FACTORS AFFECTING GAS-ANALYSIS OF INCLUSION FLUID BY QUADRUPOLE MASS-SPECTROMETRY

Quadrupole mass spectrometric (QMS) analysis of small amounts of inclusion fluid (< 1 milligram) released by crushing and decrepitation requires methods to: (1) determine the amount of molecular fragmentation and the relative sensitivity to water and other gases, (2) evaluate differential adsorption of gases in the analytical system, (3) calibrate detector response to amount of released fluid, and (4) detect gas from noninclusion fluid sources. Fragmentation of gases during ionization in the source is pressure dependent. Because the amount of fluid released from individual inclusions and crushed samples varies over a wide range, corrections are made for this pressure dependence during data reduction. This procedure is especially critical for water, the dominant component in most fluid inclusions. Adsorption of H2O is not quantitatively significant from decrepitated individual inclusions (over a range of 1 x 10(-6) to 1 milligram) or crushed samples that contain > 1 x 10(-4) milligram of H2O. However, adsorption of H2O onto newly created surfaces by crushing samples containing < 1 x 10(-4) milligram of H2O will result in lower mol% water reported in the gas analysis than present in inclusion fluid prior to release. Gases from noninclusion fluid sources are incorporated into inclusion fluid during both release methods. N-2, O-2, and Ar from air in the inlet system are entrained into released inclusion fluid. Gases including SO2 and HCl can be generated when inclusion fluid is released into vacuum. Thermal decomposition of minerals and organic compounds can produce CO2 CH4, CO, N-2, H-2, and other gases that mix with those released from inclusion fluid. The relative contributions of gas from inclusion fluid vs. these other sources can be differentiated using real-time (direct) QMS analysis.