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  • Author or Editor: M. Peyrovi x
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Abstract

In this paper, we have studied an increase in the conversion of methane dehydroaromatization (MDA) over Mo and W catalysts supported on HZSM-5. The effects of preactivation of the catalysts and the use of methane/hydrogen cycles on the catalytic activity and stability have been investigated. It was found that the activity was directly related to Brønsted sites on the external surface of HZSM-5 and the regeneration of these sites can augment the conversion in the MDA reaction. Moreover, the use of methane/hydrogen cycles removed a fraction of the coke formed during the reaction and improved the catalytic stability.

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Summary

Although conventional solid phase extraction (SPE) is an applicable routine method for extraction of different analytes from various matrices, it requires more time and volume of solvent and sample rather than other routine laboratory extraction methods. In this study, a rapid and simplified sample preparation method based on SPE was studied by eliminating some steps, such as conditioning and washing, for extraction of diosmin, eriocitrin, narirutin, naringin, and hesperidin in orange, tangerine, and lime juice samples. The separation of these flavonoids was achieved by using a C8 column with a mobile phase comprised of water-acetonitrile-acetic acid (78:21:1, v/v/v) at a flow rate of 0.85 mL min−1 and UV detection at 280 nm. To examine the applicability of this method, effective parameters such as type of adsorbent, type and volume of elution solvent, ionic strength, and pH of the sample were studied and applied to the comparison between the conventional SPE and the simplified method. The best recoveries were obtained, using the proposed method, with a small volume of citrus fruit juice (0.5 mL), silica gel (0.5 g) as adsorbent, and 3 mL of methanol as elution solvent. Limits of detection, limits of quantification, intra-day and inter-day precision of the method for the analytes were 0.0244–0.0587 μg mL−1, 0.0739–0.178 μg mL−1, 2.5–3.1%, and 3.1–4.8%, respectively.

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