A new direct-current microwave argon plasma source was designed and constructed for use in mass spectrometry. Solid samples and analytes on solid materials were examined by means of mass spectrometry. The microwave source was used to generate argon plasma allowing the ionization of analyte particles thermally released from the heated crucible whose temperature could be regulated from 100 to 250 degrees C. A microwave argon plasma ionization source in ambient mass spectrometry was used for analysis of pure compounds, analytes in molecular imprinted polymers (MIPs) and drugs in medical tablets. Results suggest that ionization occurred mainly through protonation, with only a small contribution of fragmentation and adduct formation. In this technique, ion fragmentation analysis (MS2) gives good results in the analysis of low molecular weight compounds in complex matrices. Limits of detection and limit of quantification for several small organic molecules were determined for investigation of the analytes in difficult matrixes.