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
Website: @unf

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Classification: Environmental -> water -> lake

Citations 37

"Colorimetric Flow Injection Analysis Of Dissolved Iron In High DOC Waters"
Water Res. 2001 Volume 35, Issue 2 Pages 363-372
Michael J. Pullin and Stephen E. Cabaniss

Abstract: An iron flow-injection analysis system has been optimized for the analysis of iron in waters high in dissolved organic carbon. The method detects either dissolved iron(II) or total dissolved iron with a detection limit of 10 nM, precision of 0.65% at 1 µM, and a dynamic range of four orders of magnitude. There are minimal interferences (<1%) from other metals at environmental concentrations. The iron(II) method measures iron(II) in the presence of excess iron(III) with less than 1% interference. When used with pre-acidified samples, the total dissolved iron method agrees well with electrothermal atomic absorption spectrometry for a variety of natural waters with a range of dissolved organic carbon (3-36 mg C/L) and iron (1-28 µM) concentrations. When used with samples at their ambient pH, the total dissolved iron method detects dissolved iron, but not colloidal iron (size fraction 0.05-0.45 µm).
Iron(2+) Spectrophotometry Optimization Interferences Heated reaction

"Determination Of Phenol In Water By Pervaporation-flow Injection Analysis"
Anal. Chim. Acta 2000 Volume 419, Issue 1 Pages 9-16
Sami Y. Sheikheldin, Terence J. Cardwell, Robert W. Cattrall, Maria D. Luque de Castro and Spas D. Kolev

Abstract: A pervaporation-flow injection method for the determination of phenol in aqueous samples is described. The method involves sample injection into a concentrated sodium chloride (25 wt.%) donor stream at pH 2 and stopping the flow of the acceptor stream containing 0.1 M KNO3 and 0.01 M NaOH in the acceptor chamber of the pervaporation unit for 12 min. This period allows the completion of phenol transfer from the headspace of the donor chamber of the pervaporation unit through the membrane into the static solution in the acceptor chamber. After restarting the flow through the acceptor chamber the phenol concentration is detected amperometrically at a glassy carbon electrode set at +0.6 V. At 20°C the linear detection range was found to be 1-50 mg L-1 with RSD varying between 1 and 4% for n=3. The detection Limit and sample throughput were determined as 0.9 mg L-1 and 5 hr-1, respectively. Excellent agreement with the standard 4-aminoantipyrine (4-AAP) method was observed when validating the method with lake samples containing suspension and spiked with phenol.
Phenol Amperometry Electrode Pervaporation Method comparison

"Spectrophotometric Determination Of PH By Flow Injection"
Anal. Chim. Acta 1990 Volume 231, Issue 1 Pages 21-26
Stephen H. Pia, Donna P. Waltman and Daniel C. Hillman, Kenneth W. Street, Jr

Abstract: An appropriate combination of pH indicators was used in a flow injection system (manifold illustrated); e.g., for the pH range 3 to 8 the methyl red - methyl yellow - neutral red mixture of Tucker et al. (J. Chem. Educ., 1989, 66, 769) was used, with detection at 555 nm. The degree of rectilinearity of the response is discussed. The sample throughput is ~100 h-1, and the precision and accuracy are ±0.2 pH. Use of the system for determining the pH of lake waters is described.
pH Spectrophotometry pH

"Online Microwave Sample Pre-treatment For The Determination Of Mercury In Water And Urine By Flow Injection Cold Vapor Atomic Absorption Spectrometry"
Anal. Chim. Acta 1992 Volume 261, Issue 1-2 Pages 91-103
Bernhard Welz*, Dimiter L. Tsalev and Michael Sperling

Abstract: Conditions yielding high recoveries of Hg from inorganic and organic Hg compounds (used in method development) and urine were developed for use with a system incorporating an auto-sampler, a microwave digester, a hydride system, an amalgamation accessory and an AAS instrument. Samples were mixed offline with 1% (v/v) of aqueous stabilizer solution [0.5% of K2Cr2O7 in HNO3 (1:1)] and, in the autosampler vessels, with 1 to 2% (v/v) of bromination reagent (aqueous 2.23% KBrO3 - 8% KBr) before introduction into a carrier stream of 0.3% HCl or, for the lower ng L-1 concentration. range, water and passage to the microwave digester. The effluent from the digester (at 50°C to 90°C) was merged with a reductant containing 0.2 g L-1 each of NaBH4 and NaOH plus, for urine samples, 400 µL L-1 of Dow Corning 110A antifoaming agent and passed through a hydride manifold and a gas-liquid separator before filtration and cold vapor AAS with or without amalgamation. Peak area or peak height could be measured. Recoveries were improved in some instances by using amalgamation. Sample throughput was 30 to 40 h-1 without and 24 h-1 with amalgamation. The method was successfully applied to rain and to lake and river waters; for 10 mL samples the detection limit with amalgamation was 10 ng L-1. Results on certified reference samples of urine agreed fairly well with certified values. A system for online treatment of liquid samples in a microwave oven and determination of mercury by cold vapor atomic absorption spectrometry was designed and evaluated. The system consisted of an atomic absorption spectrometer, equipped with a mercury-hydride system and amalgamation accessory, a flow injection system, an autosampler and a microwave digestor. Urine and environmental water samples were stabilized with potassium dichromate-nitric acid and were mixed with a bromination reagent. The recoveries of eight mercury compounds from aqueous solutions and five compounds from dilute urine were studied. At an applied microwave power of 75 W, the recoveries of mercury(II) nitrate, methylmercury chloride, amidomercury chloride, phenylmercury chloride and diphenylmercury were between 92 and 102% for 1 + 2 - diluted urine without amalgamation and between 94 and 111% for 1 + 5 diluted urine with amalgamation, respectively. The sample throughput was 30-40 h-1 without amalgamation and 24 h-1 in the amalgamation mode. Good agreement with certificate values was obtained for urine samples. A limit of detection (3s) of 10 ng L-1 was obtained using 10 mL sample volumes of environmental waters (river, lake, rain) and the amalgamation technique. The results compared well with those from an external lab. with correlation coefficients of 0.9302 and 0.9028 (n = 22) for integrated absorbance and peak-height absorbance, respectively.
Mercury Spectrophotometry Sample preparation Microwave Online digestion Amalgamation Reference material

"Continuous-flow Method For The Determination Of Total Trihalomethane Formation Potential In Waters"
Anal. Chim. Acta 1992 Volume 261, Issue 1-2 Pages 335-338
Toyoaki Aoki*, Kouji Kawakami

