The application of 2,4,6-trinitrobenzene-1-sulphonic acid in the differential pulse polarographic determination of amines

The differential pulse polarographic behaviour of 2,4,6-trinitrophenyl (TNP) derivatives of several primary amines and amino acids was investigated in the presence of sulphite ion. All the derivatives produced a polarographic peak for their complexes with sulphite (1 × 10^?2 M) in pH 8.0 phosphate buffer (0.05 M)/0.1 M potassium chloride. The derivatives of proteins and peptides did not give such a peak. A 5-min reaction time at room temperature (or 50°C for lysine) and pH 10.5 using 1 × 10^?4 M 2,4,6-trinitrobenzene-1-sulphonic acid provides the optimal conditions for the determination of 5 × 10^?6?2.5 × 10^?5 M amines. The relative standard deviation for determining 1 × 10^?5 M glycine (n = 5) was 1%.     

Polarographic determination of pirimicarb

A sensitive and selective polarographic method for the determination of pirimicarb is proposed. Linear calibration graphs were obtained by differential-pulse polarography in the 3.0 × 10^?7–9.0 × 10^?5 mol l^?1 range, the limit of determination being 2.8 × 10^?7 mol l^?1. No interferences were observed from other carbamate pesticides such as aminocarb, bendiocarb or carbaryl and only a matrix effect occurs in the presence of methiocarb. The method was applied to the determination of Pirimicarb in water samples with good recoveries.     

Polarographic determination of pilocarpine using the catalysed pre-wave of nickel(II)

On the basis of a detailed study of the pilocarpine-induced nickel(II) pre-wave using various polarographic techniques, an electrode process mechanism is proposed in which the formation of a catalytic complex between aquo-nickel(II) and veronalate-nickel(II) on the one hand and unprotonated pilocarpine adsorbed on the electrode surface on the other is followed by the reduction of nickel(II) in the complex and the release of the catalytic ligand. The pre-peak recorded by differential-pulse polarography in the system 1 × 10^?3 M Ni(II)-1 × 10^?2 M sodium veronal, nitric acid (pH 8.5) (with ionic strength maintained at 0.2 with sodium nitrate) can be used for quantitative determination of pilocarpine at concentrations in the range 2.5 × 10^?7-8 × 10^?6 M.     

Polarographic determination of nitrate in concentrated sulphuric acid solutions

The possibility of the polarographic determination of nitrates in the presence of hydroquinone in 65–95% sulphuric acid solutions was investigated. It has been found that nitrates in 95% acid have one polarographic wave without inflection point the height of which is proportional to nitrate concentration. In 85% sulphuric acid and in other acids investigated with lower concentrations, nitrates are not polarographically active. If both nitrate and hydroquinone are present in H₂SO₄, two waves are observed on the polarogram. The more negative wave is completely defined. The height of this wave is proportional to nitrate concentration in the range 5×10^?5?5×10^?3M.     

Determination of Nitrite by Single-Sweep Polarography

Abstract

A new method for determining nitrite is proposed. the mechanism for the polarographic waves and the condition for determining nitrite are discussed in this paper. In cathodic sweeps, the peak height is directly proportional to the concentration of nitrite over the range 5×10^?9?6×10^?7 g/ml, the detection limit is 4×10^?9g/ml. the experiments showed that this polarographic wave is an adsorption wave, and useful in determination of nitrite in water sample.     

Indirect Determination of Trace Tetraborate by Differential Pulse Polarography Using Its Copper Complex and Application to Waste and Drinking Water

A new differential pulse polarographic (DPP) method has been developed for the trace determination of boron. Its most stable copper complex is used in 0.5 M KNO₃ electrolyte since boron is not electroactive. By continuous addition of tetraborate to copper solution, the copper peak decreased first but then the peak became very small and nearly constant. This point was used for the boron determination. It was found that one mole of copper used two moles of tetraborate. Using this relationship, 1×10^?5 M tetraborate could be determined. The quantification limit was 2.5×10^?6 M and detection limit was 8×10^?7 M. In the presence of complex forming ions such as Pb, Zn, and Cd, the borate found in sample was somewhat smaller because of their reaction with borate. But since their complexes were not as strong as copper, only a few percent of borate were used. No interference was observed in the presence of calcium, chloride and sulfate. This method is applied for the determination of B in borax ore, waste water of borax industries and tap water of Ankara city.     

