A sandwich temperature control membrane inlet mass spectrometer for dissolved gases and volatile organic compounds in aqueous solution

A sandwich temperature control membrane inlet system based on a miniature mass spectrometer is presented that demonstrates improved analytical performance for the measurement of dissolved gases and volatile organic compounds (VOCs) in aqueous solution. Aqueous solution is directly brought to the monolayer flat membrane interface at a constant flow rate. A heating resistor and a thermocouple are fixed on the side of the membrane and aqueous solution respectively. This new strategy allows for a temperature compensation method, affording an improvement of sensitivity and a reduction of response time compared with the conventional heating solution temperature control strategy. Furthermore, a static heating mode is applied to effectively remove the memory effect. Automatic sampling and measurement are achieved by using the membrane inlet system with silicone sheeting of 50 mu m thickness. The vacuum is below 3 x 10(-5) Torr, which can make the instrument work normally. A good linear response is observed for benzene in the range of 0.1 ppm-10 ppm and the detection limit is 50 ppb. The analytical capacity of this system is demonstrated by the on-line analysis of VOCs in aqueous solution, in which the dominant ions are detected rapidly. The results indicate that the sandwich temperature control membrane inlet mass spectrometer (STC-MIMS) has a potential application for on-line analyzing organic pollution in aquatic environments.

Automated summary

The sandwich temperature control membrane inlet mass spectrometer (STC-MIMS) presented in this study demonstrates improved analytical performance for the measurement of dissolved gases and VOCs in aqueous solution. The system allows for temperature compensation, increased sensitivity, reduced response time, and effective removal of memory effect. This new method has the potential for online analysis of organic pollution in aquatic environments.