Dynamic versus static ultrasonic sample treatment for the solid–liquid pre-concentration of mercury from human urine

Dynamic and static ultrasonic procedures involving ultrasonic bath and tandem focused ultrasound (i.e. two probes were used in the same sample treatment) have been assessed in order to implement a reliable solid–liquid back extraction of mercury from commercial resins (dowex and chelex-100), previously used to concentrate Hg(II) from treated urine. The urine had been previously treated with an advanced oxidation process provided by the conjunction of potassium permanganate, hydrochloric acid and high intensity focused ultrasound, which allowed that organic matter degradation was achieved in less than 3 min. 95 ± 10% of mercury in the certified urine and 97 ± 6% of the spiked methyl-mercury was recovered with the dowex resin plus the static ultrasonic procedure, whilst 96 ± 11% of the spiked mercury was recovered with the dowex resin plus the dynamic procedure, for which ultrasonication was not necessary. The Hg pre-concentration factor used in this work was 8 (20 mL of urine to 2.5 mL of acid), but different volume ratios can be used in order to increase this factor.