 s. Fluorescence intensity was then measured at 464 nm (excitation at 340 nm). A diagram of the manifold used is given. The calibration graph was linear from 0.14-8.8 µg/ml ascorbic acid. The throughput was 80 samples/h. The method was applied to pharmaceuticals, fruit juices and soft drinks. The results obtained agreed with those obtained by the standard 2,6-dichlorophenolindophenol method.
Ascorbic acid Fluorescence Redox Method comparison Standard method Buffer Merging zones

"Optosensor For Cinchona Alkaloids With C18 Silica Gel As A Substrate"
Analyst 1997 Volume 122, Issue 3 Pages 283-285
Zhilong Gong, Zhujun Zhang and Xiaofeng Yang

Abstract: A sample was mixed with 5 mL 0.5 M H2SO4 then diluted to 25 mL with water. A portion (2 ml) was injected into a carrier stream of 0.1 M H2SO4 at a flow rate of 1 ml/min and passed through a flow cell packed with C18 silica gel. The fluorescence intensity of the alkaloid(s) retained on the silica gel was measured at 430 nm (excitation at 346 nm) for quinine (I) and quinidine (II) and at 436 nm (excitation at 363 nm) for cinchonine (III) and cinchonidine (IV). The calibration graphs were linear from 5-20 000 ng/ml I and II and from 200-20 000 ng/ml III and IV. The detection limits were 2.3 ng/ml for I and II and 31.6 ng/ml for III and IV. RSD were 0.9% at the 20 ng/ml level of I and II, and 1.1% at the 4 µg/ml level of III and IV (n = 7). Sample throughput was 10 samples/h. The method was successfully applied to the determination of I in pharmaceuticals and soft drinks. A flow-through optosensor for cinchona alkaloids with C18 silica gel as a substrate is proposed. The sensor is developed in conjunction with a flow injection analysis system and is based on the retention of the cinchona alkaloids on a C18 column and the enhancement of their fluorescence. The analytical performance characteristics of the proposed sensor for the detection and quantification of these alkaloids were as follows: the detection limits of quinine, cinchonine, quinidine and cinchonidine were 2.3, 31.6, 2.3 and 31.6 ng mL-1, respectively, with relative standard deviations of 0.9% for quinine and quinidine (20 ng mL-1, n = 7) and 1.1% for cinchonine and cinchonidine (4.0 µg mL-1, n =7), respectively. Most of the common species did not interfere. The recommended method has been successfully tested for determination of quinine in pharmaceutical preparations and soft drinks.
Alkaloids Quinine Cinchonine Quinidine Cinchonidine Fluorescence Sensor C18 Column Detection limit Selectivity Silica gel Interferences Optosensing

"Modulation Of The PH In The Determination Of Phosphate With Flow Injection And Fourier Transform Infrared Detection"
Analyst 1997 Volume 122, Issue 6 Pages 525-530
R. Vonach, B. Lendl and R. Kellner

Abstract: A sample (1.5 ml) was injected into a carrier stream at a flow rate of 1.1 ml/min (carrier not specified) and mixed with a stream of acetate buffer at a flow rate of 0.055 ml/min to adjust the pH to 5. The FTIR spectrum (reference spectrum) was recorded from 900-1300 cm-1. A second portion (1.5 ml) of the sample was then injected into the carrier stream and mixed with 100 µL of either carbonate buffer (method A) or NaOH solution (method B) to adjust the pH to 10 or >13, respectively. The FTIR spectrum (sample spectrum) was again recorded. Phosphate was quantified from the difference between the reference and sample spectra, using the peaks at 1085-1095 and 999-1009 cm-1 for methods A and B, respectively. The calibration graph was linear from 0.1-1 g/l phosphate. The throughput was 60 samples/h. The methods were applied to the analysis of soft drinks (results presented).
Phosphate Spectrophotometry pH gradient Buffer

"Sensitive Method For Determination Of Lead By Potassium Dichromate-lactic Acid Hydride Generation Inductively Coupled Plasma Atomic-emission Spectrometry"
J. Anal. At. Spectrom. 1993 Volume 8, Issue 6 Pages 821-825
M. C. Valdés-Hevia y Temprano, M. R. Fernández de la Campa and Alfredo Sanz-Medel

Abstract: For the continuous-flow determination of Pb as PbH4 by hydride-generation ICP-AES, generation with use of 0.3% K2Cr2O7/3% lactic acid and 5% NaBH4 in 0.1% NaOH as reagents was chosen and optimization of the detection limit was studied. With use of a r.f. forward power of 700 W and detection at 220.353 nm, a detection limit of 2 ng/ml of Pb was obtained with an RSD of 1.3% at 50 ng/ml. The cited method was applied to the determination of Pb in soft-drinks, sediment and lichen reference materials. Soft drinks, containing 11-66 ng/ml, were injected directly and Pb was determined with the aid of a standard-additions procedure.
Lead Spectrophotometry Reference material Optimization Standard additions calibration Volatile generation

