Determination of mercurial species in fish by inductively coupled plasma mass spectrometry with anion exchange chromatographic separation

This work demonstrated the feasibility of mercury speciation analysis by anion exchange chromatographic separation with inductively coupled plasma mass spectrometry detection. For the first time, by complexing with the mobile phase containing 3-mercapto-1-propanesulfonate into negatively charged complexes, fast separation of inorganic mercury (Hg²⁺), monomethylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) was achieved within 5 min on a 12.5-mm strong anion exchange column. The detection limits for Hg²⁺, MeHg, EtHg and PhHg were 0.008, 0.024, 0.029 and 0.034 μg L⁻¹, respectively. The relative standard deviations of peak height and peak area (5.0 μg L⁻¹ for each Hg species) were all below 3%. The determined contents of Hg²⁺, MeHg and total Hg in a certified reference material of fish tissue by the proposed method were in good accordance with the certified values with satisfactory recoveries. The relative errors for determining MeHg and total mercury were −2.4% and −1.2%, respectively, with an acceptable range for spike recoveries of 94–101%. Mercury speciation in 11 fish samples were then analyzed after the pretreated procedure. The mercury contents in all fish samples analyzed were found compliant with the criteria of the National Standards of China.     

Determination of mercury species by the diffusive gradient in thin film technique and liquid chromatography – atomic fluorescence spectrometry after microwave extraction

A diffusive gradient in thin films technique (DGT) was combined with liquid chromatography (LC) and cold vapor atomic fluorescence spectrometry (CV-AFS) for the simultaneous quantification of four mercury species (Hg²⁺, CH₃Hg⁺, C₂H₅Hg⁺, and C₆H₅Hg⁺). After diffusion through an agarose diffusive layer, the mercury species were accumulated in resin gels containing thiol-functionalized ion-exchange resins (Duolite GT73, and Ambersep GT74). A microwave-assisted extraction (MAE) in the presence of 6 M HCl and 5 M HCl (55 °C, 15 min) was used for isolation of mercury species from Ambersep and Duolite resin gels, respectively. The extraction efficiency was higher than 95.0% (RSD 3.5%). The mercury species were separated with a mobile phase containing 6.2% methanol + 0.05% 2-mercaptoethanol + 0.02 M ammonium acetate with a stepwise increase of methanol content up to 80% in the 16th min on a Zorbax C18 reverse phase column. The LODs of DGT–MAE–LC–CV-AFS method were 38 ng L⁻¹ for CH₃Hg⁺, 13 ng L⁻¹ for Hg²⁺, 34 ng L⁻¹ for C₂H₅Hg⁺ and 30 ng L⁻¹ for C₆H₅Hg⁺ for 24 h DGT accumulation at 25 °C.     

A simple method for methylmercury,inorganic mercury and ethylmercury determination in plasma samples by high performance liquid chromatography–cold-vapor-inductively coupled plasma mass spectrometry

A simple and sensitive method with a fast sample preparation procedure is proposed for the determination of mercury species in plasma/serum. The method combines online high-performance liquid chromatography separation, Hg cold-vapor formation and inductively coupled plasma mass spectrometry detection. Prior to analysis, plasma (250 μL) was accurately pipetted into 15 mL conical tubes. Then, an extractant solution containing mercaptoethanol, L-cysteine and HCl was added to the samples following sonication for 10 min. Quantitative mercury extraction was achieved with the proposed procedure. Separation of mercury species was accomplished in less than 8 min on a C8 reverse phase column with a mobile phase containing 3% v/v methanol + 97% v/v (0.5% v/v 2-mercaptoethanol + 0.05% v/v formic acid). The method detection limits were found to be 12 ng L⁻¹, 5 ng L⁻¹ and 4 ng L⁻¹ for inorganic mercury, ethylmercury and methylmercury, respectively. Method accuracy is traceable to Standard Reference Material (SRM) 966 Toxic Metals in Bovine Blood from NIST. Additional validation was provided by the analysis of a secondary reference serum sample from the INSQ-Canada. Finally, the method was successfully applied for the speciation of mercury in plasma samples collected from volunteers exposed to methylmercury through fish consumption. For the first time to our knowledge, levels of different species of Hg in plasma samples from riverside populations exposed to MeHg were determined.     

