11 research outputs found
Total hydrocarbon analysis by ion mobility spectrometry
Astronauts must be alerted quickly to chemical leaks that compromise their health and the success of their missions. An ideal leak detector would be equally sensitive to all compounds that might constitute a hazard and insensitive to nontoxic compounds. No ideal sensor exists; thus, selection of a methodology is a series of compromises. The commonly used methods are either insensitive at the low exposure levels set by OSHA, NASA, and other organizations or are selectively insensitive to important classes of chemicals such as Freons. After extensive study and experience, the Toxicology Group at JSC has selected ion mobility spectrometry (IMS) for development into a broad range, sensitive detector. In addition to the sensing method, signal processing is important leak detection because a background signal can be expected at all times. The leak-detecting instrument must be programmed to discriminate between authentic leaks and background fluctuations caused by routine operations. The results of an evaluation of the prototype THA is presented in terms related to spacecraft operations. The evaluation included determination of instrumental parameters such as stability and response times. We also included responses to some common components of spacecraft atmospheres in pure form and in binary and ternary mixtures. The output of the four algorithms to the mixtures was found to be noticeably different. These responses are compared on the basis of their utility for signaling a chemical leak. As a means of evaluating its resistance to a falsely positive response, the THA was challenged with carbon dioxide and methane, compounds whose concentrations normally increase in spacecraft air during human habitation. The instrument showed virtually no response to these interferences. Although the prototype THA is designed for space flight, this detector is expected to be useful for field screening at chemical waste dumps and other environmentally sensitive locations
A combustion products analyzer for contingency use during thermodegradation events on spacecraft
The Toxicology Laboratory at JSC and Exidyne Instrumentation Technologies (EIT) have developed a prototype Combustion Products Analyzer (CPA) to monitor, in real time, combustion products from a thermodegradation event on board spacecraft. The CPA monitors the four gases that are the most hazardous compounds (based on the toxicity potential and quantity produced) likely to be released during thermodegradation of synthetic materials: hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen cyanide (HCN), and carbon monoxide (CO). The levels of these compounds serve as markers to assist toxicologists in determining when the cabin atmosphere is safe for the crew to breathe following the contingency event. The CPA is a hand-held, battery-operated instrument containing four electrochemical sensors, one for each target gas, and a pump for drawing air across the sensors. The sensors are unique in their small size and zero-g compatibility. The immobilized electrolytes in each sensor permit the instrument to function in space and eliminate the possibility of electrolye leaks. The sample inlet system is equipped with a particulate filter that prevents clogging from airborne particulate matter. The CPA has a large digital display for gas concentrations and warming signals for low flow and low battery conditions. The CPA has flown on 13 missions beginning with STS 41 in Oct. 1990. Current efforts include the development of a microprocessor, an improved carbon monoxide sensor, and a ground-based test program to evaluate the CPA during actual thermodegradation of selected materials
Evaluation of a Gas Chromatograph-Differential Mobility Spectrometer for Potential Water Monitoring on the International Space Station
Environmental monitoring for manned spaceflight has long depended on archival sampling, which was sufficient for short missions. However, the longer mission durations aboard the International Space Station (ISS) have shown that enhanced, real-time monitoring capabilities are necessary in order to protect both the crewmembers and the spacecraft systems. Over the past several years, a number of real-time environmental monitors have been deployed on the ISS. Currently, volatile organic compounds (VOCs) in the station air are monitored by the Air Quality Monitor (AQM), a small, lightweight gas chromatograph-differential mobility spectrometer. For water monitoring, real-time monitors are used for total organic carbon (TOC) and biocide analysis. No information on the actual makeup of the TOC is provided presently, however. An improvement to the current state of environmental monitoring could be realized by modifying a single instrument to analyze both air and water. As the AQM currently provides quantitative, compound-specific information for VOCs in air samples, this instrument provides a logical starting point to evaluate the feasibility of this approach. The major hurdle for this effort lies in the liberation of the target analytes from the water matrix. In this presentation, we will discuss our recent studies, in which an electro-thermal vaporization unit has been interfaced with the AQM to analyze target VOCs at the concentrations at which they are routinely detected in archival water samples from the ISS. We will compare the results of these studies with those obtained from the instrumentation routinely used to analyze archival water samples
