Method for detecting atmospheric vapors at parts per quadrillion (PPQ) concentrations

Procédé pour détecter des vapeurs atmosphériques en parties par quadrillion (PPQ) des concentrations

Verfahren zum Nachweis von atmosphärischen Dämpfen in Konzentrationen von 1 Teil pro Billiarde (PPQ)


Various improvements are taught in the detection of atmospheric vapors by ionizing them near ambient pressure, and analyzing them as ions. Lowest detection limits of parts per quadrillion (ppq) concentrations are enabled by a combination of improvements in background noise and statistical noise reduction. One improvement involves the counter-intuitive use of a filter to remove occasional intense signal from explosive particles, whose high statistical noise does more damage than good. Several important sources of chemical background are identified and solutions for their reduction or elimination are presented. Important gains in the response time of the system are achieved by operating at elevated temperature. When the ionizer is an electrospray source, the use of selected combinations of high boiling point solvents is indicated. An increased selectivity is achieved by operating a differential mobility analyzer (DMA) in series with a mass spectrometer. However, ppq sensitivities require various improvements in the DMA system including a special coupling to the ionizer, controlling the temperature in the DMA pump circuit, avoidance of induction on the DMA electrodes from heating devices, etc.




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