Sample preparation method for liquid chromatography

A method of selectively analyzing a plurality of analytes in a liquid biological sample containing many components which can interfere with analysis by liquid chromatography, said method comprising the steps of:

• (a) passing a biological liquid sample containing a plurality of analytes of interest and molecules which can interfere with analysis by liquid chromatography into a first passage of a dialyzer;
• (b) selectively removing the molecules in the sample which can interfere with analysis by liquid chromatography from the analytes of interest by passing a first diluent through a second passage of the dialyzer, the first and second passages being separated by a semipermeable membrane having holes sufficiently large to permit the analytes of interest to pass through the membrane into the first diluent but sufficiently small to prevent passage of the molecules which can interfere with analysis by liquid chromatography, and passing the analytes of interest from the sample, through the membrane, and into the first diluent to form a dialyzed sample which still contains the molecules which can interfere with analysis by liquid chromatography;
• (c) passing the first diluent containing the analytes of interest through a passage in a retaining element which contains material for temporarily retaining the analytes of interest by either adsorption, partition or both;
• (d) subsequently passing a second diluent through the passage in the retaining element in order to remove the analytes of interest;
• (e) passing the second diluent containing the analytes of interest through a chromatography column and detector means in order to perform chromatographic analysis of the analytes of interest;
• and
• (f) passing the dialyzed sample which contains the molecules which can interfere with analysis by liquid chromatography to waste.