"Chemiluminescence Flow Injection Analysis Determination Of Sucrose Using Enzymatic Conversion And A Microporous Membrane Flow Cell"
Anal. Chem. 1986 Volume 58, Issue 1 Pages 116-119
Cathy A. Koerner and Timothy A. Nieman

Abstract: Sucrose is initially converted into glucose by β-fructofuranosidase and aldose-1-epimerase (immobilized on controlled-porosity glass) in 0.1 M phthalate buffer (pH 5.65). The solution is then mixed with a stream containing luminol, haemin and horse-radish peroxidase in 0.1 M Tris (pH 10.5) and passes finally into a flow cell where it mixes with glucose oxidase in 0.1 M acetate buffer (pH 5). The H2O2 formed reacts with the luminol to produce chemiluminescence. The working range is 5 µM to 1 mM and analysis time is 2 min. For detection of sucrose in food products, a separate determination of glucose or a catalytic destruction of glucose in the sample is necessary to distinguish glucose originally present from that formed from sucrose.
Sucrose Glucose Chemiluminescence Immobilized enzyme Microporous membrane Flowcell

"Simultaneous Determination Of Glucose, Fructose, And Sucrose In Mixtures By Amperometric Flow Injection Analysis With Immobilized Enzyme Reactors"
Anal. Chem. 1988 Volume 60, Issue 2 Pages 147-151
Kiyoshi Matsumoto, Hideaki Kamikado, Hiroaki Matsubara, and Yutaka Osajima

Abstract: The flow injection system (described) incorporated three immobilized-enzyme reactors (prep. described), one each for glucose(I), fructose(II) and sucrose(III), in parallel, a I-eliminating enzyme reactor (placed in series with the III reactor), and a multi-channel flow-through amperometric detector. Sample solution was injected into the system by an injection valve and into each of the three carrier streams by valve switching. For I determination, the carrier stream was 0.1 M phosphate buffer (pH 6.0), the reactor contained immobilized I oxidase, and the H2O2 produced was determined at +0.65 V vs. Ag - AgCl. For II determination, the carrier stream was McIlvaine buffer (pH 5.0) containing 6 mM K3Fe(CN)6 and 0.1% of Triton X-100, the reactor contained immobilized II 5-dehydrogenase, and the Fe(CN)64- formed was determined at +0.385 V vs. Ag - AgCl. For III determination, the carrier stream was 0.1 M phosphate buffer (pH 7.0), the reactor contained immobilized β-fructofuranosidase, aldose 1-epimerase and I oxidase, and the H2O2 formed was determined as before. The coefficient of variation (n = 10) for 1 mM I, -II and -III were 1.8, 1.8 and 1.6%, respectively. Calibration graphs (response vs. concentration.) were rectilinear from 0.02 to 1 mM for I, II and III. The method was applied to food samples.
Glucose Fructose Sucrose Amperometry Immobilized enzyme Multicomponent Triton X Valve Surfactant

"Determination Of Citric Acid By Means Of Competitive Complex Formation In A Flow Injection System"
Microchim. Acta 1994 Volume 113, Issue 3-6 Pages 203-210
Achim Krug and Robert Kellner

Abstract: Citric acid (100 µL; I) in a KCl/HCl buffer carrier (concentration not given) at pH 2 was mixed with 2.6 mM [Fe(SCN)2]+ (2.4 ml/min), passed through a reaction coil (50 cm x 0.97 mm i.d.) and the absorbance measured at 460 nm. The calibration graph was linear from 1-8 mM I. The RSD (n = 8) were 2.5% and 1.6% for 4 mM I and 8 mM I, respectively. Analysis capacity was 180 samples/h. Other organic species, including oxalate, tartrate, EDTA and inorganic phosphate, which form complexes with [Fe(SCN)2]+ can be determined and conversely interfere with citrate determination. The procedure was applied to the determination of citrate in a number of non-alcoholic soft drinks (listed) which contained little or no other complexing agents. Citrate levels measured by this procedure were in most cases higher (deviation -4.9% and 16.6%) than those obtained with an appropriate enzymatic procedure (described). This was probably due to interference from other organic acids.
Citric acid Spectrophotometry Interferences

"Determination Of Sucrose By Flow Injection Analysis With Fourier Transform Infrared Detection"
Microchim. Acta 1995 Volume 119, Issue 1-2 Pages 73-79
Bernhard Lendl and Robert Kellner

Abstract: The cited analysis was based on the invertase-catalyzed cleavage of sucrose (I) to α-D-glucose and β-D-fructose in a reactor (3 cm x 3 mm i.d.) packed with invertase immobilized on aminopropylated controlled pore glass using glutaraldehyde (details given). A manifold (diagram given) incorporating two internally-coupled injection valves enabled FTIR spectra of the unreacted and reacted sample to be obtained. Sample (75 µL) was injected into 0.2 M acetate buffer of pH 4.2 (2.1 ml/min) and FTIR spectra were recorded continuously at 8 cm-1 resolution with use of Brucker OPUS GC-IR software and the difference spectrum of the unreacted and reacted sample was obtained. The difference in absorption at 998 and 1038 cm-1 was used to determine I. The calibration graph was linear for 10^-100 mM I. No detection limit or RSD is given. Sample throughput was 45/h. The method was applied to soft drinks.
Sucrose Spectrophotometry Immobilized enzyme Controlled pore glass

