A novel tetrachlorothallate (III)-PVC membrane sensor for the potentiometric determination of thallium (III)

A novel tetrachlorothallate (III) (TCT)-selective membrane sensor consisting of tetrachlorothallate (III)-2,3,5-triphenyl-2-H-tetrazolium ion pair dispersed in a PVC matrix plasticized with dioctylphthalate is described. The electrode shows a stable, near-Nernstian response for 1×10⁻³-4×10⁻⁶ M thallium (III) at 25 °C with an anionic slope of 56.5±0.5 over the pH range 3-6. The lower detection limit and the response time are 2×10⁻⁶ M and 30-60 s, respectively. Selectivity coefficients for Tl(III) relative to a number of interfering substances were investigated. There is negligible interference from many cations and anions; however, iodide and bromide are significantly interfere. The determination of 0.5-200 μg ml⁻¹ of Tl(III) in aqueous solutions shows an average recovery of 99.0% and a mean relative standard deviation of 1.4% at 50.0 μg ml⁻¹. The direct determination of Tl(III) in spiked wastewater gave results that compare favorably with those obtained by the atomic absorption spectrometric method. The electrode was successfully applied for the determination of thallium in zinc concentrate. Also the tetrachlorothallate electrode has been utilized as an end point indicator electrode for the determination of thallium using potentiometric titration.     

Renewable sol-gel carbon ceramic electrodes modified with a Ru-complex for the amperometric detection of l-cysteine and glutathione

A renewable three-dimensional chemically modified carbon ceramic electrode containing Ru [(tpy)(bpy)Cl] PF₆ was constructed by sol-gel technique. It exhibits an excellent electro-catalytic activity for oxidation of l-cysteine and glutathione at pH range 2-8. Cyclic voltammetry was employed to characterize the electrochemical behavior of the chemically modified electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for l-cysteine and glutathione by hydrodynamic amperometry. Optimum pH value for detection is 2 for both l-cysteine and glutathione. The catalytic rate constants for l-cysteine and glutathione were determined, which were about 2.1×10³ and 2.5×10³ M⁻¹ s⁻¹, respectively. Under the optimized condition the calibration curves are linear in the concentration range 5-685 and 5-700 μM for l-cysteine and glutathione determination, respectively. The detection limit (S/N=3) and sensitivity is 1 μM, 5 nA/μM for l-cysteine and 1 μM, 7.8 nA/μM for glutathione. The relative standard deviation (RSD) for the amperogram's currents with five injections of l-cysteine or glutathione at concentration range of linear calibration is <1.5%. The advantages of this amperometric detector are: high sensitivity, good catalytic effect, short response time (t<3 s), remarkable long-term stability, simplicity of preparation and reproducibility of surface fouling (RSD for six successive polishing is 3.31%). This sensor can be used as a chromatographic detector for analysis of l-cysteine and glutathione.     

Adsorptive Stripping Voltammetric Determination of Phenol at an Electrochemically Pretreated Carbon-Paste Electrode with Solid Paraffin as a Binder

An adsorptive stripping voltammetric method for determination of phenol at an electrochemically pretreated carbon-paste electrode has been developed. Solid paraffin was used as the binder of the carbon-paste electrode. The carbon-paste electrode was pretreated in the solution of 0.001 mol L⁻¹NaOH by holding it at +1.8 V (versus an Ag/AgCl electrode) for 5 min. On the pretreated electrode, the adsorption of phenol was greatly enhanced. Phenol was accumulated in NH₃–NH₄Cl (pH 9.25) medium at the potential of +0.1 V (versus Ag/AgCl electrode) for a certain time and then determined by second order differential anodic stripping voltammetry. An oxidative peak was observed at about +0.66 V. The relationship between second order peak current and phenol concentration was linear in the range of 2.5 × 10⁻⁷–5.0 × 10⁻⁶mol L⁻¹phenol, and the detection limit was 5.0 × 10⁻⁸mol L⁻¹. The method has been applied to the determination of phenol in tap water and waste water. The relative standard deviation (six determinations) was less than 3.5%.     

