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PubMed1997

A polarographic method for measuring dissolved nitric oxide.

A polarographic method for measuring the concentration of authentic nitric oxide (NO) in aqueous solutions is described. When solutions of NO were injected into aqueous solutions containing dissolved oxygen, NO reacted with oxygen to give nitrite. The amount of nitrite formed in this reaction (analyzed by capillary electrophoresis) was compared with the amount of oxygen consumed (measured by polarography). We observed a linear relationship between the amount of consumed oxygen and the amount of nitrite formed in the measured range (20-100 nmol NO-2) (R2 = 0.89). These results demonstrate that polarographic measurements of the amount of oxygen consumed in the reaction with NO could be used to estimate the concentration of dissolved NO in authentic NO solutions. There are several advantages to measuring consumed oxygen by polarographic methods: The method is simple and can be performed immediately prior to utilization of the NO solutions, it does not require any NO calibration standards and it fully discriminates between NO and oxidation products of NO. An additional advantage is, therefore, that stock solutions of NO can be stored for an indefinite period of time prior to measurement. Both the preparation of authentic NO solutions and the measurement of their NO content are therefore simplified. We also demonstrate that a slow infusion of authentic NO solution to cell suspensions in vitro makes it possible to study the rapid, reversible biological effects of NO.

Humans↗

PubMed1998

Polarographic investigation of beta 2-microglobulin and ferritin thermal denaturation.

A temperature dependence of the corresponding signals, obtained by differential pulse (d.p.) and alternating current (a.c.) polarography, from a buffered aqueous solution of ferritin and beta 2-microglobulin is used for the characterization of a protein thermal denaturation process. The method is based on the significant differences in the interaction of folded and unfolded protein forms with a dropping mercury electrode due to a different accessibility, for the redox process, of protein electroactive groups. From the analysis of the resulting current, or capacitance, signals in function of temperature the thermal transition reversibility of different protein forms in the solution, protein melting points, and the apparent activation energies of the corresponding processes were determined.

Balkan Nephropathy↗

PubMed1978

Determination of water soluble imidazo-1,4-benzodiazepines in blood by electron- capture gas--liquid chromatography and in urine by differential pulse polaragraphy.

A sensitive and specific electron-capture gas--liquid chromatographic (GLC--ECD) assay was developed for the determination of 8-chloro-6-(2'-fluorophenyl)-1-methyl-4H-imidazo(1,5a)(1,4)benzodiazepine (I) or 8-chloro-1,4-dimethyl-6-(2'-fluorophenyl)-4H-imidazo (1,5a)(1,4)benzodiazepine (II) in blood. The assay for both compounds involves extraction into benzene--methylene chloride (9:1) from blood buffered to pH 12.6 The overall recovery of I and II from blood is 86% +- 5.0 (S.D.) and the sensitivity limit of detection is of the order of 2 to 3 ng of I or II per milliltre of blood. The major urinary metabolite of I is 8-chloro-6-(2'-fluorophenyl)-1-hydroxymethyl-4H-imidazo(1,5a)(1,4)benzodiazepine, (IA) present as a glucuronide conjugate while 8-chloro-6-(2'-fluorophenyl)-4-hydroxyl-1-methyl-4H-imidazo(1,5a)(1,4)benzodiazepine, (IB) and 8-chloro-6-(2'-fluorophenyl)-4-hydroxy-1-hydroxymethyl-4H-imidazo(1,5a)(1,4) benzodiazepine, (IC) are minor metabolites. The major metabolite IA is extracted into benzene--methylene chloride (9:1) from urine buffered to pH 11.0 (after incubation with glucuronidase--sulfatase as pH 5.0), and analyzed by differential pulse polarography (DPP) in 0.1 M phosphate buffer PH 3). The overall recovery of IA is 84 +- 3.0% (S.D.) with a sensitivity limit of 50 ng per millilitre of urine. The metabolites of compound II have not as yet been elucidated. The GLC--ECD and DPP assays were applied to the determination of blood levels and urinary excretion in dogs following single 10 mg/kg intravenous and oral doses of I and following single 6 mg/kg intravenous and 10 mg/kg oral doses of II. Blood levels of compound I were also evaluated in man following intravenous infusion of single 10 mg doses.

