Determination of phenoxyacid herbicides in water. Polymeric pre-column preconcentration and tetrabutyl-ammonium...

Optimum conditions for preconcentration of phenoxyacid herbicides from water on polymeric material and separation on an analytical column (PLRP-S) and PRP-1 respectively) have been achieved. The method consists of (a) an on-line preconcentration at pH 3, (b) clean-up with four (precolumn) bed volumes of acetonitrile-water (30:70) at pH 3 and (c) isocratic analytical separation at pH 11 with 0.01 mol/l tetrabutylammonium as the ion-pair reagent and acetonitrile-water (30:70) as the eluent. Data on the repeatability of the method, sample flow dependence and sorption capacity are reported. For reliable integration of the chromatogram a clean-up step was introduced. This washing procedure however is more effective for tap-water than for surface water samples. The results of the method are promising and indicate that 10-50 ml of surface water can be applied to the precolumn without breakthrough. Detection limits in surface water samples are 0.1-0.5 micrograms/l whereas those in tap water are 10-50 ng/l. The applicability fo the method was tested. The results of this method were in good agreement with gas chromatographic-mass spectrometric results, and only ca. 0.1 microgram/l lower over the entire range, whereas the analysis time was much shorter. The potential of this technique for automation was demonstrated using a microprocessor-controlled column-switching unit, resulting in a reduction of the total analysis time to ca. 20 min.