The accuracy in predicting different chemometric methods was compared when applied on ordinary UV spectra and first order derivative spectra. Principal component regression (PCR) and partial least squares with one dependent variable (PLS1) and two dependent variables (PLS2) were applied on spectral data of pharmaceutical formula containing pseudoephedrine (PDP) and guaifenesin (GFN). The ability to derivitize in resolved overlapping spectra chloropheniramine maleate was evaluated when multivariate methods are adopted for analysis of two component mixtures without using any chemical pretreatment. The chemometrics models were tested on an external validation dataset and finally applied to the analysis of pharmaceuticals. Significant advantages were found in analysis of the real samples when the calibration models from derivative spectra were used. It should also be mentioned that the proposed method is a simple and rapid way requiring no preliminary separation steps and can be used easily for the analysis of these compounds, especially in quality control laboratories.

New rapid, sensitive, and accurate kinetic spectrophotometric methods were developed, for the first time, to determine omeprazole (OMZ) in its dosage forms. The methods were based on the formation of charge-transfer complexes with both iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The variables that affected the reactions were carefully studied and optimized. The formed complexes and the site of interaction were examined by UV/VIS, IR, and (1)H-NMR techniques, and computational molecular modeling. Under optimum conditions, the stoichiometry of the reactions between OMZ and the acceptors was found to be 1 : 1. The order of the reactions and the specific rate constants were determined. The thermodynamics of the complexes were computed and the mechanism of the reactions was postulated. The initial rate and fixed time methods were utilized for the determination of OMZ concentrations. The linear ranges for the proposed methods were 0.10-3.00 and 0.50-25.00 mug mL(-1) with the lowest LOD of 0.03 and 0.14 mug mL(-1) for iodine and DDQ, respectively. Analytical performance of the methods was statistically validated; RSD was <1.25% for the precision and <1.95% for the accuracy. The proposed methods were successfully applied to the analysis of OMZ in its dosage forms; the recovery was 98.91-100.32%+/- 0.94-1.84, and was found to be comparable with that of reference method.

An analytical method based on CZE to determine lansoprazole enantiomers in pharmaceuticals was developed. The primary factors affecting its separation efficiency, which include chiral selector, pH, buffer concentration, capillary temperature and injection time, were optimised. The best results were obtained by using a background electrolyte consisting of 50 mM phosphate adjusted to pH 2.2, 12 mM beta-CD and 5 mM sodium sulphite, in combination with hydrodynamic injection and a 15 kV separation voltage. Detection limits were calculated from baseline noise and found to be 0.64 mg L(-1) for the R enantiomer and 0.72 mg L(-1) for the S enantiomer. The proposed method was used to analyse three different pharmaceutical preparations with recoveries of 91-102% of the label content.

The purpose of the study is to perform the in vitro and in vivo evaluation of multi-layer film coatings for omeprazole. The system consists of drug-layered or drug-containing core pellets coated with salt (sodium chloride and disodium hydrogen phosphate), hydroxypropyl methyl cellulose (HPMC), and enteric film-coating layer, respectively. The drug-layered core pellets were prepared by a coating layer of omeprazole on inert pellet cores in fluidized bed coater. An in vitro/in vivo gastro-resistance study was conducted, and a dissolution study was performed in pH 7.4 phosphate buffer for omeprazole release. The multi-layer coated pellets were stable in gastric pH conditions and upper gastrointestinal (GI) tract in rats. Salt layer improved the drug stability, and its coating levels had little influence on the dissolution profiles of omeprazole. The rate of drug release was significantly delayed by HPMC layer. The salt layer could function as a separated layer, and substitute part of the HPMC layer and decrease the coating levels of HPMC. The bioavailability (AUC) of the multi-layer coated drug-layered and drug-containing pellets was 3.48+/-0.86 and 2.97+/-0.57 microg*h/ml, respectively. The drug-layered pellets with multi-layer film coatings not only provided delayed and rapid release of omeprazole, but also could provide a good stable property for omeprazole. It was confirmed that rapid in vitro drug release rate resulted in better absorption.

