An internal surface reversed phase column for the effective removal of humic acid interferences in the trace analysis of mecoprop in soils with coupled-column RPLC-UV

In the development of a screening method for the determination of residues of mecoprop in soils involving coupled-column RPLC-UV (228 nm) the cleanup performance of a 5 mu m GFF-II internal surface reversed phase (ISRP, Pinke rton) analytical column (50 x 4.6 mm I.D.) as a first column was investigat ed. In comparison to an analytical C18 column the ISRP column substantially improved the separation between acidic analyte and co-extracted humic subs tances. Under the selected coupled-column conditions soil extracts obtained after hydrolysis with an aqueous alkaline solution, acidifying and centrif ugation could be analyzed directly allowing the determination of mecoprop i n soils to a level of about 0.02 mg/kg. A rapid concentration step on a 100 mg C18 solid phase extraction (SPE) cartridge was adopted into the procedu re providing a limit of detection (S/N = 3) of 0.01 mg/kg of mecoprop in so il. The method was validated by analyzing freshly spiked soil samples and s amples with aged residues. In case of freshly spiked samples the overall re covery was 87% (n = 18, spiked level 0.02-8.0 mg/kg) with a repeatability o f 6.8% and a reproducibility of 8.3%. No significant decrease of the recove ry was observed for samples with aged residues (n = 15, spiked level 0.1 an d 8.0 mg/kg) during a storage of 29 days in the refrigerator at about 4 deg rees C; a storage of 67 days provided a mean recovery of 76% (n = 14, spike d level 8.0 mg/kg).