Evaluation of a Gas Chromatograph-Differential Mobility Spectrometer for Potential Water Monitoring on the International Space Station
No abstract availabl
Performance Evaluation of the Operational Air Quality Monitor for Water Testing Aboard the International Space Station
Real-time environmental monitoring on ISS is necessary to provide data in a timely fashion and to help ensure astronaut health. Current real-time water TOC monitoring provides high-quality trending information, but compound-specific data is needed. The combination of ETV with the AQM showed that compounds of interest could be liberated from water and analyzed in the same manner as air sampling. Calibration of the AQM using water samples allowed for the quantitative analysis of ISS archival samples. Some calibration issues remain, but the excellent accuracy of DMSD indicates that ETV holds promise for as a sample introduction method for water analysis in spaceflight
Electro-Thermal Vaporization Direct Analysis in Real Time-Mass Spectrometry for Water Contaminant Analysis during Space Missions
The development of a direct analysis
in real time-mass spectrometry
(DART-MS) method and first prototype vaporizer for the detection of
low molecular weight (∼30–100 Da) contaminants representative
of those detected in water samples from the International Space Station
is reported. A temperature-programmable, electro-thermal vaporizer
(ETV) was designed, constructed, and evaluated as a sampling interface
for DART-MS. The ETV facilitates analysis of water samples with minimum
user intervention while maximizing analytical sensitivity and sample
throughput. The integrated DART-ETV-MS methodology was evaluated in
both positive and negative ion modes to (1) determine experimental
conditions suitable for coupling DART with ETV as a sample inlet and
ionization platform for time-of-flight MS, (2) to identify analyte
response ions, (3) to determine the detection limit and dynamic range
for target analyte measurement, and (4) to determine the reproducibility
of measurements made with the method when using manual sample introduction
into the vaporizer. Nitrogen was used as the DART working gas, and
the target analytes chosen for the study were ethyl acetate, acetone,
acetaldehyde, ethanol, ethylene glycol, dimethylsilanediol, formaldehyde,
isopropanol, methanol, methylethyl ketone, methylsulfone, propylene
glycol, and trimethylsilanol
Electrothermal Vaporization Sample Introduction for Spaceflight Water Quality Monitoring via Gas Chromatography-Differential Mobility Spectrometry
In the history of manned spaceflight,
environmental monitoring
has relied heavily on archival sampling. However, with the construction
of the International Space Station (ISS) and the subsequent extension
in mission duration up to one year, an enhanced, real-time method
for environmental monitoring is necessary. The station air is currently
monitored for trace volatile organic compounds (VOCs) using gas chromatography-differential
mobility spectrometry (GC-DMS) via the Air Quality Monitor (AQM),
while water is analyzed to measure total organic carbon and biocide
concentrations using the Total Organic Carbon Analyzer (TOCA) and
the Colorimetric Water Quality Monitoring Kit (CWQMK), respectively.
As mission scenarios extend beyond low Earth orbit, a convergence
in analytical instrumentation to analyze both air <i>and</i> water samples is highly desirable. Since the AQM currently provides
quantitative, <i>compound-specific</i> information for air
samples and many of the targets in air are also common to water, this
platform is a logical starting point for developing a multimatrix
monitor. Here, we report on the interfacing of an electrothermal vaporization
(ETV) sample introduction unit with a ground-based AQM for monitoring
target analytes in water. The results show that each of the compounds
tested from water have similar GC-DMS parameters as the compounds
tested in air. Moreover, the ETV enabled AQM detection of dimethlsilanediol
(DMSD), a compound whose analysis had proven challenging using other
sample introduction methods. Analysis of authentic ISS water samples
using the ETV-AQM showed that DMSD could be successfully quantified,
while the concentrations obtained for the other compounds also agreed
well with laboratory results