Differential-pulse voltammetric determination of molybdenum in nitrate medium in the presence of 8-hydroxyquinoline

The determination of Mo(VI) by differential-pulse voltammetry based on catalytic currents in nitrate medium is described. The existence of catalytic currents in the system Mo(VI)NO₃^? in the presence of 8-hydroxyquinoline was proved by various polarographic techniques. The optimum background electrolyte is 20 ml 0.5 M KNO₃?0.005 M HNO³ with the addition of 1 ml of 1 × 10^?2 M 8-hydroxyquinoline. The detection limit is 7 × 10^?10 M under these conditions. Cr(VI), Cu(II), Cd(II) and Pb(II) interfere when present at higher concentrations then Mo(VI) and W(VI) interferes at an equal concentration to Mo(VI). The method was successfully used in analyses of environmental samples.     

Batch and flow-injection determination of ethylenediamine in pharmaceutical preparations

the ethylenediamine/pyridine-2-carbaldehyde/copper(I) system is used in a new spectrophotometric method for the determination of ethylenediamine. The batch procedure involves the formation of an orange chelate between the Schiff's base and copper(I) ions at pH 8.5 (borate buffer) and measurement of the absorbances at 475 nm against water after 10/2-15 min; Beer's law is obeyed over the range 0.5/2-11.2 μg ml^?1 and the molar absorptivity is 6.21 × 10³ l mol^?1 cm^?1. Tolerance limits for different amines [36] and other organic compounds [12] are reported. In the optimized flow-injection system, ethylenediamine (1.4/2-84.6 μg ml^?1 is determined at a sample throughput of 55 h^?1. The method is sensitive and selective and is satisfactory for the determination of the diamine in aminophylline and pharmaceutical preparations (ethylenediamine contents from 0.031 to 3.23%) with relative errors ranging from ?7.4 to +11.1% and relative standard deviations of about 0.65% for both procedures.     

Selectivity Enhancement of a Bacterial Arginine Electrode

Abstract

The selectivity of a previously reported bacterial arginine electrode has been greatly enhanced, with no loss of response to arginine. The response of this sensor to glutamine and asparagine was found to be due to a contaminant growing in the bacterial layer of the electrode. The addition of 1 × 10^?3 M sodium azide to the working buffer and cold storage of the electrode effectively controlled the growth of the contaminating bacteria and maintained the low initial response of the electrode to these amino acids in the concentration range of 4 × 10^?5 to 1.5 × 10^?3 M. At these optimum conditions, the response of the sensor to arginine was unaffected by the presence of a mixture of amino acids at physiological levels.     

Flow-injection methods for the determination of uracil derivatives with voltammetric detection

Flow-injection methods are described for the determination of 18 uracil derivatives and related compounds, by means of differential-pulse amperometry (d.p.a.) or differential-pulse cathodic stripping voltammetry (d.p.c.s.v.). The carrier stream is a borax/KNO₃/HNO₃ (of NaOH) solution containing 0.001% (v/v) Triton X-100. This surfactant displaces the oxygen reduction peak to such negative potentials that deaeration is unnecessary for detection of compounds having peak potentials in the range 180–70 mV (vs. Ag/AgCI) at pH 7.6. At the hanging mercury drop electrode, the uracil derivative is deposited from the flowing sample at a fixed potential more positive than the relevant peak potential and stripped under stopped-flow or slow-flow conditions. In the amperometric mode, a constant potential also more positive than the relevant peak potential is applied to the dropping mercury electrode and the resulting peak is measured under flow conditions. Linear calibration graphs were found for most of the compounds at 10^?6–10^?7 M by d.p.a, and about one order of magnitude lower by d.p.c.s.v.. The limit of determination for 5-iodouracil was 5×10^?9 M (ca. 1.2 ng ml^?1). Separation is needed for applications to blood or urine. Simple deproteination followed by high-performance liquid chromatography with a reversed-phase column proved satisfactory. Separations of various uracil derivatives, and of 5-fluorouracil, uric acid and 5-fluorodeoxyuridine, are described; spectrophotometric and amperometric detectors were used sequentially to check performance.     