Animals↗

PubMed2000

Voltammetric determination of isoxsuprine and fenoterol in dosage forms and biological fluids through nitrosation.

A simple and highly sensitive voltammetric method was developed for the determination of isoxsuprine HCl (I) and fenoterol HBr (II) in dosage forms and biological fluids. The method is based on treatment of the two compounds with nitrous acid followed by measuring the cathodic current produced by the resulting nitroso derivatives. The voltammetric behavior was studied adopting Direct Current (DCt), Differential Pulse (DPP) and Alternating Current (ACt) polarography. Both compounds produced well-defined, diffusion-controlled cathodic waves over the whole pH range in Britton-Robinson buffers (BRb). At pH 11 and pH 9, the values of diffusion-current constants (Id), were 9.4 +/- 0.3 and 7.7 +/- 0.4 for I and II, respectively. The current-concentration plots for I were rectilinear over the range of 0.6-12 microg/ml and 0.1-12 microg/ml in the DCt and DPP modes, respectively. As for II, the range was 1-20 microg/ml and 0.1-20 microg/ml in the DCt and DPP modes, respectively. The minimum detectability (S/N = 2) were 0.02 microg/ml (approximately 6 x 10(-8) M) and 0.01 microg/ml (approximately 2.6 x 10(-8) M) for I and II, respectively, adopting the DPP mode. The proposed method was applied to the determination of both compounds in dosage forms and the results obtained were in good agreement with those obtained using reference methods. The proposed method was further applied to the determination of isoxsuprine in spiked human urine and plasma. The percentage recoveries adopting the DPP mode were 98.84 +/- 1.18 and 99.26 +/- 0.97, respectively.

Aerosols↗

PubMed2001

Voltammetric determination of vitamins in a pharmaceutical formulation.

Direct current polarography and differential pulse polarographic methods have been developed for the qualitative as well as quantitative analysis of vitamin B1, B2 and B6. Thiamin (vitamin B1) produced a well-defined wave in 0.1 M KCl at pH 5.2 with E(1/2)=-1.2 V and E(p)=-1.22 V versus saturated calomal electrode (SCE). Riboflavin (vitamin B2) gave two distinct waves in Britton Robinson buffer at pH 1.8 with E(1/2) values=-0.13 and -0.34 V versus SCE and at pH 6.5 with E(1/2)=-1.10 V and E(p)=-1.2 V versus SCE. Pyridoxin (vitamin B6) produced a well-defined wave in Britton Robinson buffer at pH 6.5 with E(1/2)=-1.7 V and E(p)=-1.68 V versus SCE. All the three vitamins under study are reversibly reduced at the electrode surface. The number of electrons involved in the electrode process for vitamin B1 and B6 is one in each case where as for the two waves of B2 it is one and two, respectively. This has been confirmed by the measurement of E(3/4)-E(1/4) values and also from the log plot slopes for the reduction waves. The wave height of polarogram was found to be proportional to the vitamin concentration. The developed methods have been standardised for the determination of these compounds in pharmaceutical formulation. The concentration of vitamin B1, B2 and B6 are found to be 9.96, 9.92 and 3.01 mg, respectively in 240 mg of capsule powder of a standard company (name has not been disclosed due to secrecy purpose). The results have been found to be in excellent agreement to that claimed by the manufacturer. The observed data has been subjected to statistical analysis, which revealed high reliability and precision.

Buffers↗

PubMed2001

Voltammetric determination of nilvadipine in dosage forms and spiked human urine.

The voltammetric behaviour of nilvadipine was studied adopting direct-current, differential-pulse and alternating current polarography. Nilvadipine-being nitroderivative-exhibited well-defined cathodic waves over the whole pH range in Britton-Robinson buffers. At pH 5, the diffusion-current constant, (Id) was 4.78. The current-concentration plots are rectilinear over the range 1.5-20 and 0.2-10 microg/ml using the direct current and differential pulse-polarographic techniques with minimum detectability of 0.05 microg/ml (1.3 x 10(-7) M) using the latter technique. The proposed method was applied to commercial capsules containing the drug. The percentage recoveries were in agreement with those obtained by a reference method. Furthermore, the method was applied to spiked human urine, the percentage recovery was 95.54+/-2.137.

