N. Takahata et al., CONTINUOUS MONITORING OF DISSOLVED-GAS CONCENTRATIONS IN GROUNDWATER USING A QUADRUPOLE MASS-SPECTROMETER, Applied geochemistry, 12(4), 1997, pp. 377-382
An apparatus has been developed for fully automated, continuous measur
ement of the concentration of selected gases in groundwater using a qu
adrupole mass spectrometer. The apparatus has several advantages over
conventional methods: (1) since a gas-permeable microporous film is at
tached to the head of a sampling tube, gases dissolved in groundwater
are separated from water by putting the sampling tube into water; (2)
by continuously introducing gases separated from water into an on line
mass spectrometric system, we have successfully made isotopic measure
ments such as Ar-40/Ar-36 in groundwater on a continuous basis; and (3
) very short intervals of measurement, less than several minutes, are
attained by switching the electric voltage of the mass spectrometer di
scontinuously from peak to peak of arbitrarily chosen gas species. Som
e experiments are described to evaluate the basic performance of the a
pparatus such as the reproducibility in repeated measurements, depende
nce on the total amount and chemical composition of gases, and the res
ponse time to a sudden change of dissolved gas contents. An example is
presented of observation of distilled water, which demonstrates that
the new apparatus is sufficient for continuous monitoring of selected
dissolved gases in water for various purposes. (C) 1997 Elsevier Scien
ce Ltd.