Comparison of the properties of polymeric and C8 based materials for solid phase extraction

The extraction properties of two polymeric solid phase extraction materials, styryldivinyl benzene (SDB) and 'Oasis' have been compared with those of a base deactivated C8 bonded silica gel using a range of acidic and basic test analytes. In the case of the two polymer phases good extraction of all the test compounds from aqueous buffer was obtained over the pH range 2-10. On the C8 material, efficient extraction of the most polar acidic analyte, anisic acid, was only obtained between pH 2 and 6. The use of methanol water mixtures, or methanol water mixtures modified with either trifluoroacetic acid (TFA) or triethylamine (TEA) as eluents was investigated for the recovery of the analytes following extraction. The use of TFA or TEA as ionic modifiers strongly influenced the efficiency of the elution step. The effect of a plasma matrix on extraction efficiency was also investigated, with the result depending upon the analyte. An approach to assessing the performance of the three phases has been developed based on the percentages of methanol in the eluent resulting in the recovery of 50% of the analyte, and in determining the difference between eluents giving recoveries of 10 and 90%.