Antihypertensive Agents↗

PubMed2002

Polarographic determination of propranolol in pharmaceutical formulation.

Propranolol was reacted with nitric acid to give nitropropranolol and was then measured in Britton-Robinson solutions in the pH range 2.0-12.0 by differential-pulse polarography. Nitropropranolol gave rise to a well-resolved differential-pulse polarographic peak at pH 2.0. A linear calibration graph in the range 5.0 x 10(-7)-5.0 x 10(-5) M and a detection limit of 5 nM was obtained. The relative standard deviation was 1.95% (n = 10) at 5 x 10(-6) M. The effect of common exceipient on the peak height was evaluated. The method was applied for the determination of the drug in the tablet dosage form.

Chemistry, Pharmaceutical↗

PubMed2002

Voltammetric analysis of trazodone HCl in pharmaceuticals and biological fluids.

The voltammetric behavior of trazodone (TRZ) HCl was studied using direct current (DC(t)), differential pulse (DPP) and alternating current (AC(t)) polarography. The drug manifests cathodic waves over the pH range of 10-14. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. At pH 10, the diffusion current-concentration relationship was found to be rectilinear over the range 4-32 and 0.8-24 microg ml(-1) using DC(t) and DPP modes, respectively, with minimum detectability (S/N=2) of 0.104 microg ml(-1) (2.45 x 10(-6) M) and 0.314 microg ml(-1) (7.397 x 10(-6) M) using the DPP and DC(t) modes, respectively. The diffusion-current constant (I(d)) is 4.31+/-0.02 (n=6). The proposed method was successfully applied to the determination of the studied compound either in pure form or in formulations. The results obtained were favorably compared with those given using a reference method. Furthermore, the proposed method was applied to the determination of TRZ in spiked human urine and plasma adopting the DPP technique. No prior extraction step is needed in case of urine. The percentage recoveries were 98.43+/-0.79 and 97.44+/-0.705 (n=4) in spiked human urine and plasma, respectively. A pathway for the electrode reaction was postulated.

Body Fluids↗

PubMed2002

Polarographic determination of benzaldehyde in benzyl alcohol and sodium diclofenac injection formulations.

A rapid and sensitive polarographic method was developed for qualitative as well as quantitative analysis of the neurotoxic contaminant benzaldehyde in Na-diclofenac injections and in benzyl alcohol used for parental formulations. A well-defined differential pulse (DP) polarographic peak or a sampled direct current (SDC) wave was obtained at -1.39 V (vs. silver-silver chloride reference electrode) in Britton-Robinson buffer (pH 9.15) and at -1.41 V in 0.1 M LiCl solution. The reduction step involves a two-electron process, corresponding to the formation of benzyl alcohol. No peaks were observed in the anodic branch of the cyclic voltammogram, emphasizing the occurrence of an irreversible process. The peak current versus concentration relationship was found to be linear up to 50 microg/ml with the detection limit of 10 ng/ml and quantitation limit of 30 ng/ml. The relative standard deviations (S.D.) obtained for concentration levels of benzaldehyde as low as 25 microg/ml with the SDC and DP methods were 1.5 and 0.78% (n=10), respectively. Benzyl alcohol and Na-diclofenac are not electrochemically active, and metabisulfite reductions at -0.664 and -1.240 V do not interfere with the benzaldehyde reduction peak. The proposed methods (DP and SDC polarography) have been applied satisfactorily to the determination of benzaldehyde traces in benzyl alcohol and in different pharmaceutical products such as Na-diclofenac injectable formulations.

Benzaldehydes↗

PubMed2003

Voltammetric determination of isradipine in dosage forms and spiked human plasma and urine.

The voltammetric behavior of isradipine was studied using direct current (DC(t)), differential-pulse (DPP) and alternating current (AC(t)) polarography. Isradipine exhibited well-defined cathodic waves over the whole pH range in Britton-Robinson buffer (BRb). At pH 5, the analytical pH, the diffusion-current constant (Id) was 8.27+/-0.52. The current-concentration plots were rectilinear over the range 1-20 and 0.1-18 microg/ml using the DC(t) and DPP modes, respectively, with minimum detectability of 0.01 microg/ml (2.7 x 10(-8) M) using the latter technique. The current has been characterized as being diffusion-controlled, although adsorption phenomenon played a limited role in the electrode process. The proposed method was applied to commercial tablets and capsules. The percentage recoveries were in good agreement with those given by the manufacturer. The method was further extended to the in-vitro determination of the drug in spiked human urine and plasma, the percentage recoveries were (n = 4) 100.12+/-1.42 and 103.88+/-5.13, respectively. The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented.

