Second-order Derivative Peak Current Research Articles

Electrochemical oxidation mechanism of ambroxol and its voltammetric determination in the presence of dodecyl sulfate

The voltammetric behavior of ambroxol (AMB) at carbon paste electrode (CPE) in acidic aqueous solution was studied in this work. The possible oxidation mechanism was suggested that amine group of AMB underwent a two-electron and two-proton oxidation to produce an anilino-radical at the higher potential around 1V (vs. SCE), showing an irreversible oxidation peak. Subsequently, the anilino-radicals dimerized via ‘head-to-tail’ coupling to yield a corresponding 4-amino-diphenylamine derivative in its oxidized form. This generated dimer was reduced and oxidized in the lower potential range of 0.1–0.39V (vs. SCE), showing a pair of quasi-reversible redox peak. With the mechanism, the different scavenging effect of AMB on reactive oxygen species (ROS) was attributed to that different species of AMB take part in the reaction with ROS. In the case of electrochemical oxidation of AMB, anionic surfactant sodium dodecyl sulfate (SDS) was found to play a dual function in eliminating the electrostatic repulsion between the protonated AMB and the CPE with high positive potential and prolonging the lifetime of the anilino-radical of AMB oxidation. In 0.1M HAc-NaAc buffer (pH 5.0) solution containing 3.0×10−4M SDS, the oxidation peak of amine group of AMB appeared at 0.93V (vs. SCE) and the peak current enhanced by 4.5 times in comparison to that in the absence of SDS. Based on this, a single-sweep voltammetric method was proposed for the determination of AMB. The second-order derivative peak current of AMB was rectilinear with its concentration in the range of 3.0×10−8–4.0×10−7M. The limit of detection was 5.4×10−9M. The sensitivity of the determination of AMB was improved, the oxidation potential of AMB was reduced and the experimental condition was moderated.

Single-Sweep Voltammetric Determination of Tamoxifen at Carbon Paste Electrode

A single-sweep voltammetric method was proposed for the determination of tamoxifen. The proposed method took advantage of both the accumulation of carbon paste electrode toward tamoxifen and the rapidity of single-sweep voltammetry. In HAc-NaAc (pH 4.1) buffer/methanol (85:15 v/v) mixed solution, an irreversible oxidation peak of tamoxifen was observed at 1.1 V (versus SCE). The second-order derivative peak current of tamoxifen and its concentration plots were rectilinear over the range of 7.0 × 10−10 ∼ 3.0 × 10−8 mol · l−1 with a detection limit of 1.0 × 10−10 mol · l−1 without any preconcentration. The proposed method was evaluated by analyzing tamoxifen citrate tablets, which was characterized by rapidity and higher sensitivity.

High-sensitive determination of coenzyme Q 10 in iodinate–β-cyclodextrin medium by inclusion reaction and catalytic polarography

A novel polarographic method for the determination of coenzyme Q 10 in β-cyclodextrin (β-CD) and iodinate system is proposed. The stability of coenzyme Q 10 to light was improved by the formation of coenzyme Q 10–β-CD inclusion complex. In addition, the sensitivity for the determination of coenzyme Q 10 was enhanced by both the formation and the polarographic catalytic wave of the inclusion complex in the presence of iodinate. In 0.1 mol/L HAc-NaAc (pH 4.7)–5.0 × 10 −5 mol/L β-CD–1.2 × 10 −3 mol/L potassium iodinate–ethanol/water (60:40, v/v) medium, coenzyme Q 10–β-CD inclusion complex yielded a sensitive association/parallel catalytic wave. The second-order derivative peak current of the catalytic wave was proportional to coenzyme Q 10 concentration in the range of 6.0 × 10 −8–2.5 × 10 −7 mol/L, and the detection limit was 1.0 × 10 −8 mol/L. The proposed method has high analytical sensitivity and is allowed to determine coenzyme Q 10 under light.

Catalytic adsorptive stripping voltammetric determination of copper(II) on a carbon paste electrode

A catalytic adsorptive stripping voltammetric method for the determination of copper(II) on a carbon paste electrode (PCE) in an alizarin red S (ARS)-K2S2O8 system is proposed. In this method, copper(II) is effectively enriched by both the formation and adsorption of a copper(II)-ARS complex on the PCE, and is determined by catalytic stripping voltammetry. The catalytic enhancement of the cathodic stripping current of the Cu(II) in the complex results from a redox cycle consisting of electrochemical reduction of Cu(II) ion in the complex and subsequent chemical oxidation of the Cu(II) reduction product by persulfate, which reduces the contamination of the working electrode from Cu deposition and also improves analytical sensitivity. In Britton-Robinson buffer (pH 4.56+/-0.1) containing 3.6 x 10(-5) mol L(-1) ARS and 1.6 x 10(-3) mol L(-1) K2S2O8, with 180 s of accumulation at -0.2 V, the second-order derivative peak current of the catalytic stripping wave was proportional to the copper(II) concentration in the range of 8.0 x 10(-10) to approximately 3.0 x 10(-8) mol L(-1). The detection limit was 1.6 x 10(-10) mol L(-1). The proposed method was evaluated by analyzing copper in water and soil.