"Flow Injection Spectrophotometric Determination Of Oxalate, Citrate And Tartrate Based On Photochemical Reactions"
Anal. Lett. 1998 Volume 31, Issue 8 Pages 1413-1427
Tomás Pérez-Ruiz; Carmen Martínez Lozano; Virginia Tomás; Antonio Sanz

Abstract: A flow injection configuration for the spectrophotometric determination of oxalate, citrate and tartrate is proposed. The procedure is based on the photochem. decomposition of the complexes formed between iron(III) and these anions. The iron(II) produced in the photochem. reactions was detected by measuring the absorbance after complexation with ferrozine (λmax=562 nm). Linear calibration graphs were obtained over the concentration. ranges 5.0 x 10^-6 - 1.0 x 10^-4 M, 8 x 10^-6 - 1.8 x 10^-4 M and 1.0 x 10^-6 - 2 x 10^-5 M for oxalate, citrate and tartrate, respectively. The relative standard deviations at the 1 x 10^-5 M concentration. level were within the range 1.29 - 1.47%. The sampling frequency was about 40 samples/h. The usefulness of the method was tested in the determination of oxalate in urine and spinach, of citrate in pharmaceuticals and soft drinks and of tartrate in pharmaceuticals. For the determination of oxalate in urine samples a prior separation of the analyte by precipitation with calcium chloride is recommended.
Oxalate Citrate Tartrate ion Spectrophotometry Photochemistry Complexation

"Simultaneous Determination Of Glucose And Sucrose By A Dual-working-electrode Multi-enzyme Sensor Flow Injection System"
Electroanalysis 1994 Volume 6, Issue 5-6 Pages 361-367
Xianen Zhang, Garry A. Rechnitz

Abstract: Two working electrodes, each consisting of carbon paste covered with a cross-linked enzyme membrane, were mounted in a flow injection flow cell (diagram presented). The membrane of the upstream electrode was prepared from glucose oxidase and that of the downstream electrode from glucose oxidase with an outer layer of β-fructofuranosidase/aldose 1-epimerase. A layer of cross-linked catalase was formed on the wall of the flow cell between the two electrode membranes. A 50 µL sample was injected into a carrier stream of phosphate buffer solution (pH 6.8); both electrodes were maintained at 0.9 V vs. Ag/AgCl, so that glucose was detected at the upstream and glucose plus sucrose at the downstream electrode. The method of calculating the two concentrations is described. When the method was applied to Cola beverages, the relative errors for glucose and sucrose were ~3 and ~4%, respectively.
Glucose Sucrose Amperometry Electrode Electrode Electrode Sensor

"Amperometric Differential Determination Of Ascorbic Acid In Beverages And Vitamin C Tablets Using A Flow Cell Containing An Array Of Gold Microelectrodes Modified With Palladium"
Electroanalysis 1998 Volume 10, Issue 13 Pages 887-890
Renato C. Matos, Márcio A. Augelli, Jairo J. Pedrotti, Claudimir L. Lago, Lúcio Angnes

Abstract: A simple and attractive method for quantification of ascorbic acid (AA) in beers, soda, natural juices, and commercial vitamin C tablets was developed by combining flow injection analysis and amperometric detection. An array of Au microelectrodes electrochemically modified by deposition of Pd was employed as working electrode which was almost unaffected by fouling effects. AA was quantified in beverages and vitamin tablets using amperometric differential measurements. The method is based on three steps involving the flow injection of the sample plus a standard addition of AA, of the pure sample, and of the enzymatically-treated sample. The enzymatic treatment was carried out with Cucumis sativus tissue, which is a rich source of ascorbate oxidase, at pH 7. The calibration plots for freshly prepared AA standards were linear in the concentration. range of 0.18-1.8 mg/L with a relative standard deviation (RSD) <1%, while for real samples the deviations were 2.7-8.9%.
Ascorbic acid Amperometry Electrode Electrode Differential detection Standard additions calibration Enzyme

"Online Dialysis With High Performance Liquid Chromatography For The Automated Preparation And Analysis Of Sugars And Organic Acids In Foods And Beverages"
J. Chromatogr. A 1995 Volume 705, Issue 2 Pages 195-203
Eric V&eacute;rette*, Fran&ccedil;ois Qian and Fabrice Mangani

Abstract: A quick, simple and robust technique is described for on-line clean-up and analysis of raw liquid food samples containing complex matrices such as dairy products, soft drinks, and fermented beverages. A completely automated sample preparation system (ASTED XL) provides an efficient way of removing macromolecular and microparticulate interferents by high-performance dialysis, prior to HPLC analysis of the sugars, organic acids and related compounds. Processing samples on-line in the concurrent mode permitted both high reproducibility and optimal throughput.
Sugars Acids, organic HPLC Sample preparation Dialysis

