Capillary electrophoresis of herbicides .1. Precolumn derivatization of chiral and achiral phenoxy acid herbicides with a fluorescent tag for electrophoretic separation in the presence of cyclodextrins and micellar phases

A novel, selective precolumn derivatization reaction was introduced and evaluated in the fluorescence labeling of phenoxy acid herbicides with 7-aminonaphthalene-1,3-disulfonic acid (ANDSA). The ANDSA-phenoxy acid derivatives were readily detected by capillary electrophoresis/laser-induced fluorescence (CE-LIF) at 0.2 ppb, a concentration at which environmental herbicide samples are expected to occur. The precolumn derivatization was very quantitative (99.7% yield) and produced stable derivatives and no side products. Furthermore, the ANDSA-phenoxy acid herbicide enantiomers exhibited higher chiral resolution than their underivatized counterparts in the presence of cyclodextrin (CD) in the running electrolyte. Several native and modified CDs were investigated in the enantiomeric separation of chiral phenoxy acid herbicides. The best enantioselectivity was achieved when 2,3,6-tri-O-methyl-beta-cyclodextrin (TM-beta-CD) was used as the chiral selector. To effect the enantiomeric resolution of a large number of ANDSA-phenoxy acid enantiomers, electrolyte systems based on mixed CDs were utilized and evaluated. Mixed CDs based on beta-CD and TM-beta-CD proved to be the most effective as far as the enantiomeric resolution of the chiral analytes is concerned. To provide different selectivity for the various ANDSA-phenoxy acid herbicides, novel micellar systems containing cyclodextrins were evaluated.