Analysis Of Natural Water Samples Research Articles

Solid Phase Spectrophotometric Determination of Traces of Arsenate and Phosphate in Water Using Polyurethane Foam Sorbent

A simple and sensitive method for the determination of arsenate and phosphate in the µg L−1 concentration range using solid phase spectrophotometry has been developed. The method utilizes the quantitative sorption of the heteropoly blue species of arsenomolybdic and phosphomolybdic acids by polyurethane foam (PUF) sorbent prior to direct spectrophotometric measurement of the solid phase. In the same time the difference in formation behavior between the arsenomolybdic and phosphomolybdic acids at different pH values of sample solution has allowed their determination in the presence of each other. A preconcentration factor of 150 has been achieved for 100 mL samples. The detection limits are 5.4 and 1.66 µg L−1 for arsenate/As and phosphate/P, respectively and the working analytical ranges are from 5.4–54 µg L−1 and 1.6–40 µg L−1 respectively. The different experimental parameters such as rate of color development, acidity of solution and the analyte concentration have been thoroughly investigated. Analysis of natural water samples has been performed.

Factors Affecting Multiresidue Determination of Priority Herbicides when Using Solid-Phase Microextraction

A solid-phase microextraction (SPME) procedure was developed for the determination of 10 selected organonitrogen herbicides (s-ethyl dibropylthiocarbamate [EPTC], molinate, propachlor, trifluralin, simazine, atrazine, propazine, terbuthylazine, alachlor, and prometryn) and was tested with various natural waters. Gas chromatography coupled with flame thermionic and mass spectrometric detection was used for quantitation. For this purpose, polydimethylsiloxane and polyacrylate fibers were used and the factors affecting the SPME process such as pH, ionic strength, methanol content, memory effect, stirring rate, and adsorption-time profile were investigated and optimized. By using spiked liquid chromatography water, optimal factors were determined to be 25% salt, <0.5% methanol, stirring rate of 960 rpm, pH 4, and an equilibrium time of 30 min. These conditions were used in further studies of the fibers and in analysis of natural water samples. The method was applied to spiked natural waters such as ground water, sea water, lake water, and river water at a concentration range of 0.5-10 microg/L. Limits of detection ranged from 5 to 90 ng/L, and precision ranged from 5 to 15% (as relative standard deviation), depending on the pesticide, fiber, and detector used. The recoveries of herbicides were 70.2-118.4%, and the average r2 values of the calibration curves were >0.99 for all analytes. The results demonstrate the suitability of the SPME method to determine these organonitrogen herbicides in various natural waters. River water samples originating from the Epirus region (Northwestern Greece) were analyzed to verify the performance of the optimized method by comparing the results obtained by SPME with those obtained by using conventional solid-phase extraction of the selected herbicides.

Flame atomic absorption spectrometric determination of chromium(VI) by on-line preconcentration system using a PTFE packed column

A new, sensitive and robust time-based flow injection (FI) method for on-line preconcentration and determination of ultra trace amounts of chromium(VI) by flame atomic absorption spectrometry (FAAS) has been elaborated. The sample is initially mixed on-line with ammonium pyrrolidine dithiocarbamate (APDC) and the Cr(VI)–PDC chelate is absorbed quantitatively on a mini-column packed with polytetrafluoroethylene (PTFE) turnings at a pH range 0.8–1.4. The complex is subsequently eluted with isobutyl methyl ketone (IBMK) and introduced directly into the nebulizer–burner system. The optimized system offered improved performance characteristics, with unlimited lifetime of the proposed column. The enhancement factor was 80, for a 3-min preconcentration time and the sample frequency was 18 h −1. The calibration curve was linear over the concentration range 1–40 μg l −1 with a detection limit of c L=0.8 μg l −1 and a relative standard deviation of s r=3.2%, at the 20 μg l −1 level. The proposed method was evaluated by analyzing samples of certified and spiked water, and it was applied to the analysis of natural water samples and sediments.

DETERMINATION OF TRACE ELEMENTS BY INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROMETRY (ICP-AES) AFTER PRECONCENTRATION ON A SUPPORT IMPREGNATED WITH PIPERIDINE DITHIOCARBAMATE

A procedure is developed for the determination of Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn in water by inductively coupled plasma-atomic emission spectrometry (ICP-AES) after preconcentration on a piperidine dithiocarbamate supported polyurethane foam. The sorbed elements are subsequently eluted with 4 mol L−1 HNO3, and the acid eluates are analysed by ICP-AES. A 20-mL disposable syringe served as a chromatographic preconcentration column. The sorption recoveries of elements except Co and Cr were higher than 97%. The method is also applied for the analysis of natural water samples.