Speciation of mercury in water samples by dispersive liquid-liquid microextraction combined with high performance liquid chromatography-inductively coupled plasma mass spectrometry

The dispersive liquid-liquid microextraction (DLLME) combined with high performance liquid chromatography-inductively coupled plasma mass spectrometry for the speciation of mercury in water samples was described. Firstly methylmercury (MeHg⁺) and mercury (Hg²⁺) were complexed with sodium diethyldithiocarbamate, and then the complexes were extracted into carbon tetrachloride by using DLLME. Under the optimized conditions, the enrichment factors of 138 and 350 for MeHg⁺ and Hg²⁺ were obtained from only 5.00 mL sample solution. The detection limits of the analytes (as Hg) were 0.0076 ng mL⁻¹ for MeHg⁺ and 0.0014 ng mL⁻¹ for Hg²⁺, respectively. The relative standard deviations for ten replicate measurements of 0.5 ng mL⁻¹ MeHg⁺ and Hg²⁺ were 6.9% and 4.4%, respectively. Standard reference material of seawater (GBW(E)080042) was analyzed to verify the accuracy of the method and the results were in good agreement with the certified values. Finally, the developed method was successfully applied for the speciation of mercury in three environmental water samples.     

Improvement of analytical performances for mercury speciation by on-line derivatization, cryofocussing and atomic fluorescence spectrometry

A modified automated on-line hyphenated system for simultaneous inorganic ionic mercury (Hg²⁺) and monomethylmercury (MeHg⁺) analysis by hydride generation (HG) or ethylation (Eth), cryofocussing, gas chromatography (GC) separation and atomic fluorescence spectrometry (AFS) detection has been improved. Both derivatization methods are investigated with respect to the chromatographic and analytical performances. They can be both affected by interferences when the AFS detection system is used. Water vapor removal using a soda lime moisture trap improves significantly the chromatographic performances, the reproducibility and the detection limits for Hg²⁺ and MeHg⁺ analyzed with both methods. For ethylation (Eth) derivatization, a scattering interference generated from low-quality ethylation reagent has also been eliminated. For HG, improved detection limits are 0.13 ng l⁻¹ and 0.01 ng l⁻¹ for Hg²⁺ and MeHg⁺, respectively (0.1 l water sample), and reproducibility are 5% for Hg²⁺ (20 ng l⁻¹) and MeHg⁺ (5 ng l⁻¹). Improved detection limits for Eth are 0.22 ng g⁻¹ for Hg²⁺ and 0.02 ng g⁻¹ for MeHg⁺ (1 g dry sediment sample) and the reproducibility are 5-6% for Hg²⁺ and MeHg⁺ (1-2 ng g⁻¹).     

Non-chromatographic screening method for the determination of mercury species. Application to the monitoring of mercury levels in Antarctic samples

A simple non-chromatographic method for the determination of mercury (Hg²⁺), methylmercury (MeHg⁺), dimethylmercury (Me₂Hg), and phenylmercury (PhHg⁺) employing atomic fluorescence spectrometry (AFS) as detection technique was developed. Mercury species showed a particular behavior in the presence of several reagents. In a first stage SnCl₂ was employed for Hg²⁺ determination; in a second step, [Hg²⁺ + PhHg⁺] concentration was determined using SnCl₂ and UV radiation. MeHg⁺ decomposition was prevented adding 2-mercaptoethanol. In a third stage, [Hg²⁺ + PhHg⁺ + MeHg⁺] concentration was determined using K₂S₂O₈. Finally, the four species were determined employing NaBH₄. Reagents concentration and flow rates were optimized. The extraction technique of mercury species involved the use of 2-mercaptoethanol as ion-pair reagent. The limits of detection for Hg²⁺, PhHg⁺, MeHg⁺, and Me₂Hg were 1, 40, 68, and 99 ng L⁻¹ with a relative standard deviation of 1.5, 3.1, 4.7 and 5.8%, respectively. Calibration curve was linear with a correlation factor equal to 0.9995. The method was successfully applied to the determination of the mercury species in two Antarctic materials: IRMM 813 (Adamussium colbecki) and MURST-ISS-A2 (Antarctic Krill).     

