T.P. Hadjiioannou

Continuous-flow chemiluminescence determination of acetaminophen by reduction of cerium(IV)

A rapid and precise continuous-flow method is described for the determination of acetaminophen (1.00–10.0 µg ml–1) based on the chemiluminescence produced by its reaction with cerium(IV) in acidic solution. When applied to tablets, the method is relatively free from interferences from common excipients and co-existing drugs. The results obtained for the assay of commercial pharmaceutical preparations compared well with those obtained by a reference method and demonstrated good accuracy and precision.

FLOW-INJECTION STOPPED-FLOW KINETIC SPECTROPHOTOMETRIC DETERMINATION OF DRUGS, BASED ON MICELLAR-CATALYSED REACTION WITH 1-FLUORO-2,4-DINITROBENZENE

A flow-injection stopped-flow kinetic spectrophotometric method for the determination of hydrazines, hydrazides, amines and amino-acids, based on the cetyltrimethylammonium bromide catalysed reaction with 1-fluoro-2,4-dinitrobenzene is described. With the proposed method dihydralazine, isoniazid, levodopa and aspartame can be determined at concentrations of 0.1-6 x 10(-4)M. The calibration ranges can be varied by adjusting the pH and surfactant concentration. The determination of amphetamine, cysteine, s-carboxymethylcysteine, cephalexin, tobramycin and gentamicin is also feasible. The method has been applied to the determination of levodopa, isoniazid and aspartame in commercial pharmaceutical formulations. The determination of isoniazid in formulations containing the highly coloured antibiotic rifamycin, and of aspartame in coloured beverages was also accomplished. The results were in good agreement with those obtained by reference methods and the throughput was 40 measurements per hour with 0.4-3.9% RSD.

Kinetic identification and determination of certain carbohydrates with a periodate-sensitive perchlorate-selective electrode

Abstract The reactions between periodate and carbohydrates are easily monitored with a perchlorate-selective electrode as a periodate sensor. The relative reaction rate constant of each carbohydrate compared to glucose is introduced as a new characteristic constant, the “periodate index”, which could be related to the molecular configuration. Since appreciable differences are observed between the “periodate index” values of various carbohydrates, this constant can be used for the identification of 20-mg amounts of single pure compounds. An automatic potentiometric reaction rate method is described and shown to be simple, rapid and accurate for the determination of glucose. Amounts of glucose in the range 7–54 mg were determined in 20–140 s with precision and relative errors of about 0.4 and 0.8 %, respectively.

Potentiometric titration of organic cations with sodium tetraphenylborate and a liquid-membrane tetraphenylborate ion-selective electrode

Abstract Simple potentiometric titrations are described for the determination of various organic cations (usually 5–25 μ mol) with 0.01 M sodium tetraphenylborate. A liquid-membrane electrode with tetrapentylammonium tetraphenyiborate dissolved in 4-nitro-m-xylene as liquid ion-exchanger is used successfully in the semi-automatic titration of quaternary ammonium compounds, cationic surfactants, alkaloids and other substances of pharmaceutical importance which are precipitated by tetraphenyiborate. Analysis of pharmaceutical preparations gave satisfactory results.

Continuous-flow chemiluminometric determination of dihydralazine, rifampicin and rifamycin SV by oxidation with N-bromosuccinimide

Abstract A continuous-flow chemiluminometric method for the determination of dihydralazine sulphate (2.00–30.0 μg ml −1 ), rifampicin (0.0200–1.00 μg ml −1 ) and rifamycin SV (0.00500–1.00 μg ml −1 ) is described. The solutions are allowed to stand for about 4 h in alkaline solution before measurement in order to degrade to chemiluminogenic products. The method is based on the chemiluminescence produced during oxidation of these products by N -bromosuccinimide in alkaline medium. The emission intensity is greatly enhanced by the presence of ammonia. The procedure is automated and solutions can be analysed at a rate of 105 h −1 with a relative error of 1–3%. The method was evaluated by carrying out an interference study with common excipients and other co-existing compounds, by a recovery study and by the analysis of commercial formulations. The results obtained compared well with those obtained by an official method and demonstrated good accuracy and precision.

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.

Catalytic determination of selenium with a picrate-selective electrode

Abstract A method is described for the determination of selenium, based on its catalytic effect on the picrate—sulfide reaction. The determination involves a variable-time kinetic procedure using potentiometric monitoring with a picrate-selective electrode and automatic measurement of the time required for the potential to change by a preselected amount (5.0 mV). Selenium in the range 3–30 μg was determined with an average error of about 4% and relative standard deviations of about 2%. The reaction can also be followed spectrophotometrically.

EDTA titration of calcium and magnesium with a calcium-selective electrode

Direct semi-automatic and automatic derivative potentiometric EDTA procedures for the determination of calcium and/or magnesium with a calcium-selective electrode are described. Calcium is titrated in the presence of magnesium at pH 12.0 and the total calcium and magnesium is determined at pH 9.7. Calcium in the range 1-8 mg and magnesium in the range 0.7-5 mg are determined semi-automatically with average errors of about 0.2 and 0.3% respectively and automatically with average errors of 0.4 and 0.7%. Titration times vary from a few seconds to a few minutes.

Potentiometric determination of nicotine in tobacco products with a nicotine-sensitive liquid membrane electrode

Abstract A simple potentiometric method with standard additions is described for the rapid determination of nicotine in tobacco products. A nicotine-sensitive electrode with a liquid membrane of nicotine hydrogen tetra(m-chlorophenyl)borate dissolved in o-nitrotoluene is used. The electrode exhibits near-Nernstian response to monoprotonated nicotine cation activity from 0.08 to 10-5 M, in the pH range 4–7. Nicotine down to 2 mg per g of sample can be determined with a standard deviation of about 0.5 mg of nicotine. Comparison with an official method gave satisfactory results.

Construction of ion-selective electrodes for chlorpromazine, amitriptyline, propantheline and meperidine: analytical study and application to pharmaceutical analysis

Liquid-membrane ion-selective electrodes that respond to the cationic forms of chlorpromazine, amitriptyline and meperidine and to the quaternary ammonium compound propantheline are described. The liquid ion exchangers used were the salts of chlorpromazine or amitriptyline with eosin and tetraphenylborate in p-nitrocumene, propantheline with tetraphenylborate in 2-nitrotoluene and meperidine with tetrakis(m-chlorophenyl)borate in p-nitrocumene. The electrodes exhibited near-Nernstian response in the range 6 × 10–3–4 × 10–5M, working pH range 1–6 (chlorpromazine); 6 × 10–3–6 × 10–5M, pH 1–6 (amitriptyline); 6 × 10–3–3 × 10–6M, pH 1–9 (propantheline); and 10–2–7 × 10–6M, pH 1–7 (meperidine). The interferences from the alkali and alkaline earth metals were negligible but cationic molecules of similar structure interfered strongly. The electrodes were applied successfully to the assay of active compounds in pharmaceutical preparations. The major advantages of the proposed methods are their simplicity and speed.