A New Differential Pulse Voltammetric Method for the Determination of Nitrate at a Copper Plated Glassy Carbon Electrode

A differential pulse voltammetric method for the determination of nitrate has been described, which is applicable to the analysis of natural water samples with nitrate levels greater than 2.8 × 10−6 M. A reduction peak for the nitrate ions at a freshly copper plated glassy carbon electrode was observed at about −0.50 V vs Ag ∣AgCl∣KClsatd electrode in a solution of 2.0 × 10−2 M Cu2+, 0.5 M H2SO4 and 1.0 × 10−3 M KCl and exploited for analytical purposes. The working linear range was established by regression analysis and found to extend from 2.8 ×10−6 M to 8.0 × 10−5 M. The proposed method was applied for the determination of nitrate in natural waters. The detection limit of the method was 2.8 × 10−6 M and the sensitivity was 0.9683 A·L/mol. The possible interferences by some ions such as phosphate, nitrite and some halides were determined and found to lead to shifts of the peak position and increasing the peak heights.

Determination of traces of nitrite and nitrate in water by solid phase spectrophotometry

A simple and sensitive method for the determination of nitrite and nitrate in water using solid phase spectrophotometry is described. The method utilizes the quantitative and rapid sorption of the dye formed from nitrite, using the Griess reaction, into a thin layer of polyurethane foam (PUF) where a preconcentration factor of >140 has been achieved. Nitrate is pre-reduced using a cadmium reductor before applying the Griess reaction. The direct spectrophotometric measurement of the dye enriched in the solid foam phase has allowed the detection of as little as 5 and 40ngml−1 nitrite and nitrate, respectively. Optimization of the parameters affecting the quantitative formation and sorption of the dye into PUF has been considered. Analysis of natural water samples has been performed.

A rapid and precise method for measuring stable carbon isotope ratios of dissolved inorganic carbon

Abstract We describe a method for rapid preparation, concentration and stable isotopic analysis of dissolved inorganic carbon ( δ 13 C -DIC). Liberation of CO2 was accomplished by placing 100 μl phosphoric acid and 0.9 ml water in an evacuated 1.7-ml gas chromatograph (GC) injection vial. Following equilibration, the vial headspace gas was injected into a gas chromatograph-combustion-isotope ratio mass spectrometer (GC-C-IRMS) using a standard GC autosampler. A correction factor of −1.0‰ must be added to all isotopic measurements due to the equilibrium isotopic fractionation between the aqueous and gaseous phases in the sample vials. The method allows for the preparation and analysis of 48 samples, in triplicate, in a 40-h period. We report on the analysis of an inter-laboratory CaCO3 standard, as well as two natural water samples. Samples analyzed between 15 and 36 h after preparation exhibited standard deviations of ±0.2‰, while standards analyzed at varying concentrations and injection volumes had standard deviations of ±0.1‰ with a minimum concentration of 0.20 mM DIC. Additionally, chromatographic area vs. concentration of standard carbon yielded an r2=0.996, indicating that DIC concentrations can also be obtained from the GC-C-IRMS data, if desired. Further, the standard deviations observed during the analysis of natural water samples from a seagrass dominated lagoon with diel variations of 1.5‰ were consistent with those observed in laboratory standard analysis.

Reverse Polarity Capillary Zone Electrophoretic Analysis of Nitrate and Nitrite in Natural Water Samples

This paper describes the application of reverse polarity capillary zone electrophoresis (CZE) for rapid and accurate determination of nitrate and nitrite in natural water samples. Using hexamethonium bromide (HMB) as an electroosmotic flow modifier in a borate buffer at pH 9.2, the resolution of nitrate and nitrite was accomplished in less than 3 min. CZE was compared with ion chromatographic (IC) and cadmium reduction flow injection analysis (Cd-FIA) methods which are the two most commonly used standard methods for the analysis of natural water samples for nitrate and nitrite. When compared with the IC method for the determination of nitrate and nitrite, CZE reduced analysis time, decreased detection limits by a factor of 10, cut laboratory wastes by more than 2 orders of magnitude, and eliminated interferences commonly associated with IC. When compared with the cadmium reduction method, CZE had the advantage of simultaneous determination of nitrate and nitrite, of being able to be used in the presence of various metallic ions that normally interfere in cadmium reduction, and of decreased detection limits by a factor of 10.

