Ismail I. Hewala

High-Performance Liquid Chromatographic and Derivative Difference Spectrophotometric Methods for the Determination of Acetaminophen and Its Degradation Product in Aged Pharmaceutical Formulations

Abstract Two stability-indicating methods, HPLC and derivative difference spectrophotometry, have been described for the determination of acetaminophen as well as its degradation product, 4-aminophenol. The former method is based on the selection of two chromatographic systems using an octadecylsilane (C18) stationary phase. The latter involves the use of derivative (first and second) difference spectrophotometric technique. Interference from the coformulated excipients (colorant, flavour, preservative) of liquid formulations is completely eliminated. Accuracy, precision and the limit of detection of 4-aminophenol are discussed. The proposed methods are applied for determination of acetaminophen and 4-aminophenol in pharmaceutical formulations.

Determination of Two Binary Vitamin Mixtures Using Difference and Derivative Spectrophotometry

Abstract Simple, sensitive, rapid and accurate spectrophotometric procedures are described for the analysis of binary mixtures of vitamins. The first mixture: pyridoxine hydrochloride (PYRD) and thiamine hydrochloride (THIA): is analyzed using a combination of first- and third- derivative spectrophotometry for the determination of PYRD and THIA, respectively. The method is applied for the analysis of turbid mixtures and adopted for studying the dissolution of tablets. The second mixture; menadione sodium biphosphate (MENA) and ascorbic acid (ASCO); is analyzed using a second derivative and difference spectrophotometric methods for determination of MENA and ASCO, respectively. The validation of the proposed methods is discussed and their application for the analysis of tablets and ampoules are presented.

Enantioselective HPLC-DAD method for the determination of etodolac enantiomers in tablets, human plasma and application to comparative pharmacokinetic study of both enantiomers after a single oral dose to twelve healthy volunteers

An enantioselective high performance liquid chromatographic method with diode array detection (HPLC-DAD) was developed and validated for the determination of etodolac enantiomers in tablets and human plasma. Enantiomeric separation was achieved on a Kromasil Cellucoat chiral column (250 mm × 4.6mm i.d., 5 µm particle size) using a mobile phase consisting of hexane: isopropanol: triflouroacetic acid (90:10:0.1 v/v/v) at a flow rate of 1.0 mL min(-1). The chromatographic system enables the separation of the two enantiomers and the internal standard within a cycle time of 8 min. The resolution between the two enantiomers was 4.25 and the resolution between each enantiomer and the internal standard was more than 2.0. Detection was carried out at 274 nm, and the purity assessment was performed using a photodiode array detector. Solid phase extraction technique using C-18 cartridge was applied to extract the analytes from the plasma samples, and the percentage recovery was more than 95% for the lower quantification limit. The method has been validated with respect to selectivity, linearity, accuracy and precision, robustness, limit of detection and limit of quantification. The validation acceptance criteria were met in all cases. The linearity range for the determination of each enantiomer in human plasma was 0.4-30.0 µg mL(-1) and the limits of quantification of R-etodolac and S-etodolac were 0.20 and 0.19 µg mL(-1), respectively. The validated method was successfully applied to the determination of etodolac enantiomers in tablets and to a comparative pharmacokinetic study of the two enantiomers after the administration of 300 mg single oral dose etodolac racemate tablets to twelve healthy volunteers.

Development and application of a validated stability-indicating HPLC method for simultaneous determination of granisetron hydrochloride, benzyl alcohol and their main degradation products in parenteral dosage forms

A simple, rapid and sensitive reversed phase high performance liquid chromatographic method using photodiode array detection was developed and validated for the simultaneous determination of granisetron hydrochloride, benzyl alcohol, 1-methyl-1H-indazole-3-carboxylic acid (the main degradation product of granisetron) and benzaldehyde (the main degradation product of benzyl alcohol) in granisetron injections. The separation was achieved on Hypersil BDS C8 (250 mm x 4.6 mm i.d., 5 microm particle diameter) column using a mobile phase consisted of acetonitrile:0.05 M KH(2)PO(4):triethylamine (22:100:0.15) adjusted to pH 4.8. The column was maintained at 25 degrees C and 20 microL of solutions was injected. Photodiode array detector was used to test the peak purity and the chromatograms were extracted at 210 nm. Naphazoline hydrochloride was used as internal standard. The method was validated with respect to specificity, linearity, accuracy, precision, limit of quantitation and limit of detection. The validation acceptance criteria were met in all cases. Identification of the pure peaks was carried out using library match programmer and wavelengths of derivative optima of the spectrograms of the peaks. The method was successfully applied to the determination of the investigated drugs and their degradation products in different batches of granisetron injections. The method was proved to be sensitive for the determination down to 0.03 and 0.01% of granisetron degradation product and benzaldehyde, respectively, which are far below the compendia limits for testing these degradation products in their corresponding intact drugs.

Spectrofluorimetric and derivative absorption spectrophotometric techniques for the determination of loperamide hydrochloride in pharmaceutical formulations.