Six impurities in pantoprazole sodium bulk drug substance were detected by a simple high performance liquid chromatographic method (HPLC) whose area percentage ranged from approximately 0.05 to 0.34%. Liquid chromatography-mass spectrometry (LC-MS) was performed to identify the molecular weight of the impurities. A thorough study was undertaken to characterize these impurities. These impurities were synthesized, subsequently characterized and were co-injected with the sample containing impurities and found the retention time match of the spiked impurities. Based on their spectral data (IR, NMR and MS), these impurities were characterized as; 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]thio]-1H-benzimidazole (Impurity-I); 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfonyl]-1H-benzimidazole (Impurity-II); 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-1-oxide-2-pyridinyl)methyl]sulfonyl]-1H-benzimidazole (Impurity-III); 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]thio]-1-((3,4-dimethoxy-2-pyridinyl)methyl)-1H-benzimidazole (Impurity-IV); 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1-((3,4-dimethoxy-2-pyridinyl)methyl)-1H-benzimidazole (Impurity-V); 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-1-oxide-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole (Impurity-VI). The formation of these impurities was proposed. The structure of the Impurity-II was unambiguously confirmed by single crystal X-ray diffraction (XRD) studies.

Omeprazole, a gastric acid pump inhibitor, dose-dependently controls gastric acid secretion; the drug has greater antisecretory activity than histamine H(2)-receptor antagonists. Omeprazole has been determined in formulations and biological fluids by a variety of methods such as spectrophotometry, high-performance liquid chromatography with ultraviolet detection and liquid chromatography coupled with tandem mass spectrometry. The overview includes the most relevant analytical methodologies used in its determination since the origin still today.

First-derivative spectrophotometry, applying the peak-zero method, was developed for the determination of rosiglitazone (RSG) in coated tablets. The solutions of standard and sample were prepared in ethanol. Quantitative determination of the drug was performed at 331.4 nm (N = 4; delta lambda = 3.2 nm) and was evaluated for the parameters specificity, linearity, precision, and accuracy. The specificity test showed that there was no interference from excipients commonly found in the commercial pharmaceutical formulation at 331.4 nm. The standard curve showed a correlation coefficient of 0.9997. Precision was demonstrated by a relative standard deviation value of 0.50%. The recovery test resulted in an average of 100.06%, which confirmed the accuracy of the method. The results for first-derivative spectrophotometry (D(1)), liquid chromatography, and micellar electrokinetic chromatography were compared by analysis of variance (ANOVA), and there were no significant differences among these methods. Therefore, D(1) can be easily and directly applied to analyze RSG in coated tablets.

A simple sensitive, selective and accurate reversed-phase high performance liquid chromatographic method was developed and validated for the quantitative determination of lansoprazole, omeprazole and pantoprazole sodium sesquishydrate in the presence of their acid-induced degradation products. The three compounds were monitored at 280 nm using Nova-Pak C(18) column and a mobile phase consisting of 0.05 M potassium dihydrogen phosphate : methanol : acetonitrile (5 : 3 : 2 v/v/v). Linearity ranges were 2-20 microg ml(-1), 2-36 microg ml(-1) and 0.5-20 microg ml(-1) for lansoprazole, omeprazole and pantoprazole, respectively. The corresponding recoveries were 100.61+/-0.84%, 100.50+/-0.80% and 99.78+/-0.88%. The minimum detection limits were 0.55, 0.54 and 0.03 microg ml(-1) for lansoprazole, omeprazole and pantoprazole, respectively. The method could be successfully applied to the determination of pure, laboratory prepared mixtures and pharmaceutical dosage forms. The results obtained were compared with the reported methods for lansoprazole and pantoprazole or the official U.S.P method for omeprazole.

An extensive study on the application of the "zero-crossing" technique for the analysis of a binary mixture of the photosensitive drug lacidipine and its corresponding by-product by derivative spectrophotometry is described. The technique has been compared to either conventional and recently developed UV spectrophotometric procedures, including chemometric methods. The prediction ability of the different analytical techniques has been checked by using the first-order derivative spectra of drug and photoproduct in binary mixtures. Relative advantages and drawbacks have been discussed. The zero-crossing technique suffers from several limitations, mostly ascribed to the selection of suitable signals along slopes of the spectral curve, giving rise to low accurate and precise results. The mean recovery from the zero-crossing analysis was calculated to lie in the 95.1-98.4% range for lacidipine, and 91.2-118.9% for the photoproduct. Chemometric methods showed a greater prediction ability with a 101.4-103.0% and 96.3-98.4% recovery for drug and degradation product, respectively.

