AUTOMATED ONLINE LIQUID-SOLID EXTRACTION FOLLOWED BY LIQUID CHROMATOGRAPHY-HIGH-FLOW PNEUMATICALLY ASSISTED ELECTROSPRAY MASS-SPECTROMETRY FOR THE DETERMINATION OF ACIDIC HERBICIDES IN ENVIRONMENTAL WATERS

Liquid chromatography-high-now pneumatically assisted electrospray mass spectrometry with negative ionization was used for the determination of several acidic herbicides: benazolin, bentazone, 2,4-D, MCPA, MCPP, MCPB, and 6- and 8-hydroxybentazone. To achieve good LC separation, acidification of the LC eluent and subsequent postcolumn addition of a neutralization buffer are needed to avoid ion signal suppression. This method was combined with a prior automated on-line liquid-solid extraction step using an OSP-2 autosampler containing C-18 cartridges, and it was applied to the trace determination of acidic herbicides in environmental waters. The proposed method required only 50 mL of water with a limit of detection between 0.01 and 0.03 mu g/L, generally employing selected ion monitoring of the [M - H](-) ion and extraction voltages of 20 V. Examples of the trace level determination of 8-hydroxybentazone, bentazone, and MCPA in real estuarine water samples from the Ebro River delta (Tarragona, Spain) are shown. Only when extraction voltages above 30 V were used was it possible to distinguish between 6- and 8-hydroxybentazone.