"Determination Of L-ascorbic Acid By Flow Injection Analysis With Copper(II)-mediated Electrochemical Detection"
Anal. Sci. 1995 Volume 11, Issue 3 Pages 405-409
A. SANO, T. KUWAYAMA, M. FURUKAWA, S. TAKITANI and H. NAKAMURA

Abstract: A 20 µL portion of standard ascorbic acid (I) solution was injected into a steam of 70 mM acetic acid at 0.5 ml/min and mixed with 5 mM Cu(II) solution in 0.3 M acetate buffer of pH injected into the flow at 1.5 ml/min in a PTFE reaction coil (60 cm x 0.5 mm i.d.). The electrochemical response was recorded at a vitreous C electrode vs. Ag/AgCl at an applied potential of +20 mV. The calibration graph was linear from 0.1-20 µM-I and the detection limit was 0.05 µM. RSD (n = 10) was 1% at 10 µM-I. The average recovery of I from fruit juice spiked at the 50 mg/100 mL level was 96.7%. When equimolar amounts of glutathine, cysteine and catechol were coexistent with 10 µM-I recoveries decreased to 54.2, 60.7 and 90%, respectively. The method was applied to the determination of I in fresh fruit juices and soft drinks. The results agreed well with the certified values obtained by HPLC.
l-Ascorbic acid Electrode Method comparison Interferences Reference material

"Flow Injection Analysis With Spectrophotometric Determination Of Amino Acids With Chloranil"
Acta Cient. Venez. 1988 Volume 39, Issue 3 Pages 323-327
Burguera, M.;Burguera, J.L.;Granado, D.D.;Alarcon, O.M.

Abstract: A flow-injection system is described that permits the simple and rapid determination of microgram amounts of various amino acids based on the formation of mol. complexes with chloranil at pH 9.0 in 50% (v/v) aqueous ethanol solutions Sample solutions (30 mL) were used which permitted a sampling rate of ~80 measurements/h. The effect of temperature, chloranil concentration, pH, and flow-injection system variables on sensitivity were studied. The method is illustrated by the determination of glycine in dietetic soft drinks; accuracy was good. (SFS)
Amino Acids Spectrophotometry

"Flow Injection With Diaphragm Pump And Amperometric Detector"
Anal. Commun. 1996 Volume 33, Issue 2 Pages 75-77
Teiji Kakizaki, Kazunori Imai and Kiyoshi Hasebe

Abstract: A FIA system is described which has a diaphragm micropump with a moving section (actuator) and a pump section diaphragm). The actuator consists of two layers of piezoelectric elements of ceramic cemented together with three foil electrodes on the outer and inner surfaces. This vibrator is moulded in to rubber (diagram and details given). The driving source for the actuator was 0-100 V a.c., 50 Hz. Amperometric measurements were made with a Pt-disc, Ag/AgCl and Pt coil was working, reference and counter electrodes, respectively. This system enabled reliable amperometric measurements to be made in a FIA system with a carrier delivery system that gave a fluent constant flow of solutions without the use of pulse pumping devices. The method could be applied to the monitoring of ascorbic acid in soft drinks.
Ascorbic acid Amperometry Electrode Apparatus Pump

"Simultaneous Determination Of Ascorbic Acid And Sulfite In Soft Drinks By Flow Injection Analysis"
Analusis 1987 Volume 15, Issue 4 Pages 183-187
Lazaro, F.;Luque De Castro, M.D.;Valcarcel, M.

Abstract: The method is based on the reactions of SO32- and ascorbic acid with chloramine T. By means of a dual valve system a portion of sample containing both analytes, together with KI and Na oxalate (stabilizer), is introduced into the system and yields a signal corresponding to both species; at the same time a second portion of sample is mixed with 0.1 M NaOH and heated to 45°C, thereby eliminating the ascorbic acid before reaction and thus producing a signal due almost entirely to SO32-. Four calibration graphs are prepared, corresponding to ascorbic acid and SO32- via each valve. Calibration graphs cover the range 4 to 140 µg mL-1. Advantages of this method are a high sampling frequency (90 h-1) and reduced sample and reagent consumption.
Ascorbic acid Sulfite Dual valve Heated reaction Simultaneous analysis Reagent consumption

"Flow Injection Determination Of Sugars In Foods By Use Of A Porphinatotitanium(IV) Reagent"
Bunseki Kagaku 1995 Volume 44, Issue 5 Pages 355-362
Yokoi, Y.;Matsubara, C.;Takamura, K.

