Stripping Voltammetric Procedure Research Articles

Catalytic adsorptive stripping voltammetric determination of Cr(VI) in EDTA extracts from solid samples

A catalytic adsorptive stripping voltammetric procedure which allows for Cr(VI) determination in EDTA extracts is presented. EDTA used for extraction can be exploited as a masking agent for Cr(III). The calibration graph for Cr(VI) for an accumulation time of 60 s was linear in the range from 2 × 10 −10 to 3 × 10 −8 mol L −1. The relative standard deviation for a Cr(VI) concentration of 2 × 10 −9 mol L −1 was 5.1% ( n = 5). The detection limit estimated from three times the standard deviation of low Cr(VI) concentration and accumulation time of 60 s was about 7 × 10 −11 mol L −1. The influence of foreign ions commonly present in extracts from solid samples is presented. The proposed voltammetric procedure was applied to determine Cr(VI) in EDTA extractable chromium from soil certified reference materials CRM 483 and CRM 041. The performance of the method was also verified by studying the recovery of Cr(VI) from spiked river water.

A Validated Voltammetric Procedure for Quantification of the Antifungal Drug Griseofulvin in Bulk Form, Tablets, and Biological Fluids at a Mercury Electrode

Griseofulvin is an antifungal antibiotic used to treat various pathogenic mycotic diseases. The voltammetric behavior of griseofulvin at a hanging mercury drop electrode in Britton‐Robinson buffers of pH 2–11.5 was studied and discussed. A fully validated sensitive square‐wave adsorptive cathodic stripping voltammetric procedure was described for direct determination of bulk griseofulvin substance. The procedure was based on the reduction of the >C˭O double bond of griseofulvin molecule following its preconcentration onto a hanging mercury drop electrode in a Britton‐Robinson buffer of pH 10. Limits of detection (LOD) and quantitation (LOQ) of 5.8×10−10 M and 1.93×10−9 M bulk griseofulvin were achieved, respectively. The proposed stripping voltammetric procedure was successfully applied to assay griseofulvin in tablets and in spiked human serum and urine samples. LOD of 8.65×10−10 M and 6.6×10−9 M and LOQ of 2.88×10−9 M and 2.2×10−8 M griseofulvin in spiked human serum and urine samples, respectively, were achieved.

Voltammetric behavior and assay of the antibiotic drug cefazolin sodium in bulk form and pharmaceutical formulation at a mercury electrode

The electrochemical behavior of the antibiotic drug cefazolin sodium (CFZ) in Britton–Robinson buffers (pH 2–11) at the mercury electrode was studied by means of dc-polarography, cyclic voltammetry, controlled-potential coulometry and square-wave adsorptive stripping voltammetry techniques. A validated square-wave adsorptive cathodic stripping voltammetric procedure was described for the trace determination of cefazolin in bulk form up to limits of detection and quantitation of 2.6 × 10 −10 M and 8.6 × 10 −10 M, respectively. The method was successfully applied for determination of cefazolin in pharmaceutical preparation without the necessity for samples pretreatment or any time-consuming extraction or evaporation steps prior to the analysis.

Voltammetric Determination of Dialifos in Soils with a Mercury Film Ultramicroelectrode

An extraction‐adsorptive stripping voltammetric procedure for the determination of the pesticide dialifos in soil samples using microwave‐assisted solvent extraction and a mercury film ultramicroelectrode was developed. The method is based on the use of hexane‐acetone solvent (1:1, v/v) and on controlled adsorptive accumulation of the insecticide at the potential of −0.10 V (versus Ag/AgCl) in the presence of Britton‐Robinson buffer (pH 2.0). Soil sample extracts were analyzed directly after drying and redissolution with the supporting electrolyte, but without other pre‐treatment. The limit of detection obtained for a 10 sec collection time was 2.0×10−8 mol L−1. Recovery experiments for the global procedure, at the 0.100 µg g−1 level, gave satisfactory average and standard deviation results for the two different soils tested.

Utilisation of polypyrrole modified electrode for the determination of pesticides

Cyclic voltammetric studies of isoproturon and carbendazim using polypyrrole modified glassy carbon electrode were carried out. The electrode and reaction conditions, which yielded maximum current signal, were selected for the development of stripping voltammetric procedure for the determination of the pesticides. The oxidation peak around 1.3 V obtained for isoproturon and carbendazim while employing polypyrrole modified electrode showed maximum current response. This peak was chosen for stripping analysis using square wave mode. The experimental parameters were optimized and the calibration plot was obtained. The LOD was 0.5 ng mL−1 for isoproturon and 5 ng mL−1 for carbendazim. The relative standard deviation for 5 identical measurements was 2.81% and 3.33% for isoproturon and carbendazim respectively. The applicability of the method was verified by determining the pesticides in spiked soil and water samples.

