Colourimetric and atomic absorption spectrometric determination of some f luoroquinolone derivatives

Three simple, accurate, sensitive and selective procedures for the determination of ten fluoroquinolones (amifloxacin, ciprofloxacin hydrochloride, difloxacin hydrochloride, enoxacin, enrofloxacin, lomefloxacin hydrochloride, lovefloxacin, norfloxacin, ofloxacin and pefloxacin mesylate) were described. Procedures I and II are based on the formation of ion-pair complexes between the drugs and ammonium reineckate reagent in an acidic medium at 25 ±2°C and the formed precipitates are quantitatively determined either colourimetrically (procedure I) or by atomic absorption spectrometrically (procedure II). Procedure I is based on dissolving the formed precipitate with acetone, the volume was completed quantitatively and the absorbance of the solution was measured at 527 nm against pure solvent blank. The formed precipitates on the atomic absorption spectrometric procedure (procedure II) are quantitatively determined either directly or indirectly through the chromium precipitate formed or the residual un-reacted chromium in the filtrate at 358.6 nm and the optimum conditions for precipitation have been carefully studied. Procedure Ill is based on the reaction of the studied drugs with 2,2-diphenyl-1-picrylhydrazyl reagent (DPPH). The latter is employed to abstract a hydrogen atom from the drugs thereby promoting a process of radical coupling. This results in a reduction of the violet color of DPPH with the formation of the yellow colored 2,2-diphenyl-1-picrylhydrazine (DPPH2). The decrease in the intensity of the violet color is used to measure the concentration of the drugs. All measurements are made at λ = 520 nm on methanolic solutions of the reagent and drugs. Beer's law is obeyed for the studied drugs in the range 2-36 µg ml−1 with correlation coefficients not less than 0.9992. All procedures hold well accuracy and precision when applied to the analysis of the cited fluoroquinolones in different dosage forms with good recovery percent ranged from 98.88±0.40 to 100.99±0.44 without interference from additives.

Gas-Solid Chromatographic Determination of Moisture in Lyophilized Pharmaceutical Products

A gas-solid chromatographic procedure is described for the analysis of low levels of moisture in individual lyophilized vials of pharmaceutical products. Dry ethanol, which contains methanol as the internal standard, is injected through the septum of the vial to dissolve the lyophilized contents. An aliquot of this solution is then withdrawn and injected onto a Porapak QS column at 110°C where the components are separated and detected using thermal conductivity detection. A solvent blank correction allows quantitation of the water in the individual vial. The method is conveniently applied to samples containing as little as 50 μ g water/vial, and as many as 25 vials can be assayed/day. A simple technique is also described for removing water from the ethanol solvent to < 1 0 0 ppm, using a molecular sieve.

Colorimetric Determination of Diazepam in Pharmaceutical Preparations

A colorimetric method is presented for the estimation of diazepam as the pure drug and in formulations. Diazepam is hydrolyzcd with 6N HC1 to 2-methyIamino-5-chlorobenzophenone, which is extracted with chloroform to give a yellow solution whose absorbance is measured at 410 nm against a solvent blank. The color obeys Beer's law in the concentration range of 0–30 μg/ml. In 5 determinations, recovery was 99.0±1.9%. The method is applicable to pure diazepam and its formulations for oral and parenteral use. No interferences were observed from pyridoxine hydrochloride and commonly used preservatives, vehicles, and colors.

SERUM TRIIODOTHYRONINE DETERMINATION BY SATURATION ANALYSIS

ABSTRACT An improved method for the determination of serum triiodothyronine (T3) has been developed. After addition of a tracer amount of the hormone, T3 was extracted from 1 ml serum under conditions of pH and ionic strength which favoured T3 extraction (89%) over thyroxine (T4) extraction (58%). Chromatography of the extracted material on Sephadex LH-20 separated T3 completely from residual T4. The T3 eluate was dried, then re-dissolved in 0.5 ml NaOH 0.04 n. To 0.2 ml duplicate aliquots, a standard amount of TBG was added for the competitive protein analysis. After one hour incubation at 4°C, separation of bound from free T3 was achieved on small Sephadex G-25 columns. Overall recovery was 67 ± 10.8% and correction for the loss was made. The solvent blank was 37 ± 27 (sd) ng/100 ml. Accuracy of measurement of known quantities of T3 added to serum was 98.4%. The coefficient of variation within the assay was 6.2% and between the assays it was 11.4%. The limit of detection (0.1 ng) corresponded to a concentration of 25 ng/100 ml. T4 added to serum did not interfere with T3 determination until high non-physiological values were reached. The mean ± sd serum T3 in 54 euthyroid subjects was 153 ± 58 ng/100 ml and in 24 hyperthyroid patients it was 428 ±186 ng/100 ml; 4 out of the 24 hyperthyroid values were within 2 sd of the mean euthyroid group. All the values found in the euthyroid group were well above the limit of detection of the method.