Determination of bacitracin by differential pulse polarography.

Differential pulse polarograms of pharmaceutical-grade bacitracin exhibit a well-defined double wave at the dropping mercury electrode over the entire pH range 1–8. The current is diffusion-controlled and proportional to the concentration as well as to the biological activity of the sample. The concentration of bacitracin and of zinc—bacitracin can be determined by pulse polarography with a standard deviation less than 2%. The biologically inactive oxidation product (bacitracin F) is reduced at less negative potentials and can easily be determined in the presence of the biologically active components of bacitracin.     

Determination of platinum in urine by differential pulse polarography

A method has been developed for determination of platinum in urine, after administration of cis-dichlorodiammineplatinum(II). The diethyldithiocarbamate complex of the platinum(II) is formed and extracted into chloroform, then mineralized with aqua regia. After removal of nitric acid the platinum is complexed with ethylenediamine. This chelate yields a catalytic current at a dropping mercury electrode, which is measurable by differential pulse polarography. The detection limit is ~10 ng ml . The calibration graph is linear over the range 20-800 ng ml .     

Determination of crotonaldehyde in ethanol by differential pulse polarography

The extraction constant of gold bisdiethyldithiocarbamate chloride has been determined (log K' = 81.5± 0.7) by studying the competition from palladium in the extraction of gold with an excess of copper diethyldithiocarbamate in chloroform. Gold bisdiethyldithiocarbamate chloride is an ion pair which can dissociate: a dissociation constant of this compound has been determined by studying the influence of chloride concentration on the extraction of gold with the same reagent. In sulphuric acid medium, the low extraction ratio of gold observed cannot be attributed to extraction of gold bisdiethyldithiocarbamate sulphate as dependence on sulphate concentration has not been obtained. A program for the computation of this type of stability constant from extraction data for mixtures of cations and ligands is given.     

Determination of acipimox in capsules by differential pulse polarography

A differential pulse polarographic (DPP) method has been developed for the determination of acipimox in its pharmaceutical formulations. Using Sörensen buffer pH 6.0 as supporting electrolyte a single, irreversible peak occurred at –0.79 V vs an Ag/AgCl reference electrode. The peak height vs concentration plot was found to be linear over the range of 10^–6 to 6 × 10^–4 mol/l. The detection limit is 60ng/ml. The analysis of a series of 10 Olbetam® 250 mg capsules showed an overall standard deviation of ± 4.18 mg and a S_rel of ± 1.66%, respectively.     

Determination of microamounts of neptunium by differential pulse polarography

Neptunium is produced in significant amounts in the “light-water” reactors and must be controlled at different steps of fuel reprocessing. For this purpose, we have developed a method of differential pulse polarography. A tight cell containing 10 ml solution is set up in a Faraday cage. Adjustment to the tetravalent state, Np(IV), is carried out electrochemically on a mercury layer and the Np(IV) concentration is determined by differential pulse polarography, using a dropping mercury electrode. In 0.5M sulfuric acid medium, the redox potential of the reversible couple Np(IV)/Np(III) is-0.3V/SCE. Concentrations as low as 5·10⁻⁷M neptunium can be measured and detection at the 2·10⁻⁷ M level is still possible. (0.5μg in the polarographic cell). Precision is about 2% in the 10⁻⁵M and 10% in the 10⁻⁶M range. The method has been applied to aqueous and organic (TBP_dodecane) solutions. Neptunium can be determined without separation in the presence of plutonium or uranium at M/Np ratios of 10³ and 5·10⁴, respectively. In the presence of fission products a separation is needed.     

Determination of arsenite and arsenate by differential pulse polarography

Summary Arsenate was determined by differential pulse polarography in acidic solutions in the presence of polyhydroxy compounds. The best medium was found to be 2.0 M aqueous HClO₄ containing 4.5 g d-mannitol in 50 ml solution. The peak heights measured at –0.55 V gave linear calibration curves in the concentration range 20 g/l to 160 mg/l As. Arsenite was similarly determined with mannitol at –0.34 V or without mannitol at –0.42 V. When arsenite and arsenate were present in solution, the simultaneous determination of these compounds in the presence of mannitol was generally not possible because the peak heights at –0.34 V and –0.55 V were influenced by arsenite as well as arsenate. In these cases arsenite was determined at –0.42V in the absence of mannitol. After oxidation of arsenite to arsenate by chlorine water and addition of mannitol, total inorganic arsenic was determined as arsenate at –0.55 V. The arsenate concentration in the sample was found as the difference between the concentrations of total inorganic arsenic and arsenite. The detection limit for arsenite and arsenate was found to be approximately 10 g/l As. This method was successfully used to determine arsenite and arsenate in a synthetic river water sample and some arsenic-containing drinking water samples.