Simultaneous determination of zirconium and hafnium as ternary complexes with 5-Br-PADAP and fluoride using solid-phase extraction and reversed-phase liquid chromatography

Solid-phase extraction (SPE) along with reversed-phase liquid chromatography (RP-LC) was used for the simultaneous determination of Zr(IV) and Hf(IV) by means of their ternary chelates with fluoride and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). The conditions of SPE sorption were examined in detail: type of SPE column, volume of the sample, volume of the eluent, concentrations of metal ions, fluoride salt, chromogenic reagent, organic phase, and pH. It was established that the sorption of Zr(IV) and Hf(IV), as their ternary chelates, on SPE Zorbax SPE C18 (EC) cartridge was the most efficient, when the sample containing metal ion (Zr(IV), Hf(IV), both, up to 2 μg), 5-Br-PADAP 1.5×10⁻⁴, NaF 7.5×10⁻⁵ mol l⁻¹, methanol 40%, pH 4.5±1 was applied for the SPE sorption. The chelates were discarded from SPE cartridge using acetonitrile/water (99.75+0.25, v/v) eluent containing 3.8×10⁻⁴ mol l⁻¹ sodium fluoride and subsequently separated by RP-LC method. The RP-LC separation of both chelates was optimized and Zorbax SB-C18 analytical LC column along with acetonitrile/water (65+35, v/v) eluent containing the 1.5×10⁻⁴ mol l⁻¹ sodium fluoride was used. The established SPE/LC conditions allow Zr(IV) 0.08-2.0 μg and Hf(IV) 0.04-2.0 μg determination in a sample volume up to 150 ml. The detection limits, 0.03 μg Hf(IV) and 0.05 μg Zr(IV), were obtained. Recoveries, (94±2)% for Hf(IV) chelate and (106±2)% for Zr(IV) chelate were obtained, when 1 μg of Zr(IV) and Hf(IV) ions were determined by the present SPE/LC method from the sample volume of 100 ml. The established, pre-concentration SPE conditions, along with the LC separation and determination allow the assay of Zr(IV) and Hf(IV) in complicated matrix materials. The present SPE/LC method was applied to the determination of Zr(IV) and Hf(IV) in tap water and reference geological material (rock, NCS DC 73303; certified content: Zr, 27.7×10⁻³% (w/w) and Hf, 6.5×10⁻⁴% (w/w)).     

Flow injection electrochemical enzyme immunoassay based on the use of an immunoelectrode strip integrate immunosorbent layer and a screen-printed carbon electrode

A flow injection amperometric immunoassay system based on the use of screen-printed carbon electrode for the detection of mouse IgG was developed. An immunoelectrode strip, on which an immunosorbent layer and screen-printed carbon electrode were integrated, and a proposed flow cell have been fabricated. The characterization of the flow immunoassay system and parameters affecting the performance of the immunoassay system were studied and optimized. Amperometric detection at 0.0 V (versus Ag/AgCl) resulted in a linear detection range of 30-700 ng ml⁻¹, with a detection limit of 3 ng ml⁻¹. The signal variation among electrode strips prepared from variant batch did not exceed 8.5% (n=7) by measuring 0.5 μg ml⁻¹ antigen standard solution.     

Potentiometric determination of antihistaminic diphenhydramine hydrochloride in pharmaceutical preparations and biological fluids using screen-printed electrode

The performance characteristic of sensitive screen-printed (SPE) and carbon paste (CPE) electrodes was investigated for the determination of diphenhydramine hydrochloride (DPH) drug in pure, pharmaceutical preparations and biological fluids. Different experimental conditions namely types of materials used to prepare the working electrode (plasticizer), titrant, pH, temperature and life time were studied. Under these conditions, the SPE shows the best performance than CPE with respect to total potential change and potential break at the end point. The SPE and CPE exhibit suitable response to DPH in a concentration range of 1.0.10^{− 2} to 1.0.10^{− 6} mol/L with a limit of detection 9.70.10^{− 7} and 9.80.10^{− 7} mol/L, respectively. The slope of the system was 55.2 ± 1.0 and 54.7 ± 1.0 mV/decade over pH range 3.0–8.0 and 3–7 for SPE and CPE, respectively. Selectivity coefficients for DPH relative to a numbers of potential interfering substances were investigated. The SPE and CPE show a fast response time of 10 and 16 s and were used over a period of 2 months with a good reproducibility. The sensors were applied successfully to determine DPH in pharmaceutical preparations and biological fluids. The results are compared with the official method.     

