Direct Detection of Volatile Organic Compounds through Cationization Using ICP-MS/MS

We have developed a new analytical technique for the detection of volatile organic compounds (VOCs) using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). Eight VOCs of various polarities (acetic acid, 2-butanone, pyridine, 2-methylfuran, ethylene, benzene, toluene, and limonene) were introduced into the collision/reaction cell (CRC) of the ICP-MS/MS, bypassing the ICP ion source. This approach enabled a softer ionization than the typical ICP, allowing the detection of the molecules in their intact form. In this study, to explore the potential of cationization as a soft ionization approach, the interaction of the above VOCs with various elements (<i>i.e</i>., Li, Be, Na, Mg, V, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Ru, Pd, Ag, Cd, Cs, Ba, Pt, and Hg) was investigated. The production ratio of cation adducts was evaluated using benzene as a model compound by monitoring [C₆H₆ + E]⁺/E⁺ values (E represents each element). The resulting [C₆H₆ + E]⁺/E⁺ showed a wide variation, covering ranges from 0.0001% to 1%, and the elements with ionization energies between 650 and 900 kJ mol^-1 exhibited the highest [C₆H₆ + E]⁺/E⁺ values. The data obtained here revealed that several elements, including Co, Ni, Cu, Ru, Pd, and Ag, can be suitable elements for cationization. The reduction in fragmentation resulted in easier detection of specific compounds based on their <i>m</i>/<i>z</i> values. To demonstrate the practicality of the present technique, several VOCs released from coffee beans through laser-induced evaporation were monitored. The data obtained here envisage a possibility that the detection of VOCs through cationization achieved in ICP-MS/MS can become an effective choice as a rapid analytical tool for VOCs in solid samples.