Adsorptive Catalytic Voltammetry of Physcion in the Presence of Dissolved Oxygen at a Carbon Paste Electrode

A novel electroanalytical method for the determination of physcion is described for the first time. Physcion yields an adsorption catalytic voltammetric peak at −0.74 V (vs. SCE) in 0.4 mol L−1 NH4Cl–NH3·H2O buffer solution (pH 10.5) at a carbon paste electrode (CPE). The experimental results indicated that physcion is efficiently accumulated at a CPE by adsorption. In the subsequent potential scan, physcion was reduced to a homologous anthrahydroquinone compound. The compound was then immediately oxidized to physcion by the dissolved oxygen in the solution, and then physcion was again reduced at the CPE. As a result, a cyclic catalytic reaction was established. The second-order derivative peak current is proportional to the physcion concentration in the ranges of 2.0×10−10 ∼ 4.0×10−9 mol L−1 (accumulation 90 s) and 4.0×10−9 ∼ 2.0×10−8 mol L−1 (accumulation 60 s). The limit of detection is 8×10−11 mol L−1 (S/N=3) for a 120 s accumulation time. The method was applied to the direct determination of physcion in the medicinal plant polygonum multiflorum Thumb with satisfactory results.

Polarographic behavior of cephalexin and its determination in pharmaceuticals and human serum

Cephalexin gives a reduction wave in 0.03 mol/l HCl medium at ca. −1.24 V. With cephalexin concentration higher than 2.5×10 −5 mol/l, another reduction wave is observed at ca. −0.90 V. These reduction waves are attributed to the reduction of ethylenic bond of a six-membered dihydrothiazine ring. When H 2O 2 is present, the reduction wave at ca. −0.90 V is catalyzed by H 2O 2 and its reduction intermediate hydroxyl radical OH, producing a catalytic wave. However, the reduction wave at ca. −1.24 V remains nearly unchanged. A sensitive polarographic method for the determination of cephalexin is proposed based on the reduction wave of cephalexin. The second-order derivative peak current of the wave at ca. −1.24 V is rectilinear to the cephalexin concentration in the range 1.0×10 −7 to 2.5×10 −5 mol/l, and the detection limit is 5.0×10 −8 mol/l. The proposed method is applied to the individual tablet dosage form and human serum.

Study and application of parallel catalytic hydrogen wave of lincomycin in the presence of persulfate

The polarographic currents of lincomycin in the absence and the presence of persulfate are studied by linear potential scan polarography and cyclic voltammetry. The reduction wave of lincomycin in phosphate buffer is a catalytic hydrogen wave, which is the reduction of the proton combined with lincomycin in nature. When S 2O 8 2− is present, the atomic hydrogen as intermediate product from the reduction of the combined proton is oxidized by both S 2O 8 2− and its reduction intermediate, sulfate radical anion SO 4 − , to regenerate the original proton, producing the parallel catalytic hydrogen wave. Based on the parallel catalytic hydrogen wave, a novel method for the determination of lincomycin is proposed. In 0.48 mol l −1 KH 2PO 4–Na 2HPO 4 (pH 7.4)–8.0×10 −3 mol l −1 K 2S 2O 8 supporting electrolyte, the peak potential of the parallel catalytic hydrogen wave is −1.82 V ( vs. SCE). The second-order derivative peak current is rectilinear to the lincomycin concentration in the range of 8.5×10 −8–9.0×10 −5 mol l −1 and the detection limit is 4×10 −8 mol l −1. The parallel catalytic hydrogen wave is three orders in magnitude higher than that of the corresponding catalytic hydrogen wave in analytical sensitivity. The proposed method is applied to the rapid determination of lincomycin hydrochloride in eye drops without previous separation.

