Differential pulse polarographic determination of traces of molybdenum in solar-grade silicon

After dissolution of silicon with hydrofluoric and nitric acids and matrix volatilization as hexafluorosilicic acid, 0.2 M nitric acid and 1.8 M ammonium nitrate are added to the residue. Molybdate is then determined by means of its catalytic wave in nitrate media. The limit of determination is ca. 0.1 μg g^-1 and calibration graphs are linear up to 0.2 μg Mo(VI) ml^-1.     

Differential pulse polarographic determination of sulfuric acid

Acetonitrile is used as a solvent for the determination of micromolar amounts of sulfuric acid by differential pulse polarography. Contaminants in the supporting electrolyte and solvent present the biggest problems to the accurate determination of sulfuric acid. The detection limit is 2 × 10^-7 M. Nitric acid. bromide, soluble sulfates, and ammonium hydrogensulfate interfere under certain conditions.     

Differential pulse polarographic determination of cyanuric chloride

Cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) can be determined by fastscan differential pulse polarography in methanolic acetate buffer solution at pH 5.6 at a hanging mercury drop electrode. At positive potentials, the insoluble salt formed between cyanuric chloride and mercury(I) is adsorbed on the mercury surface and the d.p.p. current is enhanced. The detection limit is 0.2gmg ml^?1. Cyanuric chloride in air can be determined after absorption in methanol.     

乙醛酸的微分脉冲极谱法定量分析

建立了乙醛酸的微分脉冲极谱定量分析方法, 乙醛酸在100 g/L KOH底液中, 于-1.35 V (vs. Ag/AgCl)处出现一良好的微分脉冲极谱峰, 并能排除主要杂质草酸的干扰. 乙醛酸浓度与其电流峰幅值呈显著的线性关系, 当标准加入的极谱电流峰高和样品极谱电流峰基本一致时, 测量误差小于0.5%.     

Differential pulse polarographic determination of pyridoxine in multivitamins tablets

Pyridoxine (vitamin B₆) is easily oxidized to pyridoxal by active manganese dioxide. Pulse polarograms recorded from alkaline media (pH 12–13) containing pyridoxal are very well-defined. The current is diffusion-controlled and the peak current is proportional to the concentration of pyriodoxine. This provides a simple determination of pyridoxine in multivitamin tablets. There is no interference from other vitamins; nicotinamide can be determined simultaneously from the same polarogram. The method is not applicable to tablets containing the coloids Methocel 4000 or Kollidon, which are strongly adsorbed on the electrode and inhibit the electroreduction of pyridoxal.     

Differential pulse polarographic determination of nitrate in environmental materials

Nitrate can be determined with reliable accuracy and sensitivity by differential pulse polarography utilizing the catalytic reaction between nitrate and uranyl ion in the presence of potassium sulphate. The differential pulse polarographic peak-height is proportional to nitrate concentration from 1 to 50 muM. The calculated detection limit for nitrate is 8 x 10(-7)M in pure aqueous solution. The method has been applied to determination of nitrate in fresh snow, and river waters and animal feeds.     

Differential pulse polarographic determination of hydrocortisone in pharmaceutical preparations

Differential pulse polarograms of hydrocortisone recorded from acetate buffer pH 4.6 exhibit a well-defined peak at —1.25 V vs. SCE and the peak current is proportional to the concentration in the range 10^-5–8 × 10^-5 M. The electrode reaction involves one electron and one hydrogen ion. A simple rapid method is proposed for the determination of hydrocortisone in creams and ointments. The procedure does not involve time-consuming extractions, but it is not applicable to samples containing surfactants like polyethyleneglycol which are more strongly adsorbed on the electrode than hydrocortisone. Because degradation in the side chain of hydrocortisone is not detected polarographically, the method is suitable for production control but not for stability tests.     

Differential pulse polarographic determination of orthophosphate in aqueous media

The determination of orthophosphate in aqueous media by differential pulse polarography is described. It is based on determination of the molybdenum in 12-phosphomolybdic acid. High sensitivity is achieved by measuring the polarographic wave due to the catalytic reduction of perchlorate or nitrate in the presence of molybdenum(VI). The method is suitable for samples as small as 3.5 ml which contain as little as 9 ng of phosphorus per ml. The average relative deviation is 3.0% at the 0.045 mg/l. phosphorus level and 1.6% at the 1.2 mg/l. level. Results for the analysis of EPA quality-control water and real surface-water samples are reported.     

Differential pulse polarographic determination of chromium in gallium arsenide

Summary The proposed method for the determination of Cr in gallium arsenide is based on the catalytic activity of chromium(VI)-DTPA complex in the presence of nitrate ions. After dissolution of gallium arsenide with hydrochloric and nitric acids and volatilization of arsenic, chromium is oxidised to chromate with potassium chlorate in nitric acid. After nitric acid removal, the 0.012 M DTPA — 2.5 M LiNO₃ supporting electrolyte buffered with 0.2 M CH₃COONa — 0.05 M CH₃COOH is directly added to the residue. Differential pulse polarography of this solution provides a detection limit of about 100 ng g^–1, with a relative standard deviation of ±2–5% and a reproducible calibration curve up to at least 1 g of Cr(VI) ml^–1.