Abstract: In the system described and illustrated, the sample stream is mixed with 10 mM NaClO in a 3-m PTFE reaction coil heated at 98°C, and the resulting solution is merged with 10% Na2SO3 solution (to remove surplus NaClO) before passage into a unit equipped with a microporous PTFE membrane and maintained at 50°C, where the trihalomethanes formed diffuse into a stream of 0.2 M NaOH. The alkaline stream is mixed with 30% nicotinamide solution in a 3-m PTFE coil at 98°C and cooled in ice before fluorescence measurement at 467 nm (excitation at 372 nm). For calibration with humic acid, the trihalomethane production was rectilinearly related to C concentration. from 1 to 5 mg l-1. The detection limit was 2.2 µg L-1 of trihalomethanes. The coefficient of variation was 4.3% for 5 mg L-1 of C as humic acid and 2.6% for 5 mg L-1 of C as albumin (n = 5). An analysis took 20 min, as compared with >26 h for the conventional Japanese method. The method was successfully applied to lake and river waters. A double-tube separation system with an inner tube of microporous poly(tetrafluoroethylene) (PTFE) and an outer tube of PTFE is proposed for the continuous determination of trihalomethane (THM) formation potential in waters. The THMs in the sample, after reaction with NaClO solution at 98°C and reduction of the residual ClO- with Na2SO3, are separated with the double-tube system at 50°C. They are then mixed with alkaline nicotinamide solution and heated at 98°C. After being cooled in an ice-bath, the reaction product is fed to a spectrofluorimeter, and the emission of fluorescence excited at 372 nm is measured at 467 nm. The response was obtained within 20 min. The detection limit (signal-to-noise ratio = 3) was 2.2 µg/L. The total THM formation potentials obtained by the present method for lake and river waters were in good agreement with those obtained by the Japanese standard batch method.
Methanes, trihalo Fluorescence Teflon membrane Heated reaction Method comparison

"Flow Injection Determination Of Subnanogram Amounts Of Manganese By Catalysis Of The Oxidative Coupling Of NN-dimethyl-p-phenylenediamine With M-phenylenediamine"
Anal. Chim. Acta 1992 Volume 261, Issue 1-2 Pages 183-188
Shigenori Nakano*, Masahiro Nozawa and Maki Yanagawa, Takuji Kawashima

Abstract: The sample solution (183 µL) is injected into a carrier stream of HCl (1 mM or 0.1M), which is merged with, first, 0.5 M H2O2 and then a pre-merged stream of (a) 6 mM NN-dimethyl-p-phenylenediamine - 0.8 mM tiron - 10 mM L-cysteine and (b) 3 mM m-phenylenediamine - 8 mM triethylenetetramine - 0.4 M NH3; each of the four solution is pumped at 0.8 mL min-1. The resulting solution is passed through a reaction coil (8 m) at 35°C and the increase in absorbance over a reagent blank is measured at 650 nm vs. air. The development of these optimum conditions is described. The calibration graph is rectilinear for 0.05 to 1.0 ng mL-1 of Mn(II), the detection limit is 10 pg mL-1, sample throughput is 25 h-1 and the coefficient of variation at 0.3 ng mL-1 was 1.5% (n = 10). Few foreign ions interfered seriously; Fe(III) was masked by the L-cysteine. The method was successfully applied to water samples pre-diluted 20 to 500-fold with 0.1 M HCl; results on tap-, river and lake water are tabulated. A spectrophotometric flow injection method was developed for the determination of subnanogram amounts of manganese(II) based on its catalytic effect on the oxidative coupling of N,N-dimethyl-p-phenylenediamine with m-phenylenediamine in the presence of hydrogen peroxide. The catalytic activity was greatly enhanced by the presence of triethylenetetramine and 1,2-dihydroxybenzene-3,5-disulfonate together. The proposed method allows the determination of as little as 50 pg mL-1 of manganese(II) with relative standard deviations below 3% at a rate of 25 samples h-1. The method can be applied to the determination of manganese in natural waters.
Manganese Spectrophotometry Catalysis Interferences Heated reaction Tiron

"Continuous-flow Method For The Determination Of Total Inorganic Carbonate In Water"
Anal. Chim. Acta 1993 Volume 284, Issue 1 Pages 167-171
Toyoaki Aoki*, Yoshiko Fujimaru, Yuko Oka and Kimiko Fujie

Abstract: Water (5.1 ml/min) was mixed with 0.5 M H2SO4 (1.5 ml/min) and the mixture passed into a membrane separation unit (cf. Anal. Chem., 1983, 55, 1620). The CO2 liberated by acidification permeated through a microporous PTFE tubular membrane (50 cm x 1 mm i.d.) and was collected in a stream of 5 mM NaOH (1.5 ml/min) flowing through an outer PTFE tube (3 mm i.d.). The total inorganic carbonate was determined from the change in electrical conductivity of the NaOH collector stream which was measured using two conductivity detectors; one placed before the membrane separator and one located after it. The calibration graph (relative electrical conductivity vs. concentration) was linear for 0.05-5 mM total inorganic carbonate with a detection limit of 10 µM and RSD (n = 5) of 3.4 and 1.8% at 0.1 and 0.6 mM carbonate, respectively. The response time (98% of steady-state signal) was ~2 min. The effects of various foreign ions were investigated; sulfite interference was prevented by the addition of 0.1 M Cr(VI) to the acid reagent. The method was applied to lake water and the results agreed well with those obtained by nondispersive IR.
Carbonate Conductometry Teflon membrane Gas diffusion Interferences Method comparison

"Method Comparison For The Determination Of Labile Aluminum Species In Natural Waters"
Anal. Chim. Acta 1994 Volume 286, Issue 3 Pages 401-409
Ben Fairman and Alfredo Sanz-Medel*, Mercedes Gallego and Maria Jos&eacute; Quintela, Phil Jones and Richard Benson

Abstract: The results of an inter-laboratory project for the determination of labile monomeric Al in lake and tap water are presented. A modified Driscoll-pyrocatechol violet (PCV) fractionation method (cf. Fairman and Sanz-Medel, Int. J. Environ. Anal. Chem., 1993, 50, 161), with a 10 min reaction time, 3.5 mL samples, a 1 mL column of Amberlite IR-120 conditioned from the Na+ form and split calibration was used as a reference method; each laboratory also used an alternative method (FIA 8-hydroxyquinoline-5-sulfonic acid, LC and FIA Driscoll-PVC methods; details given). High-density polyethylene containers were suitable for sample storage after leaching with 10% HNO3 for 48 h and samples were stable for 30 days. The value of a quality control program whereby solution containing 11 and 55 µg/l of Al in 0.01 M HNO3 are analyzed (preferably by electrothermal-AAS) periodically over the test period was demonstrated. Samples containing 100-200 µg/l of Al gave the best speciation results. The Driscoll-PCV method was fully portable and gave RSD of 15% for toxic labile monomeric Al in the more stable samples.
Aluminum LC Spectrophotometry 8-hydroxyquinoline-5-sulfonic acid Amberlite Speciation

