Analysis of glyphosate using capillary electrophoresis with indirect detection

A method has been developed for the analysis of glyhosate and aminomethylphosphonic acid (AMPA) in water. Using a pH 7.5, 10 mM phthalate background electrolyte containing 0.5 mM tetradecyltrimethylammonium bromide (TTAB) as an electro-osmotic flow modifier, the analytes were separated in less than 4 min under reverse polarity conditions and detected indirectly. Response was shown to be linear for over two orders of magnitude, calibration in the range 0.01-1.0 mM (1.7-170 mu g ml(-1) glyphosate, 1.1-110 mu g ml(-1) AMPA) giving least squares correlation coefficients of 0.9998 and 0.9999. Precisions of migration times and normalised peak areas were typically less than 0.7 and 2.0% respectively. Calibration slopes gave transfer ratios for glyphosate (0.98) and AMPA (0.75) in good agreement with values computed from theory using coupled transport equations. With stacking from water, the limit of detection for glyphosate was 5 mu M, i.e. 0.8 mu g ml(-1) (twice peak-to-peak noise) for a 6.7 nl injection, calculated from a 0.05 mM standard solution. Field-amplified sample injection has enabled 0.01 mu M (2 ng ml(-1)) to be detected, a factor of similar to 1000 in signal enhancement being obtained over conventional hydrodynamic injection with no stacking.