Determination of ametryn in soils via microwave-assisted solvent extraction coupled to anodic stripping voltammetry with a gold ultramicroelectrode

An extraction-anodic adsorptive stripping voltammetric procedure using microwave-assisted solvent extraction and a gold ultramicroelectrode was developed for determining the pesticide ametryn in soil samples. The method is based on the use of acetonitrile as extraction solvent and on controlled adsorptive accumulation of the herbicide at the potential of 0.50 V (vs. Ag/AgCl) in the presence of Britton-Robinson buffer (pH 3.3). Soil sample extracts were analysed directly after drying and redissolution with the supporting electrolyte but without other pre-treatment. The limit of detection obtained for a 10 s collection time was 0.021 microg g(-1). Recovery experiments for the global procedure, at the 0.500 microg g(-1) level, gave satisfactory mean and standard deviation results which were comparable to those obtained by HPLC with UV detection.

Three validated stripping voltammetric procedures for determination of the anti-prostate cancer drug flutamide in tablets and human serum at a mercury electrode

Flutamide is a nonsteriodal anti-androgen drug, which is commonly used in the treatment of advanced prostate cancer. Based on the reduction of the nitro organic moiety of the drug molecule in acetate buffer of pH 5 at the hanging mercury drop electrode, three adsorptive cathodic stripping voltammetric procedures were optimized for determination of flutamide in bulk, tablets, and human serum applying linear-sweep, differential-pulse, and square-wave waveforms. The achieved limits of detection of the bulk drug were 1.9 × 10–7, 8.7 × 10–8, and 9.7 × 10–9 mol L–1 by using the optimized differential-pulse, linear-sweep, and square-wave adsorptive stripping voltammetric procedures, respectively. Repeatability of the results was studied for 1 × 10–6 mol L–1 of the drug and the recoveries obtained were 98.51 ± 1.56% (LSV), 98.89 ± 0.87% (DPV), and 99.21 ± 1.03% (SWV). The proposed procedures were successfully applied to the determination of the drug in pharmaceutical formulation (Eulexin® tablets) and human serum. The detection limits of the drug in bulk, pharmaceutical formulation, and human serum achieved by means of the proposed procedures showed that the square-wave mode was more reliable for determination of the drug especially in its low concentration levels.Key words: flutamide, linear-sweep, differential-pulse, square-wave, cathodic adsorptive stripping voltammetry, determination, Eulexin® tablets, human serum.

Adsorptive stripping voltammetric quantification of the antipsychotic drug clozapine in bulk form, pharmaceutical formulation and human serum at a mercury electrode

Using the cyclic voltammetry technique and the Britton–Robinson buffer (pH 2–10) as a supporting electrolyte, clozapine was found to reduce at the hanging mercury drop electrode in a single two-electron irreversible step corresponding to reduction of the azomethine group of the seven-member heterocyclic ring. Based on the interfacial adsorptive character of clozapine onto the hanging mercury drop electrode, a validated square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure was described for the quantification of bulk clozapine with limits of detection and quantitation of 4.5×10 −10 and 1.5×10 −9 M, respectively. The proposed procedure was successfully applied to the quantification of the drug in pharmaceutical formulation (Leponex ®) and human serum without the necessity for samples’ pretreatment or any time-consuming extraction or evaporation steps prior to the analysis. The limits of detection and quantitation of clozapine in spiked human serum were found to be 1×10 −9 and 3.3×10 −9 M, respectively. The proposed procedure for quantification of clozapine in bulk form, tablets and human serum has the advantage of being simple, rapid, sensitive, precise and inexpensive compared to most of the reported methods.