Simple, sensitive and rapid spectrofluorimetric and derivative absorption spectrophotometric procedures are described for the accurate determination of loperamide hydrochloride. The spectrofluorimetric method involves the measurement of the fluorescence of the compound in an ethanol-sulphuric acid mixture (90:10, v/v) using either the direct or the synchronous modes of measurement. Optimum conditions for maximum fluorescence are described. The derivative spectrophotometric method involves the measurement of either the second derivative peak amplitude (crest to trough, i.e. maximum to minimum) between 258 and 263 nm or the second derivative peak height (i.e. maximum to zero line) at 224 nm of an ethanolic solution of the drug. The proposed methods have been used for the determination of loperamide in pharmaceutical formulations. Compared to the pharmacopoeial method, the proposed methods give equally accurate (t-test) and precise (f-test) results. The proposed methods have the advantages of being highly sensitive for the determination of small concentrations of loperamide, a weak UV-absorbing compound prescribed in low doses.

Stability - Indicating Hplc Assay for Paracetamol, Guaiphenesin, Sodium Benzoate and Oxomemazine in Cough Syrup.

Abstract A stability-indicating, specific, sensitive and validated reversed-phase HPLC assay for paracetamol, guaiphenesin, sodium benzoate and oxomemazine in the presence of degradation products, i.e. 4-aminophenol and guaicol, as well, as the co-formulated adjuvants and 5-hydroxymethylfurfural, a commonly formed compound in syrups during formulation and/or storage of pharmaceutical syrups, has been developed to allow simultaneous determination of these compounds in a cough syrup. The HPLC method includes the use of a two-line solvent delivery system. The specificity, precision in term of both repeatability (i.e. intraday precision) and reproducibility (i.e. interday precision), limit of detection of the degradation products and ruggedness due to column to column batch and source variation have been discussed. The developed method has been applied for the determination of the main drugs and their degradation products in freshly prepared as well as in stored samples of cough syrup.

Difference spectrophotometric assay of benzaldehyde in benzyl alcohol

A simple and rapid procedure is described for the selective determination of benzaldehyde in benzyl alcohol intended for use in the manufacture of parenteral dosage form. The assay is based upon the measurement of the difference absorbance between two equimolar solutions of benzaldehyde in buffer solution pH 5.75, one of which also contains sodium bisulphite. The difference absorbance which has a maximum at 248 nm is due to the different spectral characteristics of benzaldehyde and its adduct form with sodium bisulphite is proportional to concentration of benzaldehyde. The accuracy, precision, sensitivity and specificity of the procedure are discussed. Application of the assay is described for different batches of benzyl alcohol. The results are compared with the official (BP) GLC method.

New concept for HPTLC peak purity assessment and identification of drugs in multi-component mixtures

Simple methods for HPTLC peak purity assessment and identification of the HPTLC peaks were presented. The spectrodensitograms - selected at different time intervals across the elution time of the HPTLC peak - were extracted and digital algorithms for manipulating the data were carried out in the wavelength domain. Three different methods were developed for testing the HPTLC peak purity using the mathematically transformed data of the spectrodensitograms. These included the method of relative absorption, the method of logA versus the wavelength plots and the derivative (first, second, third and fourth) method. The identification of the HPTLC peaks was based on the use of the derivative profile of the spectrodensitogram and the derivative ratios as fingerprints for the compounds. The wavelengths of absorbance and derivative (first, second, third and fourth) optima of the extracted spectrodensitograms were allocated. The data were compared with those obtained using the corresponding reference standard. The validity of the proposed methods was performed by chromatography of a mixture containing mebendazole and methylparaben as a model versus the winCATS(®) spectral correlation method as a reference method. The study indicated that the proposed concept is a reliable non-confusing valuable tool for testing the purity and identity of the HPTLC peaks as the results are easily and rigorously interpreted.

Development and application of a novel, dual-mode gradient, stability-indicating HPLC-DAD method for the simultaneous determination and purity assessment of mebeverine hydrochloride, diloxanide furoate and their corresponding major degradation products in combination with some gastrointestinal drugs in the form of oral doses

A simple, precise, rapid, stability-indicating reversed phase high performance liquid chromatographic method with photodiode array detection was developed and validated for the determination of mebeverine hydrochloride in combination with sulpiride or with diloxanide furoate and metronidazole in the presence of their corresponding degradation products. Optimum separation was achieved in less than 10 min using an X-Bridge C18 column (150 mm × 4.6 mm i.d., 3.5 μm particle size); elution was accomplished via the application of a dual-mode solvent and flow rate gradient system. This elution system enables the separation of nine components within a cycle time of 15 min and with a resolution greater than 2.5. Detection was conducted at 230 nm, and purity assessment was performed using a photodiode array detector. The method has been validated with respect to specificity, linearity, accuracy, precision, limit of quantitation, limit of detection, robustness and ruggedness. The validation criteria were met in all cases. The developed HPLC method was successfully applied to commercial tablets. It was shown that this method is very sensitive to the determination of the degradation products, downward to 0.1 w/w% levels, which is far below the limits for testing these degradation products within their corresponding intact drugs.

First derivative spectrophotometric and colourimetric determination of non-steroidal antiestrogens

Abstract Three methods have been described for the determination of clomiphene citrate and tamoxifen citrate. The first is based on using the first derivative spectra of UV absorption spectra. The second is based on the formation of colored ionpair compounds between the drugs and methyl orange in chloroform and measure the absorbance at 420 nm. The third is based on the reaction of the drugs with citric acid/acetic anhydride reagent and measure the absorbance at 605 nm. The proposed methods are applied for determination of the drugs in tablets. Compared with the pharmacopoeial methods, the proposed methods gave equally accurate (t-test) and precise (f-test) results. The proposed methods are selective and more sensitive than the pharmacopoeial methods.