A polarographic enzyme-immunoassay for Hepatitis B Surface Antigen(HBsAg) has been established, in which horseradish peroxidase(HRP) is used as the labeled enzyme, o-phenylenediamine(OPD) as the substrate, and the enzyme-generated product,2,2'-diaminoazobenzene (DAA), is detected by linear-potential scan polarography. Under optimal conditions, the second derivative current of DAA is linear with the concentration of HBsAg from 0.1 to 5 ng/mL. The correlation coefficient(r) is 0.9994. The detection limit is 0.05ng/mL and the relative standard deviation is 6.7%(8 replicates). The sensitivity of the assay is about 20-fold higher than that of ELISA. The assay has been successfully applied for minute determination of HBsAg in both human serum and the negative control serum from ELISA kits. Copyright (C) 1996 by Marcel Dekker, Inc.

A new flow-injection chemiluminescence (CL) method for determination of chloroquine is proposed based on a stronger chemiluminescence of chloroquine in hydrogen peroxide–nitrite–sulfuric acid medium. The proposed method allows the measurement of chloroquine over the range of 3.0×10−7 to 1.0×10−5moll−1. The detection limit is 8.6×10−8moll−1, and the relative standard deviation for 1.0×10−6moll−1 chloroquine (n=11) is 1.6%. The CL mechanism is also discussed.

The advances in polarographic catalytic wave of organic compound in the presence of oxidant are reviewed with 62 references. The classification and name of the catalytic wave are proposed as follows: (1) the parallel catalytic wave, which includes the parallel catalytic wave, the induced adsorption-parallel catalytic wave and the association-parallel catalytic wave. (2) the parallel catalytic hydrogen wave, which includes the parallel catalytic hydrogen wave and the association-parallel catalytic hydrogen wave. The polarographic catalytic waves of organic compounds, such as protein, flavone, steroide, quinone, α, β-unsaturated carbonyl compound, nitrogen-containing substances and charged surfactants, and their application are briefly introduced.

A new method for the determination of diazepam was proposed based on its polarographic catalytic wave in the presence of persulfate. In 0.20M NaAc–HAc (pH 4.7)–2.0×10−2M K2S2O8 supporting electrolyte, the reduction wave of diazepam with peak potential −0.89V (versus SCE) was catalyzed, producing a parallel catalytic wave. The peak current of the catalytic wave was 15 times higher than that of the corresponding reduction wave for 4.0×10−6M diazepam, and was rectilinear to diazepam concentration in the range of 5.6×10−8 to 8.8×10−6 and 8.8×10−6 to 2.0×10−4M. The detection limit was 9.6×10−9M. The mechanism of the parallel catalytic wave of diazepam was discussed.

A faradaic response of anionic surfactants (AS), such as linear aikylbenzene 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 0.1mol/L HAc/NaAc (pH=6.2±0.1)/1.0×10^-3mol/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 of 3.0×10^-6-2.5×10^-4mol/L, without the interference of other surfactants. The proposed method was evaluated by quantitative analysis of AS in environmental wastewater.

In persulfate-acetate, dimethyl sulfoxide or tert -butyl alcohol systems, in situ generation and detection of methyl free radical are realized with voltammetry. It includes the following successive processes. The persulfate S 2 O 8 2− is polarographically reduced via one-electron addition to sulfate radical SO 4 −· , the SO 4 −· initiates chain reaction with acetate, dimethyl sulfoxide, or tert -butyl alcohol on the electrode surface to produce a methyl radical, and one-electron reduction of the methyl radical yields its polarographic reduction wave. In comparison with the known techniques such as ultraviolet radiolysis coupling with electron spin resonance, etc., the proposed method is simple, sensitive and selective.

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 NH3·H2O–NH4Cl (pH 8.58) buffer. When 1.0×10−2M K2S2O8 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 K2S2O8, 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 1:1.0×107 to 1:8.4×106. 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 1:3.0×107 to 1:6.0×106. 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.

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 S2O82− is present, the atomic hydrogen as intermediate product from the reduction of the combined proton is oxidized by both S2O82− and its reduction intermediate, sulfate radical anion SO4−, 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 KH2PO4–Na2HPO4 (pH 7.4)–8.0×10−3 mol l−1 K2S2O8 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.

