Uses of field desorption mass spectrometry in the pharmaceutical industry.

Field desorption (FD) is a gentle method of ionizing molecules from the solid state. The method is still in its infancy and remains more of an art than a science. Purines, pyrimidines, pteridines, and nucleosides represent some of the compound classes which are studied repeatedly in our laboratory. Often the primary information sought is the molecular weight. Many of these compounds are thermally unstable or nonvolatile. In these instances, FD mass spectrometry has proven to be quite helpful. Molecular weights are obtained in a short time, eliminating the need for more time-consuming derivatization or chemical degradation methods. FD has been applied to the study of drug metabolism and has shown great promise in determining polar metabolites, including direct analysis of glucuronide, sulfate, and amino acid conjugates. Some problems have been encountered in handling samples of biological origins. Salt impurities introduced by the separation procedure may interfere with the desorption process. Cluster ions and background noise make it difficult to assign molecular ions, and some compounds do not yield molecular ions with FD.