Refractive index of planktonic cells as a measure of cellular carbon and chlorophyll a content

Current methods for determining carbon content in individual planktonic cells from particle volume alone may involve large errors, and no routine technique exists for determining chlorophyll a content in individual phytoplankters. In this study the concept of using the refractive index of cells as a measure of intracellular concentrations of carbon and chlorophyll a is discussed. Specifically, the real part of the refractive index n (at light wavelengths where absorption is negligible or very small) is shown to correlate well with the intracellular concentration of carbon, C i. The imaginary part of the refractive index n′ (in the red band of chlorophyll a) correlates well with the intracellular chlorophyll concentration, Chl i. These relationships were found to be nearly identical for two species, a cyanobacterium Synechococcus and a diatom Thalassiosira pseudonana, over a two-fold range in C i and Chl i. This range was associated with interspecies differences and intraspecies variations in the cell properties over a day–night cycle. These observations and the underlying theoretical considerations suggest that the relationships C i vs. n and Chl i vs. n′ may be robust and hold for a variety of planktonic species regardless of interspecies and intraspecies variability in cellular carbon content, Chl a content, and cell size. In addition, these relationships may be applicable to single-particle analysis of natural water samples, which promises a unique capability to acquire information about the distribution of carbon and chlorophyll a among individual cells, different size classes, and taxonomic groups of planktonic microorganisms in the ocean. Further research with various planktonic species is needed to examine the generality of the relationships C i vs. n and Chl i vs. n′ before the approach can be implemented in field studies.

Double-disk solid-phase extraction: simultaneous cleanup and trace enrichment of herbicides and metabolites from environmental samples.

Phenylurea and triazine herbicides, including some metabolites, were isolated from water and soil extracts by solid-phase extraction using a layered system of two extraction disks, a method called double-disk solid-phase extraction. The first disk consisted of strong anion exchange (SAX) of 10-micron styrene divinylbenzene (SDB) particles embedded in Teflon, and the second disk was a C18 disk of 10-micron particles also embedded in Teflon. A volume of 500 mL of water or aqueous soil extract is passed through the layered system with the SAX disk first. The purpose of the SAX disk is to remove the humic and fulvic acids from the water or aqueous soil extract by ion exchange through their carboxyl groups. Even during methanol elution of herbicides, the humic substances remain bound to the SAX disk with > 85% retention. Elution with methanol results in more than 90% recovery of the herbicides from the layered extraction disks. Removal of the humic and fulvic acids results in greater sensitivity for diode array detection quantitation (0.05 micrograms/L for herbicides) by substantially reducing the absorbance of the humic peak on the LC chromatogram. The herbicides adsorb to the SAX disk either through hydrogen bonding to the anion-exchange sites or by hydrophobic interaction with the SDB surface of the anion-exchange disk. The method was tested for the analysis of natural water samples from the Mississippi Embayment, a cotton-growing area of the southeastern United States.

Preconcentration of trace elements on a support impregnated with sodium diethyldithiocarbamate prior to their determination by inductively coupled plasma-atomic emission spectrometry

A procedure is developed for determination of As, Co, Se, Cr, Pb, Zn, Cu, Mn, Cd, Sb, and Sn in water by ICP-AES analysis of alcohol eluates after pre-concentration of the samples. The pre-concentration is performed on a sodium diethyldithiocarbamate supported soft polyurethane foam. The sorbed elements are subsequently eluted with 1-propanol and the alcohol eluates are analysed by ICP-AES. A eight-fold concentration is achieved. An increased sensitivity in the analysis of propanol–water (30:70, v/v) solution is established as compared with aqueous solutions. The strongest effect is observed for As, Se, Pb, Cr, Sn, and Cd-increasing is more than twice. For other elements the matrix influence is by a factor of 1.45 (Cu), 1.36 (Sb), 2.08 (Zn). The method is applied to the analysis of natural water samples.

Automated Chromatographic Analysis of Atmospheric Gases in Environmental Samples

AbstractThe need for a single‐injection gas chromatographic procedure for detection of the principal atmospheric gases found in environmental samples has led to development of an automated system that permits measurement of CO2, N2O, O2‐Ar, and N2 in a single detector without interference from water vapor in samples. The injection of gas samples on the system was automated by interfacing a commercial headspace sampler with a gas chromatograph (GC) that was fitted with an ultrasonic detector and two automated multiport switching valves. The first switching valve was configured with short precolumns of Porapak Q (PQ) to retain and vent the water vapor in samples. The other valve was configured with two analytical columns connected in series that permit separation of the gas components. After water is removed by the precolumn, the gas sample flows onto a PQ column where CO2 and N2O are retained and separated while the composite peak of N2 and O2‐Ar elutes onto a molecular sieve (MS) column. The valve is then switched, causing reversal of the order of columns with respect to the gas flow without reversing the direction of flow through the columns. This allows the CO2 and N2O peaks to elute from the PQ column to the detector while the O2‐Ar and N2 components are separated on the MS column and later flow to the detector. The system has proven to be robust in that it permits routine, unattended analyses of moist gas samples with high sensitivity and without interference from water peaks. This, in conjunction with the highly controlled equilibrium conditions permitted by use of the headspace sampler, makes the system suitable for gas analysis of environmental samples including dissolved gas analysis of natural water samples.

