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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Tea

Classification: Beverage -> non alcoholic -> tea

Citations 8

"Application Of Square-wave Voltammetry For The Determination Of Ascorbic Acid In Soft Drinks And Fruit Juices Using A Flow Injection System"
Anal. Chim. Acta 1992 Volume 261, Issue 1-2 Pages 375-380
Ying-Sing Fung* and Song-Ying Mo

Abstract: A portion (100 µL) of test solution was injected into a stream of the supporting electrolyte (Britton - Robinson buffer) for transfer to a thin-layer electrochemical cell (volume 16 µL) equipped with vitreous-carbon working, stainless-steel counter and Ag - AgCl reference electrodes. The normal flow rate was 0.5 mL min-1, and the potential of the working electrode was scanned from +0.2 to +0.7 V in 1 s, with application of a computer-generated square waveform and measurement of the oxidation peak current at +0.46 V. The buffer pH was 2.87 to stabilize the ascorbic acid. The peak signal was rectilinearly related to ascorbic acid concentration. from 2 µM to 6 mM; food additives at normal concentration. levels did not interfere. Results obtained on blackcurrant juice, lemon tea, sugar-cane juice and apple juice were satisfactory. The application of square-wave voltammetry for detection in the flow injection determination of ascorbic acid in soft drinks and fruit juices was investigated. The pH of the solution was buffered at 2.87 to stabilize the ascorbic acid prior to anal. Parameters such as scan rate, square-wave amplitude, step height and flow-rate of electrolyte were found to have little effect on the potential, but a significant effect on the current. The anal. current is only slightly affected by the flow-rate of the electrolyte and a max. scan rate of 0.5 V/s can be used. As a compromise between sensitivity and selectivity, 40 mV was chosen as the amplitude of the square wave and 10 mV as the potential step height. Similarly, a flow-rate of 0.5 mL/min and an injection volume of 100 µL were chosen as a compromise between the sensitivity and resolution of the FIA method. With these procedures, the max. number of samples that could be analyzed was 120/h. The linear calibration range was from 2 x 10^-6 to 6 x 10^-3 M and the determination limit (10s) was 2 x 10^-7M. No significant interference was found from additives commonly found in juice and drink samples within their normal concentration. ranges. Four juice samples were analyzed using the developed method and the results were compared with those given by the established AOAC method. No significant difference was observed between the two methods used for the four samples studied.
Ascorbic acid Voltammetry Electrode Standard method Method comparison Interferences

"Coupled Flow Injection Analysis - Flame-atomic Absorption Spectrometry For The Quantitative Determination Of Aluminum In Beverages And Waters Incorporating Online Cation-exchange"
Anal. Chim. Acta 1992 Volume 269, Issue 1 Pages 1-7
Henryk J. Salacinski, Philip G. Riby, Stephen J. Haswell*

Abstract: Tea leaf samples (0.5 g) were digested at 85°C for 45 min in a mixture of HNO3 (4 ml) and HClO4 (1 ml) and diluted to 10 mL with 5% HNO3. Samples of tea and coffee infusions and water were acidified with 5% HNO3. These samples (250 µL) were injected via a loop into a SCX preparative column (500 mg) with water as the carrier, followed by elution with 4 M HCl (250 µL) directly into the nebulizer of a flame AAS for the determination of Al. The AAS and nebulizer were optimized for max. absorbance prior to the determination and the peristaltic pump of the flow system set to give an equivalent delivery. Rectilinear calibrations were obtained from 0.07 to 6.45 µg mL-1 of Al from various timed depositions with a coefficient of variation of 1.1% and a detection limit of 75 ng mL-1. A method for determining the aluminum levels in local water, tea leaf digest, tea and coffee infusions by means of online cation exchange flow injection - flame atomic absorption spectrometry (FIA-FAAS) is described. Quant. results can be carried out down to 75 ng mL-1 of Al using sample volumes in the range 6.0-24.0 mL. The method using a conventional FAAS system was found to be rapid, simple and relatively inexpensive offering good selectivity and typical relative standard deviation of 1-2% (n=10) with a relative error of about 2%.
Aluminum Ion exchange Sample preparation Sample preparation Spectrophotometry Nebulizer Column

"Indirect Flow Injection Determination Of Tannins In Wines And Tea By Atomic Absorption Spectrometry"
Anal. Chim. Acta 1995 Volume 308, Issue 1-3 Pages 357-363
M. C. Yebra, M. Gallego and M. Valcárcel*

Abstract: The automated procedure for the indirect determination of tannins in food was based on the precipitation of tannins with copper acetate complex and the determination of the unprecipitated Cu by AAS. The precipitating reagent contained 200 µg/ml of Cu in 0.1 M ammonium acetate of pH 5.2. The flow injection manifold allowed 50 µL of precipitating reagent to be injected into a stream (0.7 ml/min) of sample solution. The flow was propelled through a precipitation coil (2.5 m x 0.5 mm i.d.) and a screen-type stainless-steel filter (pore size 0.5 µm, filter area 3 cm2). The filtrate was diluted with a water stream (2.5 ml/min) and aspirated into the AAS system. Cu was determined at 324.7 nm with an air/acetylene flame. The calibration graph was linear for 1-25 µg/ml of tannic acid with a detection limit of 0.7 µg/ml. The RSD (n = 11) for the determination of 10 µg/ml tannic acid was 2%. The sampling frequency was 80-100 samples/h. The method was applied to white and red wine, and tea. Wine was diluted 50-250-fold before analysis and the pH was adjusted to 5-5.5 with NH3. A 1 g portion of tea was boiled for 10 min with 50 mL water. The mixture was filtered and the filtrate was analyzed after dilution. Recoveries of 250-500 µg of tannic acid from spiked wine and tea were 96.1-104.3%.
Tannins Spectrophotometry Precipitation Filter Complexation Indirect