Abstract: Sample solution (20 µL) was injected into a stream (0.4 ml/min) of 0.05 M phosphate buffer/1 mM MgCl2 (pH 6.6). To determine glucose, the stream passed directly to a column of glucose oxidase, merged with a stream (0.4 ml/min) of 30 µM-oxo-[5,10,15,20-tetra-(4-pyridyl)porphinato]titanium(IV), and then passed through a mixing coil (15 m x 0.5 mm i.d.) maintained at 75°C before absorbance measurement at 450 nm. To determine maltose, lactose or sucrose, the stream after injection of the sample passed first through a column of glucose oxidase/catalase, then through a column of α-glucosidase, β-galactosidase, or β-fructofuranosidase/aldose 1-epimerase, respectively, and then through a column of glucose oxidase before merging with the reagent stream. Calibration graphs for glucose and for maltose, lactose or sucrose were linear over the ranges 0.5-500 µM and 1-1000 µM, respectively, and the respective RSD (n = 10) at 100 µM-glucose, -maltose, -lactose or -sucrose were 0.74, 0.84, 0.49 and 0.75%. The four carbohydrates were determined in milk, soft beverages and wine.
Glucose Maltose Lactose Sucrose Spectrophotometry Immobilized enzyme Heated reaction

"Direct And Simultaneous Determination Of Ascorbic Acid And Glucose In Soft Drinks With Electrochemical Filter/biosensor FIA System"
Bunseki Kagaku 1998 Volume 47, Issue 7 Pages 443-445
Yusuke Okawa, Hiroyuki Kobayashi and Takashi Ohno*

Abstract: An FIA system capable of the direct and simultaneous determination of ascorbic acid and glucose in commercial soft drinks is described. The system features a flow-through electrolysis cell (electrochemical filter, ECF) for a coulometric determination based on the quantitative electrolysis of ascorbic acid and a glucose oxidase monolayer electrode for the amperometric determination of glucose. Although ascorbic acid interferes with the glucose biosensor, quantitative electrooxidation in the ECF supresses the error. The glucose biosensor did not exhibit saturation for 0.1 M-order glucose samples. The measured values for nine commercial soft drinks without any pretreatment, such as dilution, showed a good correlation to those determined with conventional methods.
Ascorbic acid Glucose Sensor Electrochemical analysis Interferences

"Flow Injection Analytical System For Simultaneous Determination Of Glucose And Sucrose Utilizing Immobilized Enzyme Bioreactors"
Chem. Express 1988 Volume 3, Issue 1 Pages 13-16
Yao, T.;Akasaka, R.;Wasa, T.

Abstract: A flow-injection anal. system with immobilized enzyme bioreactors (invertase-mutarotase-glucose oxidase) is described for the highly selective and highly sensitive simultaneous determination of glucose and sucrose. The simultaneous determination of glucose and sucrose in soft drinks could be performed on 30 samples/h with satisfactory precision (<1% relative standard deviation). (SFS)
Glucose Sucrose Immobilized enzyme Multicomponent

"Online Elimination Of Electroactive Interferents For Flow-type Electrochemical Biosensor System"
Chem. Lett. 1991 Volume 20, Issue 5 Pages 849-852
Yusuke Okawa, Hiroyuki Kobayashi and Takashi Ohno

Abstract: A flow-through electrolytic cell containing a C felt working electrode separated from a Pt wire counter electrode by a Nafion membrane was combined with a glucose oxidase monolayer electrode in a flow injection analysis system (diagram given). The system was evaluated for the elimination of L-ascorbic acid (I) interferent in the determination of D-glucose. The elimination efficiency for I, as well as the biosensor response, were considerably increased by the addition of 0.1 M K3Fe(CN)6 to the carrier stream of 0.067 M-phosphate buffer (pH 6.4). Down to 1 mM glucose could be detected. The system was applied in the determination of glucose content in soft drinks; results agreed well with those of an enzyme-based colorimetric method.
Glucose Electrode Electrode Sensor Buffer Interferences Nafion membrane

"Determination Of Sugars By Liquid Chromatography With Post-column Catalytic Derivatization And Fluorescence Detection"
Chromatographia 1994 Volume 38, Issue 1-2 Pages 12-16
A. Coquet, W. Haerdi, R. Degli Agosti, J. -L. Veuthey

Abstract: Reducing sugars such as fructose and glucose, and non-reducing sugars such as sucrose were separated on a column (30 cm x 6.5 mm i.d.) packed with Sugar-Pak I operated at 70°C, with water as mobile phase (0.4 ml/min). The column eluate was passed at 0.4 ml/min through an online hydrolytic reaction column (7.5 cm x 3.8 mm i.d.) packed with Dowex 50 WX2, operated at 100°C, in order to hydrolyse the sucrose into reducing subunits. The reactor eluate was mixed online with 30 mM benzamide and 1 M KOH (1 ml/min) and the reaction mixture was heated at 100°C in a 530 µL reaction coil before online fluorimetric detection of the derivatized reducing carbohydrates at 470 nm (excitation at 360 nm). Calibration graphs were linear from 0.5-10 mM for the three sugars, and detection limits (10 µL injections) were 32 pmol (sucrose) and 60 pmol (glucose and fructose). The method was used to determine the sugar content of a barley extract, natural and commercial lemon juices and cola beverages. The results were comparable to those of an enzymatic glucose assay (for the barley extract) and a conventional LC method (lemon juices and cola).
Sugars LC Fluorescence Post-column derivatization Catalysis

"Flow Injection Analysis Of Carbonate, Sulfite And Acetate In Food"
Dtsch. Lebensm. Rundsch. 1996 Volume 92, Issue 10 Pages 323-328
SHI R. ; STEIN K. ; SCHWEDT G.