Gas chromatography coupled with atomic absorption spectrometry — a sensitive instrumentation for mercury speciation

New instrumentation for the speciation of mercury is described, and is applied to the analysis of natural water samples. The separation of mercury species is effected using gas chromatography of derivatized mercury species on a widebore capillary column. The solvent is vented using a bypass valve and the separated mercury species are pyrolysed on-line at 800°C for production of mercury atoms. These are then detected by atomic absorption spectrometry (AAS) at the 253.7 and 184.9 nm lines simultaneously in a quartz cuvette. The use of the 184.9 nm line provides a more than five-fold increase in sensitivity compared with the conventional 253.7 nm line and an absolute detection limit of 0.5 pg of mercury. The dynamic range of the combined analytical lines provides a linear response over more than three orders of magnitude. A number of organic compounds not containing mercury are also detected following pyrolysis, especially at the 184.9 nm line. These background species must not co-elute at the retention times for methyl- and inorganic mercury, as otherwise a positive interference would result. By maximizing the chromatographic resolution and minimizing the band broadening in the cuvette by use of a make-up gas, the retention times of interest are freed from co-eluting background peaks. The instrumentation has been applied to the determination of ng l −1 concentrations of methyl- and inorganic mercury in Lake Constance, Germany and within the Lake Constance drinking water supply organization, Bodenseewasserversorgung (BWV). The accuracy for the sum of methyl- and inorganic mercury has been assessed by comparison with an independent method for total mercury based on AAS detection implemented at BWV. Relative detection limits using 1 litre water samples and 15 ml injections of the final hexane extract were 0.03 ng l −1 for methylmercury and 0.4 ng l −1 for inorganic mercury based on the 3j criterion.

Application of ion interaction chromatography to the determination of metal ions in natural water samples

The retention behaviour of Fe(III), Cu, Pb, Zn, Ni, Co, and Mn in ion interaction chromatography was investigated to optimise metal ion separation and detection in water samples. A solution of an alkanesulfonate, the ion interaction reagent (IIR), tartaric acid, and acetonitrile (or methanol) was used as eluent. Retention times were found to be accelerated by increasing the following: organic modifier concentration, tartaric acid concentration, and the pH of the eluent solution. In contrast, increasing the length of the IIR carbon chain was found effective in enhancing the retention times of metal ions. An analytical method for the determination of metals at the μg/1 level was developed and applied to the analysis of natural water samples.

Determination of Selenium in Natural Water by AAS after Solvent Extraction Preconcentration

The method described in this paper is based on the use of diethyldithiocarbamate (DEDC) to complex the trace selenium from the natural waters, with subsequent separation of the complex by solvent extraction and quantification by graphite furnace-atomic absorption spectrometer. The concentration coefficient is 10 3. The limit of detection is 0.01 ppb for 250 ml of sample. The precision (RSD) at the 10-ng level is better then 5%. The recovery is 96.6% (93.5-99.6%). Accuracy of results was assessed by independent, analytical techniques (ICP-MS). Comparison of results of GF-AAS and ICP-MS analysis of natural water samples indicates good agreement.

Chemical equilibrium calculation for evaluating the buffering capacity of acidic natural water equilibria with the mineral phase gibbsite

A simple computer model based on the chemical equlibrium calculation is developed to evaluate the buffering capacity, β, of acidic natural water equilibria with the mineral gibbsite. The influence of various factors [temperature, equilibrium constant for solubility of Al(OH)3 solid-phase Ksp, concentrations of fluoride, dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC)] on the β values calculated were investigated. This model has been tested with real water quality data and applied to the practical analysis of natural water samples. The uncertainties in theoretical calculation of buffering capacity associated with the errors from variations in thermodynamic constants and measured input data were evaluated by the Monte Carlo method.

