Micellar electrokinetic capillary chromatography as a powerful tool for pharmacological investigations without sample pretreatment: A precise technique providing cost advantages and limits of detection to the low nanomolar range

A number of pharmaceuticals (e.g., acetaminophen, salicylic acid, sulfameth oxazole, theophylline, tolbutamide and trimethoprim) have been determined i n human plasma by micellar electrokinetic chromatography (MEKC), without sa mple pretreatment, using underivatized fused-silica capillaries. The total analysis time was only 10 min. A sodium dodecyl sulfate (SDS)-containing be rate buffer (60 mM with 200 mM SDS) at pH 10 was used. Between runs, protei ns adsorbed to the capillary wall are removed by rinsing with SDS buffer an d either acetonitrile (e.g., 50% v/v) or isopropanol (e.g., 10% v/v). Other rinsing procedures are discussed (salts, enzyme-containing solutions, orga nic solvents, sodium hydroxide, hydrofluoric acid). The separation system i s tested in a concentration range between 10 ng/mL and 100 mu g/mL; a detec tion limit of about 20 ng/mL can readily be obtained. The sensitivity was s ubstantially improved using isopropanol as buffer additive. A day-to-day pr ecision for relative peak areas of 1-2% relative standard deviation (RSD, n > 40) was reached in the upper concentration range. Under repeatability co nditions, these values could also be obtained for low mu g/mL concentration s. Thus, not only drug monitoring but also pharmacokinetic investigations f rom blood plasma become possible without further sample pretreatment.