ACCURATE MASS MEASUREMENT OF POSITIVE-IONS PRODUCED BY AMMONIA CHEMICAL IONIZATION

A technique is described which enables the accurate mass measurement of positive ions produced under ammonia chemical ionization (NH3-CI) conditions using a mixture of perfluorinated alkanes (referred to commonly as perfluorokerosene or PFK) as the secondary mass reference even though these perfluorinated compounds do not form positive ions under NH3-CI conditions. By creating a 'composite' spectrum of analyte under NH3-CI conditions, and PFK under electron ionization (EI) conditions, while signal averaging in memory, mass measurement of the analyte peaks can be accomplished. Combined capillary gas chromatography/accurate mass measurements of components at sub-part-per-million levels in environmental extracts are described as well as confirmation of novel eicosanoid structures.