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  • Author or Editor: W. Ali x
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Abstract  

Headspace analysis by means of sensor arrays has been successfully applied to a wide range of qualitative applications. In this study, a six element array of coated Quartz Crystal Microbalance (QCM) sensors was used for the headspace analysis of milk volatiles. The sensors were exposed to uncontaminated samples of milk and samples contaminated with Pseudomonas fragi (Ps. fragi) or Escherichia coli (E. coli). Principal component analysis (PCA) was used to analyse the sensor array responses. No discrimination between uncontaminated milk samples and those contaminated with Ps. fragi was observed. This can be explained by Ps. fragi being a poor fermenter of milk. However, encouraging results were found for the discrimination between the milk samples and those contaminated with E. coli.

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Abstract  

The extraction of Co2+ from a 0.1M ionic strength acetate buffer by acetylacetone, and a mixture of acetylacetone and pyridine or triethylamine was investigated at various temperatures. The enthalpy and entropy change data for the synergistic extraction support a model in which the Co2+ ion in the acetylacetonate complex expands its coordination number from four to six in order to accomodate the two N-base molecules. The steric hindrance caused by triethylamine is also reflected in the thermodynamic data.

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Abstract  

Quartz crystal microbalances have high mass sensitivities. Their application in gas sensing has been limited because they are required to have both high selectivity and reversibility. Yet by the inherent nature of their operation these properties are mutually exclusive. One approach to this problem is to use an array of quartz crystal microbalances. We have used an array of six coated quartz crystal microbalances for the classification of methanol, propan-1-ol, butan-1-ol, hexane, heptane and toluene. A novel classification scheme using fuzzy membership functions was found to be highly efficient.

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Three accurate, sensitive, simple, and precise spectrophotometric methods along with thin-layer chromatography (TLC)–densitometric method were developed, optimized, and validated for the determination of folic acid in the presence of its two impurities (photodegradation products), namely, pteroic acid and para-aminobenzoic acid. Method A is the ratio difference spectrophotometric method (RDSM) which depends on measuring the difference value in the ratio spectrum, where the difference between 291 and 313 nm was used for the determination of folic acid, while the difference between 305 and 319 nm was selected for the estimation of para-aminobenzoic acid; on the other hand, pteroic acid can be determined using the first derivative of ratio spectra spectrophotometric method at 262 nm. Method B is the double-divisor spectrophotometric method (DDSM); this method is based on using the ratio spectrum obtained by the division of the spectrum of ternary mixture by the spectrum of binary mixture containing two of the three mentioned components, and in this method, folic acid, para-aminobenzoic acid, and pteroic acid were measured at 242, 313, and 258 nm, respectively. Method C is the mean-centering of ratio spectra spectrophotometric method (MCR); in this method, folic acid, para-aminobenzoic acid, and pteroic acid can be measured using the mean-centered second ratio spectra amplitudes at 317–318 (peak to peak), 264–265 (peak to peak), and 232 nm, respectively. Lastly, method D is a TLC‒densitometric one that depends on the separation and quantification of the mentioned components on TLC silica gel 60 F254 plates, using methanol‒ iso-propanol‒water‒acetic acid (9:0.5:0.5:0.2, by volume) as the developing system, followed by densitometric measurement of the separated bands at 280 nm. Method validation was carried N.W. Alia, N.S. Abdelwahaba, M.M. Abdelrahmana, and S.I. Tohamy, Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Beni-Suef University, Alshaheed Shehata Ahmed Higazy St., 62514, Beni-Suef, Egypt; and B.A. El-Zeiny, Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Kasr EL-Aini Street, ET 11562, Cairo, Egypt. *E-mail: salwatohamy2015@yahoo.com out according to the International Conference on Harmonisation (ICH) guidelines, and the proposed methods were successfully applied to the analysis of folic acid in pharmaceutical formulations, where no interference from additives has been found. The results obtained by the proposed methods were statistically compared with those obtained by the official reversed-phase high-performance liquid chromatography (RP-HPLC) method, in which no significant difference was observed.

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Abstract  

An electronic nose utilising an array of six-bulk acoustic wave polymer coated Piezoelectric Quartz (PZQ) sensors has been developed. The nose was presented with 346 samples of fresh edible oil headspace volatiles, generated at 45°C. Extra virgin olive (EVO), Non-virgin olive oil (OI) and Sunflower oil (SFO), were used over a period of 30 days. The sensor responses were then analysed producing an architecture for the Radial Basis Function Artificial Neural Network (RBF). It was found that the RBF results were excellent, giving classifications of above 99% for the vegetable oil test samples.

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Abstract  

The effect of different relative humidity (RH) on the response of a six-polymer coated Quartz Crystal Microbalance (QCM) sensor based electronic nose (EN) was investigated, RH 30 and 50% respectively. Increases in the sensor responses were observed for an increase in RH. A stainless steel pre-concentration tube (PCT) containing Porapak-S and a nichrome heating element was developed to minimise the effect and allow for chromatographic pre-separation. Breakthrough times of chemical compounds through the PCT were experimentally determined and used to select a mixture of water and toluene as a suitable sample for pre-separation. The PCT was capable of separating the water from the toluene and the EN was competent at evaluating the concentration of toluene in the solution.

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Abstract

A series of CoMo/γ-Al2O3 catalysts was prepared with [Co/(Co + Mo)] ratios of 0.3, 0.4 and 0.5 while maintaining a total metal content of 19 wt%. These catalysts were tested in a batch autoclave reactor after presulfiding with the objective of studying the influence of Co/(Co + Mo) ratio on the hydrodesulfurization (HDS) pathways of benzothiophene (BT) and dibenzothiophene (DBT). The results of this study have clearly demonstrated that the Co/Co + Mo ratio has a significant influence on the overall HDS of BT and DBT as well on the direct desulfurization (DDS) pathway, but showed no influence on the hydrogenation pathway. A Co/Co + Mo ratio of 0.4 was found to be optimum for both overall HDS as well as the HDS by DDS pathway.

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Summary

Ashwaghanda, Withania somnifera, is one of the most widely used herbs in Ayurvedic medicine. Leaves and roots are the traditionally used parts of the plant. An RP-HPLC method using a binary acetonitrile-water gradient containing 0.1% acetic acid has been developed for analysis of withaferin A. The method was validated in accordance with ICH guidelines and used for analysis of the withanolide content of the flowers, leaves, and roots of W. somnifera. The withanolide content was highest in the flowers.

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A validated, sensitive, and highly selective stability-indicating high-performance thin-layer chromatographic (HPTLC) method has been adopted for the quantitative determination of pyridostigmine bromide in the presence of its alkaline-induced degradation product and in pharmaceutical formulations. 3-hydroxy-N-methyl pyridinium bromide (3-OH NMP) is the metabolite, impurity, and alkaline-induced degradation product of pyridostigmine bromide (PB). Pyridostigmine bromide and its alkaline-induced degradation product were separated on silica gel HPTLC F254 plates using methanol–ethyl acetate–triethyl amine–glacial acetic acid (9:1:0.5:0.05 by volume) as the developing system followed by scanning of the separated bands at 270 nm over a concentration range of 2–10 μg band−1 with mean percentage recoveries of 99.84% (SD 1.384). The proposed method was successfully applied to the analysis of pyridostigmine bromide both in bulk powder and in pharmaceutical formulation without interference from other dosage form additives. The results obtained by the proposed method were statistically compared with those obtained by the reported HPLC method with no significant difference regarding both accuracy and precision, indicating the ability of the proposed method to be reliable and suitable for routine analysis of a drug product.

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