---

Bestimmung von Arsenit und Arsenat durch Differential-Pulspolarographie

Zusammenfassung Arsenat wurde durch Differential-Pulspolarographie in saurer Lösung in Gegenwart von Polyhydroxyverbindungen bestimmt. Das günstigste Medium war 2,0 M wäßrige HClO₄ mit 4,5 g d-Mannit in 50 ml. Die bei –0,55V gemessenen Peakhöhen ergaben eine lineare Eichkurve für den Bereich von 20 g/l bis 160 mg/l As. Arsenit wurde auf ähnliche Weise mit Mannit bei –0,34 V oder ohne Mannit bei –0,42 V bestimmt. Bei Anwesenheit von Arsenit + Arsenat in Lösung war eine Simultanbestimmung in Gegenwart von Mannit im allgemeinen nicht möglich, weil die Peakhöhen bei –0,34 V und –0,55 V sowohl von Arsenit als auch von Arsenat beeinflußt werden. In diesen Fällen wurde Arsenit ohne Mannit bei –0,42 V bestimmt. Nach Oxidation zu Arsenat mit Chlorwasser und Zugabe von Mannit wurde dann das Gesamtarsen als Arsenat bei –0,55 V bestimmt; der Arsenatgehalt in der Probe ergab sich aus der Differenz. Die Nachweisgrenze für Arsenit und Arsenat lag bei etwa 10 g/l As. Das Verfahren wurde mit gutem Erfolg für eine synthetische Flußwasserprobe sowie einige Trinkwasserproben angewendet.

---

---

On leave from Jadavpur University, Calcutta, India     

Determination of nisoldipine in film tablets by differential pulse polarography

Summary A differential pulse polarographic (DPP) method was developed for the determination of nisoldipine in Baymycard^® film tablets without interference from excipients. Nisoldipine is reduced at the dropping mercury electrode in a single, irreversible peak. Linearity between the nisoldipine concentration and the peak height was observed in the 5·10^–4–10^–7 M concentration range. The detection limit is 22 ng/ml. The analysis of a series of 10 Baymycard^® 5 mg film tablets showed a standard deviation of ±0.115 mg and aS _rel of ±2.30%, respectively.

---

Gehaltsbestimmung von Nisoldipin in Filmtabletten mittels differentieller Pulspolarographie

Zusammenfassung Eine Bestimmung von Nisoldipin in Baymycard^® Filmtabletten mittels differentieller Pulspolarographie (DPP) wurde entwickelt, die keine Störungen durch Tablettenhilfsstoffe aufweist. Nisoldipin wird an der tropfenden Quecksilberelektrode in einem einzigen, irreversiblen Peak reduziert. Linearität zwischen Nisoldipinkonzentration und Peakhöhe wurde im Konzentrationsbereich von 5·10^–4–10^–7 M festgestellt. Die Bestimmungsgrenze beträgt 22 ng/ml. Die Analyse einer Serie von 10 Baymycard^® 5 mg Filmtabletten ergab eine Standardabweichung von ±0.115 mg, dies entspricht einerS _rel von ±2.30%.

     

Determination of niobium in pyrochlore ore by differential pulse polarography

A differential pulse polarographic method has been developed for the quantitative determination of niobium in pyrochlore ore. One-step polarographic curves were obtained in 0.01 mol L(-1) EDTA as supporting electrolyte. Analytical curves indicated that response was linearly dependent on Nb(V) concentration between 1.6 and 8.6 mg L(-1) in the pH range 2-5. The system is quasi-reversible and controlled by diffusion in 0.01 mol L(-1) EDTA as supporting electrolyte; the electrode process involves one-electron reduction of Nb(V) to Nb(IV). The results obtained so far for niobium in pyrochlore ore were comparable with those obtained by X-ray fluorescence determination. Ions such as Fe(III), Cr(III), As(III), Cu(II), Ni(II), Co(II), Mn(II), Sn(IV), Zn(II), V(V), Ta(V), W(VI), Ce(IV), and Ti(IV) did not interfere. Possible interference from Pb(II) can be avoided by complexation with the supporting electrolyte in the pH range 3.5 to 4.6; Mo(VI) ions can be tolerated when their concentration is one-tenth that of Nb(V).     

Determination of ciclazindol in biological fluids by differential pulse polarography

A differential pulse polarographic method has been developed for determination of the antidepressant, 10-(m-chlorophenyl)-2,3,4,10-tetrahydropyrimido[1,2a]indol-10-ol hydrochloride in plasma and urine. The method involves solvent extraction of the drug from the plasma or urine, evaporation to dryness and dissolution of the residue in 10% methanolic 0.01 M tetraethylammonium chloride solution followed by differential pulse polarography. The mean recovery of the drug from plasma containing 0.5–5.0 μg ml^-1 is 80%; the coefficient of variation is 5.5% at the 1.0-μg ml^-1 (2.98 × 10^-6 M) level on 2-ml samples. The method is not subject to interference from the chemical degradation products and metabolites. The techniques described have been applied to the analysis of human plasma; the polarographic and gas Chromatographic results showed good agreement.     

Determination of ascorbic acid in asparagus by differential pulse polarography

A useful method for the determination of ascorbic acid in a vegetable product (asparagus) by differential pulse polarography has been set up and evaluated. Extraction and instrumental conditions were optimized. The analytical parameters are: linearity (0–18.18 g/ml); detection limit (0.182 g/ml); instrumental and method precision (2.77% and 4%, respectively); accuracy (96.9–113.4%). These data show that the method is sufficiently sensitive, reliable and accurate. It was also compared with the official fluorometric AOAC method.     

