Abstract: An accurate, simple, solvent free and inexpensive turbidimetric method is presented for the determination of ascorbic acid in pharmaceutical preparations and fruits. It needs no special reagents or precautions. In this method HgCl2 oxidizes ascorbic acid in citrate buffer at a pH of about 4 and produced Hg2Cl2 precipitate as monitored by turbidance measurements. The procedure is very simple and the experimental conditions such as temperature, ionic strength, stirring and time are not critical. High sensitivity and selectivity are two other advantages of this method. Linear dynamic range of the calibration curve is between 3-120 µg/mL with limit of detection (LOD) 1 µg/mL, which allows the ascorbic acid contents of most fruits and vegetables to be analyzed. On the other hand, the interference studies show that common compounds in real samples and colored substances have no considerable effect on the determination. Only filtration of some samples is necessary and other treatments, which are performed prior to determination of ascorbic acid by other analytical methods, are eliminated. Finally, ascorbic acid concentration in different samples is determined by the proposed method and obtained results are compared with the results of the official 2,6-dichlorophenolindophenol or iodimetric methods and a good agreement is obtained. This method is very sensitive in comparison with iodimetry and is very fast relative to the 2,6-dichlorophenolindophenol method.

Abstract: A solution (200 µL) of adrenaline or isoprenaline was injected into a 3 ml/min stream of 0.1% NaIO4 carrier, passed through a 4.3 m-long reactor and mixed with 0.05 M acetic acid/acetate buffer of pH 4.8 also flowing at 3 ml/min. The absorbance was monitored at 491 nm. The calibration graph was linear in the range 5 µM-1 mM, with a working range of 20 µM-0.2 mM. The RSD was 0.5% (n = 10) and the throughput was 120 samples/h. The method was applied to the analysis of pharmaceutical preparations. Powders were dissolved in 0.02 M buffer and liquids were diluted with the buffer prior to injection. The concentrations of the catecholamines were determined from calibration graphs or by the standard additions method.

Abstract: The alkylating antitumor drugs carboquone, cyclophosphamide, thiotepa, busulfan, and melphalan in commercial preparations (powders, tablets, or injections) were dissolved in suitable solvents and determined by spectrometry with the flow injection system, using 4-(4-nitrobenzyl)pyridine as reactant and detection at 580 nm. This method is simple and fast, and the results are comparable with those from other methods (HPLC, gas chromatography, etc.). (SFS)