"Flow Injection Extraction Without Phase Separation Based On Dual-wavelength Spectrophotometry"
Anal. Chim. Acta 1994 Volume 288, Issue 3 Pages 237-245
Hanghui Liu and Purnendu K. Dasgupta*

Abstract: A flow injection extraction (FIE) system is described. The absorbance was measured radially on the same PTFE tube that formed the extraction coil. The detector used a LED-based dual-wavelength photometric system with PC-based data acquisition and processing. One non-specific wavelength was used to recognize the phases and the other to monitor the analyte. The FIE system was used to determine anionic surfactants (AS) by ion-pairing with methylene blue (MB) and extraction into CHCl3. A water carrier stream (0.45 ml/min) was merged with the MB reagent stream (0.06 mg/ml; 0.16 ml/min). After passing through a mixing coil (15 cm x 0.17 mm i.d.), the stream passed to the segmenter. A CHCl3 stream (0.05 ml/min) was pumped to the segmenter and alternate segments of aqueous and organic phase were pumped to the extraction/detection coil (2.8 m x 0.38 mm i.d.). The MB-AS ion-pair was determined at 660 nm with identification at 850 nm. The calibration graph was linear up to 2.5 ppm of C-12 alkylbenzene sulfonate with a detection limit of 0.025 ppm and an RSD of 1.5%. The method was applied to tap- and lake-water. Recoveries were >94.4%.
Surfactants, anionic Spectrophotometry Sample preparation Light emitting diode Computer Extraction

"Determination Of Phosphorus In Turbid Waters Using Alkaline Potassium Peroxodisulphate Digestion"
Anal. Chim. Acta 1995 Volume 315, Issue 1-2 Pages 123-135
L. Woo and W. Maher*

Abstract: The evaluation of the use of alkaline peroxodisulphate digestion with autoclaving or microwave heating for the determination of total phosphorus in turbid lake and river water is described. Procedures were evaluated by the analysis of suspensions (20, 50 and 100 g P/l) of two standard reference materials, National Institute of Environmental Science, Japan No. 3 Chlorella and No. 2 Pond Sediment. Suspensions were prepared by adding these materials to distilled deionized water (pH 6) and homogenisation using shaking, sonification and stirring. Best recoveries of phosphorus were found when the final solution was 0.045 M in potassium peroxodisulphate and 0.04 M in sodium hydroxide and solutions digested in an autoclave at 120°C for 60 min. or heated in a microwave oven at 450 W for 10 min. Complete recoveries of phosphorus (99-103%) from 20, 50 and 100 g P/l Chlorella suspensions were obtained using both autoclave and microwave heating. For the Pond Sediment complete recoveries of phosphorus (99-107%) from the 20 and 50 g P/l suspensions were obtained using both heating methods. Higher recoveries from the 100 g P/l Pond Sediment suspensions were obtained using microwave heating (96 ± 1%) than autoclaving (88 ± 5%). Recoveries of phosphorus compounds (phosphates, and phosphonates) added to distilled deionized water and turbid lake water were near quantitative (91-117%) for both digestion procedures. Further analysis of Pond Sediment suspensions showed that complete recovery of phosphorus (98 ± 1%) from 60 g/l suspensions was achieved with incomplete recoveries (92.3 ± 0.7%, 91 ± 2% and 91 ± 1%) from 70 g P/l, 80 g P/l and 90 g P/l suspensions respectively. Comparison with the APHA-AWWA WPCF, nitric-sulphuric acid digestion method showed no difference in phosphorus measurements for the microwave procedure but that the autoclave procedure gave significantly lower recoveries of phosphorus (p < 0.01), however, differences were only 2-8%.
Phosphorus Sample preparation Sample preparation Reference material Method comparison

"Direct Determination Of Ultratraces Of Thallium In Water By Flow Injection Differential Pulse Anodic-stripping Voltammetry"
Anal. Chim. Acta 1996 Volume 318, Issue 2 Pages 159-165
Zenon Lukaszewski*, Wlodzimierz Zembrzuski and Anna Piela

Abstract: Filtered water samples were diluted with 0.2 M ETDA (3:1) and 100 mL of the solution was continuously circulated at a flow rate of 15 ml/min through a voltammetric cell during the deposition period. The voltammetric cell was equipped with a Hg film working electrode on an epoxy resin impregnated graphite substrate (3.14 mm2), a SCE as the reference electrode and a Pt wire auxiliary electrode. The deposition was carried out at -900 mV for up to 120 min. At the end of the deposition period the flow was stopped and after 30 s the voltammogram was recorded by scanning the potential to ~e;-300 mV at 11.1 mV/s with a pulse amplitude of 50 mV. The calibration graph was linear from 25-100 pM-Tl with a 90 min deposition period and the detection limit was 10 pM. The RSD (n = 6-8) was 0.14% within the calibration range. The method was tolerant of a 1000-fold excess of Pb. The method was applied to the analysis of tap, river, lake and sea waters.
Thallium Voltammetry Ultratrace Interferences

"Paraquat Sensors Containing Membrane Components Of High Lipophilicities"
Anal. Chim. Acta 1997 Volume 338, Issue 1-2 Pages 89-96
Bahruddin Saad*, Marinah Mohd. Ariffin and Muhammad Idiris Saleh

Abstract: Membrane-type ISE for paraquat were prepared using PVC membranes containing octamethylcyclotetrasiloxane as the sensing substance, bis-(1-butylpentyl)decane-1,1-diyl diglutarate or tetra-n-undecyl-3,3',4,4'-benzophenone tetracarboxylate as the plasticizer and sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate or potassium tetrakis-(4-chlorophenyl)borate as additive. The optimum compositions for the membranes were 3.6% sensor substance, 63.5% plasticizer, 30% PVC and 3% additive. The ISE were fabricated by casting the PVC membranes onto Pt electrodes and the potentiometric response to paraquat was measured against a Ag/AgCl reference electrode. All the ISE exhibited a Nernstian response to paraquat with response times of ~20 s for paraquat concentration greater than 10 µM. The detection limit was 1 µM-paraquat. The ISE were used in a FIA system with Trizma buffer at pH 5.5 as the carrier stream (2.6 ml/min) and an injection volume of 50 µL. The mean recoveries of 10 µM-paraquat from well, river and lake waters were 96.3%, 94.7% and 93.9%, respectively. The sample throughput was 85/h.
Paraquat Potentiometry Electrode Electrode Sensor Buffer

