Strategies in using analytical restricted access media columns for the removal of humic acid interferences in the trace analysis of acidic herbicidesin water samples by coupled column liquid chromatography with UV detection

In this comprehensive study, analytical restricted access media (RAM) colum ns were investigated to determine their performance in decreasing the humic acid interference encountered in the trace analysis of acidic herbicides i n environmental water samples when employing reversed-phase liquid chromato graphy with UV detection (RPLC-UV). The selected analytical column RAM mate rials are 5-mu m Semi-Permeable-Surface (SPS, Regis), 5-mu m Internal Surfa ce Reversed Phase (ISRP, Pinkerton, Regis), and 5-mu m Hisep (Supelco); a p recolumn containing 25-mu m alkyl-diol-silica (ADS) RAM material (Merck) wa s also included in this study. Different LC configurations were investigate d, including the single RAM column mode and column switching (LC/LC), emplo ying one RAM column in combination with an analytical C18 column, or two RA M columns. Concerning methodology, both the single-residue method (SRM) app roach and the multiresidue method (MRM) approaches were tested by analyzing SPE C18 extracts of reference water samples spiked with the analyte(s) at the 0.5-1.0 mu g/L level and containing dissolved organic carbon (DOC) betw een 3 and 12 mg/L Mecoprop (MCPP) was used as a model compound in SRM, and the more polar compounds metsulfuron methyl, bentazone, bromoxinyl, and MCP A were included to investigate the MRM approach. With regard to SRM using t he LC/LC mode, the use of at least one analytical RAM column improved the r esolution between the analyte and the humic interferences sufficiently to t race the analyte in extracts from water samples containing a high level of DOC (12 mg/L) without a preceding cleanup. In the MRM approach, ISRP/C18 wa s most favorable for the simultaneous analysis of the heterogeneous group o f pesticides in water with a high DOC level. For samples with a medium DOC content (6 mg/L), C18/SPS using short columns (50 x 4.6 mm i.d.) and isocra tic elution is an efficient alternative, The performance of the useful MRM procedures was tested by analyzing water samples containing 6 and 12 mg/L D OC and spiked with the analytes at the 0.5-1.0 mu g/L level. Mean recoverie s (n = 5, each DOC level) ranged between 86 and 102%, with RSDs between 3 a nd 7.0%, The use of RAM columns in the different LC/LC configurations teste d allows us to develop rapid, selective, and sensitive methods for the anal ysis of acidic herbicides, which are very adequate for screening purposes i n environmental water samples.