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Differential-pulspolarographische Bestimmung von Chrom in Galliumarsenid

Zusammenfassung Das vorgeschlagene Verfahren beruht auf der katalytischen Aktivität des Chrom(VI)-DTPA-Komplexes in Gegenwart von Nitrationen. Nach Auflösung des Galliumarsenids mit Salz- und Salpetersäure, wird Arsen verflüchtigt und Chrom mit KClO₃/HNO₃ zu Chromat oxidiert. Die Salpetersäure wird entfernt und der Rückstand direkt mit dem Trägerelektrolyt versetzt (0,012 M DTPA — 2,5 M LiNO₃, gepuffert mit 0,2 M CH₃COONa — 0,05 M CH₃COOH). Durch Differentialpulspolarographie dieser Lösung erhält man eine Nachweisgrenze von etwa 100 ng g ^–1. Die relative Standardabweichung beträgt ± 2–5%, die Eichkurve ist reproduzierbar bis 1 g Cr(VI) ml^–1.

     

Differential pulse polarographic determination of procymidone in formulations and wine

The dicarboximide fungicide procymidone was studied systematically by using direct current polarography, cyclic voltammetry, differential pulse polarography (DPP), controlled potential electrolysis, and millicoulometry in the universal buffer medium with dimethylformamide as the solvent. Procymidone exhibited a single well-defined polarographic wave in the pH range 2.0-6.0, leading to the formation of the hydroxy compound. The overall reduction process was diffusion-controlled and adsorption-free. The variation of half-wave potential with pH, the concentration of the analyte, and other experimental conditions are described. The reduction mechanism proposed is an overall 4-electron process, in which the dicarboximide group is reduced. DPP was used to determine procymidone in agricultural formulations and wine at the optimum conditions found; a detection limit of 2.4 x 10(-9) M was estimated. The results obtained by the proposed method were also compared with those obtained by other methods.     

Spectrographic determination of trace elements in solar-grade silicon

Summary An optical emission spectrographic method is described for the estimation of fourteen trace metallic impurities such as B, Pb, Sn etc., in solar-grade silicon. The silicon is ground under liquid nitrogen, then mixed with high-purity graphite powder and sodium fluoride (the latter to improve the line-to-background ratio). The mixture is excited in a d. c. arc (12 A) in a nitrogen atmosphere. The spectra of the sample and standards over the wavelength region 2400–3350 Å are photographed. The detection limits for the various elements range from 1 to 25 ppm. A matrix line of silicon is chosen as the internal standard. The mean coefficient of variation in the determination of the various elements is between 9 and 24%.

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Spektrographiscbe Bestimmung von Spurenelementen in Solarzellensilicium

Zusammenfassung Eine emissionsspektrographische Methode zur Bestimmung von 14 Spurenelementen wie Bor, Blei, Zinn usw. in Solarzellensilicium wurde beschrieben. Das Silicium wird unter flüssigem Stickstoff zerkleinert und dann mit hochreinem Graphitpulver und Natriumfluorid gemischt. Letzteres dient zur Verbesserung des Verhältnisses Linie zu Untergrund. Das Gemisch wird im Wechselstrombogen (12 A) in Stickstoff atmosphäre angeregt. Die Spektren der Probe und der Standards zwischen 2400 und 3350 Å werden photographiert. Die Nachweisgrenzen für die verschiedenen Elemente liegen zwischen 1 und 25 ppm. Eine Linie der Silicium-Matrix dient als interner Standard. Der Variationskoeffizient bei der Bestimmung der verschiedenen Elemente liegt zwischen 9 und 24%.

     

Differential pulse polarographic determination of salicylaldehyde as its Girard-P derivative

A method for the determination of salicylaldehyde (2 × 10^–6–10^–4 M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.5% (ten determinations of 4 × 10^–5 M level). The applicability of this method was checked in synthetic samples containing salicyl alcohol,o-aminophenol, 2-methylphenol, salicylic acid and 4-aminobenzoic acid.     

Differential pulse polarographic determination of nitrate and nitrite in nuclear wastes

Summary Solid particles for nuclear fuel fabrication can be produced by gel-supported precipitation. Process by-products are aqueous wastes containing organic materials, ammonium nitrate and ammonia that can be decomposed into nitrogen compounds. A differential pulse polarographic determination of nitrate- and nitrite-nitrogen in such mixtures is described.The proposed method is based on the previous separation of nitrate and nitrite ions from inorganic and organic interferents. After ammonia volatilization, the separation is achieved with a column of Amberlite IRA 410 (Cl^– form) anion exchange resin that is then eluted with 2.5M NaCl. An aliquot of the eluate is made 1M NaCl, 0.012M HCl and 0.0001M U(VI) and polarographic cumulative determination of nitrite and nitrate follows at –0.93 V (vs. Ag/AgCl) potential. Then a solution 6.5·10^–5 M in diphenylamine, 2.5·10^–3 M in sodium thiocyanate and 3·10^–2 M in perchloric acid is added to a second aliquot of the eluate and differential pulse polarographic determination of nitrite follows at –0.52 V (vs. Ag/AgCl).The proposed method permits determinations of nitrite-nitrogen levels as low as 5 ng N ml^–1 and of nitrate-nitrogen levels at 200 ng N ml^–1. Relative standard deviations less than 4% may be routinely achieved. Analysis time is approximately one hour per sample.

