According to “National standards for the management of odor pollution”, most of the eight odor gas (hydrogen sulfide, methanthiol, dimethyl sulfide, carbon disulfide, trimethylamine, etc.) are volatile sulfur compounds (VSCs). Those compounds, which are closely related to human’s daily life, are usually highly toxic and even a ppbv level can cause health problems. Besides, VSCs can be disease markers in exhaled breath gas for medical diagnostics (e.g., hydrogen sulfide and dimethyl sulfide for cirrhosis and hepatic coma). Development of highly-sensitive and rapid-analysis techniques for detection of VSCs becomes necessary, because of its high reactive and adsorptive properties.

Prof. LI Haiyang’s research group (Rapid Separation and Detection Group) developed a photoionization-generated dibromomethane cation chemical ionization (PDCI) source. This new ion source combined with mass spectrometry significantly improves the detection sensitivity of odor sulfur compounds.

A Highly-sensitive Technique for Detection of Odor Sulfur Compounds (Image by JIANG Jichun and WANG Yan)

By using a Vacuum Ultra Violet (VUV) lamp, a stable flux of CH₂Br²⁺ was generated with high concentration of dibromomethane (CH₂Br₂) as the reagent gas, then the VSCs were further ionized by reaction with CH₂Br₂⁺ cation via charge transfer and ion association and realized the highly-sensitive detection. As a result, the limits of detection (LODs) of five typical VSCs (hydrogen sulfide, methanthiol, dimethyl sulfide, etc.) were obtained at pptv level within 1 min. Moreover, the formation of special adduct [M⁺CH₂Br₂]⁺ ions enhanced the capacity of chemical identification.

This new method has been demonstrated by analysis of trace VSCs in breath gases of healthy people and sewer gases. Its good sensitivity and rapid analysis speed imply that this PDCI ion source has a huge potential for medical diagnostics and environmental chemistry. The work has been published on Analytical Chemistry (DOI: 10.1021/acs.analchem.6b00428).