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A first-derivative spectrophotometric method for the simultaneous determination of propacetamol hydrochloride (PRO) and paracetamol (PA) is described. Measurements are made at the zero-crossing wavelengths at 242.0 for PRO and 239.0 nm for PA. The calibration graphs were linear up to 20.0 and 15.0 mg l −1 of PRO and PA, respectively, the limits of quantification were 0.75 and 0.46 mg l −1 . The possible interfering effects of other substances were studied. The method was applied to determining the stability of PRO in ethanolic solutions and in glucose and saline parenteral solutions.

A first-derivative spectrophotometric method for the simultaneous determination of piroxicam (PX) and its major metabolite 5'-hydroxypiroxicam (OH PX) in human plasma is described. The method consists of direct extraction of the two drugs from the plasma samples with hydrochloric and trichloroacetic acid prior to their determination by measuring the first-derivative signals at 337.0 nm for PX and at 327.0 nm for OHPX (zero-crossing wavelength). The calibration graphs were linear up to 10.0 and 8.0 mg l-1 of PX and OH PX, respectively, and the limits of quantification were 0.27 and 0.56 mg l-1. The possible interfering effects of other substances were studied.

Sensitive and fast spectrophotometric methods for the determination of cephradine or ceftazidine in human urine, based on the formation of compounds between these drugs and Pd(II), are described. In the batch procedures the calibration graphs resulting from the measurement of the absorbance at 330 nm is linear over the range 5.0-60.0 micrograms. ml-1 for cephradine and 3.0-60.0 micrograms ml-1 for ceftazidine. The methods were successfully adapted to FI-systems, the peak heights being proportional to cephalosporin concentration over the range 5.0-60.0 micrograms ml-1 for cephradine and 3.0-60.0 micrograms ml-1 for ceftazidine. The sampling frequency was 60 h-1 with a sample injection of 72 microliters.

A simple spectrophotometric assay for the determination of cefepime and L-arginine in injections is described. Since zero-order spectra showed considerable overlap, second-derivative spectrophotometry was used to enhance the spectral details. A linear relationship between second-derivative amplitude and concentration of each compound was found. Beer's law was obeyed up to 50 and 22 micrograms ml-1 of cefepime and arginine, respectively, in the second-derivative mode. Detection limits were 0.31 and 0.58 micrograms ml-1 for cefepime and arginine, respectively. The method, which is rapid, simple and does not require any separation step, has been successfully applied to the assay of commercial injections containing cefepime and arginine.

A flow-injection method using spectrophotometric detection at 325 nm, is proposed for the determination of carbimazole or methimazole. The procedures are based on the formation of yellow complexes between these antithyroid drugs and Pd(II) in 0.5 M HC1. Methimazole or carbimazole are determined over the range 1 × 10 −5 −5 × 10 −4 M. The sampling frequency is 90 h −1 . The proposed methods are applied to the determination of methimazole or carbimazole in pharmaceuticals and methimazole added to human urine.

A simple, spectrophotometric assay to measure the concentrations of cefoperazone and sulbactam in injectable formulations is described. Since zero-order spectra are subject to interference, derivative spectrophotometry was used to enhance the spectral details. A linear relationship between derivative amplitudes and the concentrations of the compounds was found. Beer's law is obeyed up to 75 and 80 micrograms ml-1 of cefoperazone in the first and second derivative modes, respectively, and up to 75 micrograms ml-1 of sulbactam in the second derivative mode. Detection limits were 0.64 and 0.88 microgram ml-1, respectively for cefoperazone in the first and second derivative modes and 0.30 micrograms ml-1 for sulbactam in the second derivative mode. The method is rapid, simple, does not require a separation step and has successfully been applied to the assay of commercial injections containing cefoperazone and sulbactam.

A flow injection spectrophotometric method for the determination of captopril involving measurement of the absorbance of the captopril complex with palladium(II) in a 0.12 M HCl medium at 400 nm is presented. The calibration graph was linear over the range 2 x 10(-5)-6 x 10(-4) M. The sampling frequency was 90 h-1 with sample injections of 70 microliters. The proposed method was applied to the determination of captopril in pharmaceutical samples.

Two flow injection (FI) methods, involving spectrophotometric detection, are proposed for the determination of N-acetylcysteine (NAC). Both methods are based on the formation of a yellow complex between NAC and PdII in a medium of 1 mol dm–3 HCl. In the first method, which is based on the conventional Fl technique, NAC is determined over the range 5 × 10–5–5 × 10–3 mol dm–3, and in the second, in which the doublet-peak Fl mode is used, the working range is extended (5 × 10–5–5 × 10–2 mol dm–3). The Fl methods were applied to the determination of NAC in pharmaceutical samples.

A first-derivative spectrophotometric method for the determination of irbesartan (IRB) alone and in the presence of hydrochlorothiazide (HCT) is described. Measurements are made at the zero-crossing wavelength at 263.0 nm for IRB. The calibration graph was linear over the range 1.0–12.0 mg l−1 of IRB, detection limit was 0.15 mg l−1. HCT, in the presence of IRB was determined by direct spectrophotometric method at 317 nm. The calibration graph was linear over the range 2.0–50.0 mg l−1 of HCT, detection limit was 0.25 mg l−1. The proposed methods were successfully applied to the determinations of IRB and HCT in combined tablets.

Two sensitive and fast flow-injection spectrophotometric methods are proposed for the determination of frusemide or sulphathiazole based on the formation of coloured complexes between these compounds and Pd(II) at pH 5.0 and 55°C. Using the peak height as a quantitative parameter, frusemide or sulphathiazole was determined at 410 nm over the range 2.0 × 10 −5 –4.0 × 10 −4 M or 5.0 × 10 −5 –3 × 10 −4 M, respectively. The methods were applied to the determination of these sulphonamides in pharmaceuticals.

Two flow injection analysis (FIA) methods, using spectrophotometric detection, are proposed for the determination of penicillamine or tiopronin [N-(2-mercaptopropionylglycine)]. The procedures are based on the formation of yellow complexes between these thiol-containing drugs and Pd(II), in a 1 M or 0.25 M HCl medium, respectively. With peak height as a quantitative parameter, penicillamine is determined over the range 1.0 × 10−5−7.0 × 10−4 M; for tiopronin the range is 1.0 × 10−5−6.0 × 10−4 M. The methods have been applied to the routine determination of the drugs in pharmaceutical preparations.

First- and second-derivative spectrophotometry has been used for the quantitation of mixtures of imipenem and cilastatin sodium, compounds that have closely overlapping spectral bands. Beer's law was obeyed at concentrations up to 100 micrograms ml-1 of imipenem in both the first- and second-derivative modes and up to 75 micrograms ml-1 of cilastatin in the first-derivative mode. Detection limits at the P = 0.05 level of significance were calculated to be 0.40 and 0.52 micrograms ml-1 of imipenem and cilastatin sodium, respectively, in the first-derivative mode, and in a range from 0.45 to 0.68 micrograms ml-1 for imipenem in the second-derivative mode. The method, which is rapid, simple and does not require a separation step, has been successfully applied to the assay of commercial injections.