High Selective Determination of Anionic Surfactant Using Its Parallel Catalytic Hydrogen Wave

AbstractA faradaic response of anionic surfactants (AS), such as linear alkylbenzene sulfonate (LAS), dodecyl benzene sulfonate and dodecyl sulfate, was observed in weak acidic medium. The faradaic response of AS includes (1) a catalytic hydrogen wave of AS in HAc/NaAc buffer that was attributed to the reduction of proton associated with the sulfo‐group of AS, and (2) a parallel catalytic hydrogen wave of AS in the presence of hydrogen peroxide, which was due to the catalysis of the catalytic hydrogen wave of AS by hydroxyl radical OH electrogenerated in the reduction of hydrogen peroxide. The parallel catalytic hydrogen wave is about 50 times as sensitive as the catalytic hydrogen wave. Based on the parallel catalytic hydrogen wave, a high selective method for the determination of AS was developed. In 0.1 mol/L HAc/NaAc (pH = 6.2 ± 0.1)/1.0 ± 10−3 mol/L H2O2 supporting electrolyte, the second‐order derivative peak current of the parallel catalytic hydrogen wave located at‐1. 33 V (vs. SCE) was rectilinear to AS concentration in the range or 3.0 × 10–6‐2.5 × 10–4 mol/L, without the interference of other surfactants. The proposed method was evaluated by quantitative analysis of AS in environmental waste water.

Adsorptive Voltammetric Study of Thorium?Alizarin Complexon Complex at a Carbon Paste Electrode

A new sensitive adsorptive voltammetric procedure is described for trace measurement of thorium. It is based on the cathodic stripping peak of the thorium–alizarin complexon (ALC) complex at a carbon paste electrode (CPE). The complex of Th(IV) with alizarin is adsorbed at a CPE in a mixed buffer solution (pH 5.0) which consists of 0.1 mol·L−1 sodium acetate and 0.04 mol·L−1 potassium biphthalate, yielding a sensitive cathodic voltammetric peak corresponding to the reduction of alizarin in the complex at −0.57 V (vs. SCE). The second-order derivative peak current of the complex is linearly dependent upon the concentration of Th(IV) over the range of 3.0×10−9 ∼8.0×10−7 mol·L−1. The detection limit is 1.0×10−9 mol·L−1 for 180 s accumulation. The molar ratio of each component in the complex was estimated as nTh(IV):nALC=1:1 by a continuous variation method. The electrode processes of the Th(IV)–alizarin complex at a CPE were investigated. The procedure was successfully applied to the trace determination of thorium in ore and clay samples.

Sensitive determination of platinum by the parallel catalytic hydrogen wave of Pt (IV) in the presence of persulfate

A sensitive polarographic method for the determination of platinum is proposed, based on the so-called parallel catalytic hydrogen wave of the Pt (IV)–EDTA complex in the presence of persulfate. At mercury electrodes, the Pt (IV)–EDTA complex produces a catalytic hydrogen wave at −1.10 V (vs. SCE) in 1.0 mol l −1 HOAc+NaOAc (pH 4.4) buffer. When K 2S 2O 8 is present, the catalytic hydrogen wave is catalyzed further by S 2O 8 2− and its reduction intermediate sulfate radical anion SO 4 −, producing a kinetic wave, described as the parallel catalytic hydrogen wave. The second-order derivative peak current of the wave is rectilinear to the platinum concentration in the range 1.3×10 −10 to 7.7×10 −9 mol l −1 with a detection limit of 6.8×10 −11 mol l −1. The proposed method is free of interference from other metal ions except for Ru (IV), and is evaluated by the determination of platinum content in standard reference alloy materials and platinum catalysts.

Polarographic direct determination and homogeneous immunoassay of anti-human serum albumin (HSA) by parallel catalytic hydrogen wave of anti-HSA or HSA

Human serum albumin (HSA) or anti-human serum albumin (anti-HSA) yields a catalytic hydrogen wave at about −1.85 V (vs Ag/AgCl) in 0.25 M NH 3·H 2O–NH 4Cl (pH 8.58) buffer. When 1.0×10 −2 M K 2S 2O 8 is present, the catalytic hydrogen wave is further catalyzed, producing a parallel catalytic wave of hydrogen as catalyst in nature, termed the parallel catalytic hydrogen wave. The sensitivity of the parallel catalytic hydrogen wave is higher by two orders of magnitude than that of the catalytic hydrogen wave. Using the parallel catalytic hydrogen wave of anti-HSA or HSA in the presence of K 2S 2O 8, two sensitive methods for the determination of anti-HSA were developed. One is a direct determination based on the parallel catalytic hydrogen wave of anti-HAS itself, and the other is a homogeneous immunoassay based on measuring the decrease of the peak current of the parallel catalytic hydrogen wave of HSA after homogeneous immunoreaction of HSA with anti-HSA. In the direct determination, the second-order derivative peak current of the parallel catalytic hydrogen wave of anti-HSA itself is rectilinear to its titer in the range from 1:1.0×10 7 to 1:8.4×10 6. In the homogeneous immunoassay, the decrease in the second-order derivative peak current of the parallel catalytic hydrogen wave of HSA is linearly related to the added anti-HSA in the titer range from 1:3.0×10 7 to 1:6.0×10 6. These assays are highly sensitive and rapid in operation and can be used to evaluate such antigens and their antibodies as those that could yield the parallel catalytic hydrogen wave.

