Michael E. El-Kommos

Spectrofluorometric determination of certain quinolone antibacterials using metal chelation

Simple, rapid, reliable, and sensitive spectrofluorometric methods were developed for the determination of eight quinolone antibacterials namely ciprofloxacin, norfloxacin, lomefloxacin, difloxacin, amifloxacin, pefloxacin, ofloxacin, and nalidixic acid. The methods depend on the chelation of each of the studied drugs with zirconium, molybdenum, vanadium or tungsten to produce fluorescent chelates. Different factors affecting the relative fluorescence intensity of the resulting chelates were studied and optimised. At the optimum reaction conditions, the drug-metal chelates showed excitation maxima ranging from 274 to 295 nm and emission maxima ranging from 409 to 495 nm. The chelates were found to be stable at room temperature for 2 days and show good stability upon increasing temperature to 50 degrees C for about 1 h. Rectilinear calibration graphs were obtained in the range of 10-60 ng ml(-1) for each of the investigated drugs and the limits of detection and quantitation ranged from 1.214 to 2.046 and from 4.047 to 6.819 ng ml(-1), respectively. The molar ratios of the formed chelates were determined by Jobs method and their association constants were also calculated. The developed methods were applied successfully for the determination of the studied drugs in their pharmaceutical dosage forms with a good precision and accuracy compared to official and reported methods as revealed by t- and F-tests. They were also applied for the determination of studied drugs in spiked urine and plasma samples.

Spectrophotometric determination of isoniazid using 6,7-dichloroquinoline-5,8-dione

A spectrophotometric procedure for the determination of isoniazid and a number of its pharmaceutical preparations has been developed that offers advantages of simplicity, speed, sensitivity and stability indication over the official BP (1980) method. The proposed method is based on the formation of a green condensation product by the reaction between isoniazid and 6,7-dichloroquinoline-5,8-dione in an alkaline aqueous ethanolic medium. At the maximum absorption of 645 nm, Beers law is obeyed in the range 2–25 µg ml–1. The structure of the condensation product was confirmed by ultraviolet, infrared and microanalysis data and the mechanism of the reaction is discussed. Congenial drugs, common carbohydrates and excipients used as additives in pharmaceutical formulations did not interfere in the proposed method. The method can be used as a selective stability-indicating assay of isoniazid.

Spectrophotometric determination of certain local anaesthetics using 3-methylbenzothiazolin-2-one hydrazone

A rapid spectrophotometric procedure for the determination of benzocaine, procaine hydrochloride and amethocaine hydrochloride in pure and dosage forms has been developed. It is based on coupling the local anaesthetic drug with 3-methylbenzothiazolin-2-one hydrazone in the presence of ammonium iron(III) sulphate in an acidic medium. The resulting stable blue product has a λmax. of either 575 nm (for benzocaine and procaine hydrochloride) or 615 nm (for amethocaine hydrochloride). The molar absorptivities range from 0.6 × 103 to 5.5 × 104 l mol–1 cm–1. Job plots of absorbance versus molar ratio of amine to reagent indicate a 1 : 1 ratio for benzocaine and procaine hydrochloride and a 1 : 2 ratio for amethocaine hydrochloride. Results of analyses of pure drugs and their dosage forms by the proposed method are in good agreement with those obtained by the USP XXI method.

Determination of phenyltoloxamine salicylamide, caffeine, paracetamol, codeine and phenacetin by HPLC.

A reversed-phase high-performance liquid chromatographic method for the determination of six common analgesics (phenyltoloxamine dihydrogen citrate, salicylamide, caffeine, paracetamol, codeine phosphate and phenacetin) is presented. The method is specific for detection and determination of each of these compounds in a complex mixture, without pretreatment. A 10-mum C(18) silica gel stationary phase is used with a methanol-acetonitrile-water-tetrahydrofuran mixture (20:20:55:5 v/v) and spectrophotometric detection at 254 nm. All six components are eluted within 7 min. The method has given good results for three commercial products containing two, three and five active ingredients respectively. Phenacetin, a common analgesic which might be found in other formulations, is used as an internal standard.

Spectrophotometric determination of epinephrine and norepinephrine with sodium periodate

A simple and accurate spectrophotometric method is described for the determination of epinephrine (EP), norepinephrine (NE) and their bitartrate salts. The method is based on the development of a red colour (lambda(max) 490 nm) with sodium periodate in aqueous alcoholic medium. The colour is stable for at least 1 hr. The molar reacting ratio of EP or NE to periodate is 1:2. The proposed method is particularly suitable for routine analysis of EP and NE injections. The interference due to the sodium metabisulphite normally used as antioxidant can be overcome by addition of acetone. Results for analysis of bulk drugs and injections agree well with those of official methods.

