Sensitive determination of Se(IV) and tSe in rice and water samples using L-cysteine modified carbon paste electrode-based electrolytic hydride generation and atomic fluorescence spectrometry analysis.

This work illustrates an accurate method for determination of Se by electrolytic hydride generation technique based on a novel carbon paste electrode for sample introduction combined with atomic fluorescence spectral analysis. The studies show that Se(IV) can be converted efficiently to SeH2 on an L-cysteine modified carbon paste electrode (CMCPE), which has never been reported before. Significantly, generation from Se(IV) implies that the use of carbon paste electrode-based electron-induced hydride generation system to achieve efficiency is almost 90% to that obtained by chemical hydride generation, and the response obtained from CMCPE is 2 and 3 times of that from the Pb and graphite electrode, respectively. Results also display that the lifetime and the stability of the CMCPE is superior to that of L-cysteine ornamented graphite electrode fabricated by covalently bonding. Under the optimal conditions, a low concentration limit of detection 0.065µgL-1 of Se(IV) is achieved. The repeatability denoted as % RSD is 2.2% for 1.0µgL-1 Se(IV). The utility of the studied method is compared with certified reference materials as well as several edible samples. The advantages and limitations of this method, compared with existing techniques, are also discussed.

Selective and sensitive determination of As(III) and tAs in Chinese herbal medicine samples using L-cysteine modified carbon paste electrode-based electrolytic hydride generation and AFS analysis.

A novel non-chromatographic speciation technique for ultra-trace arsenite [As(III)] and total arsenic (tAs) in Chinese herbal medicine (CHM) is developed and validated by electrolytic hydride generation (EHG) coupled with atomic fluorescence spectrometry (AFS). The studies show that As(III) can be converted efficiently to AsH3 on an L-cysteine modified carbon paste electrode (CMCPE), which has never been reported before. Significantly, other arsenic species such as arsenate [As(V)], monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) do not form any or only less volatile hydrides at low applied current mode (<1.0 A). The results also demonstrate that L-cysteine and graphite powder play different roles in the electrolytic generation of AsH3. Comparing with the traditional graphite electrode, CMCPE has better stability, sensitivity and interference tolerance. Under the optimal conditions, the limit of detection (LOD) of tAs and As(III) for this method are 0.087µgL-1 and 0.095µgL-1 respectively. The accuracy of the method is verified through the analysis of reference materials (CRM 08231 and SRM1568a), and the proposed method has been applied satisfactorily to the determination of As(III) and tAs in several CHM samples.

Preparation of biodiesel catalysed by KF/CaO with ultrasound.

Biodiesel, chemically consists of fatty acid methyl ester (FAME) produced by methanolysis of natural triglycerides, such as animal fats and vegetable oils, is a kind of biomass energy, which is renewable and ecofriendly. In this article, KF/CaO was used as solid base catalyst for transesterification of soya bean oil and methanol, while ultrasound as supplementary means. Compared to mechanical stirring, ultrasound treatment is an effective method to increase the yield of FAME and shorten reaction time. By single-factor method, the optimisation of reaction conditions has been studied. The research showed that the optimum reaction conditions were: w(catalyst)/w(oil): 3%, reaction temperature: 65°C, n(methanol)/n(oil): 12, reaction time: 1 h, sound intensity: 1.01 W cm(-2), frequency: 20 kHz, the yield of FAME could be 97%.