Abstract: For carbonate, drinking water was analyzed directly, mineral water was ultrasonically degassed, and orange drink was ultrasonically degassed and diluted with water (1:2). Sulfite in white wine was determined directly. For acetate, pickled gherkins and pepperoni were extracted with water. Solutions were injected into a water carrier, the stream was mixed with 5 mM H3PO4 to release the acidic gas or vapor, and this diffused into bromocresol violet/bromothymol blue/cresol red/KCl indicator in carbonate buffer (pH 8.3) for photometric detection at 430 nm or into dilute NaOH of pH 9.5 for potentiometric detection, or into iodine/KI/starch solution of pH 9.5 for photometric detection of sulfite at 620 nm. Alternatively, for acetate, the sample solution was adjusted to pH 8.4 with NaOH and injected into FeCl3 for photometric determination of the Fe-acetate complex at 405 nm. Conditions were optimized (details given), and means of overcoming interference are given. The iodimetric method was preferred for sulfite. Results agreed well with those of standard methods.
Sulfite Carbonate Acetate ion Spectrophotometry Potentiometry Interferences Standard method Method comparison Optimization

"Determination Of Polyphosphates By High Performance Liquid Chromatography. Application To Soft Drinks"
Eisei Kagaku 1988 Volume 34, Issue 1 Pages 70-74
AKINOBU MATSUNAGA, ATSUSHI YAMAMOTO, EIICHI MIZUKAMI, KAZUICHI HAYAKAWA, MOTOICHI MIYAZAKI

Abstract: Linear polyphosphates (P2 to P9) were separated by anion-exchange HPLC on a column (7.5 cm x 7.5 mm) of TSK gel DEAE-5 PW, protected by a column (1 cm x 6 mm) of TSK guard gel DEAE-5 PW, with a gradient mobile phase (1 mL min-1) of 0.02 to 0.15 M NaNO3 (held for 5 min) in 0.01 M HNO3 over 25 min and then to 0.02 M NaNO3 (held for 25 min) over 5 min. The polyphosphates were detected online at 500 nm after post-column reaction with 0.5 mM FeCl3 containing 2.5 mM sulfosalicylic acid at room temperature (flow rate 0.5 mL min-1). The method was applied to soft drinks after mixing the sample with an equal volume of 0.01 M HNO3 and filtration (0.45 µm). The determination limit was 0.02 mmol kg-1 of all polyphosphates.
Polyphosphates HPIC Spectrophotometry Post-column derivatization

"An Automatic Determination Of Caffeine In Soft Drinks Using Flow Injection System With Amperometric Detection"
Food Addit. Contam. 1998 Volume 15, Issue 3 Pages 265-269
Lima JL, Delerue-Matos C, Nouws HP, Vaz MC

Abstract: An automatic procedure based on a flow injection analysis manifold was developed for the determination of caffeine in soft drinks using an amperometric detection (+1.70 V vs. AgCl/Ag). The sample and standards were injected without pre-treatment, with a sampling rate of 120 determinations per h. The determination of caffeine in several soft drinks available in Portugal using the developed automatic system provided results with mean recovery values between 98% and 103% and a mean standard deviation between 2% and 5%. The results obtained were compared with those given by the reference method recommended by AOAC. Relative deviation was always <4%. Reproducibility of the method was assessed by the relative standard deviation (relative standard deviation%), values of which were <2%.
Caffeine Amperometry Method comparison

"Enzymic Determination Of Glucose, Sucrose And Maltose In Food Samples By Flow Injection Analysis"
Food Chem. 1990 Volume 35, Issue 2 Pages 109-116
S. M. Tzouwara-Karayanni* and S. R. Crouch

Abstract: Wheat flour (1 g) was mixed with ethanol (1 ml) and the mixture was diluted to 10 mL with water. After centrifugation (20 min at 1000 rpm), the supernatant solution was analyzed. Soft drinks were degassed, and honey was diluted (1:10) before analysis. Wine needed no pre-treatment. For determination of glucose (I), sample solution (0.1 to 1 ml) were diluted to 10 mL with 0.05 M phosphate buffer and then passed through a single bead string reactor containing glucose oxidase. The eluate from this reactor was mixed with a reagent stream containing peroxidase (0.8 mg mL-1), 1 mM 4-aminoantipyrine and 1 mM 3,5-dichloro-2-hydroxyphenylsulfonic acid in 0.05 M phosphate buffer and passed through a plain single bead string reactor. The absorbance was measured at 510 nm. For determination of sucrose (II), the samples were treated with invertase; for the determination of maltose (III) samples were treated with maltase. Calibration graphs were rectilinear from 0.01 to 0.08% of I and III and from 0.01 to 0.12% of II. Results compared well with those by the AOAC method. Recoveries were quantitative.
Glucose Sucrose Maltose Spectrophotometry Immobilized enzyme Dilution Buffer Enzyme Calibration Single bead string reactor Method comparison