Lansoprazole and omeprazole degrade in water leading to sulfides, benzimidazolones and a red complex material. Degradation is accelerated in acid medium and by solar simulator irradiation. Benzimidazoles, dianilines and pyridines have also been identified.

The photodecomposition of nisoldipine ((+/-)3-isobutyl-5-methyl-1,4- dihydro-2,6-dimethyl-4-(2-nitrophenyl)-pyridine-3,5-dicarboxylate), whereby its 4-(2-nitrosophenyl) pyridine analogue is obtained as the photolytic product, was investigated under daylight exposure by means of UV derivative spectrophotometry. The optimal instrumental parameters (120 nm/min scan speed; 2 nm slit width; delta gamma = 10 nm and 5 s response time) for analogue derivative spectra were established for amplitudes 1D285 and 2D291 (measured to the baseline) of the nitroso analogue assay, as well as for 1D386 of the parent compound-nisoldipine assay. Using the first-order derivative spectrum, the minimum detectable amount of nitroso analogue in the presence of nisoldipine was equivalent to an impurity level of 5% and by the second-order derivative spectrum, the determination limit was equivalent to an impurity level of 2%. The degradation of nisoldipine followed within 30 days and the calculated maximal degradation rate was 1.6% per day for nisoldipine raw material, but significantly lower values of 0.19 and 0.15% per day were obtained for Nisoldin tablets (10 and 5 mg, respectively).

A method has been developed for separation of nitrendipine and its impurities of reaction partners and side reaction products by high-performance liquid chromatographic method on a RP-18 column and detection at 238 nm. The mobile phase composition that provided an acceptable nitrendipine resolution, in large excess and possible impurities, in a short elution time, is methanol:water (70:30) and pH 3. Linearity (r> or =0.999), reproducibility (RSD=0.8--1.4%), determination limit (0.5--2%) and recovery (99.8--102.3) were validated and found to be satisfactory. This method enables monitoring of the process of synthesis, as well as the choice of the synthetic design.

A simple and reliable thin-layer chromatographic method for determining sulpiride and impurities of 2-aminomethyl-1-ethylpyrrolidine and methyl-5-sulphamoyl-2-methoxybenzoate was developed and validated. A methylene chloride-methanol-ammonia solution (25%; 18 + 2.8 + 0.4, v/v) solvent system is used for separation and quantitative evaluation of chromatograms. The chromatographic plate is first scanned at 240 nm to locate chromatographic zones corresponding to sulpiride and methyl-5-sulphamoyl-2-methoxybenzoate. Then 2-aminomethyl-1-ethylpyrrolidine is derivatized in situ with ninhydrin, and resulting colored spots are measured at 500 nm. The method is reproducible and convenient for quantitative analysis and purity control of sulpiride in its raw material and in its dosage forms.

Involvement of imidazoline receptors (IR) in the regulation of vasomotor tone as well as in the mechanism of action of some centrally acting antihypertensives has received tremendous attention. To date, pharmacological studies have allowed the characterization of three main imidazoline receptor classes, the I(1)-imidazoline receptor which is involved in central inhibition of sympathetic tone to lower blood pressure, the I(2)-imidazoline receptor which is an allosteric binding site of monoamine oxidase B (MAO-B), and the I(3)-imidazoline receptor which regulates insulin secretion from pancreatic β-cells. All three imidazoline receptors represent important targets for cardiovascular research. The hypotensive effect of clonidine-like centrally acting antihypertensives was attributed both to α(2)-adrenergic receptors and nonadrenergic I(1)-imidazoline receptors, whereas their sedative action involves activation of only α(2)-adrenergic receptors located in the locus coeruleus. Since more selective I(1)-imidazoline receptors ligands reduced incidence of typical side effects of other centrally acting antihypertensives, there is significant interest in developing new agents with higher selectivity and affinity for I(1)-imidazoline receptors. The selective imidazoline receptors agents are also more effective in regulation of body fat, neuroprotection, inflammation, cell proliferation, epilepsy, depression, stress, cell adhesion, and pain. New agonists and antagonists with high selectivity for imidazoline receptor subtypes have been recently developed. In the present review we provide a brief update to the field of imidazoline research, highlighting some of the chemical diversity and progress made in the theoretical studies of imidazoline receptor ligands.

