PREPARATIVE CAPILLARY ISOTACHOPHORESIS AS A SAMPLE PRETREATMENT TECHNIQUE FOR COMPLEX IONIC MATRICES IN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Preparative capillary isotachophoresis (ITP) was studied for sample pr etreatment in the high-performance liquid chromatography (HPLC) of ion ogenic analytes present in complex ionic matrices (urine and humic sub stances). Sulphanilate, methyl (4-aminobenzenesulphonyl)carbamate (asu lam), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophen oxyacetic acid (MCPA) served as model analytes. A high sample load of the ITP pretreatment was achieved by performing the preparative separa tions in tubes of 2.0 and 1.0 mm I.D. in the column-coupling configura tion of the separation unit. The ITP separation according To ionic mob ilities was combined with gradient elution HPLC in the ion-suppression mode to achieve highly dissimilar (orthogonal) separation systems in both techniques. The pretreatment provided the sample fraction for the HPLC analysis containing in addition to the analyte (sulphanilate) on ly ca. 2-3% of the urine matrix (spread along the complete elution pro file) when a pair of discrete spacers defined the trapped constituents . Under these conditions the limit of detection for sulphanilate in ur ine could be reduced by more than two orders of magnitude. A high reco very of the pretreatment procedure [99 +/- 1.5% for a 1.7 ppm (w/w) co ncentration of sulphanilate] was typical. For asulam, 2,4-D and MCPA p resent in a humic matrix it was shown that the ITP pretreatment may al so be effective for multi-residue procedures while favourable analytic al characteristics of the pretreatment such as recovery and efficient sample clean-up are maintained.