Simple charging current correction in dc polarography

This paper demonstrates the strong interaction between molecular iodine and surface atoms of III - V compounds such as InP and GaP.The mechanism of the iodine reduction is determined.     

The analytical performance of direct current,normal pulse and differential pulse polarography with static mercury drop electrodes

The recently developed static mercury drop electrode (SMDE) provides a fundamentally new approach to electrodes for polarography. An analytical evaluation of the electrode is presented. For a range of electrode processes, current-sampled d.c. polarography at the SMDE is useful down to at least the 10^-7 M concentration level when short drop times and fast potential scan rates are used. The improvement in the limit of detection for d.c. polarography is therefore very substantial. Improvements in sensitivity associated with normal pulse and differential pulse polarography at the SMDE compared with the dropping mercury electrode (DME) are marginal. It is concluded that at the SMDE, the analytical performance and response characteristics of d.c., normal pulse and differential pulse polarography tend to converge.     

Quick charging pulse polarography: Theory for a reversible system

The theory for quick charging pulse polarography (QCPP) is described. It has been developed to calculate, a priori, the best pulse shape in order to enhance the sensitivity, the signal to background ratio, and the scan rate of pulse polarography techniques. A general potential-time relation, independent of the pulse shape, is first deduced using the variational approach in the case of a reversible system involving two soluble species. The optimization procedure is then performed in order to cancel the undesirable charging current a short time after the pulse start. The resulting pulse shape exhibits some similitude with that of the double pulse technique but is expected to be more efficient.     

Instrumentation for charging current compensation in d.c. polarography

It is shown that the non-linear charging current in d.c. polarography can be fairly well compensated by a method (suggested by Barker), which consists in applying a small a.c. voltage to the polarographic cell, rectifying the a.c. response, integrating it and subtracting a suitable fraction from the total d.c. response. An instrument incorporating such an automatic compensation for the nonlinear charging current is described. Results obtained with this instrument are presented to show that the limit of measureable concentrations is about 10^?7M for reversible waves and the precision is ±2.5 to ±3.0%. It is possible to obtain, with the instrument described here, well defined polarograms even when the supporting electrolyte concentration is low.     

Adsorption effects in normal pulse polarography of adenine

Dependences of the wave height (h) of normal pulse polarograms of adenine on prepolarization potential (E_pp) were found. This effect was investigated in more detail exploiting the advantage of the A 3100 pulse polarograph after G.C. Barker in changing the pulse polarographic parameters over a wide range. From the results it was concluded that this effect is caused by the adsorption of adenine during the prepolarization. The results were compared with on principle similar results of nucleic acids.     

Contribution to the study of pulse polarography part II. Digital simulation of ce mechanisms in normal pulse polarography

Several CE electrode processes have been introduced in a digital simulator of normal pulse polarography with widely varying values of the homogeneous and heterogeneous kinetic parameters. The effects on the shape of the normal pulse polarograms are described.     

Evaluation of derivative normal pulse polarography for use in metal speciation studies

A simple inexpensive microcomputer-orientated approach for obtaining pseudo-derivative polarograms is demonstrated. The method, called derivative normal pulse polarography (d.n.p.p.), produces better signal-to-noise ratios, and therefore lower detection limits, than differential pulse polarography (d.p.p.). The foremost advantage of d.n.p.p. is its relative freedom from influences of homogeneous chemical kinetics which makes it an excellent method for metal speciation studies. Response curve shapes for Pb(II) between 2 × 10^-4 and 8 × 10^-4 M exhibit excellent agreement with theory. Titration of EDTA with 0.01 M Cu(II) and 0.01 M Cd(II) using d.n.p.p. for detection exhibited recoveries of 98.0 and 99.5%, respectively.     

Modified normal pulse polarography of alkali-metal ions in acid solution

Well-defined polarograms of five alkali-metal ions in 0.01M hydrochloric acid were obtained by means of modified normal pulse polarography. The method uses the procedure of anodic stripping chronoamperometry during the life-time of a drop from a dropping mercury electrode, namely preparation of electrode, accumulating step and anodic stripping step of a metal. The instantaneous polarographic currents were sampled only once per mercury drop after the fall of each pulse. The wave heights for alkali-metal ions by the present method are free from the interference caused by 0.01M hydrochloric acid. The present method is applicable to monitoring of alkali-metal ions in fluid acid streams.     

A new and direct method for the trace element determination in cauliflower by differential pulse polarography

Using the DPP polarograms of wet digested cauliflower sample in acetate buffer at pH values of 2, 4 and 6, Fe, Zn, Mo, Se, Cr, Cd, Pb, Ti and Cu quantities were determined. The best separation and determination conditions for Zn, Se and Mo was pH 2; for Cr, Zn, Mo and As was pH 4; for Pb pH 6, for Ti, Cu and Fe was pH 6-7 EDTA, for Cd pH 2 EDTA and for lead pH 6, all in acetate buffer. The trace element ranges for cauliflowers from two different seasons were (first figure for winter, the second for summer) for Se 120-250 μg g⁻¹, Fe 70-85 μg g⁻¹, Cu 320-150 μg g⁻¹, Ti 90-120 μg g⁻¹, Cr 130-630 μg g⁻¹, Zn 90-550 μg g⁻¹, Mo 170-230 μg g⁻¹, Cd 20 μg g⁻¹ (in winter) and Pb 130-300 μg g⁻¹ in dry sample. Cd was under the detection limit in summer. The length of digestion time had no effect on the recovery of copper, iron, molybdenum and zinc between 15 and 3 h of digestion.     