Determination of sunset yellow and tartrazine by differential pulse polarography

A study has been made of the polarographic (DC and DPP) behaviour of the food dyes Sunset Yellow and Tartrazine in acid and alkaline media and in the absence and presence of polyvinylpyrrolidone. Methods are proposed for the determination of both dyes by DPP over a concentration range of 0.1-10 ppm. The methods have been applied to their determination in soft drinks.     

Determination of total phthalate esters in wastewaters by differential pulse polarography

A reliable procedure for the determination of total phthalate esters as phthalic acid in environmental samples is based on differential pulse polarography (d.p.p.). The phthalate esters are extracted from the sample water with hexane; concentrated sulphuric acid/hexane partitioning provides effective removal of organic interferences. The individual phthalate esters are hydrolyzed by refluxing with 10 M potassium hydroxide to phthalic acid, which is extracted with ethyl acetate followed by evaporation of the extract. This procedure gives recoveries of 83–90%. The residue is dissolved in 0.1 M acetic acid/0.1 M potassium chloride for d.p.p. The otpimal conditions for polarography are discussed. The calibration graphs are linear over the range 2 × 10^?6–1 × 10^?4 M and the detection limit for phthalic acid is 5 × 10^?7 M. The method was successfully applied to determine total phthalate esters over the range 0.3–30 μg l^?1 in crude and treated wastewaters.     

Determination of N-methyl-N′-nitro-N-nitrosoguanidine in aerosol by differential pulse polarography

Summary The application of a sensitive electroanalytical technique for the analysis of N-methyl-N-nitro-N-nitrosoguanidine (MNNG) in aerosol was investigated. Cyclic voltammetric studies of the reduction of MNNG in acidic media showed three reduction waves. The first reduction step was assigned to be the reduction of the nitroso group and the second and third steps the reduction of the nitro group. The second peak was selected for the analysis as it was found to give a constant high current at pH below 1 and it was stable up to 40 days under normal daylight exposure and bubbling air at slow flow rate. Optimised parameters for the sensitive differential pulse polarographic technique were determined and the sampling conditions were investigated. The standard addition method was used to reduce the marix interference and the peak current was measured by the difference of current before and after UV irradiation so as to eliminate the interference caused by trace metals and electroactive and UV stable organic compounds present in air. The developed method was used to analyse MNNG aerosol in an animal room. The detection limit was found to be about 3 g/m³ for a sampling period of 48 h with a flow rate of 100 ml/min for the scrubbing method, whereas for the membrane filter method it was about 0.1 g/m³ for a sampling period of 8h at a flow rate of 4.9 l/min.

---

Bestimmung von N-Methyl-N-nitro-N-nitrosoguanidin in Aerosol mit Hilf der Differentialpuls-Polarographie

     

Determination of methylviologen (Paraquat) by differential pulse polarography

Summary Determination of Methylviologen (Paraquat) by Differential Pulse Polarography The second reduction wave of methylviologen (Paraquat) has been studied at pH 2 by different polarographic techniques. The limiting current is diffusion-controlled. Evidence for dimerization of the radical formed in the first reduction step has been obtained. The n values for the reduction process have been calculated at concentration levels where the dimer and the monomer predominate. Paraquat can be determined by differential pulse polarography in the 6.0×10^–5–4.0×10^–7 M concentration range, the limit of determination being 1.7×10^–7 M. The method has been applied to paraquat determination in commercial herbicides.     

Determination of soluble cyanide in soil samples by differential pulse polarography

Soluble cyanide can be determined ins oil samples by differential pulse polarography. Interference from sulphide is avoided by treating the alkali-stabilized sample solutions with lead carbonate prior to distillation of cyanide from the soil extract. Less than 10 μg l^?1 cyanide can be determined accurately, depending on teh weight of sample taken and the final collection volume. For a 100-g soil sample, the detection limit is 5 ng g^?1, which is similar to the limit of a standard spectrophotometric method. Relative standard deviations are 1–3%.     

Determination of 1,4-benzodiazepines in biological fluids by differential pulse polarography

The determination of various 1,4-benzodiazepines and their metabolites by differential pulse polarography is reviewed and compared with that by other methods, and the general applicability of the polarographic methods, in terms of simplicity and flexibility, is demonstrated.     

Determination of elemental sulfur in jet fuel by differential pulse polarography

A sensitive method based on differential pulse polarography is described for the determination of elemental sulfur in jet fuels. Its sensitivity makes it suitable for following small changes in the sulfur content of jet fuel during storage. The supporting electrolyte is 0.19 M ammonium acetate/0.088 M acetic acid in 1:1 toluene/methanol. In this medium, the peak potential is ?0.56 V vs. Ag/AgCl. Calibration is linear from 2 to 30 mg l^?1. The limit of detection is 0.1 mg l^?1. Accuracy is better than 5%. Interferences from oxygen, hydrogen sulfide, thiols, organic sulfides and disulfides, organic peroxides and fuel additives are shown to be of very minor significance.