OPTIMIZED INJECTION TECHNIQUES FOR MICRO AND CAPILLARY LIQUID-CHROMATOGRAPHY

Large volume injections -involving on-column focusing- were evaluated for packed micro and capillary liquid chromatography columns of 300 mu m and 1.0 mm inner diameter (I.D.) respectively. It was found that th e I.D. of the injection loop plays a critical role in sample dispersio n, effecting peak asymmetry and injection reproducibility. The use of injection loops with too large or too small an I.D. resulted in a redu ced injection performance. Ideally the I.D. should be in between 100-1 50 mu m. Further it was investigated what influence the loop volume an d the use of a low dispersion injection technique had on the column st ability. The combination of large volume injections -up to 1 mu l and 5 mu l for 300 mu m and 1.0 mm I.D. columns, respectively- and additio nal switching of the injection valve did not affect column lifetime. T ypical decreases of only 10% in efficiency over 1500 injections were f ound.