Abd El-Aziz B. Abd El-Aleem

A smart simple spectrophotometric method for simultaneous determination of binary mixtures

A new simple spectrophotometric method was developed for the simultaneous determination of drugs with interfering spectra in binary mixtures without previous separation. The new method is based on a simple modification for the ratio subtraction method. This modification enabled wider range of application. The proposed ratio difference method was applied for the determination of brimonidine and timolol in laboratory prepared mixtures with mean percentage recoveries 100.40±2.29 and 101.23±1.30 respectively, and in their pharmaceutical formulation with mean percentage recoveries 101.08±0.44 and 100.66±0.52 respectively. The suggested ratio difference method was validated according to USP guidelines and can be applied for routine quality control testing.

Hydration characteristics of β-C2S in the presence of some pozzolanic materials

Abstract There are four polymorphs for dicalcium silicate designated as α, α, β and γ. The γ form is essentially non-hydraulic. The common form in commercial cement clinker is the β-C 2 S. The hydration products of β-C 2 S are Ca(OH) 2 and calcium silicate hydrate gel which is poorly crystallized substance known as tobermorite. The aim of the present work is to prepare B 2 O 3 -stabilized β-C 2 S and investigate the hydration characteristics in the presence of granulated slag, fly ash and silica fume. The results indicated that the presence of these materials leads to the consumption of the liberated Ca(OH) 2 and forming hydration products such as CSH and/or calcium aluminate hydrate. Also, these pozzolanic materials accelerate the hydration of β-C 2 S.

Stability-indicating chemometric methods for the determination of tazarotene

Two multivariate calibration methods-principal component regression (PCR) and partial least square (PLS)-have been used to determine tazarotene in the presence of its degradation products. Both methods are useful in spectral analysis because of the simultaneous inclusion of many spectral wavelengths instead of the single wavelength used in derivative spectrophotometry. A great improvement in the precision and predictive abilities of these multivariate calibrations was observed. A calibration set was constructed for the mixture and the best model was used to predict the concentration of the selected drug. The proposed methods were applied successfully in the determination of tazarotene in laboratory-prepared mixtures and in commercial preparations. Tazarotene was analyzed with mean accuracies of 100.006 ± 0.695 and 100.007 ± 0.690 using the PCR and PLS methods, respectively. The validity of the proposed methods was assessed using the standard addition technique. The proposed methods were found to be rapid, simple and required no preliminary separation. They can therefore be used for the routine analysis of tazarotene in quality-control laboratories.

Determination of Residues of Diazinon and Chlorpyrifos in Lavender and Rosemary Leaves by Gas Chromatography

A sensitive gas chromatographic (GC) GC method has been developed for the determination of diazinon and chlorpyrifos residues in lavender and rosemary leaves. The developed method consists of blending weighed samples of chopped leaves with sodium sulfate as the dehydrating agent, extraction with ethyl acetate, filtration, evaporation with a rotary evaporator, and, finally, capillary GC determination of the pesticides. The recoveries of the method were greater than 90%, and the LOQ was less than 0.1 µg/mL. The method was applied to determine the rate of disappearance of diazinon and chlorpyrifos from lavender and rosemary leaves pretreated with the studied pesticides. The half-life values (t1/2) of diazinon were found to be 5.93 and 6.35 days for lavender and rosemary leaves, respectively, whereas the t1/2 values of chlorpyrifos were calculated to be 7.86 and 9.52 days for lavender and rosemary leaves, respectively. The safe harvest interval (preharvest interval; PHI) was suggested to be after 21 and 24 days for diazinon and chlorpyrifos, respectively. The PHI refers to the amount of time that must lapse (in days) after a pesticide application before a crop can be cut.

SELECTIVE CHROMATOGRAPHIC METHODS FOR THE DETERMINATION OF ROSUVASTATIN CALCIUM IN THE PRESENCE OF ITS ACID DEGRADATION PRODUCTS

Two accurate and sensitive stability-indicating methods for the determination of rosuvastatin calcium in the presence of its acid degradation products are presented. The first method utilizes quantitative spectrodensitometric evaluation thin-layer chromatography (TLC) of rosuvastatin calcium in the presence of its acid degradation products, using ethyl acetate/methanol/ammonia (7:3:0.01, by volume) as a mobile phase. Chromatograms are scanned at 245 nm. This method analyzes rosuvastatin calcium in a concentration range of 0.6–3.4 µg/band with mean percentage recovery of 99.78 ± 1.42. The second method is a high-performance liquid chromatography (HPLC) method for the simultaneous determination of rosuvastatin calcium in the presence of its acid degradation products. The mobile phase consists of water/acetonitrile/methanol (40:40:20, by volume). The standard curve of rosuvastatin calcium shows a good linearity over a concentration range of 10–60 µg mL−1 with mean percentage recovery of 100.22 ± 0.86. These methods were successfully applied to the determination of rosuvastatin calcium in bulk powder, laboratory-prepared mixtures containing different percentages of the acid degradation products, and pharmaceutical dosage forms. The validity of results was assessed by applying standard addition technique. The results obtained were found to agree statistically with those obtained by a reported method, showing no significant difference with respect to accuracy and precision.