Selective imidazoline(1)-receptor (I(1)-R) ligands are used clinically to reduce blood pressure. Thus, there is significant interest in developing new imidazoline analogs with high selectivity and affinity for I(1) receptors. A quantitative structure-activity relationship (QSAR) study was carried out on 11 potent I(1)-R ligands (derivatives of imidazoline, oxazoline and pyrroline) using a multiple linear regression (MLR) procedure. The selected compounds have been studied using B3LYP/3-21G(d, p) and B3LYP/6-31G(d, p) methods. Among the 42 descriptors that were considered in generating the QSAR model, three descriptors (partial atomic charges of nitrogen in the heterocyclic moiety (N-2 charge), log D and the dipole moment of the ligands) resulted in a statistically significant model with r(2)> 0.874 and [image omitted]> 0.802. The QSAR models were validated through cross-validation and external test set prediction. The aim of the developed MLR models for the I(1)-R ligands was to link the structures to their reported I(1)-R binding affinity log(1/Ki). The proposed QSAR models indicate that an increase in log D and the dipole moment value and a decrease in N-2 charge in the heterocyclic moiety are predictors of better selectivity and affinity for I(1) receptors. The developed QSAR model is intended to predict the I(1)-R binding affinity of related compounds and aid in the rational design of new potent and selective I(1)-R ligands.

The retention constant (R(0)(m)) is determined for 11 selected adrenergic and imidazoline receptor ligands by reverse-phase-thin layer chromatography. It is established that the retention behavior of investigated compounds mostly depends on geometrical, electrostatic, and hydrogen bonding properties. Good correlations among hydrophobic parameters R(0)(m) versus log P for all eleven tested compounds are obtained. The satisfactory correlations are found between R(0)(m) versus apparent partition coefficient octanol-buffer pH 7.4 (log P') or apparent partition coefficient in four liposome systems (log K'(M)) and hypotensive activity (pC(25)) for five imidazolines. The results confirm the suitability of this parameter in quantitative structure-property and structure-activity relationships studies of these drugs.

A quantitative structure-selectivity relationships of series of structurally diverse alpha(1)-adrenergic antagonists was performed by using counter-propagation neural network (CP-ANN). The theoretical molecular descriptors have been calculated and selected using CODESSA program. The results obtained for a highly non-congeneric set of molecules have confirmed the potential of use of CP-ANN approach in prediction of relative activity (selectivity) of alpha(1)-adrenergic antagonists.

The colorimetric method for determination of triamcinolone, triamcinolone acetonide and fluocinonide in tablets, ointments and cream using isonicotinic acid hydrazide is proposed. This method provides a precise and reproducible results (recovery ranged within 97.42-101.75%, variation coefficient ranged within 0.99-2.56%).

A second order derivative spectrophotometric method for the determination of bifonazole in the presence of methyl- and propyl p-hydroxybenzoate as preservatives has been developed. The determination was performed in a 0.1 M HCl solution at 241.5 nm, a wavelength corresponding to the intersection of the second order derivative spectra (2D) of methyl- and propyl p-hydroxybenzoate with the axis (zero-crossing point). On the basis of the knowledge of acidity constants and solubility, as well as of the investigations of zero-order and 2D spectra of bifonazole and preservatives, these conditions were chosen as optimal ones. A calibration curve constructed for bifonazole concentrations ranging from 1.5 to 15 microg/ml had a correlation coefficient of 0.9998. Reliability and reproducibility of the method was checked by analyzing laboratory mixtures of bifonazole and preservatives (recovery 99.97-102.7%; RDS 0.48-1.46%). The proposed method was applied for the determination of bifonazole in a commercial cream formulation. The mean value of bifonazole obtained per 100 g cream was 1.029 g (102.9% of the labeled claim) with a RSD of 0.60%.