"Spectrophotometric Determination Of A Nanomolar Amount Of Ascorbic Acid Using Its Catalytic Effect On Copper(II) Porphyrin Formation"
Talanta 1997 Volume 44, Issue 2 Pages 151-157
Masaaki Tabata*, and Hirofumi Morita

Abstract: A solution (120 µL) containing sample (ascorbic acid), 0.1 M NaNO2, 0.01 M acetate buffer of pH 5, 18 µM-5,10,15,20-tetrakis-(1-methylpyridinium-4-yl)porphyrin and 0.1 mM trans- 1,2-diaminocyclohexane-NNN'N'-tetra-acetic acid (DCTA) was injected into a stream (1.9 ml/min) of water which merged with a stream (1.9 ml/min) of water into which a solution (120 µL) of 0.4 mM Cu(II), 0.1 mM DCTA and 0.1 M NaNO2 in 0.01 M acetate buffer of pH 5 had been injected. The flow passed through a reactor (2 m x 5 mm i.d.) to a detector where the absorbance was measured at 550 nm. The calibration graph was linear for 0.12-0.5 µM-ascorbic acid and the RSD was 2.8% for 0.1 nM-ascorbic acid. No detection limit or recoveries are given. Reducing agents such as sugars and vitamin B compounds did not interfere seriously. The method was applied to urine, tea and blood.
Ascorbic acid Spectrophotometry Indirect Interferences Buffer

"Chemical Reaction Detection Of Catechins And Proanthocyanidins With 4-dimethylaminocinnamaldehyde"
J. Chromatogr. A 1989 Volume 467, Issue 1 Pages 185-193
D. Treutter

Abstract: The cited flavanols were determined in crude plant extracts and beverages by HPLC on a column (25 cm x 4 mm) of Hypersil ODS (3 µm), with gradient elution from 5 to 90% of methanol in 5% acetic acid. Post-column derivatization was carried out with 1% 4-dimethylaminocinnamaldehyde solution in methanolic 1.5 M H2SO4 and detection was at 640 nm. Sensitivity was improved 200 to 40,000-fold for (-)-epicatechin compared with other phenols and substituted indoles; the detection limit was 2.5 ng. For terpenes, this factor ranged from 4000 to 2,000,000. The selective detection of catechins and proanthocyanidins extracted from tea and beer is described.
Catechins Proanthocyanidins HPLC Spectrophotometry Column Post-column derivatization Sensitivity Detection limit

"Fluorometric Biosensing Of The Total Amino Acid Content And The Glutamate Content Of Green Tea Infusions Using An Automated Multi-channel Flow System"
Biosci. Biotechnol. Biochem. 1996 Volume 60, Issue 1 Pages 99-102
Lee, M.H.;Chen, R.L.C.;Matsumoto, K.

Abstract: An automated multi-channel continuous-flow analyzing system was constructed for the rapid measurement of both the total amino acid content and the L-glutamate content of green tea infusions. L-Glutamate in samples was oxidized and deaminated enzymatically in a channel with a mini-reactor that was packed with L-glutamate oxidase immobilized on glass beads, and the evolved ammonium ions were measured by a fluorogenic reaction with o-phthalaldehyde and β-mercaptoethanol. The total amino acid content was measured in a channel with another mini-reactor which was filled with immobilized L-amino acid oxidase. The fluorometric method is not subject to interference by reducing substances such as tea catechins and ascorbate, and the analytes in tea infusions were measured without pretreatment of samples. The use of this system for evaluation of tea quality was investigated.
Amino Acids Glutamate Fluorescence Multichannel Immobilized enzyme Interferences Glass beads

"Novel Enzymatic Assays For The Measurement Of Gallotannin, Amino-acids And Glutamate In Green Tea Infusions: Analytical Results"
Biosci. Biotechnol. Biochem. 1996 Volume 60, Issue 2 Pages 362-363
Lee, M.H.;Chen, R.L.C.;Matsumoto, K.

Abstract: Green tea infusions prepared by extracting tea with water at 85°C for 15 min were filtered and the filtrate or canned tea drinks were analyzed for gallotannin content by the method of Chen and Matsumoto (Anal. Sci., 1995, 11, 777) and amino-acid and glutamine content were measured by enzymatic FIA (Lee et al., Biosci. Biotech. Biochem., 1996, 60, 99). Scattergrams are presented of the results obtained to show the relationship between the three analytes. Results are discussed.
Glutamine Amino Acids Gallotannins Enzyme

"Flow Injection Column Preconcentration Coupled With Atomic Absorption Spectrometry For Aluminum Determination"
Xiamen Daxue Xuebao (Ziran Kexue Ban) 1998 Volume 37, Issue 1 Pages 80-87
Yuan Dongxing, Ian L. Shuttler

Abstract: A method has been developed for the speciation anal. of Al in tea soup and water samples using an automated flow injection system coupled with an electrothermal atomic absorption spectrometer. Two pre-concentration materials, 8-quinolinol immobilized on controlled-pore glass and Amberlite XAD-2 copolymer, were investigated. Fast exchangeable Al, hydrophobic Al, and total Al can be determined by control the pre-concentration conditions.
Aluminum Spectrophotometry Preconcentration 8-Hydroxyquinoline Controlled pore glass Amberlite Column