Polarographic determination of cytisine inThermopsis alterniflora

Chemistry of Natural Compounds - A polarographic method has been developed for the determination of the content of cytisine in the combined alkaloids fromThermopsis alterniflora Rgl.     

Polarographic determination of nitramide

Nitramide gives two cathodic polarographic waves with half-wave potentials varying with pH, and having minimum values − 1·22 V at pH 4·5 and − 1·58 V at pH 8·8. Nitramide is fist reduced to nitrosamine in a two-electron reduction. In the second step, hydroxy-hydrazine may be formed in a two-electron reduction, or hydrazine itself in a four-electron step. For the polarographic determination of nitramide the first wave is used, and the supporting electrolyte is a Britton—Robinson buffer 0·1 M in KCl, at pH < 5 and at 0–2°.     

Polarographic determination of semicarbazones

Acetone, methyl isobutyl ketone, acetaldehyde, formaldehyde, cyclohexanone, butyraldehyde, crotonaldehyde, and acrolein semicarbazones all give polarographic waves suitable for quantitative analysis in an acetate buffer at pH 4.6 .The half-wave potentials are —1.3, —1.3, —1.16 —1.05, —1.2,—1.11, —1.06,–0.99 V vs. S.C.E., respectively, for the compounds listed above. The diffusion current constants of these compounds average approximately 7 in the concentration range of 10^-2 to 10^-1 mM, giving an extremely sensitive method of carbonyl compound analysis. A supporting electrolyte that is 0.1M each in acetic acid, sodium acetate, sodium chloride, and semicarbazide, and 0.0016% in Triton X-100, is satisfactory both for polarograph analysis and for the quantitative absorption of acetone, acetaldehyde, cyclohexanone, and crotonaldehyde from air samples by means of a scrubber.     

Polarographic determination of thallium

A polarographic method for the determination of thallium is described. The inclusion of DTPA and Triton X-100 in the supporting electrolyte shifts the waves of interfering metals to considerably more negative potentials while the thallium wave is completely unaffected. An acetate buffer of pH 4–5 is the preferred base electrolyte, because a Tl-DTPA complex is formed at higher pH values. The polarographic behaviour of the complex is described and the stability constant determined.     

Polarographic determination of malononitrile

A procedure is proposed for the determination of malononitrile by differential pulse polarography in methanolic 0.1M tetraethylammonium iodide/0.001M tetramethylammonium hydroxide as the supporting electrolyte. In this medium malononitrile is chemically converted into an electroactive species. With close control of timing of the steps in the procedure the error of the method is +/-1.5% in the concentration range 0.0001-0.001M. Acrylonitrile, benzonitrile and succinic acid dinitrile do not interfere.     

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 thiabendazole

Summary Polarographic Determination of Thiabendazole Thiabendazole is used as a fungistat on citrus fruit to protect it from decay.In order to work out a polarographic determination the electrochemical behaviour of thiabendazole was investigated by sampledd c polarography and differential pulse polarography. Thiabendazole shows one wave or peak in the polarogram, when a short drop time (0.4 s) is used. Detection is most sensitive at pH 8. The current measured is proportional to the concentration. The detection limit is 0.5 ppm.By evaluating further experimental data it was possible to conclude, that mercury is first oxidised. Thereby two electrons are exchanged. Then mercury(II) ions formed in this way react with two molecules thiabendazole. Two protons are involved in this chemical process.Applying drop times greater than 0.4 s and concentrations higher than 1.5·10^–4 M a polarogram with two peaks is formed. This is due to the adsorption of the reaction product.For quantitative determination several citrus fruits were peeled and the peels were extracted with ethylacetate. After removing interfering substances by shaking with sodium hydroxide solution, thiabendazole was extracted by diluted hydrochloric acid and quantitatively determined by differential pulse polarography. The recovery of thiabendazole is 70.0% with a relative standard deviation of 2.9%. For all samples investigated the thiabendazole concentrations were below the permitted value.Cordially dedicated to Univ.-Prof. Dr. Dr. h. c. K. Kratzl on the occasion of his 70th birthday.     

吡洛昔康的极谱测定

在0.06mol/LHAc NaAc(pH4.5±0.1)缓冲溶液中,吡洛昔康于-1.23V(vs.SCE)处产生一灵敏的极谱催化氢波,其二阶导数峰电流与吡洛昔康浓度在2.0×10-8～5.6×10-6mol/L范围内呈线性关系(r=0.9990,n=8),检出限为1.0×10-8mol/L。该方法可用于药剂中吡洛昔康的测定。     

Polarographic determination of deltamethrin

The electrochemical characteristics of deltamethrin have been determined by means of electrochemical techniques such as d.c. polarography, cyclic voltammetry and differential pulse polarography over a wide range of pH from 2.0-12.0. The title compound exhibits a single well defined peak due to the reduction of the CC moiety present in deltamethrin. The overall reduction process is diffusion-controlled and adsorption free in nature. The variation of half-wave potential with the pH, concentration of the title compound, and other experimental conditions is described. A possible mechanism for the reduction is suggested. The number of electrons involved in the electrode reduction is two. Investigation was also undertaken for the determination of deltamethrin in vegetables and in storage bags of rice and wheat under FCI's storage system.     

Polarographic determination of phosphorus

A method has been developed for the determination of phosphorus, as phosphate, by means of the catalytic polarographic wave for the reduction of hydrogen peroxide in the presence of Mo(VI). This reduction is combined with the previous formation and extraction of 12-molybdophosphoric acid. Depending on the extractant chosen, ethyl acetate or methyl isobutyl ketone, the determination limit is 2.3 or 3.1 mug l . respectively. The procedure has been applied to certified steel samples with good results.     

Polarographic determination of carbodiimides

N′-Cyclohexyl-N-(2-morpholinoethyl)carbodiimide metho-p-toluenesulphonate (CMCT) is irreversibly reduced via a two-electron mechanism at a mercury electrode. A differential-pulse polarographic study of this reduction led to a method for determining CMCT. From a study of CMCT hydrolysis at different pH values, the second-order rate constant of this reaction was determined at 25°C.     

Polarographic determination of nitrate in vegetables

A polarographic method for the determination of nitrate in vegetables is presented. The method is based on the reduction of nitrate to nitric oxide which reacts in solution with colbalt (II) and thiocyanate ions forming an electroactive complex that is reduced at the dropping mercury electrode at -0.5 V (vs. SCE). The nitric oxide is generated outside the polarographic cell by addition of ferrous ammonium sulfate and ammonium molybdate in hydrochloric acid to the previously triturated vegetable matrices. The calibration graph was linear in the range of 2-12x10(-6) mol nitrate. The recovery of nitrate in vegetable matrices (broccoli, kale, lettuce, radish, red beet, spinach, turnip and watercress) varied from 85.4 to 107.4 % and the nitrate content, expressed as sodium nitrate, varied from 751 to 10 806 mg kg(-1) of fresh vegetable. The relative standard deviation for the proposed method is lower than 7% and considering a sample of 5.0 g, the determination limit was 39 mg of nitrate per kg fresh vegetable weight. The precision and accuracy of the polarographic method were comparable to those of the reference spectrophotometric method (official AOAC reference method for the determination of nitrate in foodstuffs).