Simultaneous determination of methyl- and ethyl-mercury by solid-phase microextraction followed by gas chromatography atomic fluorescence detection

A method for trace level determination of organomercury species in different biota matrixes by using aqueous-phase propylation followed by headspace solid-phase microextraction (HS-SPME) and gas chromatography (GC) coupled to pyrolysis-atomic fluorescence spectrometry (Py-AFS) detection has been optimized. To maximize peak area and symmetry factors of methylmercury (MeHg) and ethylmercury (EtHg) analyzed as propyl derivatives, carrier and make-up flow rates were optimized by a user-defined experimental design. A multiple response simultaneous optimization was applied using the desirability function to achieve global optimal operating conditions. They were attained at 2 and 6 mL min⁻¹ as carrier and make-up gas flow rates, respectively. In addition, pyrolyser temperature was also optimized, yielding the best value at 750 °C. Limits of detection and quantification at the optimum conditions were 0.04 ng g⁻¹ and 0.13 ng g⁻¹ for both, MeHg and EtHg. The developed analytical procedure was validated with a certified reference material (DORM-2) and applied to the determination of organomercury incurred in waterfowl egg and fish samples.     

Sensitive pseudobienzyme electrocatalytic DNA biosensor for mercury(II) ion by using the autonomously assembled hemin/G-quadruplex DNAzyme nanowires for signal amplification

Herein, a novel sensitive pseudobienzyme electrocatalytic DNA biosensor was proposed for mercury ion (Hg²⁺) detection by using autonomously assembled hemin/G-quadruplex DNAzyme nanowires for signal amplification. Thiol functionalized capture DNA was firstly immobilized on a nano-Au modified glass carbon electrode (GCE). In presence of Hg²⁺, the specific coordination between Hg²⁺ and T could result in the assembly of primer DNA on the electrode, which successfully triggered the HCR to form the hemin/G-quadruplex DNAzyme nanowires with substantial redox probe thionine (Thi). In the electrolyte of PBS containing NADH, the hemin/G-quadruplex nanowires firstly acted as an NADH oxidase to assist the concomitant formation of H₂O₂ in the presence of dissolved O₂. Then, with the redox probe Thi as electron mediator, the hemin/G-quadruplex nanowires acted as an HRP-mimicking DNAzyme that quickly bioelectrocatalyzed the reduction of produced H₂O₂, which finally led to a dramatically amplified electrochemical signal. This method has demonstrated a high sensitivity of Hg²⁺ detection with the dynamic concentration range spanning from 1.0 ng L⁻¹ to 10 mg L⁻¹ Hg²⁺ and a detection limit of 0.5 ng L⁻¹ (2.5 pM) at the 3S_blank level, and it also demonstrated excellent selectivity against other interferential metal ions.     

Speciation analysis of mercury in sediments, zoobenthos and river water samples by high-performance liquid chromatography hyphenated to atomic fluorescence spectrometry following preconcentration by solid phase extraction

A high-pressure microwave digestion was applied for microwave-assisted extraction (MAE) of mercury species from sediments and zoobenthos samples. A mixture containing 3 mol L⁻¹ HCl, 50% aqueous methanol and 0.2 mol L⁻¹ citric acid (for masking co-extracted Fe³⁺) was selected as the most suitable extraction agent. The efficiency of proposed extraction method was better than 95% with R.S.D. below 6%. A preconcentration method utilizing a “homemade” C18 solid phase extraction (SPE) microcolumns was developed to enhance sensitivity of the mercury species determination using on-column complex formation of mercury-2-mercaptophenol complexes. Methanol was chosen for counter-current elution of the retained mercury complexes achieving a preconcentration factor as much as 1000. The preconcentration method was applied for the speciation analysis of mercury in river water samples. The high-performance liquid chromatography-cold vapour atomic fluorescence spectrometric (HPLC/CV-AFS) method was used for the speciation analysis of mercury. The complete separation of four mercury species was achieved by an isocratic elution of aqueous methanol (65%/35%) on a Zorbax SB-C18 column (4.6 mm × 150 mm, 5 μm) using the same complexation reagent (2-mercaptophenol). The limits of detection were 4.3 μg L⁻¹ for methylmercury (MeHg⁺), 1.4 μg L⁻¹ for ethylmercury (EtHg⁺), 0.8 μg L⁻¹ for inorganic mercury (Hg²⁺), 0.8 μg L⁻¹ for phenylmercury (PhHg⁺).     