Optimum phase-behavior formulation of surfactant/oil/water systems for the determination of chromium in heavy crude oil and in bitumen-in-water emulsion

An “oil in water” formulation was optimized to determine chromium in heavy crude oil (HCO) and bitumen-in-water emulsion (Orimulsion-400®) samples by transversally heated electrothermal atomic absorption spectrometry (TH-ET AAS) using Zeeman effect background correction. The optimum proportion of the oil-water mixture ratio was 7:3 v/v (70 ml of oil as the internal phase) with a non-ionic surfactant concentration (Intan-100) in the emulsion of 0.2% w/w. Chromium was determined in different crude oil samples after dilution of the emulsions 1:9 v/v with a 0.2% w/w solution of surfactant in order to further reduce the viscosity from 100 to 1.6 cP and at the same time to bring the concentration of chromium within the working range of the ET AAS technique. The calibration graph was linear from 1.7 to 100 μg Cr l⁻¹. The sensitivity was of 0.0069 s l μg⁻¹, the characteristic mass (m_o) was of 5.7 pg per 0.0044 s and the detection limit (3σ) was of 0.52 μg l⁻¹. The relative standard deviation of the method, evaluated by replicate analyses of three crude oil samples varied in all cases between 1.5 and 2.6%. Recovery studies were performed on four Venezuelan crude oils, and the average chromium recovery values varied between 95.9-104.8, 90.6-107.6, 95.6-104.0 and 98.8-103.9% for the Cerro Negro, Crudo Hamaca and Boscán crude oils and for the Orimulsión®-400, respectively. The results obtained in this work for the Cerro Negro, Crudo Hamaca and Boscán crude oils and for the Orimulsión®-400 following the proposed procedure were of 0.448±0.008, 0.338±0.004 0.524±0.021 and 0.174±0.008 mg Cr l⁻¹, respectively, which were in good agreement with the values obtained by a tedious recommended standard procedure (respectively: 0.470±0.05, 0.335±0.080, 0.570±0.021 and 0.173±0.009 mg Cr l⁻¹).     

Flow injection potentiometric detection of trimethylamine in seafood using tungsten oxide electrode

A simple flow injection gas/diffusion method for the determination of trimethylamine (TMA) in seafood with potentiometric detection using tungsten oxide electrode has been developed. The method is based on the diffusion of TMA through a PTFE membrane from a sodium hydroxide donor stream to a phosphate buffer acceptor stream. The TMA in the acceptor stream passes through an electrochemical flow cell containing a tungsten oxide wire and a silver/silver chloride electrode, where TMA was sensitively detected. The parameters affecting the sensitivity of the electrode such as sodium hydroxide concentration, buffer concentration, pH, flow rate and injected volume were studied in details. The electrode response was linear in the concentration range from 1 to 10 μg ml⁻¹ TMA with a correlation coefficient (R²) of 0.991 and a detection limit of 0.05 μg ml⁻¹ TMA. The intra- and inter-days precision (R.S.D.) was found to be, respectively, 1.20 and 1.6% (n=6). The method was applied to the determination of TMA in fish tissue and recoveries of 99-100% were obtained for fish extracts. Results were in close agreement with those obtained by the existing classical official method. Common interference from those species that can diffuse through the membrane were removed by the addition of formaldehyde to the seafood extract. The method is simple, feasible with satisfactory accuracy and precision and thus, could be used for monitoring seafood quality with a sampling rate of 20±2 sample h⁻¹.     

Sequential injection analysis for benzophenone-4 and phenylbenzimidazole sulphonic acid in sunscreen sprays by solid-phase extraction coupled with ultraviolet spectrometry

A sequential injection UV method was developed to determine benzophenone-4 (BZ4) and phenylbenzimidazole sulphonic acid (PBS) simultaneously, these being the most commonly used UV-filters in aqueous formulations used as sunscreen sprays. The selective elution of both was performed by on-line solid-phase extraction, by retention on a SAX microcolumn and separation by varying the pH of elution. The sensitivity obtained was 0.042±0.001 ml μg⁻¹ for PBS and 0.0159±0.0003 ml μg⁻¹ for BZ4. The limit of detection was 1.6 μg ml⁻¹ for PBS and 0.6 μg ml⁻¹ for BZ4. The R.S.D. of the results was 1-6% for PBS and 1-12% for BZ4. The method was validated using commercial sunscreen formulations with concentrations determined by a liquid chromatographic procedure. The two procedures gave comparable results. Automation of the method means the amount of reagents used and residues generated are decreased. The system allows the required analysis sequence to be programmed using suitable software.     