Voltammetric behavior and quantification of the anti-leukemia drug imatinib in bulk form, pharmaceutical formulation, and human serum at a mercury electrode

Imatinib (GleevecTM, ST1571) exemplifies the successful development of a rationally designed molecularly targeted therapy for treatment of a specific cancer. It is a highly promising new drug for the treatment of chronic myelogenous leukemia in blast crisis, in the accelerated or chronic phase after interferon failure or intolerance. The electrochemical behavior of imatinib was studied in Britton–Robinson (B–R) buffers of pH 2 to 11 by means of cyclic voltammetry at a hanging mercury drop electrode. The voltammograms showed a single 2-electron irreversible cathodic peak, which may be attributed to reduction of the C=O double bond of the imatinib molecule. Imatinib exhibited a strong adsorption onto the electrode surface especially in B–R buffers of pH 6 and 7. The adsorptive response of the drug was optimized with respect to the pH of the electrolysis medium, accumulation variables, and instrumental parameters using a square-wave stripping voltammetry technique. A fully validated, simple, sensitive, precise, and selective square-wave adsorptive cathodic stripping voltammetric procedure is described for trace determination of imatinib. The limits of detection (LOD) and quantitation (LOQ) of the bulk imatinib, following preconcentration for 150 s onto the hanging mercury drop electrode, were found to be 2.6 × 10–10 and 8.7 × 10–10 mol/L, respectively. The proposed procedure was successfully applied for quantitation of imatinib in pharmaceutical formulation (Glivec®) and spiked human serum, without the necessity for sample pretreatment or time-consuming extraction or evaporation steps prior to analysis of the drug. LOD and LOQ of 4.6 × 10–10 and 1.5 × 10–9 mol/L, respectively, were achieved after 120 s of preconcentration of the drug spiked in human serum.Key words: imatinib, GleevecTM, Glivec®, ST1571, cyclic voltammetry, square-wave stripping voltammetry, electrochemical behavior, quantification, pharmaceutical formulation, human serum.

Voltammetric behavior and assay of the contraceptive drug levonorgestrel in bulk, tablets, and human serum at a mercury electrode

The cyclic voltammograms of levonorgestrel (LNG) in Britton–Robinson buffers of pH 2–11 at the hanging mercury drop electrode showed a single two-electron irreversible cathodic peak over the whole pH range. This peak may be attributed to the reduction of the 3-keto-delta-4-group in the A-ring of the LNG molecule. The interfacial adsorptive character of levonorgestrel onto the surface of the hanging mercury drop electrode was identified by means of both cyclic voltammetry and chronocoulometry techniques. A simple, sensitive, and selective square-wave adsorptive cathodic stripping voltammetric procedure was developed for the quantitation of levonorgestrel. Under the optimized operational conditions, the maximum developed stripping voltammetric peak current showed a linear response with concentration of the bulk LNG substance. The achieved limits of detection (LOD) and quantitation (LOQ) were 6.7×10 −10 and 2.2×10 −9 M, or 4.8×10 −10 and 1.6×10 −9 M, following accumulation onto the hanging mercury drop electrode for 90 s or 150 s, respectively. The developed procedure was successfully applied to the determination of levonorgestrel in tablets, in spiked human serum, and in real plasma samples of healthy female volunteers following an oral administration of a 30-μg LNG single dose. The pharmacokinetic parameters ( C max=1.05 ng ml −1, t max=2.4 h and AUC 0− t =16.5 ng h ml −1) were estimated and favorably compared to those reported in literature for equivalent dose.

A validated stripping voltammetric procedure for quantification of the anti-hypertensive and benign prostatic hyperplasia drug terazosin in tablets and human serum

The electrochemical behavior of terazosin at the hanging mercury drop electrode was studied in Britton–Robinson buffer (pH 2–11), acetate buffer (4.5–5.5), and in 0.1M solution of each of sodium sulfate, sodium nitrate, sodium perchlorate and potassium chloride as supporting electrolytes. The square-wave adsorptive cathodic stripping voltammogram of terazosin exhibited a single well-defined two-electron irreversible cathodic peak which may be attributed to the reduction of CO double bond of the drug molecule. A fully validated, simple, high sensitive, precise and inexpensive square-wave adsorptive cathodic stripping voltammetric procedure was described for determination of terazosin in bulk form, tablets and human serum. A mean recovery for 1×10−8M terazosin in bulk form, following preconcentration onto the hanging mercury drop electrode for 60s at a −1.0V (versus Ag/AgCl/KCls), of 99±0.7% (n=5) was obtained. Limits of detection (LOD) and quantitation (LOQ) of 1.5×10−11 and 5×10−11M bulk terazosin were achieved, respectively. The proposed procedure was successfully applied to determination of the drug in its Itrin® tablets and human serum samples. The achieved LOD and LOQ of the drug in human serum samples were 5.3×10−11 and 1.8×10−10M THD, respectively. The pharmacokinetic parameters of the drug in human plasma were estimated as: Cmax=77.5ngml−1, tmax=1.75h, AUC0–t=602.3nghml−1, Ke=0.088h−1 and t1/2=11.32h) which are favorably compared with those reported in literature.