"Solid-phase Extraction Cleanup For Determining Ascorbic-acid And Dehydroascorbic Acid By Titration With 2,6-dichlorophenolindophenol"
J. AOAC Int. 1996 Volume 79, Issue 5 Pages 1236-1243
Krishna K. Verma, Archana Jain, Bhushan Sahasrabuddhey, Kalpana Gupta and Sanjeev Mishra

Abstract: Ascorbic acid is frequently determined by titration with 2,6-dichlorophenolindophenol. The determination is rapid, but the method is neither specific for ascorbic acid nor very sensitive. The coloring matter in the assay solution interferes with the visual endpoint, and iron(II), copper(I), sulfite, and sulfhydryl substances such as cysteine and glutathione interfere with the color reaction. Sample cleanup by solid-phase extraction with C-18 bonded silica was developed to remove the coloring matter. Extraction sorbent impregnated with 2,2'-bipyridyl, 2,9-dimethyl-1,10-phenanthroline (neocuproine) acid N-ethylmaleimide removes Fe(II), Cu(I), and sulfhydryl compounds, respectively. The procedure was applied to highly colored multivitamin pharmaceuticals, soft drinks, and fruit and vegetable juices. In contrast to the results from the original method, which is not applicable to such samples, the results obtained by the method incorporating cleanup were accurate and selective for ascorbic acid. The sample cleanup also permitted determination of dehydroascorbic acid by reducing it to ascorbic acid with cysteine and titrating the ascorbic acid formed with indophenol. As little as 3 µg ascorbic acid was determined by the method incorporating cleanup.
Ascorbic acid dehydroascorbic acid Sample preparation Spectrophotometry HPLC Titrations Interferences Solid phase extraction

"Determination Of Total Carbon Dioxide In Beer And Soft Drinks By Gas Diffusion And Flow Injection Analysis"
J. Autom. Methods Manag. Chem. 1995 Volume 17, Issue 3 Pages 105-108
ESBJ&Ouml;RN LJUNGGREN and BO KARLBERG

Abstract: Beer or carbonated soft drinks were made alkali by the addition of 10 M NaOH and a sample was injected into a carrier stream (1.2 ml/min) of water. The carrier stream merged with a reagent stream (1.2 ml/min) of 0.2 M H2SO4, passed through a mixing coil (30 cm x 0.7 mm i.d.) and went into a gas diffusion cell with bromocresol purple indicator solution as the acceptor solution. The absorbance was then read at 430 nm. Beer's law was obeyed up to 9 g/l of CO2. The CO2 contents of Tuborg and Pripps beer, coke and club soda are tabulated.
Carbon dioxide Spectrophotometry Gas diffusion

"A Multisyringe Flow Injection System With Immobilized Glucose Oxidase Based On Homogeneous Chemiluminescence Detection"
Anal. Chim. Acta 2004 Volume 508, Issue 1 Pages 23-30
Mat&iacute;as Manera, Manuel Mir&oacute;, Jos&eacute; Manuel Estela and V&iacute;ctor Cerd&agrave;

Abstract: In this paper, enzyme containing reactors are for the first time implemented in the multisyringe flow injection analysis (MSFIA) technique interfaced with chemiluminescence detection for biochemical assays. The automated methodology is based on the on-line substrate conversion in an oxidase packed-bed reactor and the post-column chemiluminogenic catalyzed-reaction of the generated oxidising species with an organic molecule (namely, 3-aminophthalhydrazide) in front of the photosensor module. Various catalysts in homogeneous phase are compared taking advantage of the benefits of the MSFIA concept. On one hand, mineral catalysts (namely, Co(II)) are assessed, on the other hand, minute and accurate volumes of soluble organic species (viz., horseradish peroxidase (HRP)) are readily handled without requiring further immobilization protocols. The potentials of the MSFIA-CL concept with immobilization of the proper oxidase protein are demonstrated using glucose as a model of substrate. Despite the different pH and kinetic requirements for both the substrate conversion in the enzyme-reactor and the Co(II)/HRP-mediated luminol oxidation integrated in the flow system, the MSFIA approach warrants maximum yields owing to the independent optimization of the physical and chemical parameters of the various reactions involved. Under the optimized configurations and experimental variables, dynamic working ranges from 2.5 x 10^-6 to 1.0 x 10^-3 mol L-1 glucose may be obtained for both detection schemes by proper photomultiplier gain selection. The detection and determination limits calculated at the 3s and 10s level were 8.6 x 10^-7 and 2.0 x 10^-6 mol L-1 glucose, respectively, for the Co(II)-luminol system, and 1.3 x 10^-6 and 2.3 x 10^-6 mol L-1 glucose, respectively, for the HRP-luminol procedure. The repeatability (n=10) at the 1.0 x 10^-5 mol L-1 level was slightly better for the Co(II)-catalyzed reaction (2.5% versus 4.0%). The developed MSFIA-CL methodology was used for kinetic studies of the mutarotation reaction between α and β anomeric forms of glucose, obtaining quantitative information of the specific glucose oxidase (GOD) anomer formed at prefixed intervals of time. It was also successfully applied to the determination of traces of glucose in complex matrices, namely, human urine, soft drinks and fruit juices, exploiting the Co(II)-mediated luminol oxidation.
Glucose Chemiluminescence Multisyringe Interferences Immobilized enzyme Optimization Column