This paper present a HPLC method for simultaneous determination of acetylsalicylic acid, paracetamol, caffeine and phenobarbital in tablets, using chromatographic system consisting a Bio Rad 18 01 solvent pump, Rheodine 71 25 injector and Bio Rad 18 01 UV-Vis Detector. Separation was achieved using Bio SiL HL C18, 5 microm, 250 x 4.6 mm column. Mixture of acetonitrile-water (25:75 v/v) adjusted to pH 2.5 with phosphoric acid was used as a mobile phase at a flow rate of 2.0 ml min(-1). UV detection was at 207 nm range 0.01 AUFS. Under the same conditions it was possible to determine the level of salicylic acid. The chromatographic parameters such as retention times, capacity factor, peak asymmetry, selectivity factor and resolution factor was determined. The validation parameters: linearity (r > 0.998), intra-day precision (RSD: 0.36-1.89%) and inter-day precision (RSD: 0.58-2.18%), sensitivity (LOD: 9 x 10(-5)-1.7 x 10(-4) mg ml(-1) and LOQ: 2.5 x 10(-4)-5.6 x 10(-4) mg ml(-1)), accuracy (recoveries: 98.35-99.14%) and reproducibility (recovery values: 98.74-102.08% for acetylsalicylic acid, 99.93-102.11% for paracetamol, 98.25-102.12% for caffeine and 98.15-102.3% for phenobarbital)(RSD: 1.21-1.85%) were found to be satisfactory. The proposed HPLC method has been applied for the determination of acetylsalicylic acid, paracetamol, caffeine and phenobarbital in Malophenum tablets. The obtained RSD values were within 0.99-1.21%. The developed method is rapid and sensitive and therefore suitable for routine control of these drugs in dosage form.

A new, simple, and original method is described for specific measurement of polyunsaturated fatty acid content in olive oil. This analytical system uses coupled enzymes, lipase and lipoxygenase. The system consists of lipase-catalyzed hydrolysis of triacylglycerol and subsequent lipoxygenation of liberated polyunsaturated fatty acids. The hydroperoxy-fatty acids formed were easily monitored by spectrophotometry at 234 nm. After being optimized, the method was validated in terms of linearity, precision sensitivity, and recovery. Linear calibration graph was obtained in the range 50-500 microg mL(-1), with a correlation coefficient higher than 0.921 and a detection limit (S/N = 3) of 15 microg mL(-1). The precision of the method (relative standard deviation) for within and between days is better than 7% and 12%, respectively. The proposed method was successfully applied to the estimation of polyunsaturated fatty acids level in olive oil samples and results obtained were in excellent agreement with those obtained by the classical official method. The proposed method is accurate, simple, cheap, and can be satisfactorily used for routine analysis of edible oils.

UV-VIS-Spectrophotometric and spectrofluorimetric methods have been developed and validated allowing the quantification of chloroaluminum phthalocyanine (CIAIPc) in nanocarriers. In order to validate the methods, the linearity, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy, and selectivity were examined according to USP 30 and ICH guidelines. Linearities range were found between 0.50-3.00 microg x mL(-1)(Y = 0.3829 X [CIAIPc, microg x mL(-1)]+ 0.0126; r = 0.9992) for spectrophotometry, and 0.05-1.00 microg x mL(-1)(Y = 2.24 x 10(6) X [CIAIPc, microg x mL(-1)]+ 9.74 x 10(4); r = 0.9978) for spectrofluorimetry. In addition, ANOVA and Lack-of-fit tests demonstrated that the regression equations were statistically significant (p<0.05), and the resulting linear model is fully adequate for both analytical methods. The LOD values were 0.09 and 0.01 microg x mL(-1), while the LOQ were 0.27 and 0.04 microg x mL(-1) for spectrophotometric and spectrofluorimetric methods, respectively. Repeatability and intermediate precision for proposed methods showed relative standard deviation (RSD) between 0.58% to 4.80%. The percent recovery ranged from 98.9% to 102.7% for spectrophotometric analyses and from 94.2% to 101.2% for spectrofluorimetry. No interferences from common excipients were detected and both methods were considered specific. Therefore, the methods are accurate, precise, specific, and reproducible and hence can be applied for quantification of CIAIPc in nanoemulsions (NE) and nanocapsules (NC).

