Sudden sampling introduction into a membrane inlet mass spectrometer (MIMS) considerably improves the selectivity of the membrane inlet and is therefore applicable even for compounds with low permeabilities through a silicone membrane. In this study the basics of cyclic non-steady-state sudden increase sample injection were studied using a three-membrane inlet and a portable sector double-focusing mass spectrometer. The operational parameters of the inlet system providing the most efficient enrichment of volatile organic compounds (VOCs) in air were defined. Simulation of the diffusion process following sudden sample introduction into the three-membrane inlet was also carried out. Experimental testing of the three-membrane inlet system with the cyclic sudden sample injection mode for benzene, toluene, styrene, and xylene in air was performed. The simulation and the experimental results demonstrated that, when this mode is used, the VOCs/nitrogen relative enrichment factor of samples introduced into the mass spectrometer equipped with a three-membrane inlet is increased by a factor of approximately 10(5) compared with a direct introduction method. This effect may be used to decrease detection limits of compounds obtained with mass spectrometry to decrease matrix flow through the inlet at the same detection limits.
In the article the features of the physical processes modeling of the ultrasonic wave interaction to the metal structures are considered. The mathematical model for calculating the acoustic field of a single element of a 32-element electromagnetic acoustic phased array of SV-waves is developed. The computer simulation of the process of reflection of the ultrasonic beam from a defect is carried out. The developed model allows to study the influence of the shape, size, location of defects in the plate, as well as the geometric parameters of the plate, on the formation of the reflected signal.
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