Gas diffusion-flow injection determination of total inorganic carbon in water using tungsten oxide electrode

A novel gas diffusion-flow injection method has been developed for the rapid and sensitive determination of total inorganic carbon (TIC) in water. The method is based on the diffusion of CO₂ across gas permeable membrane from a donor stream containing 0.1 M HCl to an acceptor stream of sodium acetate (10⁻⁵ mol l⁻¹ and pH 10). The CO₂ trapped in the acceptor stream passes through an electrochemical flow cell contains a tungsten oxide wire and a silver/silver chloride electrode, where it was sensitively detected. The parameters affecting the sensitivity of the electrode such as buffer concentration, pH, flow rate and injected volume were studied in detail. The electrode response was linear in the concentration range from 5 to 100 μg ml⁻¹ CO₃²⁻ with a correlation coefficient (R²) of 0.998. Precision (R.S.D.) was 1.42% for 20 μg ml⁻¹ standard solution of CO₃²⁻ (n=10). The detection limit was 0.20 μg ml⁻¹ CO₃²⁻. The method was evaluated by the injection of real natural water samples and an average recovery of 100.1% was obtained. The sampling rate was 30 samples h⁻¹. The method is simple, feasible with satisfactory accuracy and precision and thus could be used for monitoring TIC in water.     

Direct analysis of palladium in active pharmaceutical ingredients by anodic stripping voltammetry

Anodic stripping voltammetry, a classical electroanalytical method has been optimized to analyze trace Pd(II) in active pharmaceutical ingredient matrices. The electroanalytical approach with an unmodified glassy carbon electrode was performed in both aqueous and 95% DMSO/5% water (95/5 DMSO/H₂O) solutions, without pretreatment such as acid digestion or dry ashing to remove the organics. Limits of detection (LODs) in the presence of caffeine and ketoprofen were determined to be 11 and 9.6 μg g⁻¹, with a relative standard deviation (RSD) of 5.7% and 2.3%, respectively. This method is simple, highly reproducible, sensitive, and robust. The instrumentation has the potential to be portable and the obviation of sample pretreatment makes it an ideal approach for determining lost catalytic metals in pharmaceutical-related industries. Furthermore, the simultaneous detection of Pd(II) with Cd(II) and Pb(II) in the low μg L⁻¹ range indicates that this system is capable of simultaneous multi-analyte analysis in a variety of matrices.     

Multiwalled Carbon Nanotubes/4,4′-Dihydroxybiphenyl Nanolayered Composite for Voltammetric Detection of Phenol

This paper reports the preparation of multiwalled carbon nanotubes/4,4′-dihydroxybiphenyl (MWCNTs-DHB) nanolayered composite as a new modifier for modification of carbon paste electrode (CPE/MWCNTs-DHB). CPE/MWCNTs-DHB shows linear responses for phenol in the concentrations range of 0.04–220 μM with a current sensitivity of 0.67 μA μM⁻¹ and a detection limit of 8.0 nM (S/N=3). The electrode shows high selectivity, good repeatability (RSD=4.1 %), excellent reproducibility (RSD=3.5 %), and acceptable stability (91.2 % over one-month storage). Moreover, the modified CPE exhibits appreciable recoveries (93.0–104.0 %) indicating its acceptable performance for determination of phenol in tap and river water samples.     

On-line preconcentration and determination of cobalt by chelating microcolumns and flow injection atomic spectrometry

A simple and sensitive flow injection analysis-atomic absorption spectrometric procedure is described for the determination of cobalt. The method is based upon on-line preconcentration of cobalt on a microcolumn of 2-nitroso-1-naphthol immobilized on surfactant coated alumina. The trapped cobalt is then eluted with ethanol (250 μl) and determined by flame atomic absorption spectrometry. The analytical figures of merit for the determination of cobalt are as follows: detection limit (3 S), 0.02 ng ml⁻¹; precision (RSD), 2.8% for 20 ng ml⁻¹ and 1.7% for 70 ng ml⁻¹ of cobalt; enrichment factor, 125 (using 25 ml of sample). The method has been applied to the determination of cobalt in water samples, vitamin B₁₂ and B-complex ampoules and accuracy was assessed through recovery experiment and independent analysis by furnace AAS.     