A novel topical corticosteroid FA-21-PhP, 2-phenoxypropionate ester of fluocinolone acetonide, has been synthesized in order to investigate the possibility of decreasing systemic side effects. In this study model system for in vitro solvolytic reaction of FA-21-PhP has been analyzed in ethanol/water (90:10, v/v) with excess of sodium hydrogen carbonate. The selected conditions have been used as in vitro model for activation of corticosteroid C-21 ester prodrug. The second-order derivative spectrophotometric method (DS) using zero-crossing technique was developed for monitoring ternary mixture of solvolysis. Fluocinolone acetonide (FA) as a solvolyte was determined in the mixture in the concentration range 0.062-0.312 mM using amplitude (2)D(274.96). Experimentally determined LOD value was 0.0295 mM. The accuracy of proposed DS method was confirmed with HPLC referent method. Peak area of parent ester FA-21-PhP was used for solvolysis monitoring to ensure the initial stage of changes. Linear relationship in HPLC assay for parent ester was obtained in the concentration range 0.054-0.54 mM, with experimentally determined LOD value of 0.0041 mM. Investigated solvolytic reaction in the presence of excess of NaHCO(3) proceeded via a pseudo-first-order kinetic with significant correlation coefficients 0.9891 and 0.9997 for DS and HPLC, respectively. The values of solvolysis rate constant calculated according to DS and HPLC methods are in good accordance 0.038 and 0.043 h(-1), respectively.

Rapid and accurate binary mixture resolution of chlorpheniramine maleate-noscapine hydrochloride and chlorpheniramine maleate-guaiphenesin, was performed. Derivative spectrophotometry, by the zero-crossing measurements, was used due to the drugs closely overlapping absorption spectra. Neither sample pretreatment nor separation were required. Linear calibration graphs of first derivative values at 268.0 and 261.0 nm for chlorpheniramine-maleate-noscapine hydrochloride and at 273.2 and 261.0 nm for chlorpheniramine-guaiphenesin were obtained vs. concentration with negligible intercept on the y-axis. Thus, the derivative spectrophotometry method was applied to the determination of these drugs in binary mixtures obtaining selectivity, accuracy and precision.

Two methods for determining Tartrazine and Sunset Yellow in mixtures by first derivative spectrophotometry and by first derivative of the ratio spectra are described. The procedures do not require any separation step. By the first method, the measurements are obtained in the zero-crossing wavelengths and the calibration graphs are linear up to 20 mug/ml of Tartrazine and up to 40 mug/ml of Sunset Yellow. The determinations of Tartrazine and Sunset Yellow are also done by the first derivative of the ratio spectra. The methods are applied for determining both compounds in four commercial food products.

Two methods for determining sulphamethizol in the presence of nitrofurantoine in mixtures by first-derivative spectrophotometry and by the first derivative of the ratio spectra are described. The procedures do not require any separation step. In the first method the measurements are obtained in the zero-crossing wavelengths and the calibration graphs were linear up to 32 mug/ml of sulphamethizole at 251 and 278.5 nm. In the second method, the calibration graphs were linear up to 43 mug/ml by measuring at the maximum (263 nm), at the minimum (244 nm) and peak to peak. The methods were applied for determining sulphamethizole in a pharmaceutical product containing nitrofurantoine.

A quick and accurate method for determining triamterene and hydrochlorothiazide in complex drugs of diuretic activity by using first-derivative (D1) and second-derivative (D2) spectrophotometry was developed. The zero-crossing technique was employed in measurements, using D1 at lambda = 240.9 nm and D2 at lambda= 278.2 nm for determining triamterene and D1 at lambda = 255.7 nm and D2 at lambda = 283.2 nm for hydrochlorothiazide. The linear relationship between the values of derivatives and analyte concentrations are maintained for concentrations from 2.40 microg x mL(-1) to 12.00 microg x mL(-1) for triamterene and from 1.25 microg x mL(-1) to 6.25 microg x mL(-1) for hydrochlorothiazide. LOD for triamterene was 0.90 microg x mL(-1) or 1.02 microg x mL(-1), while LOQ was 2.73 microg x mL(-1) or 3.08 microg x mL(-1). The corresponding values for hydrochlorothiazide were: LOD 0.25 microg x mL(-1) or 0.17 microg x mL(-1) and LOQ 0.77 microg x mL(-1) or 0.51 microg x mL(-1) depending on the derivative used. The determination results of drug constituents are of high accuracy, percentage recovery ranging from 97.17% to 99.74% for triamterene and from 102.44% to 102.64% for hydrochlorothiazide, and good precision. The computed values of RSD are smaller than 2.73% for triamterene and below 1.63% for hydrochlorothiazide. Selectivity and sensitivity of the developed method are satisfactory.

