Internal standard correction of results obtained by atmospheric pressure chemical ionization mass spectrometry.

An internal standard system has been developed for a mass spectrometer equipped with an atmospheric pressure chemical ionization source. The system has been used to overcome sensitivity drift problems that are commonly encountered when the spectrometer is used for long-term environmental monitoring. Additionally, the internal standard has been used to correct sensitivity changes induced by the matrix being analyzed. Principal components of the system are a low concentration internal standard source and a flow-delivery system for introducing the standard to the reagent gas delivery stream of the spectrometer. Following an experiment, real-time data are downloaded to a personal computer where internal standard correction and data analysis are performed. Application of the internal standard to the measurement of nicotine and pyridine is demonstrated.