In situ electrode modification for direct differential pulse polarography of 2,6-diaminopurine and its metabolite, 2,6-diamino-8-purinol

Preferential adsorption of allopurinol (1H-pyrazolo-[3,4-d]-pyrimidin-4-ol) at graphite electrodes from pH 7.0 phosphate buffer solutions of 2,6-diaminopurine and 2,6-diamino-8-purinol allowed in situ electrode modification. Modified electrodes were applied to the simultaneous determination of 2,6-diaminopurine and 2,6-diamino-8-purinol in phosphate buffer at pH 7.0. Differential pulse polarography allowed both compounds to be quantified in the concentration range 1 × 10^?6–5 × 10^?4 M. The relative standard deviation of the peak current is about 10%. Calibration curve characteristics are C (μM) = 0.0094 ± 0.0002 I (μA) + 0.22 ± 0.07 μA, with r = 0.9985 and C (μM) = 0.0065 ± 0.0001 I (μA) + 0.03 ± 0.04 μA with r = 0.9990 for 2,6-diamino-8-purinol and 2,6-diaminopurine, respectively.     

Positive feedback compensation of iR-drop in modified normal pulse polarography of sodium ion in acid solution

The well-defined polarographic wave for sodium, obtained by modified normal pulse polarography in which the polarographic current is sampled after the fall of each pulse, shifts to more negative potentials with decrease in the pH of the solution. The shift is attributed to the effect of the uncompensated resistance of the sample solution, and can be compensated by a positive feedback circuit.     

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     

Electrochemical studies of berberine and jatrorubine by pulse polarography

The application of pulse polarography (PP) and differential pulse polarography (DPP) for the quantitative determination of berberine and Jatrorubine in aqueous, acidic solutions was investigated. The proposed methods could be successfully applied in the concentration range between 5·10^–7 (DPP) or 1·10^–6 (PP) and 5·10^–5 mol/dm³ of alkaloids.     

示差脉冲极谱研究 VI.胞嘧啶在滴汞电极上的极谱电流

本文对胞嘧啶在滴汞电极上的示差脉冲极谱波的性质进行了研究,探讨了电极反应过程,推导了相应的脉冲极谱电流方程式,理论与实验结果完全相符。     

Application of modified normal pulse polarography and its differential mode to alkaline-earth metal ions in acid solutions

The simultaneous determination of alkaline-earth metal ions in acid solution was studied by modified normal pulse polarography. Well-defined waves were recorded for calcium, strontium and barium, but no limiting current was found for magnesium, because of its very negative reduction potential. The differential mode of this method gives peak-type polarograms and is useful for the simultaneous determination of species for which the half-wave potentials lie close together. The interference of dissolved oxygen was eliminated by the use of tetramethylammonium chloride as a supporting electrolyte.     

Cathode ray polarography and differential pulse polarography of the catalytic molybdenum(VI) wave

The optimum conditions of electrolyte composition and pH were studied for the cathode ray polarography (c.r.p.) of the catalytic molybdenum(VI) wave; 1–2 M potassium nitrate at pH 1.6–2.2 is optimum, the detection limit is 3 × 10^-9 M (0.3 ppb) molybdenum(VI). Equal molar concentrations of foreign electroactive substances do not interfere at the potential of the molybdenum wave and 500-fold amounts of these can be tolerated if their c.r.p. peaks are separated from the molybdenum wave by 0.1 or 0.2 V. Similar conditions were used for the differential pulse polarography of the catalytic wave. The detection limit is 2 × 10^-8 M (2 ppb). being limited in part by lead impurities which contribute to the background.     

Determinations of citric acid by differential pulse polarography with immobilized enzymes

Summary Citrate lyase and oxaloacetate decarboxylase can be rapidly and simply immobilized in polyacrylamide gel to provide a selective and sensitive reactor. Conversion ratio of citric acid to pyruvic acid comes up to 90% under the optimal conditions. Generated pyruvic acid can be determined by differential pulse polarography. The bioreactor can be used for thirty determinations over several weeks. Samples of sports drinks and wine were successfully tested without pretreatment; the relative standard deviation with 1.0×10^-5 mol l^-1 citric acid in polarographic solutions was 1.17% and the detection limit was 6.6×10^-7 mol l^-1 (=2).     

Influence of reactant adsorption on limiting currents in normal pulse polarography: Part V. Theory for non-linear adsorption

The analytical theory for adsorption-influenced limiting currents in normal pulse polarography is extended to conditions where the adsorption isotherm is non-linear. The case of Langmuirian adsorption at a stationary planar electrode is treated in detail, using the Reinmuth series for the dependence of surface coverage on time, and it is explained how the measured currents are affected by the isotherm parameters. The approach to Langmuirian adsorption at stationary spherical and expanding plane electrodes is briefly indicated. Finally it is pointed out how the problem can be solved for an arbitrary type of isotherm.