A validated stripping voltammetric procedure for quantification of the anti-hypertensive and benign prostatic hyperplasia drug terazosin in tablets and human serum

A validated stripping voltammetric procedure for quantification of the anti-hypertensive and benign prostatic hyperplasia drug terazosin in tablets and human serum

Voltammetric assay of rifampicin and isoniazid drugs, separately and combined in bulk, pharmaceutical formulations and human serum at a carbon paste electrode

The electrochemical oxidation of both the rifampicin (RIF) and isoniazid (INH) drugs has been investigated by cyclic and square-wave voltammetry in Britton–Robinson buffers (pH 2–11) at a carbon paste electrode. The oxidation of rifampicin generated a well-defined pH-dependent quasi-reversible anodic-cathodic peak couple corresponding to a mechanism involving the transfer of two electrons/two protons, typical to that of hydroquinones, in addition to an irreversible anodic peak at a more positive potential which may be due to the oxidation of phenolic hydroxyl group. For the isoniazid, an irreversible anodic peak was observed, which may be attributed to the irreversible oxidation of the amide moiety of the drug molecule. A validated square-wave adsorptive anodic stripping voltammetric procedure was described to assay the two drugs separately or combined in pharmaceutical formulations and human serum. The recoveries of RIF in rimactane ® capsules (300 mg RIF) and INH in isocid ® tablets (200 mg INH) were found to be 98.57±0.81% and 100.57±0.74%, respectively. The proposed procedure was also successfully applied to simultaneous assay of rifampicin and isoniazid drugs combined in rimactazid tablets (150 mg INH+300 mg RIF) with recoveries of 98.79±0.97% and 99.54±0.74%, respectively, without the necessity for sample pretreatment or time-consuming extraction steps prior to the analysis. The results were favorably compared to those obtained by the reported USP method. Moreover, the proposed procedure was successfully applied to simultaneous assay of both drugs in human serum samples with limits of detection and quantitation of 5×10 −8 and 1.7×10 −7 M for RIF and 6.1×10 −8 and 2×10 −7 M for INH.

Behavior and quantification studies of amiloride drug using cyclic and square-wave adsorptive stripping voltammetry at a mercury electrode

The cyclic voltammograms of amiloride at the hanging mercury drop electrode showed a single well-defined four-electron irreversible cathodic peak in Britton–Robinson (B–R) buffer of pH 2. At higher pH values (pH ≥3), two irreversible cathodic peaks corresponding to the transfer of four (first peak) and two (second peak) electrons, were obtained The peak potentials were shifted to more negative values on the increase of pH of the medium, implying the involvement of protons in the electrode reaction and that the proton-transfer reaction precedes the proper electrode process. The 4-electron single peak (pH 2) or the first peak (pH ≥ 3) may be attributed to the cleavage of the CHNH double bond of the N-imidino amide group with the release of NH3 molecule. While the second peak may be due to the saturation of the CO double bond of the carboxamide moiety.Based on the interfacial adsorptive character of the drug onto the mercury electrode surface, a simple, sensitive and low cost square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure was optimized for analysis of the drug. The optimal operational conditions of the proposed procedure were: accumulation potential Eacc=−0.7V, accumulation time tacc=60–65s, scan increment=10mV, pulse-amplitude=50–60mV, frequency=120Hz using a B–R buffer of pH 8 as a supporting electrolyte. The linear concentration range was found to be 2×10−9 to 2×10−7M amiloride with limits of detection (LOD) and quantitation (LOQ) of 1.9×10−10 and 6.3×10−10M, respectively. The procedure was successfully applied for determination of amiloride in pharmaceutical formulation and spiked in human serum. The LOD and LOQ of amiloride spiked in human serum were 5.7×10−10 and 1.9×10−9M amiloride, respectively. The procedure did not require sample pretreatment or any time-consuming extraction or evaporation steps, other than deproteinization and then centrifugal separation of protein from serum sample prior to analysis of the drug.