Thin-layer chromatography fractionation and densitometric determination of residues of diazinon and chlorpyrifos pesticides in lavender and rosemary leaves

Lavender and rosemary are shrubs that have many medicinal uses. Like any other shrubs, they are susceptible to pest infection which needs pesticides treatment. Residues of pesticides in lavender and rosemary leaves may be hazardous to human health. The main objective of this study was to develop accurate and sensitive methods for the determination of residues of pesticides, namely, diazinon and chlorpyrifos, in lavender and rosemary leaves. Thin-layer chromatography (TLC) fractionation was applied to separate the desired pesticides to be analyzed and to determine the rate of the disappearance of these pesticides from lavender and rosemary leaves. Diazinon and chlorpyrifos were separated from extracts of leaves using silica gel 60 F254 plates. The mobile phase was formed of petroleum ether–ethanol–glacial acetic acid (9.5:0.5:0.1, v/v) and (9.0:1.0:0.1, v/v) as the developing systems for diazinon and chlorpyrifos, respectively, followed by densitometric measurement at 254 nm for both pesticides. The methods were validated over a range of 0.01–l.6 μg band−1 for diazinon and 0.04–2.0 μg band−1 for chlorpyrifos. The detection limits of diazinon and chlorpyrifos were 0.003 and 0.012 μg band−1, respectively. The safe harvest interval (pre-harvest interval; PHI), time in days between the last pesticide application to the crop and the time it can be safely harvested, was suggested to be 21 and 24 days for diazinon and chlorpyrifos, respectively. The developed TLC methods were used for sample cleanup and estimation of the studied pesticides residues in leaves extracts, in addition to the determination of the pre-harvest interval.

Spectrophotometric and Potentiometric Determination of Some Organophosphorus Pesticides in Bulk Powder and in their Dosage Forms

Two simple, sensitive and precise methods were developed and validated for determination of diazinon, chlorpyrifos and temefos pesticides in bulk powder and dosage forms. The spectrophotometric method involves the oxidation of these pesticides with potassium iodate in acidic medium with the liberation of iodine and subsequent extraction with cyclohexane followed by measuring the absorbance at λ = 520 nm. Beer`s law is obeyed in the concentration range of 0.05–1.00 mg ml for diazinon and chlorpyrifos and 0.05–0.6 mg ml for temefos. The apparent molar absorbitivities of the resulting coloured products are found to be 0.539×103, 0.368×103 and 0.474×103 L mol−1 cm−1 for diazinon chlorpyrifos and 0.05–0.6 mg ml−1 for 0.368×103 and 0.474×103 L mol−1 cm−1 or diazinon, chlorpyrifos and temeos, respectively, whereas Sandell sensitivities are 0.5647, 0.9527 and 0.9841 µg cm −2, respectively. The potentiometric method involves the direct titration of the studied pesticides with N-bromosuccinimide in acidic medium and the end point is determined potentiometricallyusing platinum indicator electrode. The ratio of drug: NBS was 1:3 for diazinon andchlorpyrifos and 1:6 for temefos. The proposed methods were successfully applied to the analysis of the studied pesticides in bulk powder and in dosage forms without interference from other additives.

Selective Determination of Diazinon and Chlorpyrifos in the Presence of Their Degradation Products: Application to Environmental Samples

An accurate, sensitive, and selective HPLC method was developed and validated for the determination of diazinon and chlorpyrifos. These pesticides were subjected to different stress conditions, such as acidic, alkaline, oxidative, thermal, and photolytic hydrolysis. The proposed method used a C18 Eclipse Plus column (100 × 4.6 mm, 3.5 µm) and a mobile phase consisting of acetonitrile-water (70 + 30, v/v) in an isocratic separation mode. The flow rate was 1.5 mL/min, with UV detection at 247 and 230 nm for diazinon and chlorpyrifos, respectively. The proposed method was linear over the range of 0.40-50.00 µg/mL for diazinon and 0.40-40.00 µg/mL for chlorpyrifos. The proposed method was validated per International Conference on Harmonization guidelines and subsequently applied for the successful determination of the studied pesticides in bulk form in their commercial samples in the presence of their degradation products. The developed method was used for the determination of the residues of these pesticides in lavender and rosemary leaves that were pretreated with the recommended doses of these pesticides.