A method for the isolation of the amide nitrogen of glutamine from biological samples for mass spectrometry

The amide nitrogen from L-glutamine has been isolated from an artificial plasma, in a form suitable for mass spectrometry, by a macromodification of the glutaminase reaction. The prior removal of free ammonia of free ammonia was carried out by alkaline aeration. When this was performed at zero degree for 3 h, spontaneous hydrolysis of glutamine was 1.4 percent. Cross-contamination with nitrogen liberated from the amide group of asparagine can be avoided by preincubation with asparaginase for 2 h and removal of the freed ammonia prior to reacting with glutaminase. Hydrolysis of glutamine during this step is 12 percent. Measurements of enrichment can be made on samples yielding more than æmol of glutamine amide-derived ammonia (AU)