Use of retentate chromatography to generate difference maps

A method for identifying analytes that are differentially present in a first and second biological sample comprising the steps of:

• a) selecting a plurality of different selectivity conditions to which the first and second samples will be exposed, wherein:
• i) each selectivity condition is defined by an adsorbent and an eluant;
• ii) each different selectivity condition comprises a different adsorbent and the same or different eluant;
• and
• iii) exposing a sample to a selectivity condition comprises contacting a sample with an adsorbent and washing the adsorbent with an eluant to allow retention of analytes in the sample by the adsorbent;
• b) detecting analytes in the first sample by:
• i) exposing the first sample, in parallel, to each of the different selectivity conditions, and
• ii) detecting analytes retained by the adsorbents by desorption spectrometry, wherein desorption spectrometry comprises desorbing and ionizing the analyte from the adsorbent with an energy source and detecting the desorbed and ionized analytes with a detector;
• c) detecting analytes in the second sample by:
• i) exposing the second sample, in parallel, to each of the different selectivity conditions, and
• ii) detecting analytes retained by the adsorbents by desorption spectrometry;
• and
• d) comparing the analytes detected in the first biological sample with analytes detected in the second biological sample to identify analytes that are differentially present in the first and second biological sample.