Polarographic Catalytic Wave of Prednisone in the Presence of Persulfate and its Application

A polarographic catalytic wave of prednisone in the presence of K2S2O8 was observed. The polarographic catalytic wave of prednisone as catalyst was attributed to such chemical reaction parallel to electrode reaction as \(\) oxidized the free radical from one electron reduction of the Δ1,4-3 keto group of prednisone to regenerate the original keto group. The catalytic wave can be used for the determination of prednisone with the help of conventional polarographic equipment, such as linear-potential scan polarograph. In 0.12 mol l−1 HAc-0.08 mol l−1 NaAc-0.014 mol l−1 K2S2O8 (pH 4.6) supporting electrolyte, the second-order derivative peak current of the catalytic wave was rectilinear to prednisone concentration in the range of 3.2 × 10−7∼1.6 × 10−5 mol l−1. The detection limit was 8.0 × 10−8 mol l−1.

Study and Application of Polarographic Catalytic Wave of Chlordiazepoxide in the Presence of Persulfate

AbstractPolarographic catalytic wave of chlordiazepoxide in the presence of K2S2O8 was studied in aqueous and DMF/H2O mixed solutions. The results showed that a single reduction wave in alkaline medium was the reduction of the N = C bond in 1,2‐position of chlordiazepoxide via an intermediate free radical in two one‐electron successive additions. When K2S2O8 was present, the free radical of the N = C bond was oxidized to regenerate the original, producing a parallel catalytic wave of chlordiazepoxide. It was determined that the apparent rate constant kf of the oxidation reaction was 3.2 × 103 mol−1·L·s−1. Using the catalytic wave the trace of chlordiazepoxide can be determined by linear‐potential scan polarography. In NH3/NH4Cl (pH 10.2 ± 0.1, 0.12 mol/L)/K2S2O8(0.016 mol/L) supporting electrolyte, the second‐order derivative peak current of the catalytic wave was rectilinear to chlordiazepoxide concentration in the range of 3.20 × 10−8‐1.60 × 10−7, 1.60 × 10−7‐1.44×10−6 and 1.44×10−6‐1.44x 10−5 mol/L, respectively. The limit of detection was 9.0×10−9 mol/L.

Determination of lomefloxacin, an antibacterial drug, in pharmaceutical preparations based on its polarographic catalytic wave in the presence of 2-iodoacetamide.

In a 0.125 mol/L phosphate (pH 6.6)/2.5 x 10(-4) mol/L 2-iodoacetamide solution, lomefloxacin yields a response of a polarographic catalytic current. The second-order derivative peak current of the catalytic wave of lomefloxacin is proportional to its concentration in the range of 1.0 x 10(-8)-1.0 x 10(-6) mol/L (r = 0.998). The sensitivity of the catalytic wave is 25-times higher than that of the corresponding reduction wave for 5.0 x 10(-7) mol/L lomefloxacin. The proposed method was applied to the determination of lomefloxacin in pharmaceutical preparations. The polarographic reduction wave is ascribed to a one-electron reduction of the C=C bond of lomefloxacin zwitterion accompanied by an acid-base equilibrium. The catalytic wave should be caused by regeneration of the lomefloxacin molecule at electrode surface due to the one-electron reduction product being further oxidized by electroreductive intermediate products of 2-iodoacetamide.

Determination of benzyl alcohol based on the polarographic catalytic wave of the oxidation product of benzyl alcohol in the presence of peroxydisulfate

Benzyl alcohol was oxidized rapidly to electroactive benzaldehyde through a radical-chain reaction initiated by sulfate radical SO 4 − electrogenerated from reduction of S 2O 8 2−. The benzaldehyde formed was reduced via an intermediate free radical. The free radical of benzaldehyde was oxidized by both S 2O 8 2− and SO 4 − to produce a catalytic wave. Based on this a novel method for the determination of benzyl alcohol was proposed. In 0.1 mol l −1 KH 2PO 4+Na 2HPO 4 buffer (pH 5.6±0.1)+2.0×10 −2 mol l −1 K 2S 2O 8 solution the second-order derivative peak current of the catalytic wave was linearly proportional to the benzyl alcohol concentration in the range of 9.70×10 −6–1.54×10 −4 mol l −1. The limit of detection was 8.0×10 −6 mol l −1. The proposed method was applied to determine the benzyl alcohol content in clinical injection.