Flow injection chemiluminescent detection of trace Co(II) with dibromoalizarin violet-H2O2-CTMAB system

Chemiluminescence was observed when dibromoalizarin violet was oxidized with hydrogen peroxide in alkaline solution. Trace amounts of Co (II) catalysed this CL reaction strongly, especially in the presence of the cationic surfactant cetyltrimethylammonium bromide, and the CL intensity was proportional to the concentration of Co(II). A flow injection system with CL detection was established to investigate this CL system. The optimum conditions for this CL reaction were investigated in detail, and the optimized flow injection parameters were determined by the modified simplex method. A CL analytical method for determination of ultratrace amounts of Co (II) was developed with a detection limit of 4 pg/mL. It was used for analysis of natural water samples, and the results compare very well with those from GFAAS. A possible mechanism for this CL reaction is proposed on the basis of studying CL spectra, absorption spectra, fluorescent spectra and HMO treatment for the reagent molecule. The effects of various types of surfactants on CL reaction are also discussed.

Spectrophotometric flow injection determination of formetanate and m-aminophenol in water after reaction with p-aminophenol

An automated procedure has been developed for the determination of formetanate and its metabolite m-aminophenol (MAP) in water samples. MAP can be selectively determined in the presence of formetanate by direct on-line reaction with p-aminophenol and spectrophotometric measurement of the absorbance at 576 nm in the presence of KIO 4, as oxidizing agent. The method has a limit of detection of 5 × 10 −7 M, it provides a recovery percentage from 95 to 104% and permits one to carry out 120 measurements/hr. The spectrophotometric determination of formetanate must be carried out after a previous hydrolysis to MAP. To determine formetanate in the presence of MAP, two steps are necessary. Firstly, the MAP content is selectively determined as has been mentioned above. After that, the sample is treated with 0.05 M NaOH at 90'°C, to hydrolyze the formetanate to MAP, and then the sum of both is determined spectrophotometrically. The difference between the results obtained in each step gives the formetanate concentration. The developed procedure for the determination of formetanate provides a sensitivity of 1070 absorbance units mol −1 l and a limit of detection of 1.9 × 10 −7 M, which corresponds to 50 μg/l of formetanate hydrochloride. The method has been applied to the analysis of natural water samples fortified with formetanate and MAP, and formetanate has also been quantitatively recovered in irrigation waters at a concentration level of 1.9 × 10 −6 M which corresponds to 500 μg/l. On the other hand, working in the stopped-flow mode, for a reaction time of 100 sec, the sensitivity of the formetanate determination can be increased to 4642 absorbance units mol −1 l but the limit of detection remains of the order of 44 μg/l.

Application of ion-exchanger phase photoacoustic spectroscopy to flow analysis of trace amounts of iron in water

Ion-exchanger phase photoacoustic spectroscopy has been applied to the flow analysis of trace amounts of iron in water. The reaction product of iron(II) with 4,7-diphenyl-1,10-phenanthroline-disulphonate, introduced into a carrier solution stream in the flow system, was concentrated on a small amount of QAE-Sephadex gel settled in a fused silica glass tube (1.5 mm i.d.) of a photoacoustic cell. The photoacoustic signal produced by pulsed laser irradiation of the gel beads at 532 nm was detected by a cylindrical piezoelectric transducer which was attached outside the glass tube. When 3.7 ml of a sample solution was introduced into the flow system, the sensitivity of this method was 590 times higher than that of the corresponding solution photoacoustic spectrometry and the detection limit of iron was 0.33 ng/ml. Because the coloured complex was desorbed from the cell with a desorbing agent solution, the present method could afford repeated analyses of natural water samples containing iron at ng/ml levels without any preconcentration procedures.

Flow-injection spectrophometric determination of propoxur with p-aminophenol

The spectrophotomeric determination of propoxur [2-(1-methyxlthoxy)phenyl methyl carbamate] was carried out with p-aminophenol (PAP) in a flow system. The method involves the on-line hydrolysis with NaOH of propoxur to 2-isopropoxyphenol and the oxidation of PAP to its relative quinone imine with KIO 4 and the reaction between the phenolate and the quinone imine. A four-channel flow manifold was employed to carry out all the different steps of the reaction considered, monitoring the indo dye formed at 600 nm. The developed procedure provides a typical calibration line of A = 0.000 7 + 1.8 × 10 3 C ( A = absorbance; C = concentration in M) with a regression coefficient of 0.9998 and a limit of detection, for a probability level of 95% (for K = 3) of 0.1 μg ml −1. In the analysis of synthetic samples containing propoxur and 2-isopropoxyphenol, the total concentration of proproxur was determined with a recovery from 94% to 98.3%. The method provides results comparable to those obtained by the batch analysis of natural water samples spiked with propoxur.