Determination of pseudouridine at submicromolar concentrations by cathodic stripping voltammetry at a mercury electrode

Pseudouridine (5-ribosyluracil), uridine (N,1-ribosyluracil), deoxyuridine (N,1-deoxyribosyluracil) and uracil are investigated by means of d.c. polarography and by differential and normal pulse polarography. Pseudouridine, which is known to be a cancer marker, yields anodic polarographic currents in the pH range 7–11, whereas uridine and deoxyuridine are inactive under the same conditions. The polarographic response of pseudouridine obtained is due to the formation of a sparingly soluble mercury compound. Pseudouridine can be determined by differential pulse polarography in the concentration range 2–6 × 10^?6 M and by differential-pulse cathodic stripping voltammetry at concentrations two orders of magnitude lower. Small excesses of uridine, deoxyuridine or proteins do not interfere with the determination.     

Polarographic study of uracil derivatives

Eighteen uracil derivatives were studied by d.c. polarography, differential-pulse (d.p.)polarography and d.p. cathodic stripping voltammetry. In a borax buffer at ca. pH 7.6, uracil, thymine and derivatives such as 5-halouracils, 5-trifluoromethyl-,5-aza-,5-acetyl-, 5-formyl- and 5-vinyl-uracil produced well-defined peaks at potentials between 0 V and ca. 160 mV vs. silver/ silver chloride (satd. KCl). The peaks are ascribed to the formation of sparingly soluble mercury salts. For the other derivatives tested (e.g., 5-nitro- and 5-ethynyl-uracil and 6-substituted uracils), the peaks were less well-defined and in some cases the polarographic curves were very complex. 2-Thiouracil produced a single peak at ca. ?400 mV, but only at pH 12.2. The shapes, heights and potentials of the peaks depended on the kind and position of the substituent on the pyrimidine ring. Rectilinear relationships of peak current vs. concentrations were found for most compounds (10^?5-10^?4 M) by d.p. polarography; d.c.polarography was not tested quantitatively. For 5-fluorouracil and 5-vinyluracil, linear calibrations were found for concentrations of 0.5–5 × 10^?7 M by d.p. cathodic stripping voltametry. Interference studies showed that small amounts of chloride and phosphate did not interfere but 5-fluorodeoxyuridine, which did not itself produce a peak, and proteins interfered seriously.     

Electrochemical reduction behaviour of the synthetic pyrethroid insecticide cyfluthrin and its determination in formulations and environmental samples

The polarographic behaviour of cyfluthrin (CY), an α-cynoester pyrethroid, was studied using a dropping mercury electrode and hanging mercury drop electrode in methanolic Britton–Robinson (B–R) buffer of pH 2.0–12.0 with different ionic media. The nature of the electrode process was examined, the number of electrons was evaluated, and the reduction mechanism was proposed. Quantitative determination was achieved in the concentration range of 6.0?×?10^?8 to 1.15?×?10^?5?mol?dm^?3 using a differential pulse polarographic method with a lower detection limit of 2.4?×?10^?8?mol?dm^?3. The proposed method was successfully applied in the determination of CY in formulations, grains, soils, and spiked water samples.     

Polarographic determination of picolinaldehyde in the presence of some related compounds

A d.c. polarographic method is described for the determination of picolinaldehyde (1.5 × 10^?5–2.9 × 10^?4 M), based on the in situ formation of its Girard-P derivative in aqueous solution. A mechanism of reduction (E_1/2 = ?0.71 V at pH 3.5) is proposed. The applicability of this method is checked in synthetic samples containing pyridine, picoline and pyridine carboxylic acids.     

Polarographic reduction of 2,4,6-trinitrobenzene-1-sulphonic acid and some 2,4,6-trinitrophenyl-amino acid derivatives

The rapid d.c. polarography of 2,4,6-trinitrobenzene-1-sulphonic acid and its derivatives with serine (I), threonine (II), glycine (III) and histidine (IV) revealed a 3-wave reduction and a marked pH dependence of the reduction potential. The polarographic waves of the derivatives (2.5 × 10^?4 M) showed appreciable changes when sulphite ions were present, with the development of a new wave at more negative potential in ?0.01 M sulphite solutions at pH 7.0. The E_1/2 values of these waves in pH 7.0 supporting electrolyte were: (I) ?1000; (II) ?1007; (III) ?1021; (IV) ?949 mV (vs. Ag/AgCl, sat. KCl). These waves were used to determine the amino acids investigated (1–4 × 10^?4 M) in the presence of excess of 2,4,6-trinitrobenzene-1-sulphonic acid, with good precision (2%).     