On-line coupling of dynamic microwave-assisted extraction to solid-phase extraction for the determination of sulfonamide antibiotics in soil

A rapid technique based on dynamic microwave-assisted extraction (DMAE) coupled on-line with solid-phase extraction (SPE) was developed for the determination of sulfonamides (SAs) including sulfadiazine, sulfameter, sulfamonomethoxine and sulfaquinoxaline in soil. The SAs were first extracted with acetonitrile under the action of microwave energy, and then directly introduced into the SPE column which was packed with neutral alumina for preconcentration of analytes and clean-up of sample matrix. Subsequently, the SAs trapped on the alumina were eluted with 0.3% acetic acid aqueous solution and determined by liquid chromatography-tandem mass spectrometry. The DMAE parameters were optimized by the Box-Behnken design. Maximum extraction efficiency was achieved using 320 W of microwave power; 12 mL of extraction solvent and 0.8 mL min⁻¹ of extraction solvent flow rate. The limits of detection and quantification obtained are in the range of 1.4-4.8 ng g⁻¹ and 4.6-16.0 ng g⁻¹ for the SAs, respectively. The mean values of relative standard deviation of intra- and inter-day ranging from 2.7% to 5.3% and from 5.6% to 6.7% are obtained, respectively. The recoveries of SAs obtained by analyzing four spiked soil samples at three fortified levels (20 ng g⁻¹, 100 ng g⁻¹ and 500 ng g⁻¹) were from 82.6 ± 6.0% to 93.7 ± 5.5%. The effect of standing time of spiked soil sample on the SAs recoveries was examined. The recoveries of SAs decreased from (86.3-101.9)% to (37.6-47.5)% when the standing time changed from one day to four weeks.     

Simultaneous determination of sulfamonomethoxine, sulfadimethoxine, and their hydroxy/N(4)-acetyl metabolites with gradient liquid chromatography in chicken plasma, tissues, and eggs

A simultaneous determination of sulfamonomethoxine, sulfadimethoxine, and their hydroxy/N⁴-acetyl metabolites in chicken plasma, muscle, liver, and eggs using gradient high-performance liquid chromatography (HPLC) with a photo-diode array detector is developed. All the compounds are extracted by a handheld ultrasonic homogenizer with ethanol followed by centrifugation. The separation is performed by a reversed-phase C4 column with a gradient elution (ethanol:1% (v/v) acetic acid, v/v; 10:90 → 20:80). Average recoveries from samples spiked at 0.1-1.0 μg g⁻¹ or μg ml⁻¹ for each drug were >90% with relative standard deviations within 4%. The limits of quantitation were <30 ng g⁻¹ or ng ml⁻¹.     

Diffusion layer titration of dipyrone in pharmaceuticals at a dual-band electrochemical cell

This paper describes the use of a thin-layered dual-band electrochemical cell operating at flow conditions to determine dipyrone (sodium salt of 1-phenil-2,3-dimethyl-4-methylaminomethanesulfonate-5-pyrazolone) by reaction with electrogenerated iodine. The electrolytic cell consisted of two closely spaced gold electrodes, the upper stream electrode serving as the generator electrode and the downstream electrode working as the collector electrode. A linear dynamic range from 2 to 15 μmol l⁻¹ dipyrone was obtained by using a sample volume of 100 μl, with a detection limit of 1.1 μmol l⁻¹. Standard deviation (S.D.) of 3.4% for 20 repetitive injections of a 40 μmol l⁻¹ dipyrone solution and sampling frequency of 90 h⁻¹ were achieved. The results obtained with the thin-layered dual-band electrochemical cell for dipyrone determination in three different pharmaceutical samples compared well with those found by iodimetry with coulometrically generated iodine.     

Electrochemical studies and square wave stripping voltammetry of five common pesticides on poly 3,4-ethylenedioxythiophene modified wall-jet electrode