Calcium Channel Blockers↗

PubMed1997

The new inhibitors of ribonucleotide reductase--comparison of some physico-chemical properties.

Amidox (AX), didox (DX) and trimidox (TX), compounds synthetized as new ribonucleotide reductase inhibitors, have been investigated by ultraviolet (UV) spectrophotometry, polarography and high performance liquid chromatography (HPLC). The experiments have been performed at various pH values. The changes in UV absorption of the compounds studied were recorded and it was demonstrated that these changes are related to the pH and to structural features of the investigated molecules. From the compounds included in our series of experiments, only amidox and trimidox are reduced during polarographic experiments in Britton-Robinson buffer. The reduction of both compounds proceeded in two one-electron steps in acidic pH. One two-electron diffuse irreversible wave was observed at basic pH. The values of the half-wave potential became more negative in accordance with the increasing pH. HPLC assay also showed changes in the retention of compounds investigated, particularly when the pH of the mobile phase was close to the dissociation constant of the particular drug. The changes of physico-chemical properties detected by the all used methods are related to different chemical structures (the most significant changes were observed in alkaline pH).

Benzamidines↗

PubMed1998

Polarographic determination of some penicillins through nitrosation.

Direct current and differential pulse polarography DPP were used for the determination of three penicillins, namely, ampicillin, benzylpenicillin and carbenicillin, in pure form and in their dosage forms. The method is based upon treatment of penicillins with nitrous acid followed by polarographic measurement of the produced derivatives polarographically. The nitroso derivatives formed exhibited reduction waves over the whole pH range in Britton-Robinson buffers. The waves were characterized as being diffusion-controlled and free from adsorption phenomena. The current-concentration plots were rectilinear over the concentration range 8-200 and 2-160 micrograms ml-1 for DCt and DPP, respectively, for all the studied compounds. The proposed method was further applied to determine penicillins in pharmaceutical preparations, and the results obtained were in good agreement with those given by the companies.

Ampicillin↗

PubMed1998

Development and validation of a differential pulse polarographic method for quinolinic acid determination in human plasma and urine after solid-phase extraction: a chemometric approach.

A chemometric approach was applied for determining quinolinic acid in human plasma by differential pulse polarography after solid phase extraction. A fractional factorial design was used to examine the significant experimental variables for the peak height maximization. A Doehlert design, which allowed a sequential response surface methodology to be performed, was applied to the variables scan rate and drop size. The results indicated that the scan rate had the greatest effect on the response peak height. The linear range was extended from 8.52 x 10(-8) to 1.34 x 10(-5) M and the limit of detection was 2.9 x 10(-8) M. The validation process consisted of a pre-validation study followed by the main validation in the plasma matrix. The robustness and the intermediate precision were evaluated by means of experimental design. A 3(4)//9 screening symmetric matrix and a central composite design were used to optimize the solid phase extraction procedure of the analyte from human plasma using anion exchange cartridges. The goal was to select the best retention, wash and elution solvents and their volumes in order to maximize the extraction efficiency using as the response the polarographic peak height. An extraction efficiency of 90% was found. The method was also applied to the determination of quinolinic acid in urine and the mean concentration in human plasma and urine, was found to be 3.7 x 10(-7) and 4.9 x 10(-5) M respectively.

Chemistry Techniques, Analytical↗

PubMed1999

The voltammetric behavior of nizatidine and its determination in biological fluids.

