Helium microwave-induced plasma mass spectrometry for capillary gas chromatographic detection: speciation of organotin compounds

Helium microwave-induced plasma mass spectrometry has been utilised as an element selective detector for capillary gas chromatography. Several trialkyltin and tetraalkyltin compounds were separated via capillary gas chromatography using a DB-1701 stationary phase. Two different tangential flow torches were evaluated. The major difference between the two torches is the use of a tantalum injector which extends through the microwave cavity and provides a means of introducing the effluent from the capillary column directly into the helium plasma. The optimum signal to noise ratio for the tantalum injector torch was obtained at a microwave power of 70 W with a plasma gas flow-rate of about 3 l min–1. Detection limits obtained with the tantalum injector torch ranged from 0.09 to 0.35 pg of Sn, while those achieved using the standard tangential flow torch ranged from 1 to 4 pg of Sn for the organotin species investigated. The relative standard deviation (RSD) of peak-height reproducibilities ranged from 2.4 to 4.3% for manual injection using the tantalum injector torch for 50 pg of Sn. The manual injection of 1 ng of compound resulted in an RSD of ca. 7% for peak height using the standard tangential flow torch. Linear dynamic ranges were over at least three orders of magnitude.