"Room Temperature Phosphorescence Flow-through Biosensing Of Anionic Surfactants"
Anal. Chim. Acta 1998 Volume 371, Issue 1 Pages 73-80
R. Bad&iacute;a and M. E. D&iacute;az Garc&iacute;a*

Abstract: The first flow-through biosensor for anionic surfactant determination based on a sensitive room temperature phosphorescence phase (Al-Ferron) coated with bovine serum albumin was prepared, characterized and applied to the determination of sodium dodecylbenzenesulfonate in standard aqueous solution and in spiked water samples (lake, river and spring). The optosensor response to sodium dodecylbenzenesulfonate was linear from 5 x 10^-6 M to 5 x 10^-4 M which is a suitable range for the detection of anionic surfactant concentrations in polluted natural waters. The sample anal. was rapid (90% of the total response is reached in <30 s), convenient (no-sample pretreatment) and did not require organic reagents which are harmful to the environment. This work demonstrates the anal. potential of surfactant-protein interactions as a biorecognition mechanism using suitable luminescence probes.
Surfactants, anionic Phosphorescence Sensor Apparatus Detector

"Reverse Flow Injection Analysis Of Complexing Agents And Its Application To Estimation Of Complexing Capacity"
Talanta 1993 Volume 40, Issue 1 Pages 101-106
Norio Teshima, Hideyuki Itabashi and Takuji Kawashima*,

Abstract: The redox reaction of Cu(II) with Fe(II) in the presence of neocuproine is accelerated by complexing agents such as EDTA, nitrilotriacetic acid, citrate and pyrophosphate. A CuI - neocuproine complex with max. absorbance at 454 nm is produced. A reverse flow injection system based on this reaction is described. An 80 µL portion of 0.1 mM Cu(II) - 0.5 mM neocuproine solution was injected into a carrier stream of 0.05 M acetate buffer (pH 5.6) which was merged with a 0.1 mM Fe(II) solution, followed by a complexing agent sample solution The absorbance of the complex was monitored at 454 nm. The calibration graph was rectilinear in the range 2 µM to 0.01 mM for the 4 complexing agents cited. The effects of foreign ions are discussed. For the measurement of complexing capacity (e.g., in natural water), a 20 µM concentration. of metal ion such as Al(III), Cu(II), Zn(II), Cd(II) or Pb(II) was injected into the buffer carrier which was merged with streams of complexing agent, Fe(II) and Cu(II) - neocuproine as above. The decrease in the absorbance at 454 nm was monitored. The method was applied to river and lake waters.
Complexing capacity Spectrophotometry Reverse Complexation Interferences

"Reversed Flow Injection Spectrophotometric Determination Of Trace Amount Of Ammonia In Natural-water By Oxidation Of Ammonia To Nitrite"
Talanta 1997 Volume 45, Issue 2 Pages 405-410
Renmin Liu*, Huaisheng Wang, Ailing Sun and Daojie Liu

Abstract: A new sensitive flow injection method for determination of ammonia in natural water samples have been developed, based on the oxidation of ammonia to nitrite by hypochlorite in the presence of large amount of potassium bromide. The oxidant solution obtained by online mixing of hypochlorite and potassium bromide was injected into a water carrier stream, and then mixed with sample stream. Ammonia in the sample solution was oxidized to nitrite, Nitrite was then determined by spectrophotometry with sulfanilamide and N-1-naphthylethylenediamine. By reversed injection of the oxidant solution, the interference of nitrite and turbidity of the sample can be removed. The linear range of the method for ammonia is 0.2-12 µM. The proposed method is simple and sensitive. It had been applied to the determination of ammonia in lake water samples. Recoveries of 95-104% were obtained. (C) 1997 Elsevier Science B.V. 31 References
Ammonia Spectrophotometry Reverse Redox Interferences Turbidity

"Flow Injection Analysis With Tubular Membrane Ion-selective Electrodes In The Presence Of Anionic Surfactants"
Analyst 1983 Volume 108, Issue 1292 Pages 1357-1364
Anthony J. Frend, Gwilym J. Moody, J. D. R. Thomas and Brian J. Birch

Abstract: Ion-selective electrodes for Ca(II) based on a PVC-matrix membrane containing Ca bis{bis-[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate} as sensor and trioctyl phosphate as solvent mediator are shown to be able to discriminate against Na dodecyl sulfate and Na tetradecylbenzenesulfonate in flow injection analysis. Levels of Ca(II) have been determined with use of tubular membrane electrodes in flow injection analysis for three types of tap-water, for river water and for lake water, and are in good agreement with values obtained by AAS and by EDTA titration; such electrodes allow determination of 0.1 mM Ca(II) in the presence of a moderate amount of detergent. This sensitivity compares poorly with the level of free Ca(II) (<10 µM) determinable by using a conventional-type electrode with the same membrane system under static conditions.
Calcium Electrode Electrode Electrode Tubular membrane

"Continuous-flow System For The Accurate Determination Of Low Concentrations Of Ammonium Ions Using A Gas-permeable Poly(tetrafluoroethylene) Tube Decontaminator And An Ammonia Gas-sensing Membrane Electrode"
Analyst 1994 Volume 119, Issue 8 Pages 1839-1842
Hirokazu Hara and Susumu Matsumoto

Abstract: A calibration procedure, based on a constant-dilution method, is described for the determination of low concentrations of ammonium ions. A stream of ultrapure water (2 ml/min) was merged with a reagent stream of 0.21 M NaOH (0.1 ml/min) and the residual NH3 thus formed was removed by passing the solution through a microporous gas-permeable PTFE tube immersed in 0.5 M H2SO4 and thermostatted at 30°C. A limited volume (0.02, 0.04, 0.1, 0.2 and 1 ml/min) of standard NH4Cl solution was then added to the purified water. The diluted standard solution (2 ml/min) passed to a mixing chamber and then to an NH3 gas-sensing membrane electrode for analysis. The concentration of ammonium ions was calculated and a calibration graph was constructed. A diagram of the continuous-flow system used is given. The measurable concentration range was 0.1-5 µM of ammonium ions; the RSD (n = 5) was 0.8-1.1%. The system was used to determine low concentrations of ammonium ions in lake water.
Ammonium Electrode Electrode Teflon membrane Gas diffusion Heated reaction