Determination of ultra-trace amount methyl-, phenyl- and inorganic mercury in environmental and biological samples by liquid chromatography with inductively coupled plasma mass spectrometry after cloud point extraction preconcentration

The cloud point extraction (CPE) preconcentration of ultra-trace amount of mercury species prior to reverse-phase high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS) detection was studied. Mercury species including methyl-, ethyl-, phenyl- and inorganic mercury were transformed into hydrophobic chelates by reaction with sodium diethyldithiocarbamate, and the hydrophobic chelates were extracted into a surfactant-rich phase of Triton X-114 upon heating in a water bath at 40 °C. Ethylmercury was found partially decomposed during the CPE process, and was not included in the developed method. Various experimental conditions affecting the CPE preconcentration, HPLC separation, and ICP-MS determination were optimized. Under the optimized conditions, detection limits of 13, 8 and 6 ng l⁻¹ (as Hg) were achieved for MeHg⁺, PhHg⁺ and Hg²⁺, respectively. Seven determinations of a standard solution containing the three mercury species each at 0.5 ng ml⁻¹ level produced relative standard deviations of 5.3, 2.3 and 4.4% for MeHg⁺, PhHg⁺ and Hg²⁺, respectively. The developed method was successfully applied for the determination of the three mercury species in environmental water samples and biological samples of human hair and ocean fish.     

Preconcentration and speciation of inorganic and methyl mercury in waters using polyaniline and gold trap-CVAAS

Applicability of polyaniline (PANI) has been investigated for the preconcentration and speciation of inorganic mercury (Hg²⁺) and methyl mercury (CH₃Hg⁺) in various waters (ground, lake and sea waters). Preliminary experiments (batch) with powdered PANI for the quantitative removal of both Hg²⁺ and CH₃Hg⁺ showed that the retention of Hg²⁺ was almost independent of pH while a pH dependent trend from pH 1 to 12 was seen for CH₃Hg⁺ with maximum retention at pH > 5. Time dependence batch studies showed that a contact time of 10 min was sufficient to reach equilibrium. The K_d values were found to be ∼8 × 10⁴ and ∼7 × 10³ for Hg²⁺ and CH₃Hg⁺, respectively.Subsequently column experiments were carried out with PANI and the separation of the species was carried out by selective and sequential elution with 0.3% HCl for CH₃Hg⁺ and 0.3% HCl-0.02% thiourea for Hg²⁺. This was then followed by further pre-concentration of mercury on a gold trap and its determination by CVAAS. The uptake efficiency studies showed that the PANI column was able to accumulate up to 100 mg Hg²⁺/g and 2.5 mg CH₃Hg⁺/g. This method allows both preconcentration and speciation of mercury with preconcentration factors around 120 and 60 for Hg²⁺ and CH₃Hg⁺, respectively. The interfering effects of various foreign substances on the retention of mercury were investigated.     

A new Hg-selective fluorescent sensor based on a dansyl amide-armed calix[4]-aza-crown

A new fluorescent chemosensor for Hg²⁺ based on a dansyl amide-armed calix[4]-aza-crown was reported. It exhibits high sensitivity and selectivity toward Hg²⁺ over a wide range of metal ions in MeCN-H₂O (4:1, v/v). The association constant of the 1:1 complex formation for 2-Hg²⁺ was calculated to be 1.31 × 10⁵ M⁻¹, and the detection limit for Hg²⁺ was found to be 4.1 × 10⁻⁶ mol L⁻¹.     

Sequential cloud point extraction for the speciation of mercury in seafood by inductively coupled plasma optical emission spectrometry