Three spectrophotometric methods including Vierordt's method, derivative, ratio spectra derivative, and thin layer chromatography (TLC)-UV densitometric method were developed for simultaneous determination of drotaverine HCl (DRT) and nifuroxazide (NIF) in presence of its impurity, 4-hydroxybenzohydrazide (4-HBH). In Vierordt's method,(E(1 cm)(1%)) values were calculated at 227 and 368 nm in the zero-order spectra of DRT and NIF. By derivative spectrophotometry, the zero-crossing method, drotaverine HCl was determined using the second derivative at 245 nm and the third derivative at 238 nm, while nifuroxazide was determined using the first derivative at 399 nm and the second derivative at 411 nm. The ratio spectra derivative spectrophotometry is based on the measure of the amplitude at 459 nm for DRT and at 416 nm for NIF in the first derivative of the ratio spectra. Calibration graphs of the three spectrophotometric methods were plotted in the range 1-10 microg/ml of DRT and 2-20 microg/ml of NIF. TLC-UV densitometric method was achieved on silica gel plates using ethyl acetate : methanol : ammonia 33%(10 : 1 : 0.1 v/v/v) as the mobile phase. The Rf values were 0.74, 0.50, 0.30+/-0.01 for DRT, NIF and 4-HBH, respectively. On the fluorescent plates, the spots were located by fluorescence quenching and the densitometrical area were measured at 308 and 287 nm with linear range 0.2-4 microg/spot and 0.6-12 microg/spot for DRT and NIF, respectively. The proposed methods have been successfully applied to the commercial pharmaceutical formulation without any interference of excipients. Mean recoveries, relative standard deviations and the results of the proposed methods were compared with those obtained by applying the alternate methods.

Two methods are described for the simultaneous determination of lamivudine (3TC) and stavudine (d4T) in combined pharmaceutical tablets. The first method depends on first derivative UV-spectrophotometry with zero-crossing measurement technique. The first derivative absorbances at 280 and 300 nm were selected for the determination of stavudine and lamivudine, respectively. The second method is based on the separation of both drugs by high performance liquid chromatography using methanol:water (20:80) as the mobile phase at 0.6 ml/min on a reverse phase column with detection at 270 nm. Both the methods showed good linearity, reproducibility and precision. No spectral or chromatographic interferences from the tablet excipients were found. The proposed methods were suitably applied to the assay of commercial formulations. The procedures were rapid, simple and suitable for routine quality control application.

Derivative spectrophotometry offers a useful approach for the analysis of drugs in multi-component mixtures. In this study a third-derivative spectrophotometric method was used for simultaneous determination of cyproterone acetate and ethinylestradiol using the zero-crossing technique. The measurements were carried out at wavelengths of 316 and 226 nm for cyproterone acetate and ethinylestradiol respectively. The method was found to be linear (r2>0.999) in the range of 0.5-6 mg/100 ml for cyproterone acetate in the presence of 35 microg/100 ml ethinylestsradiol at 316 nm. The same linear correlation (r2>0.999) was obtained in the range of 10-80 microg/100 ml of ethinylestradiol in the presence of 2 mg/100 ml of cyproterone acetate at 226 nm. The limit of determination was 0.5 mg/100 ml and 10 microg/100 ml for cyproterone acetate and ethinylestradiol respectively. The method was successfully applied for simultaneous determination of cyproterone acetate and ethinylestradiol in pharmaceutical preparations without any interferences from excipients.