The voltammetric behavior and the production mechanism of polarographic catalytic wave of irisquinone were studied by linear potential scan polarography, cyclic voltammetry UV spectroscopy and constant potential electrolysis in both aqueous and N,N-dimethyl formamide(DMF) media. In Na2B4O7-KH2PO4, (pH = 7.7) buffer, the quinonyl group of irisquinone was first reduced in a 1e(-), 1H(+) process to produce an intermediate free radical semiquinone, and the further reduction of the free radical semiquinone to the corresponding hydroquinone anion in the same way was accompanied by its chemical reaction. In DMF-tetraethyl ammonium bromide(TEAB) media, the reduction of irisquinone was two successive single-electron processes without the chemical reaction of the free radical semiquinone. All these processes yield the reversible reduction wave of irisquinone. When S2O82- was present, the free radical semiquinone of irisquinone was oxidized to regenerate the original quinonyl group, which resulted in the production of a polarographic catalytic wave. The apparent first-order rate constant k(f) of the oxidation reaction of the free radical semiquinone of irisquinone with S2O82- was 3.3 X 10(6) L . mol(-1) . s(-1).

A new kinetic wave, termed as parallel catalytic hydrogen wave, of human serum albumin (HSA) in the presence of potassium persulfate was observed. In 0.4 mol/L NH3-NH4Cl (pH 8.58)-0.01 mol/L K2S2O8 supporting electrolyte, HSA yielded a parallel catalytic hydrogen wave with peak potential of -1.85 V ( vs. Ag/AgCl). The second-order derivative peak current of the parallel catalytic hydrogen wave was linearly proportional to HSA concentration in the range of 3.2 x 10(-9) similar to 9.6 x 10(-9) mol/L. The parallel catalytic hydrogen wave was applied to the determination of HSA content in human serum and urine with satisfactory results.

Polarographic 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.

AIM To propose a polarographic method for the determination of irisquinone. METHODS A reduction wave of irisquinone was recorded by single sweep oscillopolarography. RESULTS In 8.0 x 10(-3) mol.L-1 Na2B4O7-1.6 x 10(-2) mol.L-1 KH2PO4 (pH 7.7) supporting electrolyte, a redution wave of irisquinone with peak potential -1.23 V (vs SCE) achieved high sensitivity. The 2nd-order derivative peak current of the reduction wave was proportional to irisquinone concentration in the range of 1.5 x 10(-7)-5.2 x 10(-6) mol.L-1 (gamma = 0.9992, n = 9). The detection limit was 6.0 x 10(-8) mol.L-1. Relative standard deviation (RSD) was 0.87% by performing 13 independent measurements on 2.0 x 10(-6) mol.L-1 irisquinone. CONCLUSION The proposed method was sensitive, simple, rapid, and can be applied to the determination of irisquinone in raw medicine and capsule.

A polarographic catalytic hydrogen wave of bovine serum albumin (BSA) at about-1.80 V (vs. SCE) in NH 4 Cl-NH 3 · H 2 O buffer is further catalyzed by such oxidants as iodate, persulfate and hydrogen peroxide, producing a kinetic wave. Studies show that the kinetic wave is a parallel catalytic wave of hydrogen, which resulted from that hydrogen ion is electrochemically reduced and chemically regenerated through oxidation of its reduction product, atomic hydrogen, by oxidants mentioned above. It is a new type of poralographic catalytic wave of protein, which is suggested to be named as a parallel catalytic hydrogen wave.

The catalytic hydrogen wave of cationic surfactant tetrabutyl ammonium halide( TBAH) was further catalyzed by H2O2 in ammonium buffer solution, producing a more sensitive parallel catalytic hydrogen wave. The peak potential is - 1.45 V (vs . Ag/AgCl). Based on this observation, a new method for the determination of TBAH was proposed. In 0.2 mol/L NH3 . H2O-NH4Cl (pH 9.2 +/- 0.1) - 6.0 x 10(-3) mol/L H2O2, base solution, the second-order derivative peak current of the parallel catalytic hydrogen wave (if TBAH is proportional to its concentration in the range of 8.0 x 10(-7) similar to 9.6 x 10(-6) mol/L ( r = 0. 9988, n = 7), with the detection limit of 4.0 x 10(-7) mol/L. The proposed method is simple and rapid, with good selectivity, and it improves about 20 times in analytical sensitivity compared with that based on purely catalytic hydrogen wave for 8.0 x 10(-6) mol/L TBAH. 50-Fold tetramethyl ammonium halide and 10-fold tetraethyl ammonium halide did not interfere with the determination.