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Bestimmung von Nitrat und Nitrit in nuklearen Abfallprodukten

Zusammenfassung Feste Teilchen für die Herstellung nuklearer Brennstoffe lassen sich durch Fällung bei Anwesenheit von Gel herstellen. Dabei entstehen wäßrige Abfälle, die organisches Material, Ammoniumnitrat und Ammoniak enthalten, woraus durch Zersetzung stickstoffhältige Verbindungen entstehen können. Die Bestimmung von Nitratund Nitrit-Stickstoff in solchen Gemischen durch Differential-Puls-Polarographie wurde beschrieben.Die vorgeschlagene Methode beruht auf der vorhergehenden Abtrennung von Nitrat- und Nitritionen von störenden anorganischen und organischen Substanzen. Nach Verflüchtigung des Ammoniaks wird die Trennung mit Hilfe einer Säule aus Amberlit IRA 410 (Cl^–-Form) durchgeführt, die dann mit 2,5M NaCl ausgewaschen wird. Ein aliquoter Teil des Eluats wird auf 1M NaCl-Konzentration gebracht, 0,012M HCl und 0,0001M U(VI) eingestellt und polarographisch die Gesamtbestimmung von Nitrat und Nitrit bei einem Potential von –0,93 V (gegen Ag/AgCl) durchgeführt. Dann wird eine Lösung, bestehend aus 6,5·10^–5 M Diphenylamin, 2,5·10^–3 M NaCNS und 3·10^–2 M Perchlorsäure, einem zweiten Aliquot des Eluates zugesetzt und die Bestimmung des Nitrits durch Differential-Puls-Polarographie bei –0,52 V (gegen Ag/AgCl) vorgenommen.Dieses Verfahren ermöglicht die Bestimmung von Nitrit-Stickstoff bis auf 5 ng N/ml und von Nitrat-Stickstoff bis auf 200 ng/ml. Relative Standardabweichungen unter 4% lassen sich erzielen. Ungefähr eine Stunde je Probe ist erforderlich.

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Presented at the 9th International Symposium on Microchemical Techniques, Amsterdam, August 1983.     

Differential pulse polarographic determination of ofloxacin in pharmaceuticals and biological fluids

A sensitive method is described for the determination of ofloxacin in its pure form, dosage forms and biological fluids. The proposed method depends upon the polarographic activity of ofloxacin in Britton Robinson buffers, whereby a well-defined cathodic wave is produced over the pH range 4.1-10.3. The wave was characterized as being irreversible, diffusion-controlled with limited adsorption properties. The current-concentration relationship was found to be rectilinear over the range 5x10(-5)-5x10(-4) M and 1x10(-5)-5x10(-4) M using the DC(t) and DPP modes respectively, with a minimum detectability (S/N=3) of 3x10(-7) M. The proposed method was successfully applied to the determination of ofloxacin in tablets and biological fluids. The results obtained were found to be in agreement with those obtained by a reference method.     

Differential pulse polarographic determination of cephalosporins and their degradation products

The differential pulse polarography (d.p.p.) of several cephalosporins — cephalothin, cephalosporin C, cephaloridine, cephalonium, cefuroxime, cephoxazole, cephalexin, cephradine, desacetylcephalosporin C, 7-aminocephalosporanic acid and 7-aminodesacetoxy-cephalosporanic acid — and some degradation products has been studied. Cephalexin, cephradine and 7-aminodesacetoxycephalosporanic acid, which contain an unsubstituted 3-methyl group but no reducible group, do not give d.p.p. peaks at the dropping mercury electrode, whereas certain of their degradation products do. The other cephalosporins, in which the 3-methyl group is substituted, give a d.p.p. peak at about—1 V (pH 2–4). Although these peaks are near the cathodic limit under the conditions used, these cephalosporins can be determined down to about 0.1 μg ml^-1. Cephaloridine exhibits two d.p.p. peaks in this region, and can be determined. Cefuroxime, in addition to the peak at —IV, has a larger peak at —0.45 V (pH 2). Cephalonium shows a large well-defined peak at —0.72 V (pH 3) and two overlapping peaks. D.p.p. data for several degradation products including the diketopiperazines formed from cephalexin and cephradine are reported.     

Differential pulse polarographic determination of trace levels of iron(III) by using the catalytic current

Trace of iron(III) are determined by differential pulse polarography in a medium of sodium hydroxide and sodium bromate using the catalytic current. Various cations do not interfere. The relative standard deviation is 2%.