Detection of several volatile organic compounds through Ar+ induced chemical ionisation using inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS)

Abstract

A new analytical technique for detection of organic compounds using inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) is described. Volatile organic compounds (VOCs) were introduced into the collision/reaction cell (CRC), instead of through the ICP ion source, and the molecules were ionised through an ion reaction, induced by collision with the primary ions (Ar⁺) produced in the ICP. The ionisation characteristics of this new approach were investigated by mass spectrometric analysis of eight VOCs (i.e., benzene, toluene, ethyl acetate, methyl butyrate, ethyl butyrate, pentyl acetate, pyridine, and 2-methylfuran). These molecules were detected as molecular ions (M⁺), protonated ions ([M + H]⁺), or deprotonated ions ([M − H]⁺), demonstrating that soft ionisation was achieved by the present ionisation protocol using ICP-MS/MS. In addition, a volatile selenium-containing organic compound, dimethyl diselenide (Se₂(CH₃)₂), was also analysed to investigate the feasibility of this ionisation protocol to achieve soft and hard ionisation simultaneously. Several Se-related ions such as Se⁺, SeH⁺, Se₂⁺, [SeCH₃]⁺, and [Se₂CH₃]⁺, together with [Se₂(CH₃)₂]⁺, were observed, suggesting that while soft ionisation was possible, ion reaction-induced-fragmentation and hard ionisation also occurred. To demonstrate the analytical capability of the present technique, volatile components released from coffee beans were subjected to the present mass spectrometric analysis. Many ion peaks originating from VOCs were detected from the coffee beans. The data obtained here demonstrated that ICP-MS equipped with a CRC can become an effective tool for analyzing both elements and molecules.