A novel nonchromatographic speciation technique for the speciation of mercury by sequential cloud point extraction (CPE) combined with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed. The method based on Hg²⁺ was complexed with I⁻ to form HgI₄²⁻, and the HgI₄²⁻ reacted with the methyl green (MG) cation to form hydrophobic ion-associated complex, and the ion-associated complex was then extracted into the surfactant-rich phase of the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114), which are subsequently separated from methylmercury (MeHg⁺) in the initial solution by centrifugation. The surfactant-rich phase containing Hg(II) was diluted with 0.5 mol L^− 1 HNO₃ for ICP-OES determination. The supernatant is also subjected to the similar CPE procedure for the preconcentration of MeHg⁺ by the addition of a chelating agent, ammonium pyrrolidine dithiocarbamate (APDC), in order to form water-insolvable complex with MeHg⁺. The MeHg⁺ in the micelles was directly analyzed after disposal as describe above. Under the optimized conditions, the extraction efficiency was 93.5% for Hg(II) and 51.5% for MeHg⁺ with the enrichment factor of 18.7 for Hg(II) and 10.3 for MeHg⁺, respectively. The limits of detection (LODs) were 56.3 ng L^− 1 for Hg(II) and 94.6 ng L^− 1 for MeHg⁺ (as Hg) with the relative standard deviations (RSDs) of 3.6% for Hg(II) and 4.5% for MeHg⁺ (C = 10 μg L⁻¹, n = 7), respectively. The developed technique was applied to the speciation of mercury in real seafood samples and the recoveries for spiked samples were found to be in the range of 93.2–108.7%. For validation, a certified reference material of DORM-2 (dogfish muscle) was analyzed and the determined values are in good agreement with the certified values.     

Langmuir-Blodgett film of p-tert-butylthiacalix[4]arene modified glassy carbon electrode as voltammetric sensor for the determination of Hg(II)

The π-A isotherms and UV-vis spectra of the transferred films suggested that the monolayer of p-tert-butylthiacalix[4]arene can coordinate with Hg²⁺ at the air-water surface. From these observations, a glassy carbon electrode coated with Langmuir-Blodgett film of p-tert-butylthiacalix[4] arene as a new voltammetric sensor is designed for the determination of trace amounts of Hg²⁺. Compared with bare glassy carbon electrode and modified glassy carbon electrode using direct coating method, the Langmuir-Blodgett film-modified electrode can greatly improve the measuring sensitivity of Hg²⁺. Under the selected conditions, the Langmuir-Blodgett film-modified electrode in 0.1 mol L⁻¹ H₂SO₄ + 0.01 mol L⁻¹ KCl solution shows a linear voltammetric response for Hg²⁺ in the range of 5.0 × 10⁻¹⁰ to 1.5 × 10⁻⁷ mol L⁻¹, with a detection limit of 2.0 × 10⁻¹⁰ mol L⁻¹. The proposed method was also applied to determine Hg²⁺ in water samples (tap, lake and river water). In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility and good stability.     

Label-free colorimetric sensor for mercury(II) and DNA on the basis of mercury(II) switched-on the oxidase-mimicking activity of silver nanoclusters

In this paper, a novel colorimetric biosensor for Hg²⁺ and DNA molecules is presented based on Hg²⁺ stimulated oxidase-like activity of bovine serum albumin protected silver clusters (BSA-Ag NCs). Under mild conditions, Hg²⁺ activated BSA-Ag NCs to show high catalytic activity toward the oxidation of 3,3′,5, 5′-tetramethylbenzidine (TMB) using ambient dissolved oxygen as an oxidant. The oxidase-like activity of BSA-Ag NCs was “switched-on” selectively in the presence of Hg²⁺, which permitted a novel and facile colorimetric sensor for Hg²⁺. As low as 25 nmol L⁻¹ Hg²⁺ could be detected with a linear range from 80 nmol L⁻¹ to 50 mmol L⁻¹. In addition, the sensing strategy was also employed to detect DNA molecules. Hg²⁺ is known to bind very strongly and specifically with two DNA thymine bases (T) to form thymine–Hg²⁺–thymine (T–Hg²⁺–T) base pairs. The hairpin-structure was disrupted and Hg²⁺ ions were released after hybridization with the DNA target. By coupling the Hg²⁺ switched-on the oxidase-mimicking activity of BSA-Ag NCs, we developed a novel label-free strategy for facile and fast colorimetric detection of DNA molecules. More important, target DNA can be detected as low as 10 nmol L⁻¹ with a linear range from 30 to 225 nmol L⁻¹. Compared with other methods, this method presents several advantages such as the independence of hydrogen peroxide, high sensitivity and good selectivity, avoiding any modification or immobilization of DNA, which holds a great potential of metal NCs for clinical application in biosensing and biotechnology.     

