Ultrasound assisted extraction for determination of mobile fractions of copper in soil

For evaluation of the mobility of metals present in soil various approaches based on sequential extraction procedures (Tessier's, BCR or modified BCR) have been proposed, but they are very laborious and time-consuming.

The aim of this study was to develop a new fast extraction procedure for the determination of mobile fractions of copper in soil.

The samples of soil that vary in terms of physicochemical properties and certified reference material (BCR-701) were used in this study. The three-stage modified BCR procedure used for fractionation of copper in soil was accelerated by ultrasound irradiation using an ultrasonic probe. The content of copper in soil extracts was determined by electrothermal atomic absorption spectrometry (ETAAS).

The extraction conditions for separation of mobile fractions of copper from soil with the use of ultrasonic probe were optimized. The working parameters of the probe were as follows: the power was 15 W for all fractions while the sonication time was 7 min, 10 min and 6 min for fraction I, fraction II and fraction III, respectively. The developed procedure was validated; linearity of calibration graphs, limit of detection and limit of quantification, accuracy and repeatability of the procedure were evaluated. The content of copper in fraction I-III in soil samples collected from Podlaskie Voivodeship was at the level of 0.09-1.92 mg x kg(-1), whereas its pseudo-total content was in the range 2.75-9.75 mg x kg(-1). CONCLUSIONS; The developed ultrasound assisted sequential extraction procedure allowed for shortening the total extraction time from 48 h to 27 minutes in comparison to conventional modified BCR procedure. The studied soil contains a low pool of copper bioavailable to plants because a sum of mobile fractions (FI-FIII) represents only 22-46% of its pseudo-total content.