Stereoselective metabolic study of famprofazone

Famprofazone (1) metabolites were studied in human urine after medication by 50 mg oral dose. The human urine was collected over 48 h from six volunteers at time intervals of 6, 12, 24 and 48 h. The amount of famprofazone metabolites were recovered from the urine samples by application of Extrelut extraction method. The resultant extracts were derivatized using N-methyl-N-trimethylsilytrifluoroacetamide (MSTFA) for trimethylsilylation followed by N-methyl-bis-trifluoroacetamide (MBTFA) for trifluoroacetylation. Methamphetamine (2) and 3-hydroxymethyl-propyphenazone (3), excreted in human urine, were identified as famprofazone metabolites by gas chromatography-mass spectrometry (GC-MS). The quantitative results revealed that the average amounts of 2 and 3, excreted in human urine were equal to 2.6 and 4 mg, respectively, through 48 h. However, 3 was analysed after enzymatic hydrolysis of the urine samples using beta-glucuronidase/arylsulphatase. The excreted methamphetamine enantiomers could be separated by application of indirect GC-technique using S-(-)-N-trifluoroacetylprolyl chloride (TPC) as a chiral derivatizing agent. The average amount of (-)-methamphetamine isomer excreted in the urine was found to be three fold those of the (+)-isomer.

Rapid spectrophotometric assay of phenothiazine drugs in pharmaceutical preparations

A simple, accurate and rapid method for the quantitative determination of ten phenothiazine drugs in either the pure form or in pharmaceutical formulations is proposed. The method is based on the development of pink or violet products with N-bromosuccinimide in a strong sulphuric acid medium. The reaction is suggested to proceed via oxidation of the phenothiazine nucleus into a semiquinonoid radica. The wavelengths of maximum absorption range from 512 to 565 nm. Molar absorptivities range from 6 × 103 to 20 × 103 l mol–1 cm–1. A linear correlation was found between absorbance (at the λmax.) and concentration. The resulting colours are well developed within 20–30 min and are stable for at least 10 h. Results of analyses of pure drugs and their dosage forms by the proposed method are in good agreement with those of the official BP 1980 and USP XX procedures.

Spectrophotometric method for the determination of dobutamine hydrochloride

A rapid, accurate and simple method is proposed for the determination of dobutamine hydrochloride in the bulk drug and in vials. This method is based on measuring the intensity of the pink colour that develops when dobutamine hydrochloride is allowed to react with thiosemicarbazide in an alkaline - acetone medium. The colour is stable for at least 3 h and can be quantified spectrophotometrically at 510 nm (Iµmax.= 1.7 × 104 l mol–1 cm–1). Beers law is obeyed in a concentration range 0.5–20 µg ml–1 in the final assay solution. The effects of reagent concentration, alkali concentration and solvent on colour formation were investigated. A Jobs plot of absorbance versus the molar ratio of dobutamine to thiosemicarbazide indicates a 1 : 1 ratio. As the catecholic group with free adjacent positions is required for colour development, the method is highly specific.

Spectrophotometric determination of some dibenzazepine drugs by electrophilic coupling

Two sensitive spectrophotometric methods for the determination of imipramine hydrochloride, clomipramine hydrochloride, desipramine hydrochloride, and trimipramine maleate in bulk and in dosage forms are described. The first method is based on the interaction of diazotized p-nitroaniline (DPNA) with the dibenzazepine drug in 5M hydrochloric acid. The second is based on the oxidative coupling of the dibenzazepine drug with 3-methylbenzothiazolin-2-one hydrazone (MBTH) in the presence of ammonium iron(III) sulphate in 0.1M hydrochloric acid. The resulting chromophores are measured at 575 nm (for the DPNA method) or at 620-630 nm (for the MBTH method), and are stable for at least 24 hr. The commonly encountered excipients and additives do not interfere with the determinations. Results from the analysis of pure drugs, commercial tablets and laboratory-prepared tablets by these methods agree well with those of official methods.

Spectrophotometric determination of dobutamine hydrochloride using 3-methylbenzothiazolin-2-one hydrazone

A spectrophotometric procedure is described for the determination of dobutamine hydrochloride. The proposed method uses 3-methylbenzothiazolin-2-one hydrazone as the chromogenic reagent. A mixture of aqueous solutions of the drug and reagent is treated with cerium(IV) ammonium sulphate in an acidic medium. Dobutamine reacts to give a pink colour with a λmax. at 510 nm (Iµmax.= 1.5 × 104 l mol–1 cm–1). Beers law is obeyed in the concentration range 4–20 µg ml–1 of dobutamine in the final assay solution. The procedure described was successfully applied to the determination of the bulk drug and its dosage form (Dobutrex vials).