A highly selective fluorescent probe for Hg based on a rhodamine-coumarin conjugate

A fluorescent probe 1 for Hg²⁺ based on a rhodamine-coumarin conjugate was designed and synthesized. Probe 1 exhibits high sensitivity and selectivity for sensing Hg²⁺, and about a 24-fold increase in fluorescence emission intensity is observed upon binding excess Hg²⁺ in 50% water/ethanol buffered at pH 7.24. The fluorescence response to Hg²⁺ is attributed to the 1:1 complex formation between probe 1 and Hg²⁺, which has been utilized as the basis for the selective detection of Hg²⁺. Besides, probe 1 was also found to show a reversible dual chromo- and fluorogenic response toward Hg²⁺ likely due to the chelation-induced ring opening of rhodamine spirolactam. The analytical performance characteristics of the proposed Hg²⁺-sensitive probe were investigated. The linear response range covers a concentration range of Hg²⁺ from 8.0 × 10⁻⁸ to 1.0 × 10⁻⁵ mol L⁻¹ and the detection limit is 4.0 × 10⁻⁸ mol L⁻¹. The determination of Hg²⁺ in both tap and river water samples displays satisfactory results.     

Triethanolamine-capped CdSe quantum dots as fluorescent sensors for reciprocal recognition of mercury (II) and iodide in aqueous solution

Water-soluble luminescent CdSe quantum dots surface-modified with triethanolamine (TEA-CdSe-QDs) were prepared with high stability. The fluorescence of the TEA-CdSe-QDs was greatly quenched only when Hg²⁺ and I⁻ coexisted in the solution, whereas addition of either Hg²⁺ or I⁻ individually has no noticeable effect on the fluorescence emission. Such a unique quenching effect could be used for reciprocal recognition of mercury (II) ions and/or iodide anions in aqueous solution with rather high selectivity and sensitivity. The detection limits of Hg²⁺ or I⁻ ion were 1.9 × 10⁻⁷ mol L^-1 or 2.8 × 10⁻⁷ mol L⁻¹, respectively. The adequate experiments showed that iodine (I) anions could bridge between TEA-CdSe-QDs and Hg²⁺ to form a stable complex (QDs-I⁻-Hg²⁺) and the following effective electron transfer from the QDs to the Hg²⁺ could be responsible for the fluorescence quenching of QDs.     

An acyclic,dansyl based colorimetric and fluorescent chemosensor for Hg(II) via twisted intramolecular charge transfer (TICT)

An efficient fluorescent chemosensor for Hg²⁺ ion, based on 5-(dimethylamino)-N-(2-mercaptophenyl)naphthalene-1-sulfonamide, has been developed. It exhibits Hg²⁺-selective on–off fluorescence quenching behavior via twisted intramolecular charge transfer (TICT) mechanism, which is rationalized by time dependent density functional theory (TD-DFT) calculations. The system exhibits visible color change from colorless to gray upon Hg²⁺ binding with very high selectivity and sensitivity (as low as 5.0 × 10⁻¹⁰ mol L⁻¹) over other metal ions such as K⁺, Na⁺, Ag⁺, Mn²⁺, Ca²⁺, Ba²⁺, Fe²⁺, Zn²⁺, Pb²⁺, Cu²⁺, Sn²⁺, Cd²⁺, Ni²⁺ and Co²⁺. The present sensing system is also successfully applied for the detection of Hg²⁺ ion in real samples.     

Photoelectrochemical determination of inorganic mercury in aqueous solutions

An analytical method using an optical probe in a photoelectrochemical cell for the sensitive and selective determination of aqueous Hg²⁺ is presented. A previously synthesized Hg²⁺ selective chemosensor, proven to be Hg²⁺ sensitive up to 2 μg L⁻¹, has been immobilized onto indium tin oxide (ITO) electrodes in a composite form with polyaniline. The coated ITO electrode was placed in a photoelectrochemical cell under closed circuit conditions in which the optical recognition of the chemosensor was converted to a measurable signal. A composite of the fluorescent chemosensor, Rhodamine 6G derivative (RS), and polyaniline (PANI) was immobilized on ITO glass plates and subjected to photovoltage measurements in the absence and presence of Hg²⁺. The optical responses of the coated electrode were used to determine the sensitivity and selectivity of the immobilized sensor to Hg²⁺ in the presence of background ions. The optical response of the PANI-dye coated electrode increased linearly with increasing Hg²⁺ concentration in the range 10-150 μg L⁻¹, with a detection limit of 6 μg L⁻¹.