CHARACTERIZATION OF THE PRECOLUMN BIOTRAP-500 C-18 FOR DIRECT-INJECTION OF PLASMA SAMPLES IN A COLUMN-SWITCHING SYSTEM

A new restricted access media (RAM) type of pre column, BioTrap 500 C- 18, for direct injection of plasma samples in column-switching systems was evaluated with respect to the elution of plasma proteins in diffe rent mobile phases, the loading capacity of plasma samples, the chroma tographic behavior during plasma injections and protein contamination of the packing and sealings. More than 95 % of plasma proteins could b e, excluded from the precolumn within three minutes for all selected m obile phases. Quantitative analyte recoveries could be obtained by inj ecting plasma samples ranging from 5 to 500 mu L with the analyte mass > 150 ng onto a BioTrap 500 C-18 column (20 x 4 mm I.D.). One precolu mn tolerated about 15 mL of plasma injection without noticeable change in retention and pressure. Clogging of the precolumn was encountered (greater than or equal to 45 mL of plasma) due mainly to the adsorptio n of proteins on the packing. The performance of the analytical column (Kromasil C-18) was also examined. The column efficiency decreased by 60 % after processing 45 mL plasma in total.