Electrochemical behavior and determination of amiloride drug in bulk form and pharmaceutical formulation at mercury electrodes

The polarographic behavior of amiloride hydrochloride has been studied in Britton–Robinson buffers of pH 1.9–11. In acidic medium at pH≤2, the dc-polarograms exhibited a single 4-electron cathodic irreversible wave, while at pH values >2, a second two-electron irreversible cathodic wave appeared at a more negative potential. The single or first wave may be attributed to the cleavage of the double bond of the CHNH of the imidino amide group with the release of NH3. While the second wave may be due to the saturation of the CO of the carboxamide moiety. A polarographic procedure of suffocate sensitivity for the determination of bulk amiloride drug in Britton–Robinson buffer at pH 2 is described. The calibration graph was obtained over the concentration range 2.5×10−5to2.5×10−4M amiloride. The limits of detection (LOD) and quantitation (LOQ) of the procedure were 1×10−5 and 3.3×10−4M bulk amiloride, respectively. Moreover, a differential-pulse adsorptive cathodic stripping voltammetric procedure has been described to assay of the drug at lower concentration levels. The optimal conditions were: Eacc=−0.9V, tacc=30s, scan rate=20mV, pulse-height=90mV and Britton–Robinson buffer of pH 8. The calibration graph was obtained over the concentration range 2×10−8to1×10−6M for bulk amiloride. Both procedures were successfully applied to the determination of amiloride in tablets without the necessity for sample pretreatment or any time-consuming extraction or evaporation steps prior to the drug analysis.

Investigation on the Usage of Clay Modified Electrode for the Electrochemical Determination of Some Pollutants

Redox behavior of three pollutants, namely endosulfan (EN), o-chlorophenol (OCP) and direct orange 8 (DO8) were investigated electrochemically using sodium montmorillonite clay modified glassy carbon electrode. Influence of pH, scan rate and concentration were studied on the voltammetric response. Suitable medium for the electrochemical studies of EN was pH 1.0 and for other two pollutants pH 13.0. EN exhibited one well-defined reduction peak accounting for irreversible 2e− transfer and leading to the removal of one chlorine atom. OCP underwent one electron oxidation to the formation of phenoxy radical resulting in an oxidation peak. DO8 showed two peaks for reductions and two peaks for oxidation as a result of the reduction of azo group and oxidation of phenoxide group. These electrochemical reactions of the three pollutants reveals the suitability of clay modified electrode for the electroanalysis. A differential pulse stripping voltammetric procedure for the determination of these pollutants was developed. The limits of determination for EN, OCP and DO8 are 5–300, 10–800 and 50–800 ppb, respectively.

Development of Electrochemical Methods for Determination of Atorvastatin and Analytical Application to Pharmaceutical Products and Spiked Human Plasma

Atorvastatin is a new synthetic inhibitor of HMG-CoA reductase that has been recently and intensively prescribed as an antihyperlipoproteinemic drug. The property was exploited in developing a highly sensitive stripping voltammetric procedure for the determination of the drug. The anodic current of adsorbed compound is measured by differential pulse and Osteryoung square wave adsorptive stripping voltammetry, preceded by a period of preconcentration. The effect of various parameters such as supporting electrolyte composition, pH, initial potential, scan rate, accumulation time, and ionic strength are discussed to characterize the interfacial and redox behavior. The methods were performed in Britton-Robinson buffer, and the corresponding calibration graphs were constructed and statistical parameters evaluated. Applying the differential pulse adsorptive stripping voltammetry and Osteryoung square wave adsorptive stripping voltammetric method at pH 2.0 linearity was achieved from 3.5 × 10−8 to 4.6 × 10−7 M for square wave adsorptive stripping voltammetry with limit detection and limit quantitation of 4.0 × 10−9 M, 2.0 × 10−9 M and 1.0 × 10−8 M, 2.0 × 10−8 M, respectively. Since the proposed methods enabled lower concentrations of atorvastatin to be determined, this method was tested for atorvastatin determination in pharmaceutical products and spiked human plasma.

Voltammetric behavior and quantification of the sedative-hypnotic drug chlordiazepoxide in bulk form, pharmaceutical formulation and human serum at a mercury electrode