Effect of Basic Amino Acids on Nickel Ion Reduction at a Mercury Electrode

In a 0.02 M borax solution (pH 8.5), basic amino acids (arginine, lysine, and ornithine) react with Ni²⁺ to form a mono‐ligand complex that is reduced at a mercury electrode at about ?0.85 V vs. Ag|AgCl|KCl (3 M). At a long time scale (staircase voltammetry; scan rate<50 mV s^?1), the complex reduction is a catalytic (EC′) process, the rate‐determining step being the regeneration of the reducible species by the reaction of the amino acid with free Ni²⁺. At a short time scale (differential pulse voltammetry or higher scan rate staircase voltammetry), the reaction rate is controlled by the diffusion of the complex. Although the same kind of complexation occurs with either basic amino acids or glycine, the last one does not induce a similar process. The peculiar effect of basic amino acids is due to the side chain that causes the ligand molecule to adopt a favorable orientation at the electrode surface. The differential pulse voltammetry peak current is proportional to the total amino acid concentration over the concentration range from 2 to 100 μM. Hence a voltammetric method for arginine determination in nutritional supplements was developed and validated using HPLC as reference method.     

Electrochemical Reduction of Metronidazole and Its Determination in Pharmaceutical Dosage Forms by D.C. Polarography

Abstract

A simple d.c. polarographic method has been developed for the determination of metronidazole in dosages forms. In Robinson - Britton buffer (pH 4.38) and in presence of 1.60 × 10^?3 % Triton X-100, the drug produced a well defined 4-electron polarographic wave followed by another wave of about half the height of the first wave. The current is proportional to the concentration and permits the drug to be determined by d.c. polarography in the concentration range 5.0 × 10^?5 -7.0 × 10^?4 M. Results obtained by the proposed method are in excellent agreement with that provided by the USP-XX method. A rapid, sensitive and accurate polarographic method for the determination of metronidazole in the tablets which are produced locally is proposed.     

Determination of trace thiocyanate by linear sweep polarography

In a thiocyanate solution containing iron (II), nitrite and ascorbic acid, a linear-sweep polarographic wave appears at ?0.42 V (vs. SCE). In anodic sweeps, the derivative peak current is directly proportional to the concentration of thiocyanate over the range 2×10^?8?1×10^?6 M; the detection limit is 1×10^?8 M. The procedure is used for the determination of trace thiocyanate (10^?3?10^?4 M) in saliva. The mechanism of the electrode process is discussed; the polarographic wave is ascribed to catalytic reduction of dissolved oxygen in the presence of an adsorbed ternary Fe/SCN/NO complex.     

Polarographic waves of tri-n-butyl phosphate and polarographic determination of uranium in the presence of tri-n-butyl phosphate

The results of a study on the polarographic behaviour of TBP and its influence on the determination of uranyl ions is presented. The half-wave potential of the adsorption wave of TBP depends on the concentration of TBP, type of supporting elec trolyte and its concentration. In the presence of TBP the polarographic wave of U(VI) ion is changed. Below 7·10^?5 M TBP the polarographic wave of U(VI) is not affected, between 7·10^?5 and 2·10^?4 M TBP the shape, height and half-wave potential of U(VI) waves are changed and above 2·10^?4 M, up to saturated solution of TBP, the waves of U(VI) do, not change further. The bes supporting electrolytes for the determination of U(VI) are KNO₃ or NaClO₄ in concentrations of 0.1 to 0.5 M, pH 1–2 and TBP concentrations from 3·10^?4 to 1.2·10^?3 M.     

Construction of an arginine enzyme electrode and determination of arginine in biological materials

The arginine electrode is based on a coupled enzymatic system consisting of arginase and urease with an ammonia gas sensor; conditions of immobilization are optimized. Arginine in the range 3 × 10^?5–3 × 10^?3 M gives a linear potential vs. log (concentration) plot with a response time of 5 min over the range specified. Several compounds structurally related to arginine do not interfere. The method is suitable for the determination of arginine in bovine insulin and human serum. Results compare well with values given in the literature or obtained by the conventional Sakaguchi method.