a method and apparatus for low pressure liquid chromatography which is particularly suitable for the testing of body fluids and in particular blood , the method comprising the steps of passing a sample through a chromatography column containing a packing material so that a constituent of the sample is retained by the packing material and passing a buffer solution having a varying concentration through the column . when the concentration of the buffer solution reaches a particular level , the constituent will be disassociated from the packing material and flows out of the column through a detector . the detector measures the light absorption of the fluid and by relating the time varying light absorption of the fluid to the time varying concentration of the buffer solution , it is possible to identify the constituent . samples of body fluid are conveniently taken by puncturing the skin and applying a capillary tube to the fluid which emerges . the capillary tube is then placed in a pre - filled sample vial containing a solution for processing the body fluid and , after a certain time , the vial is placed in the chromatography apparatus and is drawn into the apparatus for testing . the apparatus is controlled by a microprocessor operating according to a stored program , the chromatography column used is a two part plastic column about 5 mm long and adapted to operate at a pressure of about 15 psi . the two part nature of the column allows it to be filled particularly easily .