Nikos Grekas

Chemiluminescence arising from the oxidation of bilirubin in aqueous media

Abstract Novel chemiluminogenic redox reactions of bilirubin in aqueous media are reported. N-bromosuccinimide and sodium hypochlorite were the oxidants which generated the most intense radiation and the corresponding reactions were monitored using a batch chemiluminometer. Consequently, the reaction of bilirubin with N-bromosuccinimide was further investigated using a flow injection analyser and the reaction, with hypochlorite, was further examined by using a continuous flow analyser in order to automate the procedure. The results indicate that both procedures are very sensitive (batch procedure with NaClO: linear range 0.2–20 μg ml−1; 3σ detection limit 50 ng ml−1) since bilirubin at concentrations less than 1 μg ml−1 can be easily and reproducibly measured. Albumin interferes seriously by enhancing the emission.

Determination of thiamine by continuous flow chemiluminescence measurement

The chemiluminescence produced by oxidation of thiamine by ferricyanide in alkaline medium has been investigated by using a simple continuous flow analyser and a procedure developed for the determination of thiamine hydrochloride or nitrate in the range 2.00 x 10(-5)-5.00 x 10(-4)M (equivalent to 6.75-169 mug/ml thiamine hydrochloride) with coefficients of variation <2%. A measurement rate of 112/hr can be obtained. When applied to pharmaceutical formulations, the only interferent among common excipients and coexisting drugs is ascorbic acid. The results obtained for the assay of dosage forms compared well with those obtained by an official method and demonstrated an error <4%.

Continuous-flow molecular emission cavity analysis for sulphide

Abstract Sulphide (1–10 μg ml −1 ) is determined by mixing the sample with an excess of orthophosphoric acid in a segmented continuous-flow system. The hydrogen sulphide evolved is swept into the cavity for generation of S 2 emission. The analysis is completely automated, requires no sample pretreatment and samples can be analyzed at 24 h −1 .

Continuous flow molecular emission cavity analysis of sulphite and sulphur dioxide

A continuous flow method for the determination of sulphite (1–50 µg ml–1) by molecular emission cavity analysis is described. The sample is mixed with an excess of orthophosphoric acid in a flow system and the sulphur dioxide evolved is continuously transferred into the cavity for generation of the S2 molecular emission. The analysis is completely automated, requires no sample pre-treatment and samples can be analysed at a rate of 24 per hour with a relative error of 1–2%. Various anions and cations interfere and attempts have been made to eliminate their effect on the final measurement. The results obtained by the proposed procedure compare well with the expected values when the method was applied to soft drinks, wines and air samples.

Determination of thiamine using continuous flow molecular emission cavity analysis.

A continuous flow method for the determination of thiamine hydrochloride (20.0-240.0 microgram ml(-1), 5.9 x 10(-5)-7.1 x 10(-4)m) is described. The sample was mixed with an excess of sodium hydroxide and remained in the delay coil for 20 min at 90 degrees C. The solution was then mixed with an excess of orthophosphoric acid and the hydrogen sulphide evolved was transferred continuously into the cavity to generate a molecular++ emission of S2. The analysis is completely automated, requires no sample pre-treatment and samples can be analysed at a rate of 30 samples h(-1) with a relative error of 1-2%. The method was evaluated by carrying out an interference study with common excipients and other water-soluble vitamins, a recovery study and by the analysis of commercial formulations. Results compared well with those obtained using the official method. The method was also applied to content uniformity tests.

Effect of sulphite on the determination of sulphide by continuous-flow molecular emission cavity analysis Determination of both anions in admixture

Abstract The effect of sulphite on the determination of sulphide after acidification and molecular emission cavity analysis is investigated. This severe spectral interference can easily be overcome and, therefore, the determination of sulphide and sulphite in admixtures in feasible. This is accomplished by the addition of sodium chloroacetate, which reacts with sulphide in alkaline medium to produce thiodiacetate. A simple method is derived which allows the successful determination of both anions in admixture. The procedure is applied to a variety of synthetic mixtures with an average relative error of 1.3% for sulphite and 2.7% for sulphide.

Continuous flow molecular emission cavity analysis of cephalosporins by alkaline degradation to sulphide

A continuous flow method for the determination of some cephalosporins (cephradine, cephalexin, cephalosporin C, cefadroxil, cephapirin and cephalothin) in the general range 10.0-250.0 micrograms ml-1 is described. The sample is mixed with sodium hydroxide and remains for 20 min at 90 degrees C in the delay coil of an air-segmented system. The solution is then mixed with an excess of orthophosphoric acid, and the hydrogen sulphide evolved is continuously transferred into the cavity for generation of the S2 molecular emission. The analysis is automated, requires no sample pre-treatment and samples can be analysed at a rate of 30 per hour with a relative error of 1-2%. The method was evaluated by carrying out recovery experiments and by the analysis of commercial formulations. Results agreed well with those obtained by the standard methods.

Molecular emission cavity analysis for organic sulphur compounds after electrolytic generation of hydrogen sulphide

Abstract Organic sulphur compounds (thiosemicarbazide and dithioxamide) are determined in the range 5.00–30.0 μg ml −1 . Electrolysis is done between two platinum electrodes in a closed vapour-generation system. Various parameters which affect the procedure are investigated in detail. Other sulphur-containing compounds can be determined with different sensitivities.

Continuous-flow molecular emission cavity analysis for organic sulphur compounds by alkaline hydrolysis

Abstract Alkaline hydrolysis of various organic sulphur compounds (thioacetamide, thiosemicarbazide, thiodiacetic acid and dithiooxamide) in a continuous-flow analyzer produces sulphide which can be removed from the solution after acidification. Hydrogen sulphide evolved is measured by molecular emission cavity analysis. Samples can be analyzed at a rate of 30 h −1 with a relative error of 1–2%.