Comparison of Soxhlet extraction, ultrasonic bath and focused microwave extraction techniques for the simultaneous extraction of PAH´s and pesticides from sediment samples

Porevsky, Piotr Álvarez; Ruiz, Humberto Gómez; Garciadiego, Lucia Hernández

Palavras-chave: sediments, focused microwave extraction FMWE, ultrasonic bath USBE extraction, soxhlet extraction, pesticides, polyaromatic hydrocarbons, GC/MS, multivariate optimization.

Resumo: The need to develop an analytical procedure for the determination of pollutants in the Lacantun River at the “Montes Azules” Biosphere Reserve led to the evaluation of different extraction techniques. Because sediments are easier to preserve than water or biota, the evaluation of the quality of the water was assessed by analyzing the collected sediments. In order to preserve pristine rivers, water quality evaluation is fundamental. The Lacantun River borders the “Montes Azules” Biosphere Reserve, located in the state of Chiapas in Southwest Mexico. It is one of the few, perhaps the only, pristine river in Mexico. Due to the geographical location of the river, sampling and sample preservation result problematic. Sampling and analyzing the sediments in order to evaluate water quality was deemed the only solution for a sustained, monitoring of the river. In order to analyze the possible pollutants (polyaromatic hydrocarbons (16), organochlorine pesticides (11), organophosphorus pesticides (6) and permethrin) two extraction procedures where evaluated: Focused Microwave Extraction (FMWE) and Ultrasonic Bath Extraction (USBE). Both extraction techniques were compared with the classical Soxhlet Extraction (SE). In order to establish the optimum extraction conditions for USBE and FMWE techniques, a series of experiments guided by full factorial and fractional factorial designs were made. Both extraction techniques meet the validation criteria of determining a) coefficients above 0.7 in all cases and above 0.98 for 90% of the selected analytes; b) an RSD below 30% in all cases and c) a percentage of recovery between 70% and 130%. The microwave extraction and the ultrasonic extraction did not show a statistically significant difference for the extraction of PAH´s with MW<170g/mol; the Soxhlet extraction presented an efficiency 40% lower. For the rest of the PAH’s (MW>170g/mol) there are no great differences between the extraction techniques. For the organochlorine pesticides the microwave extraction produced the best results, compared to the ultrasonic and the Soxhlet extraction which presented 8% and 20% lower efficiencies, respectively. The ultrasonic extraction gave the best results for the organophosphorus pesticides, whereas the microwave extraction and the Soxlet extraction showed efficiencies 8% and 40% lower. There was no significant statistical difference between the evaluated extraction techniques for permethrin. In the case of analytes extraction, the technique with the best efficiency was ultrasonic extraction. Additionally, it is also the most versatile technique due to its simple operation and fast extraction times when many samples are analyzed; also, it is cost-efficient and does not take up much laboratory space.

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