Sample Contamination with NMP-oxidation Products and Byproduct-free NMP Removal from Sample Solutions

1-Methyl-2-pyrrolidinone (NMP) is widely used as a solvent for coal-derived products and as eluent in size exclusion chromatography. It was observed that sample contamination may take place, through reactions of NMP, during extraction under refluxing conditions and during the process of NMP evaporation to concentrate or isolate samples. In this work, product distributions from experiments carried out in contact with air and under a blanket of oxygen-free nitrogen have been compared. Gas chromatography/mass spectrometry (GC-MS) clearly shows that oxidation products form when NMP is heated in the presence of air. Upon further heating, these oxidation products appear to polymerize, forming material with large molecular masses. Potentially severe levels of interference have been encountered in the size exclusion chromatography (SEC) of actual samples. Laser desorption mass spectrometry and SEC agree in showing an upper mass limit of nearly 7000 u for a residue left after distilling "pure" NMP in contact with air. Furthermore, experiments have shown that these effects could be completely avoided by a strict exclusion of air during the refluxing and evaporation of NMP to dryness.