The polarographic catalytic wave of vitamin P in the presence of persulfate was studied by linear potential scan polarography and cyclic voltammetry. Vitamin P yielded a single reduction wave in acidic aqueous solution, which was ascribed to a 2e−, 2H+ reduction of the carbonyl group in the C-4 position. Actually, the carbonyl group CO first underwent a 1e−, 1H+ reduction to form a neutral free radical, and the further 1e−, 1H+ reduction of the free radical was simultaneous with its following chemical reactions. When S2O2−8 was present, the free radical of vitamin P was oxidized by both S2O2−8 and its reduction intermediate, the sulfate radical anion SO•−4, to regenerate the original, which resulted in the production of a polarographic catalytic wave of vitamin P. Based on this catalytic wave, a novel method for the determination of vitamin P was proposed. In 0.02 M tartaric acid–sodium tartrate (pH 3.3) buffer containing 5.0 × 10−3 M K2S2O8, the peak potential of the catalytic wave was −1.42 V (vs SCE) and the peak current was rectilinear to the vitamin P concentration in the range of 8.0 × 10−9–1.0 × 10−6 M (r = 0.9994, n = 13). The catalytic wave of 2.0 × 10−7 M vitamin P enhanced the polarographic current 70 times compared with the corresponding reduction wave. The detection limit was 2.0 × 10−9 M, and the relative standard deviation at the 2.0 × 10−7 M level was 0.7% (n = 15). The proposed method was used for the determination of vitamin P content in the pharmaceutical preparation of tablets and the medicinal plant Sophora japonica L. without previous separation.

The mechanism of the parallel catalytic wave of berberine in the presence of H2O2 was studied. The results showed that the reduction process of the CN bond of berberine was two successive one-electron transfers, in which an intermediate free radical was involved. When H2O2 was present, it oxidized the free radical to the original CN bond, producing the parallel catalytic wave of berberine. In Na2B4O7–Na2CO3 (pH 9.4, 0.08 M)–H2O2(4 mM) supporting electrolyte, the peak current of the catalytic wave was linear to the berberine concentration in the range of 1.0×10−8–3.0×10−7 M. The limit of detection was 7.0×10−9 M. The catalytic wave can be applied to direct determination of berberine in medicinal plant Coptis chinensis Franch, after sufficiently diluting the water extraction without preliminary separation.

The biamperometry for the direct determination of irreversible redox analytes in flow system has been proposed based on coupling two independent and irreversible couples to form the biamperometric detection scheme. In this work, the method is studied both theoretically and experimentally. Equations describing the current–voltage characteristics and the current–concentration relationship are presented. The influence of the applied potential difference (ΔE) and the half-wave potential difference (ΔE1/2) between two irreversible couples on the method are discussed. It shows that small ΔE1/2 is favorable to construct the biamperometric detection system and to achieve high sensitivity and selectivity. Increasing ΔE leads to an increase in sensitivity. This is, however, accompanied by a decrease in selectivity and signal-to-noise ratio. To construct the biamperometric scheme for the irreversible systems with large ΔE1/2, two approaches, adjusting acidity of supporting electroyte or adding new irreversible couple, are proposed by taking uric acid/platinum oxide and phenol/permanganate systems as examples. Uric acid and phenol are, respectively, detected in a flow injection system with a biamperometric detector.

>A polarographic catalytic hydrogen wave of bovine serum albumin (BSA) at about -1.80 V (vs. SCE) in NH4CI-NH3 · H2O buffer is further catalyzed by such oxidants as iodate, per-sulfate and hydrogen peroxide, producing a kinetic wave. Studies show that the kinetic wave is a parallel catalytic wave of hydrogen, which resulted from that hydrogen ion is electrochemically reduced and chemically regenerated through oxidation of its reduction product, atomic hydrogen, by oxidants mentioned above. It is a new type of poralographic catalytic wave of protein, which is suggested to be named as a parallel catalytic hydrogen wave.

The chemical reaction of progesterone with superoxide anion O 2 .− in 0.1 mol/L NaHCO 3 medium is studied by polarography. Differing from the indirect inhibition of O 2 .− generation by synthesized glucocorticoids in mechanism, the function that progesterone scavenges O 2 .− is ascribed to that O 2 .− directly oxidizes the C = C double bond conjugated with the carbonyl moiety of progesterone molecule to a free radical, and then is reduced to H 2 O 2 . The result obtained in this work gives new evidence for biomedical research. The equation of rate constant of the oxidization reaction is deduced, and the apparent rate constant obtained is 308 L · mol −1 · s −1 .

In a 0.125 mol/L phosphate (pH 6.6)/2.5 × 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 × 10-8 - 1.0 × 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 × 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.