CAPILLARY ZONE ELECTROPHORESIS OF NITROPHENOLS WITH OFF-LINE ISOTACHOPHORETIC SAMPLE PRETREATMENT

Preparative capillary isotachophoresis (ITP) operating in a discontinu ous fractionation mode was studied as a sample pretreatment technique for capillary zone electrophoresis (CZE) trace analysis of a group of ten nitrophenols. Different separation mechanisms employed by these ca pillary electrophoresis techniques made possible a group isolation of the studied analytes by ITP while their CZE resolutions based on diffe rences in the interactions with polyvinylpyrrolidone (PVP) provided su itable conditions for a final analytical evaluation. Experiments with model and practical water samples revealed high and reproducible recov ery rates of the ITP pretreatment for nitrophenols when sample loadabi lity limits of the preparative ITP equipment were met. A main disadvan tage of the studied ITP-CZE combination was an inefficient use of the pretreated sample as only 0.5% of the fraction containing nitrophenols was used in the final CZE step. Despite these limitations associated with the CZE sample injection, the concentration limit of detection (L OD) for nitrophenols in practical water samples could be reduced to 2- 8 ppb concentrations (photometric absorbance detector operating at a 2 54 nm wavelength) when 200 mu L sample volumes were taken For the ITP pretreatment, This was accompanied by an efficient sample clean-up as no other trace ionic constituents originating from the samples were de tected on CZE.