The voltammetric behavior of nizatidine (a newly introduced antiulcer drug) was studied using direct current (DCt), alternating current and differential pulse polarography (DPP). Well-defined cathodic waves were obtained over the whole pH range in Britton-Robinson buffers, in addition to 0.1 and 1 M HCl media. The main reduction wave was characterized as being irreversible and diffusion-controlled, although adsorption phenomena played a limited role in the electrode process. The current-concentration relationship was found to be rectilinear over the range 1x10(-5)-6x10(-4) and 2x10-6) -2x10(-4) M using DCt and DPP modes respectively, with a minimum detectability (S/N = 2) of 2x10(-7) M using the latter technique. The number of electrons involved in the reduction process was established, and the mechanism of electrode reaction was verified. The proposed method was successfully applied to determination of nizatidine in spiked human plasma and urine and the percentage recoveries were 96.12+/-0.40 and 97.12+/-0.17, respectively.

Anti-Ulcer Agents↗

PubMed1996

Interaction between trace elements: selenium and cadmium ions.

The interaction between several inorganic and organic selenium-containing compounds (selenite, selenate, selenourea and selenomethionine) and Cd2+ ions was studied by polarography. The changes in polarographic currents and half-wave potentials of the metal ions as a function of the Se-derivative concentration were followed. Experimental results suggest a different behaviour depending on the oxidation state of selenium. Any interaction between selenate and Cd2+ ions can be excluded. In the case of selenite, the presence of complexes in the solution was demonstrated. The shift in the Cd2+ reduction half-wave potential when a relatively high concentration of selenourea is present indicates formation of complexes, while the decrease in limiting current reflects the limited solubility of the complex itself. Results concerning selenomethionine suggest a very weak interaction with Cd2+ ions. These preliminary results are discussed in comparison with previous findings in cellular systems and may prove helpful in understanding cadmium ion toxicity and the in vivo altered distribution of various metal ions following the administration of selenium compounds.

Cadmium↗

PubMed1998

Study of the antioxidant effect of several selenium and sulphur compounds.

Four selenium derivatives (sodium selenate, sodium selenite, selenourea and selenomethionine) and the sulphur analogues (sodium sulfate, sodium sulfite, thiourea and methionine), together with urea, were examined by means of polarography to study their reactivity towards superoxide ion O2. In order that experimental results could be applied to physiological conditions and to control the electroreduction of oxygen, most reactions were carried out in model systems (in the presence and in the absence of triphenyl phosphine oxide and at increasing pH) which are briefly described and discussed. Sodium sulfite and thiourea react with molecular oxygen; selenourea originates an anodic wave, although under other pH conditions. Other compounds (selenate, selenite, seleno-methionine and methionine) display an interesting antioxidant capacity because they catalyse the disproportion of the superoxide ion, as documented by the increase in the limiting current. Methionine appears to be particularly efficient in this respect, since it retains its catalytic ability in a poorly protic environment. Experimental results support the view that exogenous compounds, administered for particular purposes, can display unanticipated, and sometimes positive, side effects.

Antioxidants↗

PubMed1998

Determination of Sn(II) in technetium cold kits by voltammetry at the hanging mercury drop electrode (HMDE) and relevant radiopharmaceutical applications.

A novel approach for the determination of the stannous content in cold kits for labelling with 99mTc is described. The method is based on differential pulse polarography on the hanging mercury drop electrode in a methanol/water/perchloric acid mixture and is easy to perform. Examples for the determination of tin(II) in fractionated technetium cold kits are shown. The stability of tin(II) in solution was mainly dependent on the storage temperature and the kit composition. The low stability of stannous ions under certain conditions was shown to be the main reason for low radiochemical purity. Limits and dangers of fractionating kits are discussed and related to content and instability of tin(II).

Electrochemistry↗

PubMed2001

Determination of metallothionein at the femtomole level by constant current stripping chronopotentiometry.

Metallothionein (MT) from rabbit liver was analyzed by differential pulse polarography, cyclic voltammetry, square wave voltammetry, and chronopotentiometric stripping analysis (CPSA) with a hanging mercury drop electrode under various conditions. The highest sensitivity of the MT determination was obtained with CPSA which produced a well-developed peak H due to catalytic hydrogen evolution at highly negative potentials. The highest peak H was obtained in borate buffer close to pH 8.0. In this medium, subnanomolar concentrations of MT were detectable. In the adsorptive transfer stripping (medium exchange) experiments, determination of few femtomoles of MT in 5-microL aliquots of the analyte was possible. CPSA determination of MT in various tissues of carp (Cyprinus carpio) yielded values in agreement with the published data.

Animals↗