"Catalytic Determination Of Dissolved Inorganic Carbon In Natural Waters By Flow Injection Spectrophotometry"
Analyst 1996 Volume 121, Issue 11 Pages 1617-1619
Nelson Maniasso, Sandra Sato, Maria F. Gin&eacute; and Antonio O. Jacintho

Abstract: Sample was aspirated (2 ml/min) so as to fill a 750 µL sampling loop. The loop contents were injected into a carrier stream (1.6 ml/min) of 30 mg/l silicate of a flow injection manifold (schematic shown). The sample zone was merged successively, with reagent streams of 0.5 M acetate buffer of pH 5 (0.4 ml/min), Cr(III) (3 g/l aged for 10 days before use; 0.4 ml/min) and 0.3 M EDTA (0.4 ml/min). The mixture was passed through a 200 cm coil maintained at 45°C and the absorbance was measured at 540 nm. The calibration graph was linear for 10^-300 mg/l dissolved inorganic carbon (as hydrogencarbonate). The RSD (n = 9) at the 50 mg/l level was The throughput was 36 samples/h. The method was applied to lake, river, well and tap water. The results obtained agreed with those obtained by titrimetry.
Carbon, inorganic Spectrophotometry Buffer Method comparison Heated reaction Catalysis

"Simultaneous Spectrofluorimetric Determination Of Selenium(IV) And (VI) By Flow Injection Analysis"
Analyst 1997 Volume 122, Issue 3 Pages 221-226
M. J. Ahmed, C. D. Stalikas, P. G. Veltsistas, S. M. Tzouwara-Karayanni and M. I. Karayannis

Abstract: A sample (100 µL) was injected into a carrier stream of 2 M H2SO4 at a flow rate of 0.1 ml/min and mixed with a reagent stream of 0.2 mM 2-(α-pyridyl)thioquinaldinamide in propan-2-ol at a flow rate of 0.3 ml/min. The fluorescence intensity due to Se(IV) was measured at 500 nm (excitation at 350 nm). A second portion (100 µL) was then injected into the carrier stream and passed through a coil (40 cm x 0.8 mm i.d.) where it was irradiated at 254 nm. The irradiated sample stream was then mixed with the reagent stream and the fluorescence intensity due to total Se was measured. Se(VI) was determined from the difference in the two fluorescence intensity values. The calibration graphs were linear from 0.01-2.2 and 0.1-2.4 µg/ml Se(IV) and Se(VI), respectively; corresponding detection limits were 1 and 10 ng/ml. RSD were 0.1-2% (n=5). The throughput was 25 samples/h. The method was applied to the analysis of alloys, hair, tap and lake water, sediments, soil, tea, flour and eggs. A simple, sensitive, highly selective, automatic spectrofluorimetric method for the simultaneous determination of selenium (IV) and (VI) as selenite-selenate by flow injection analysis (FIA) has been developed. The method is based on the selective oxidation of the non-fluorescent reagent 2-(α-pyridyl)thioquinaldinamide (PTQA) in acidic solution (1.5-3.0 M H2SO4) by Se(IV) to give an intensely fluorescent oxidation product (lambda ex =350 nm; lambda em = 500 nm). Selenium (VI) is reduced online to Se(IV), in a reduction coil installed in a photo- reactor, which is then treated with PTQA and the fluorescene due to the sum of Se(IV) and Se(VI) is measured; Se(Vi) is determined from the difference in fluorescence values. Various analytical parameters, such as effect of acidity, flow rate, sample size, dispersion coefficient, temperature, reagent concentration and interfering species were studied. The photo-reduction conditions were optimized, with an FIA procedure, for Se(VI) on the basis of its reduction efficiency. The calibration graphs were rectilinear for 0.1-2.4 µg mL-1 of Se(VI) and 10 ng mL-1 - 2.2 µg mL-1 of Se(IV), respectively. The method was applied to the determination of Se in several Standard Reference Materials (alloy, sediments and tea), as well as in some environmental waters (tap and surface water), food samples (flour and egg), a biological sample (human hair), soil sample and in synthetic mixtures. Up to 25 samples per hour can be analyzed with an RSD approximately 0.1-2%.
Selenium(IV) Selenium(VI) Fluorescence Speciation Photochemistry Selectivity Reference material Interferences

"Determination Of Primary Explosive Azides In Environmental Samples By Sequential Injection Amperometry"
Analyst 1997 Volume 122, Issue 4 Pages 315-319
Roger T. Echols, Ryan R. James and Joseph H. Aldstadt

Abstract: A method for determining the azide ion in water is described. The sample (~333 µL) was loaded into a holding coil then propelled by a carrier (donor) stream of 0.01 M KCl in phosphate buffer of pH 3.78 at a flow rate of 1 ml/min to a gas diffusion unit. In the gas unit, HN3 diffused across a PTFE membrane into a static acceptor stream of 0.01 M KCl in phosphate buffer of pH 6.6. Diffusion of HN3 was enhanced by carrying out four reverse and forward flows of the sample zone, after which the flow of the acceptor stream was started at a rate of 1 ml/min. The analyte was detected amperometrically at a vitreous C electrode at 1 V vs. Ag/AgCl. A diagram of the manifold used is given. The calibration graph was linear up to 0.5 ppm azide; the detection limit was 24.6 ppb. RSD was 1.7-7.7% (n = 4). The method was applied to the analysis of lake, tap and groundwater.
Azide ion Amperometry Electrode Sequential injection Gas diffusion Microporous membrane Teflon membrane

"Combination Of Flow Injection Hydride Generation And Sequestration On A Graphite Tube For The Automated Determination Of Antimony In Potable And Surface Waters"
J. Anal. At. Spectrom. 1992 Volume 7, Issue 2 Pages 433-438
Hans-Werner Sinemus, Joachim Kleiner, Hans-Henning Stabel and Bernard Radziuk

Abstract: Filtered samples of surface and potable water were acidified by addition of HCl to a final concentration. of 0.2M. The solution were mixed with 32% HCl followed by 3% KI - 5% ascorbic acid for reduction of SbV to Sb(III); the reduction time was reduced to 2 h with aqueous 10% hydroxylammonium chloride and interference from NO2- was eliminated with 15% sulfonic acid. The resulting solution was injected into a stream of NaBH4 in a fully automated microcomputer-controlled FIAS-200 flow injection system for generation of SbH3. The SbH3 was separated with a gas - liquid separator and transferred to a Perkin-Elmer HGA-500 graphite furnace for electrothermal AAS. The limit of determination was 20 pg with a detection limit of 15 pg. A method for the determination of Sb in potable and surface waters combines a flow injection app. for hydride generation with sequestration of Sb on a graphite tube, followed directly by atomization and measurement of atomic absorption. The entire measurement procedure and the acquisition of data were under microcomputer control, permitting fully automatic operation and improving measurement precision. Sample volumes of 500 µL can be manipulated using a sample loop and injection valve, whereas for larger volumes a continuous-flow technique has to be used. A study of recovery demonstrated that >90% of the Sb contained in sample volumes of 5 mL was retained on the surface of an uncoated electrographite tube. Statistical evaluation of calibration data yielded a limit of determination of 20 pg and a limit of detection of 15 pg. The method was applied to the depth profiling of total and dissolved Sb in lake water. In Lake Constance, a max. particle-bound concentration. of 25 ng/L was measured.
Antimony Spectrophotometry FIAS-200 Computer Automation Volatile generation Interferences Volatile generation

