Enantiomeric separation of chlorophenoxy acid herbicides by nano liquid chromatography-UV detection on a vancomycin-based chiral stationary phase

Enantiomeric separation of mecoprop, dichlorprop, and fenoprop herbicides in their acid form, commonly used to control the growth of broad-leaved weeds, was carried out by nano-liquid chromatography (nano-LC) at a flow rate of 60 nL/min, using a packed capillary column with vancomycin-modified silica particles of 5 microm. The length of chiral stationary phase was 21 cm, while the total and effective lengths were 43 and 33cm, respectively. Inner diameter was 0.075 mm. Separated peaks were detected at 195 nm. Several mixtures of methanol, water, and 500 mM ammonium acetate buffer at different pH's were tested as mobile phase, and experimental parameters such as resolution (Rs), capacity factor (k), efficiency (N/m), and enantioselectivity factor (alpha) were measured under all the test conditions. Baseline enantiomeric separation was obtained for the three studied herbicides with alpha in the range 1.6-1.9, using as the mobile phase aqueous solutions containing 85% methanol, 5% of 500mM ammonium acetate pH4.5 buffer, and 10% water. Experimental results show that the vancomycin stationary phase presents a great enantiorecognition capability towards chlorophenoxy acid herbicides on using nano-LC.