Investigating the potential of high-performance liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry as an alternative method for the speciation analysis of organotin compounds

Abstract

Liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) was applied for the determination of butyl- and phenyltin compounds. Chromatography was performed on a 30 x 2 mm, 3 microm C18 column, enabling the separation of mono-, di- and trisubstituted butyl- and phenyltin compounds in less than 10 min using a water/1% trifluoroacetic acid/methanol gradient. While satisfactory retention and resolution is achieved for the di- and trisubstituted butyl- and phenyltin compounds, monobutyltin and monophenyltin cannot be resolved chromatographically. Depending on the parameter values of the interface, APCI-MS detection allows both specific detection of the molecular ion or cluster ion at low to intermediate fragmentor voltages or quasi-element specific detection of the Sn+ ion released from the organotin compounds at high fragmentor voltages. The sensitivity of MS detection is similar for butyl- and phenyltin compounds, but varies largely from mono- to trisubstituted organotin compounds with tributyl- and triphenyltin being the most sensitively detectable compounds. Detection limits are in the 20-65 pg (abs.) range in SIM mode and in the 750-2000 pg (abs.) range in the scan mode for tributyl- and triphenyltin and for dibutyl- and diphenyltin, respectively. Monobutyl- and monophenyltin can be detected with much lower sensitivity which, together with their unfavorable chromatographic behavior, accounts for the fact that they cannot be analyzed at environmentally relevant concentrations. Although LC-APCI-MS is generally less sensitive than comparable GC methods, it is applicable to the analysis of environmental samples as demonstrated by the analysis of the PACS-2 sediment certified reference material. Although the derivatization of the ionic organotin compounds, which particularly in real samples is a potential source of error, is circumvented when LC-APCI-MS is used, the extraction step is still critical and may lead to underestimation when quantitation is not done by the method of standard addition.