"Kinetically Assisted Equilibrium Based Repetitive Determination Of Iron(II) With Ferrozine In Flow-through Systems"
Anal. Chem. 1976 Volume 48, Issue 8 Pages 1207-1211
V. V. S. Eswara Dutt, A. Eskander-Hanna, and Horacio A. Mottola

Abstract: Repetitive determination based on injection of the sample containing the sought-for species into a continuously circulated reagent mixture are described. Injection occurs directly into the detector chamber and the determination Is based on two consecutive processes: 1) a fast chemical reaction taking place in the detection zone, and 2) the washing out of the generated signal as a result of the Imposed flow. Practical application of the approach is illustrated with the determination of iron( It) in aqueous solutions utilizing the organic reagent Ferrozine. This method was applied to the determination of Iron In EPA Quality Control Water Samples, lake water, and tap water.
Iron(2+) Spectrophotometry Complexation Kinetic Closed loop

"Fluorimetric Measurement Of Aqueous Ammonium Ion In A Flow Injection System"
Anal. Chem. 1989 Volume 61, Issue 5 Pages 408-412
Zhang Genfa and Purnendu K. Dasgupta

Abstract: The test solution (14 µL), containing NH3 or NH4+, is injected into a carrier stream (50 µL min-1) of water freed from NH3 and NH4+ by cation exchange, and the stream is mixed with 10 mM phthalaldehyde in aqueous 25% methanol (50 µL min-1) in a knotted coil and then with 3.0 mM Na2SO3 in 0.1 M phosphate buffer of pH 11.0 (50 µL min-1). The mixture is heated for ~40 s in a stainless-steel coil at 85°C (unnecessary at high NH4+ concentration.) and its fluorescence is measured at >425 nm (excitation at 351 nm). The detection limit is better than 20 nM-NH4+. The method is unaffected by NaCl concentration, and response to amino-acids is slight. The method has been used to determine NH4+ in tap- and lake water and rain.
Ammonium Fluorescence Buffer Interferences Detection limit Knotted reactor Selectivity Method comparison

"Efficient Flow Injection System With Online Gas Diffusion Preconcentration For The Determination Of Trace Amounts Of Ammonium-nitrogen At .mu.g/l Levels By Spectrophotometry"
Fresenius J. Anal. Chem. 1993 Volume 347, Issue 3-4 Pages 103-106
Shihua Fan, Hanswilly M&uuml;ller, Bettina Schweizer and Wolfgang B&ouml;hme

Abstract: Streams of sample solution and 0.1 M NaOH merged in a PTFE coil (30 cm x 0.5 mm i.d.) and passed to a gas diffusion unit fitted with a PTFE membrane through which the liberated NH3 passed into an absorption solution, which was stationary during the 30 s absorption period and was then pumped to the 1 cm detector cell for absorbance measurement at 590 nm. The calibration graph was linear for 1-100 ng/ml of ammonium-N and the detection limit was 0.8 ng/ml. The RSD (n = 10) at 10^-15 ng/ml were 1.5-2.8%. The recoveries of 20 ng/ml of ammonium-N added to lake water were 94-112%. The sampling frequency was 60-80 samples per h.
Ammonia, nitrogen Spectrophotometry Gas diffusion Preconcentration Teflon membrane

"Determination Of Trace Amounts Of Phosphate In Natural Water By Flow Injection Fluorimetry"
Anal. Lett. 1989 Volume 22, Issue 15 Pages 3081-3090
Wei, F.;Wu, Z.;Ten, E.

Abstract: Sample (50 µL) is injected into a carrier stream of water which then merges with merged streams fo 28 mM Mo(VI) - 0.8 M HCl and 20 µM-rhodamine 6G (C. I. Basic Red 1) - 0.025% of OP, and after passage through an 88-cm mixing coil the degree of fluorescence quenching at 550 nm is measured (excitation at 350 nm). The calibration graph is rectilinear for 100 ng mL-1 of P, and the detection limit is 2 ng mL-1. Only As(V) interferes, but can be masked by a 50-fold concentration. of S2O32-. Coefficients of variation (n = 12) for 10, 20 and 50 ng mL-1 of P were 5.4, 1.8 and 1.1%, respectively, and recoveries from tap-, well-, lake and pond water ranged from 92 to 102%.
Phosphate Fluorescence Quenching Interferences

"Differential Determination Of Arsenic(III) And Total Arsenic Using Flow Injection Online Separation And Preconcentration For Graphite-furnace Atomic Absorption Spectrometry"
Spectrochim. Acta B 1991 Volume 46, Issue 14 Pages 1789-1801
M. Sperling, Xuefeng Yin and B. Welz

Abstract: Trivalent As was extracted online using Na diethyldithiocarbamate as complexing agent and As(V) was reduced to As(III) with HCl- Na2S2O3 - Na2O3 - KI (preparation described). Online solid-phase extractive pre-concentration was performed on a C18 column, and As(III) and total As were determined sequentially by graphite-furnace AAS. Detection limits were 0.32 and 0.43 ng for As(III) and total As, respectively. A 7.6-fold enhancement in peak area was obtained with a 1-min pre-concentration as opposed to the direct injection of 40 µL samples. Results obtained for synthetic mixtures agreed well with expected values. The method was applied to seawater, lake water and drinking water. The coefficient of variation (n = 10) was 5.5% for 1.65 µg L-1 of total As in seawater.
Arsenic(3+) Arsenic, total Spectrophotometry Sample preparation C18 Extraction Preconcentration

"Determination Of Manganese At Trace Levels In Natural Waters With Continuous-flow System Utilizing Online Cation-exchange Separation And Catalytic Detection"
Anal. Sci. 1986 Volume 2, Issue 2 Pages 191-195