"Automated Enzymatic Assays In A Renewable Fashion Using The Multisyringe Flow Injection Scheme With Soluble Enzymes"
Anal. Chem. 2004 Volume 76, Issue 3 Pages 773-780
Nicolau Piz&agrave;, Manuel Mir&oacute;, Jos&eacute; Manuel Estela and V&iacute;ctor Cerd&agrave;

Abstract: In this paper, a novel flowing stream scheme based upon the multisyringe flow injection (MSFI) technique is presented as a powerful tool to perform automated enzymatic assays. The exploitation of enzymes in homogeneous phase circumvents typical drawbacks associated with the commonly used packed-bead or open tubular permanent columns, namely, malfunctions of the reactor, carryover effects, flow resistance, loss of binding sites, large reagent consumption, and use of harmful organic solvents during immobilization procedures. The proposed MSFI system is able to handle minute volumes of soluble enzymes and accommodate reactions with divergent kinetic and pH demands, as demonstrated via the indirect chemiluminescence determination of trace levels of glucose. The procedure is based on the on-line glucose oxidase-catalyzed oxidation of β-glucose in homogeneous phase to β-glucono-δ-lactone and hydrogen peroxide. Subsequently, the generated oxidant merges downstream with an alkaline slug of 3-aminopthalhydrazide and a metal-catalyst zone (viz., Co(II)) at a total flow rate as high as 72 mL/min aiming to warrant maximum light collection from the fast CL reaction. Under optimum conditions for both sequentially occurring reactions, a glucose concentration as low as 90 µg/L may be easily detected at a 1000-fold photomultiplier gain. A second-order polynomial regression equation of light emission versus substrate concentration is found over the range 90 µg/L-2.7 mg/L glucose, although a maximum concentration of 180 mg/L may be determined by suitable gain selection without requiring manifold reconfiguration. An injection throughput of 20 h-1, a repeatability better than 2.5% at the 1 mg/L level, and a 3s detection limit of 72 µg/L are the analytical features of the designed analyzer. The proposed approach was applied to the analysis of ultralow glucose content soft drinks as well as fruit juices suitable for diabetic consumers. The accuracy was assessed using the spectrophotometric batch glucose-Trinder method as an external reference methodology for the determination of the target species in parenteral solutions.
Glucose Chemiluminescence Multisyringe

"Determination Of Glucose In Soft Drink And Sugar-cane Juice Employing A Multicommutation Approach In Flow System And Enzymatic Reaction"
Fresenius J. Anal. Chem. 1999 Volume 364, Issue 4 Pages 358-361
Elo&iacute;sa A. M. Kronka, Ana Paula S. Paim, B. F. Reis, Jos&eacute; L. F. Costa Lima, Rui A. Lapa

Abstract: A flow system based on a multicommutation approach was developed for the determination of glucose and sucrose employing enzymatic reactions. The determination was based on the reaction with D-glucose generating hydrogen peroxide catalyzed by glucose-oxidase (GOD). Subsequently, the H2O2 generated reacts with 4-aminefenazone plus phenol to form 4-(p-benzoquinone-mono-imine) fenazone detected at 510 nm. This reaction is catalyzed by the peroxidase enzyme (POD). The flow network comprised a set of three-way solenoid valves and was controlled by means of a microcomputer furnished with an electronic interface and running a software written in Quick BASIC 4.5. The flow network and control software were designed to implement the multicommutation approach providing facilities to handle sample and reagent solutions, so that, sample dilution could be easily performed on line. Accuracy was assessed by comparison with results obtained by known procedures and no significant difference at the 95% confidence level was observed. Other advantageous features were a linear response ranging from 0.05 to 0.20% (w/v) glucose without prior dilution, a reagent consumption of 336 µL per determination, an analytical throughput of 30 samples per hour.
Glucose Sucrose Spectrophotometry Multicommutation Immobilized enzyme Computer Method comparison

"Use Of A Laccase-column For Flow-injection Calorimetry"
Ann. NY Acad. Sci. 1998 Volume 864, Issue 12 Pages 493-496
Ikuo Satoh, Ikuko Sakurai

Abstract: A great number of enzyme-catalyzed reactions are accompanied by heat evolutions.1 Therefore, flow-injection analysis (FIA) based on calorimetry, that is, flow-injection calorimetry,2,3 in combination with biocatalysts as specific recognition elements gives convenient and versatile analytical methods for biorelated compounds. Nakatani and Shimizu purified a thermostable laccase from Trametes sp. and reported its enzymatic properties recently.4 The enzyme functioned as the catalyst in oxidative reactions of various kinds of dihydroxylated compounds (so-called polyphenol compounds). We tried to apply its enzymatic properties to the determination of L-ascorbate in soft drinks. In this paper, we describe the fundamental performance of the calorimetric FIA system with use of the enzymes immobilized onto porous glass beads.
Ascorbate Calorimetry Immobilized enzyme Controlled pore glass