The cyclic voltammetric behavior of five common pesticides such as dicofol (DCF), cypermethrin (CYP), monocrotophos (MCP), chlorpyrifos (CPF) and phosalone (PAS) was investigated at a poly 3,4-ethylenedioxythiophene modified glassy carbon electrode (PEDOT/GCE). A method was developed for the detection and determination of these pesticides in trace level flowing stream, based on their redox behavior. The square wave stripping voltammetric principle was used to analyze the selected pesticides on PEDOT/GCE. Varying the accumulation potential and accumulation time, the best accumulation conditions were found out. Effects of initial scan potential, square wave pulse amplitude, step potential and frequency were examined for the optimization of stripping conditions. The peak current responses of analyte under optimum conditions were correlated over flow rate by using wall-jet PEDOT/GCE assembly. The calibration plots were linear over the pesticide's concentration range 0.10-72.60 μg l⁻¹ for DCF, 0.41-198.24 μg l⁻¹ for CYP, 0.22-220.95 μg l⁻¹ for MCP, 0.35-259.69 μg l⁻¹ for CPF and 1.07-141.46 μg l⁻¹ for PAS. The limit of detection was obtained between <0.09 and <1.0 μg l⁻¹ for five pesticides. It is low enough for trace pesticide determination in real samples. This method is applied for the determination of the five pesticides in soil samples. The recovery values obtained in spiked soil samples are 95.4 ± 5.4% for DCF, 93.7 ± 4.2% for CYP, 85.3 ± 8.4% for MCP, 94.6 ± 6.6% for CPF and 93.5 ± 4.9% for PAS.     

Renewable Surface Sol‐gel Derived Carbon Ceramic Electrode Modified with Copper Complex and Its Application as an Amperometric Sensor for Bromate Detection

A sol‐gel technique was used for the preparation of a three dimensional carbon composite electrode modified with [Cu(bpy)₂]Br₂ complex. A reversible redox couple of Cu(II)/Cu(I) is observed at the electrode surface. The electrochemical behavior and stability of the modified electrode was characterized by cyclic voltammetry. The charge transfer coefficient (α) and charge transfer rate constant (K_s) for the modified electrode were determined by cyclic voltammetry, which were found to be 0.46 and 14.2 s^?1, respectively. The modified electrode showed excellent catalytic activity toward bromate reduction at significantly reduced overpotentials and can be used successfully for amperometric detection of bromate. Under the optimized conditions, the calibration plots are linear in the concentration range 0.5 μM ?200μM. Detection limit (signal to noise is 3) and sensitivity were found to be 0.1 μM and 20 nA / μM, respectively. These analytical parameters compare favorably with those obtained with modern analytical techniques. The modified carbon ceramic electrode doped with Cu‐Complex shows a good reproducibility, a short response time (t<2 s), remarkable long term stability (>4 months) and especially good surface renewability by simple mechanical polishing (RSD for 6 successive polishing is 1.5%).     

Stripping voltammetric determination of Cd(II) based on multiwalled carbon nanotube functionalized with 1-(2-pyridylazo)-2-naphthol

The present work has focused on the modification of multiwalled carbon nanotube with a ligand,l-（2-pyridylazo）-2-naphthol, and its potential application for the development of a new,simple and selective modified glassy carbon electrode for stripping voltammetric determination of Cd（Ⅱ）.The analytical curve for Cd（Ⅱ） ions covered the linear range varying from 0.8 up to 220.4μgL^-1.The limit of detection was found to be 0.1μgL^-1,while the relative standard deviation（RSD） at 50.0μgL^-1 was 1.8%（n=5）.This modified electrode was successfully applied for determination of Cd（Ⅱ） in some water samples.     

Determination of mercury species with a resin functionalized with a 1,2-bis(o-aminophenylthio)ethane moiety

A method for the simultaneous preconcentration and determination of Hg(II) and MeHg(I) at the ng ml⁻¹ level has been developed. This method is based on solid phase extraction using a newly synthesized chelating resin containing nitrogen and sulphur donor sites of the 1,2-bis(o-aminophenylthio)ethane moiety that is very selective for mercury. The characterization of the resin has been carried out by elemental analyses, infrared spectral data, thermogravimetric analysis and metal ion capacities. The resin is highly selective for Hg(II) and MeHg(I) with an exchange capacity of 0.38 and 0.30 mmol g⁻¹, respectively. Various parameters like pH, column flow rate, desorbing agents are optimized. Cold vapour atomic absorption spectrometry (CVAAS) was used to measure the concentration of both species of mercury. The calibration graph was linear upto 10 ng ml⁻¹ with a 3σ detection limit of 0.09 ng ml⁻¹. The recovery of Hg(II) and MeHg(I) was found to be 98.9±2.0 and 98.0±1.1%, respectively. The method has been used for routine determination of trace levels of mercury species in natural waters to comply with more stringent regulations.