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In this work, different procedures were compared for the extraction of synthetic antioxidants such as propyl gallate (PG), tert-Butylhydroquinone (TBHQ), 3-tert-butyl-4-hydroxyanisole (BHA) and 3,5-di-tert-butyl-4 hydroxytoluene (BHT) from biodiesel samples. The efficiency of target procedures was tested using liquid-liquid extraction and solid phase extraction containing different stationary phase. To accomplish this efficiency and determine the antioxidants, a method based on high performance liquid chromatography coupled with diode array detector (HPLC / DAD) was optimized. In liquid-liquid extraction was used acetonitrile and n-hexane, however, only acetonitrile presented selectivity, able to extract just PG and BHA, with recovery between 78.3 and 96.0%. Using solid phase extraction cartridges containing C-18 as stationary phase, only the PG and BHA were extracted, which the recovery was between 52.4 and 99.7%. Moreover, the macroporous poly(divinylbenzene-co-N-vinylpyrrolidone) polymer presented satisfactory results for the extraction of PG and BHA with recovery between 77.3 and 103 %. All these procedures provided elimination of the sample interferences, allowing recovery with coefficients of variation always lower than 1.00%. However, the comparison of liquid-liquid extraction and solid phase extraction techniques proved that there are many difficulties in extracting, with precision and accuracy, the PG, TBHQ, BHA and BHT antioxidants contained simultaneously in complex samples such as biodiesel. These difficulties are increased when the interest is to reduce the costs of analysis by reducing organic solvent extractors and propose extraction techniques with considerable environmental benefits. DOI: http://dx.doi.org/10.17807/orbital.v7i2.672

In this work a carbon paste electrode chemically modified with an ionic liquid (CPE-IL) was used to quantify the antioxidant propyl gallate (PG) in spiked soybean biodiesel samples by square wave voltammetry. Under the optimized conditions, the proposed method have presented a linear range from 2.0 to 47.5 μmol L-1, with limit of detection equal to 0.397 μmol L-1. Recovery studies were performed in biodiesel samples spiked with two levels of PG. In all cases, satisfactory recovery percentages and low relative standard deviation values were obtained which is a clear demonstration of the accuracy of the proposed method. It was observed that IL provides a remarkable intensification of PG voltammetric response compared to a non-modified conventional CPE, improving, therefore, the detectability of the voltammetric method. The CPE-IL used in this work does not require an IL completely free from residual water. This is a very attractive feature because time-consuming procedures for water elimination are avoided during the synthesis of the IL. Thus, the proposed CPE-IL can be prepared in a simple, fast and inexpensive way making these electrodes very practical and competitive compared to other chemically modified electrodes proposed in the literature for PG quantification.

O uso intensivo e descarte irregular de agrotóxicos na agricultura têm causado sérios problemas ambientais e de saúde. Neste trabalho foi avaliada a eficiência de UV e de alguns processos de oxidação avançada que envolva reação de foto-Fenton, O3 e O3/UV para o tratamento de soluções aquosas contendo pesticidas comerciais e padrão. Os resultados mostraram que a combinação da radiação UV em meios alcalinos com O3 aumentou significativamente a eficiência do processo de degradação e o sistema foto-Fenton é uma alternativa promissora para o tratamento de efluentes contendo pesticidas.