Abstract: The filtered (0.45 µm, Millipore) sample is made ~0.06 M in HCl and passed through a column of Hitachi Custom Resin No. 2611 (15.5 µm; strong cation exchanger), from which Mn is eluted with 0.2 M Na tartrate - 6 mM tartaric acid - 0.32 M NaCl (pH 5.1). Streams of 52 mM 3,4-dihydroxybenzoic acid (I), 1.5% H2O2 solution and 1.0 M Na2CO3 are pre-mixed in a coil, then mixed in a reaction coil (5 m long) with the Mn-containing eluate. The increase in absorbance at 480 nm, due to the Mn-catalyzed oxidation of I, is recorded. The detection limit with use of a 906 µL sample loop is 0.2 ng mL-1. For river and lake waters containing 1.4 to 11.2 ng mL-1 of Mn, the coefficient of variation was <2.5% (n = 5 or 6). The method shows good selectivity.
Manganese Ion exchange Spectrophotometry Catalysis Column Resin Optimization

"Flow Injection Spectrophotometric Determination Of Trace Amounts Of Bromide By Its Catalytic Effect On The Hydrogen Peroxide Oxidation Of Pyrocatechol Violet"
Anal. Sci. 1988 Volume 4, Issue 3 Pages 273-276

Abstract: Trace amounts of Br- were determined by flow injection analysis, by using a 10-m reaction coil operated at 37°C; 500 µL of sample solution was injected into the water carrier stream, which was then mixed with 3.5 M H2O2 and 0.1 or 0.05 mM catechol violet in 2.3 M HCl, with subsequent detection at 550 nm. The calibration graph was rectilinear from 10 to 600 µg L-1 of Br-; coefficient of variation were 2.5 and 1.4% for 20 and 105 muwg L-1 of Br-, respectively (n = 10), and recovery was 90 to 107%. Many common ions did not interfere, and the interference of others was reduced by using flow injection analysis; I- interfered at 200 µg l-1, but the effect could be decreased by suitable dilution. The method has been applied to several natural waters.
Bromide Spectrophotometry Catalysis Heated reaction Interferences

"Catalytic Spectrophotometric Determination Of Picogram Amounts Of Vanadium In Natural Fresh And Tap Water By Flow Injection Analysis"
Anal. Sci. 1996 Volume 12, Issue 2 Pages 237-242

Abstract: A spectrophotometric FIA method for the analysis of V down to 0.001 µg/l, based on its catalytic effect on the oxidation of o-phenylenediamine (OPDA) with bromate at pH 4 and 50°C in the presence of gallic acid as an activator, is presented. Portions (200 µL) of standard V solutions were injected directly into a carrier stream of water (0.8 ml/min) of a flow injection manifold (schematic shown) previously described by Kawakubo et al. Analyst [Cambridge, UK], 1995, 120, 2719). The carrier stream was merged sequentially with three reagent streams (0.2 ml/min), 14 mM gallic acid solution containing 1.5 M acetic acid and 0.35 M sodium acetate buffer of pH 4, 0.07 M OPDA and 0.7 M bromate solution in a reaction coil (4 m x 0.5 mm i.d.) in a temperature-controlled water bath and the oxidized OPDA produced was detected at 450 nm. The calibration graph was linear up to 8 µg/l for both V(IV) and V(V) and the detection limit and sampling frequency were 4 ng/l (0.8 pg) and 30 samples/h, respectively. The detection limit was 10-times lower than that obtained by the previous fluorimetric method (loc. cit.). Tolerance levels for five foreign ions (listed) and humic acid are given. The method was successfully applied to the analysis of lake, river, ground, rain and tap water samples with recoveries of 100-105%.
Vanadium Spectrophotometry

"Determination Of Organically Bound Sulfur In Swamp And Terrestrial Waters By Continuous-flow Oxidation And Ion Chromatography"
Environ. Sci. Technol. 1995 Volume 29, Issue 4 Pages 849-855
Joan Crowther, Francis B. Lo, Michael W. Rawlings, and Bernard Wright

Abstract: Swamp or lake water (1 ml/min) was mixed with air (0.32 ml/min) and 10% H2O2 and the stream passed into a UV digester containing a 50 turn 1.5 mm i.d. quartz coil. A flow rate of 2 ml/min allowed a 3.5 min exposure time. CO2 produced was released by passing through a porous PTFE tube (12 cm x 2 mm i.d.). The digested sample stream was spiked with 30 mM NaHCO3 and 24 mM Na2CO3 (0.1 ml/min) and then analyzed by ion chromatography on two columns (no dimensions given) of HPIC-AG3 with a HPIC-AG1 guard column (no dimensions given), 3 mM NaHCO3 and 2.4 mM Na2CO3 as mobile phase (2.5 ml/min). The eluate passed into an anion micromembrane suppressor with 12.5 mM H2SO4 as regenerant (4 ml/min) for detection by conductivity. The calibration graph was linear for 0.2-10 mg/l sulfate with a detection limit of 0.05 mg/l. The RSD improves as the sulfate concentration increases.
Sulfur, organically bound HPIC Conductometry Gas diffusion Teflon membrane UV reactor Photochemistry

"Oxidation Kinetics Of Iron(II) In A Eutrophic Swiss Lake"
Environ. Sci. Technol. 1998 Volume 32, Issue 19 Pages 2990-2996
Lukas Emmenegger, D. Whitney King, Laura Sigg, and Barbara Sulzberger

Abstract: The rate of oxidation of ferrous Fe was measured in samples from Lake Greifen, a eutrophic lake in Switzerland. Fe(II) concentrations were followed using an automated flow injection analysis system using luminol-based chemiluminescence detection of Fe(II). For kinetic studies at pH >7.8, the system was modified to allow a time resoln. of <1 s. Oxidation rates were measured in unfiltered samples at 2-2000 nM Fe(II). The pH was 6.8-8.3 by bubbling with CO2 and synthetic air. Above pH 7.4, rates were consistent with the rate law determined in pure carbonate systems. At pH 6.8-7.3, however, the apparent rate was independent of pH. This surprising finding may be explained by some naturally occurring (organic, colloidal, or surface) ligand(s) that accelerate the oxidation of Fe(II). The relative importance and pH dependence of the direct reaction with O in comparison to that with H2O2 was determined., and the enhancement of the overall rate was attributed to the reaction of Fe(II) with O.
Iron(2+) Chemiluminescence Kinetic Gas stream Reaction order

"Indirect Determination Of The Surfactant, Sodium Dodecylbenzenesulfonate Using Flow Injection (FI) - ICP-AES As A Diluting System"
Fenxi Kexue Xuebao 1995 Volume 11, Issue 1 Pages 58-60
Chen Wie; Jiang Zucheng; Kong Linying