Chlordiazepoxide is a sedative-hypnotic drug widely employed as a transquilizer and anti-depressant. Its electrochemical behavior in Britton–Robinson (B–R) buffers of pH 2–11 at a mercury electrode has been investigated using dc-polarography, cyclic voltammetry and controlled-potential coulometry. Polarograms of the drug in B–R buffers of pH 2–10 exhibited three 2-electron waves, while at pH>10, only a single 4-electron wave was observed. The first, second, and third waves in buffers of pH≤10 may be attributed to the reduction of N-oxide, CN and CN centers, respectively. The single wave (pH>10) may be due to the reduction of both the N-oxide and CN centers in a one step. The shift of the E 1/2, values to more negative potentials upon the increase of pH indicated the involvement of protons in the electrode reaction and that the proton-transfer reaction precedes the electrode process proper. The estimated data indicated that, one proton and two electrons are participated in the rate-determining step of each of the reduced centers. The general sequence of chlordiazepoxide reduction processes via each of its reactant centers may be expressed as: H +, e, e, H + (fast). Based on the interfacial adsorptive character of the drug onto the mercury electrode, a validated direct square-wave adsorptive cathodic stripping (SWAdCS) voltammetric procedure has been described for the trace determination of the drug in bulk form, tablets and human serum. The procedure did not require sample pretreatment or time-consuming extraction or evaporation steps prior to the assay of the drug. The optimized operational conditions of the proposed procedure have been found to be: accumulation potential E acc.=−0.9 V, accumulation time t acc.=30 s, pulse-amplitude=50 mV, scan increment=10 mV and frequency=120 Hz. The proposed procedure is much more simple, fast, sensitive, costly low and achieved much more lower limits of detection (LOD) (4.4×10 −10 M and 6.6×10 −10 M) and limits of quantitation (LOQ) (1.5×10 −9 M and 2.2×10 −9 M), respectively in pharmaceutical formulation and spiked human serum, compared to previously reported methods.

Development of an electrochemical assay for 2,6-dinitrotoluene, based on a screen-printed carbon electrode, and its potential application in bioanalysis, occupational and public health

Screen-printed carbon electrodes (SPCEs) have been successfully exploited as disposable sensors for the measurement of 2,6-dinitrotoluene (2,6-DNT) using a stripping voltammetric method. Initial investigations were undertaken using cyclic voltammetry (CV) to characterise the redox behaviour at the SPCEs. Further studies were then performed to deduce the optimum applied potential and accumulation time for the stripping voltammetric procedure. In addition, a study was carried out to ascertain whether small volumes of samples could be reliably used for analysis. From these studies it was shown that a 100 μl aliquot of sample could be analysed and the calibration plot was linear from 161 ng ml −1 to 137 μg ml −1 (R 2=0.9991), the former concentration being the detection limit. The effects of the major components of human saliva at concentrations normally present were investigated. Of the individual components tested, only Cl − and albumen were found to interfere. The presence of the latter could be easily overcome by the addition of (NH 4) 2SO 4. An interference study was also carried out on some inorganic and organic species that may be present in water samples. The sensors were evaluated by carrying out 2,6-DNT determinations on spiked and unspiked human saliva, dust wipe and potable water samples. Mean recoveries of 47.5, 73.4 and 102.4% were obtained; coefficients of variation of 7.88, 6.63 and 6.42% were calculated for a concentration of 9.1 μg ml −1 in water, 10.6 μg ml −1 saliva samples, and 141.1 ng cm −2 for dust wipe samples, respectively. The performance characteristics show that the method holds promise and reliable data may be obtained for 2,6-DNT in bioanalysis and public health.

Determination of Melatonin Hormone in Bulk Form, Tablets and Human Serum by Square‐Wave Cathodic Adsorptive Stripping Voltammetry

AbstractMelatonin hormone plays an important role in many distinct physiological functions. A fully validated, sensitive and reproducible square‐wave cathodic adsorptive stripping voltammetric procedure was described for determination of melatonin in bulk form, tablets and human serum. The procedure was based on the reduction of the adsorptive hormone onto a hanging mercury drop electrode. Reduction behavior of melatonin was studied in both Britton‐Robinson (pH 2–11) and acetate (4.5–5.5) buffers. Acetate buffer of pH 5.0 was found reasonable as a supporting electrolyte for assay of the drug. The square‐wave cathodic adsorptive stripping voltammogram of melatonin showed a single well‐defined peak at −1.45 V (vs. Ag/AgCl/KCls) using an accumulation potential of −0.65 V. This peak may be attributed to the reduction of CO double bond of the amide functional group of the reactant molecule. A mean recovery for 1×10−8 M melatonin in bulk form followed 30 s accumulation of 98.87%±0.78 and a detection limit of 3.13×10−10 M were achieved. The proposed procedure was successfully applied for the determination of the drug in tablets and human serum with mean recoveries of 97.68%±0.57 and 101.67%±0.85, respectively. A detection limit of 8.80×10−10 M was achieved for the determination of the drug in human serum. Results of the proposed method were comparable and coincided with those obtained by reported method. Vitamin B6 and common excipients, which are co‐formulated with melatonin, did not interfere. Also the effect of some interfering compounds such as serotonin, tryptophan and 5‐hydroxytryptophan on the determination of melatonin in human serum was studied, and all have no significant effect on the assay recovery.