On-line Analysis Of Volatile Organic Compounds Research Articles

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 μm thickness. The vacuum is below 3 × 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.

Vacuum Ultraviolet Single-Photon Ionization Time-of-Flight Mass Spectrometer

Abstract A home-made vacuum ultraviolet single-photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS) including vacuum system, sampling inlet system, vacuum ultraviolet ionization source, reflection time-of-flight mass analyzer and data acquisition system was introduced. Single-photon ionization with vacuum ultraviolet light is a particularly soft ionization technique. Volatile organic compounds (VOCs) with ionization energy less than the photon energy (10.6 eV) can be ionized into molecular ions. It is nearly fragmentation free compared with electron ionization, and very suitable for qualitative analysis. The mass resolution of the instrument is higher than 800 (Full width at half maximum, FWHM) and the mass accuracy is better than 100 ppm. The initial experiments detected more than 60 components in the mainstream smoke from cigarette, and the limits of detection for acetone, cyclohexane, ethyl acetate and toluene were 0.33, 0.27, 0.42 and 0.11 ppm, respectively. This instrument can be used for real-time and online analysis of VOCs in various environmental media (gas, solid, liquid), and if combined with a membrane inlet system, heating device or purge and trap system, a higher sensitivity could be achieved.

A new membrane inlet interface of a vacuum ultraviolet lamp ionization miniature mass spectrometer for on‐line rapid measurement of volatile organic compounds in air

A novel membrane inlet interface coupled to a single-photon ionization (SPI) miniature time-of-flight mass spectrometer has been developed for on-line rapid measurement of volatile organic compounds (VOCs). The vacuum ultraviolet (VUV) light source for SPI was a commercial krypton discharge lamp with photon energy of 10.6 eV and photon flux of 10(10) photons/s. The experimental results showed that the sensitivity was 5 times as high as obtained with the traditional membrane inlet. The enrichment efficiency could be adjusted in the range of 10 to 20 times for different VOCs when a buffer cell was added to the inlet interface, and the memory effect was effectively eliminated. A detection limit as low as 25 parts-per-billion by volume (ppbv) for benzene has been achieved, with a linear dynamic range of three orders of magnitude. The rise times were 6 s, 10 s and 15 s for benzene, toluene and p-xylene, respectively, and the fall time was only 6 s for all of these compounds. The analytical capacity of this system was demonstrated by the on-line analysis of VOCs in single puff mainstream cigarette smoke, in which more than 50 compounds were detected in 2 s.