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In this video, a unique liquid-liquid solid phase extraction is shown. The first step is a rapid "optional" conditioning step using methanol. An aqueous sample solution (2nd test tube) containing approximately 25% acetone and a high concentration of NaCl is mixed with the solid phase sorbent. During equilibration, the analyte partitions into the solid phase sorbent. Subsequently, a small volume of ethyl acetate (3rd test tube) is drawn into the DPX tip and mixed with the sorbent. As the immiscible solutions settle, the solid phase sorbent containing the analyte settles into the upper organic phase. The separation of the organic solution from the aqueous solution is almost immediate without the need for centrifugation nor the development of emulsions. The bottom aqueous solution is dispensed back into the 2nd test tube, and the upper organic layer containing the analytes of interest is dispensed into the 3rd test tube which will be subsequently analyzed. This method has been shown to be very effective for the analysis of multi-residue pesticides in fruit and vegetables.
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