In-situ Mass Spectrometry of Cave Atmospheres, 15-R8254
Principal Investigators
Edward L. Patrick
Kathleen Mandt
Joseph Mitchell
Evelynn Mitchell
Kerri Younkin
Inclusive Dates: 09/08/11 – 01/03/12
Background — The motivation for this project was the desire to use field-deployable mass spectrometry as an analytical chemistry tool in the harsh environment of caves. Such an application has potential benefits for cave biologists studying the disease white nose syndrome (WNS), which has killed millions of bats in the Northeastern United States. Field deployment of mass spectrometry in the harsh and poorly understood environments of caves is also an analog for a number of comparable engineering constraints imposed upon analytical instruments designed for planetary surface environments. In repeated searches of the scientific literature, no record could be found for the field deployment of a mass spectrometer in a cave environment, though many caves samples had been returned to the laboratory for subsequent analysis. Numerous groups currently developing mass spectrometers for analytical purposes have the capability to field-deploy instrumentation in caves. Furthermore, the recent discovery of caves on the surface of the Moon and Mars made successful deployment of mass spectrometry into caves relevant to future goals of NASA and the space science community. For these reasons, rapid deployment of a prototype instrument was essential for establishing SwRI as a leader in deploying mass spectrometry in harsh environments.
Approach — A prototype mass spectrometer was constructed from a commercial off-the-shelf (COTS) residual gas analyzer (RGA). The RGA was serviced by a miniature turbomolecular pump and four-stage diaphragm pump. The completed prototype system was tested in the laboratory prior to field deployment. A number of cave locations were investigated and the four selected for analysis were Bracken Bat Cave, Natural Bridge Caverns, Robber Baron Cave and Wurzbach Bat Cave. Tyvek® suits, respirators and decontamination protocol were used in Bracken Bat Cave due to the hazardous environment posed by airborne microbes, flesh-eating insects and toxic levels of ammonia and urea from millions of Mexican Freetail Bats. Air samples at Bracken Bat Cave were also obtained using stainless steel canisters for subsequent laboratory analysis by gas chromatograph mass spectrometry. In addition to these four cave sites, air from two aquifer wellheads was monitored by the cave mass spectrometer (CMS) employing a second diaphragm pump for drawing well air to the CMS from 60 meters below the surface. Atmospheric data from outside each cave and wellhead were also obtained for comparison with the cave and well data.
Accomplishments — Approval for the CMS project was granted September 9, 2011, and at 2:41 p.m., on Friday, September 16, 2011, a prototype CMS was carried into Bracken Bat Cave. It is believed that this is the first deployment of a mass spectrometer in a cave. The humidity was at 99 percent and the temperature was 110 degrees F. Data from each cave showed expected increases in CO2 concentration. Peculiar to the toxic environment of Bracken Bat Cave were data suggesting elevated levels of oxygen. The second wellhead exhibited no detectable air flow, but air at the first wellhead was moving at a significant velocity. This first wellhead also showed detectable levels of volatile, low-mass hydrocarbons. Subsequent examination of the Bracken Bat Cave air samples showed numerous organic compounds, including aldehydes, ketones and nitriles, and also suggested further investigation of this environment should be a priority for the cave, bat and environmental science communities. The prototype CMS concept was proven to be a valid analytical approach for future cave investigations.