Abstract: Solid sample was extracted with anhydrous ethanol and a 150 µL portion of the ethanolic solution was injected into a carrier stream of water (4.2 ml/min) of a flow injection system and transferred to a reaction coil (200 cm long) diluted and the solution passed through to the ICP detector where the absorbance of Na was measured at 588.995 nm by AES operated at observation height of 24 mm, with Ar as carrier gas at 0.6 l/min. Thus an indirect determination of sodium dodecylbenzenesulfonate (I) was established. Sampling frequency was 60 runs per h. The method was applied to the analysis of I in lake water.
Sodium dodecylbenzenesulfonate Spectrophotometry Indirect

"Flow Injection Spectrophotometric Analysis Of Iron Speciation In Natural Water"
Huanjing Huaxue 1989 Volume 8, Issue 4 Pages 35-40
Xu, Quan; Yuan, Xiushun

Abstract: Iron speciation in water was studied using the flow injection-spectrophotometric method. The color-development reaction of Fe2+ and 1,10-phenanthroline was used. Under optimum conditions, Fe3+ was reduced by solid ascorbic acid for the determination of total Fe before the samples were injected. Beer's law was applicable within 0-2.5 ppm ranges of Fe(II); a detection limit of 0.02 ppm was obtained. The relative error is ±0.05 ppm when the concentration of Fe(II) and Fe(III) is 1 ppm. The relative standard deviation for 2 ppm Fe2+ is 0.5% in five measurements. The method can be used at a rate of 250 injections/h. Fe(II) and Fe(III) were determination in aqueous phases and in suspension matter in rainwater and tapwater and lake water with satisfactory results.
Iron(2+) Iron(III) Spectrophotometry Injection technique Speciation Optimization

"Flow Injection Chemiluminescence Analysis And Its Application"
Huaxue Tongbao 1992 Volume 18, Issue 4 Pages 42-46
Li, G.H.;Yu, Z.N.

Abstract: A flow system was developed, based on the lumninol - CN- - Cu(II) system, and applied to the determination of Cu(II) in well, rain and lake water. Sample was filtered through a 0.454 µm filter paper and the filtrate was diluted with 10 mM Na4P2O7. The solution was injected into a flow coil in which a solution containing 0.033 mM luminol, 13.36 µg mL-1 of CN- and 0.033 M NaOH had merged with 0.1 M NaOH, and the chemiluminescence was measured. The calibration graph was rectilinear from 0.4 ng mL-1 to 0.8 µg mL-1 of Cu(II). The detection limit was 10 pg mL-1 of Cu(II). Recoveries were quantitative. The method was also applied to the determination of Co and Cr in natural water, Pb in waste water and H2O2 in tap water.
Cobalt Chromium Copper Chemiluminescence

"Determination Of Phosphate Utilizing Fluorescent Reaction Of Thiamine With Molybdovanadophosphate By Flow Injection Analysis"
J. Flow Injection Anal. 1998 Volume 15, Issue 2 Pages 234-240
Kishida, M.;Aoki, T.

Abstract: A fluorescence (FL) reaction between thiamine and molybdovanadophosphate was applied to a determination of phosphate by flow injection analysis (FIA). Phosphate was detected by measuring FL intensity of fluorophore produced by reaction of thiamine with molybdovanadophosphate. Under the condition of 1.0 x 10^-3 M vanadate, 1.8 x 10^-2 M sulfuric acid; 1.0 x 10^-3 M molybdate, and 7.5 x 10^-6 M thiamine, the calibration curve for the determination of phosphate was proportional in the concentration. range of 5.0 x 10^-7 M to 2.0 x 10^-5 M. The relative standard deviations (n = 5) at 1.0 x 10^-6 M and 1.0 x 10^-5 M were 5.0% and 2.0%, respectively. The time required to a peak after sample injection was 2 min. The addition of vanadate enabled the removal of interference from silica and increased more than 50 times the sensitivity for the determination of phosphate.
Phosphate Fluorescence Interferences Method comparison Sensitivity

"Early Diagenesis Of Mercury In The Laurentian Great Lakes"
J. Great Lakes Res. 1995 Volume 21, Issue 4 Pages 574-586
Jane M. Matty and David T. Long

Abstract: The early diagenesis of mercury in deep lake environments was investigated by examining the distribution of mercury among waters and sediments from several depositional basins in the Laurentian Great Lakes. Partitioning of mercury among different sediment phases was examined by sequential chemical extraction (using procedures specifically designed for mercury). Mercury in porewaters and sediment extracts was analyzed by flow injection/hydride-generation atomic absorption spectroscopy. Results indicate that mercury is affected by early diagenesis at all of the sites studied. Much of the mercury is enriched in the surface layer of sediments, where it is primarily associated with organic matter and iron oxides. The redox cycling of iron and manganese influences the behavior of mercury; concentration profiles suggest that as oxides begin to dissolve in reduced sediments, nearly all of the adsorbed mercury is released. Organic matter decay also appears to release significant amounts of mercury. Porewater profiles suggest that most of the dissolved mercury released from decaying organic matter or from dissolving iron oxides may be taken up by freshly deposited organic matter and iron oxides in the near-surface layers. Much of the mercury that reaches the sediment column is thus recycled near the sediment-water interface, increasing both the residence time and the concentrations of mercury in surface sediments of these deep lake basins.
Mercury Spectrophotometry Sample preparation

"Aquatic Soluble Unreactive Phosphorus: HPLC Studies On Concentrated Water Samples"
Water Res. 1995 Volume 29, Issue 9 Pages 2138-2148
Mark A. Nanny*, Seungdo Kim and Roger A. Minear*

Abstract: Soluble unreactive phosphorus (SUP) in concentrated forest stream (Walker Branch, Tenn.) and lake water (Crystal Lake, Ill.) samples was analyzed with an anion-exchange high performance liquid chromatography (HPLC) system containing a phosphorus-specific detector. The detector, which utilized the ascorbic acid-molybdate reaction, consisted of a flow injection system, a post-column reactor, and a u.v.-vis detector. Before HPLC analysis, samples were concentrated and molecular size fractionated with a series of ultrafiltration and reverse osmosis membranes. The SUP composition was found to be a function of season in both Crystal Lake and Walker Branch, as well as a function of stream length for Walker Branch. Seasonal and spatial SUP variations could be explained using contemporary knowledge of nutrient cycling in streams and lakes. A signal, seen in many of the HPLC traces and which eluted with the solvent front, was characterized but not fully identified using several extraction and degradation methods, as a function of sample concentration.
Phosphorus HPLC Spectrophotometry Post-column derivatization