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TECHNICAL ARTICLES
MICRO GAS CHROMATOGRAPHY SYSTEM FOR DISTRIBUTED ENVIRONMENTAL AWARENESS
[Hanseup Kim, KSEA Membership Director]
USTAR Assistant Professor, Electrical and Computer Engineering
University of Utah
INTRODUCTION
The World Health Organization (WHO) states that 2.4 million people die each year worldwide from causes directly attributable to
air pollution (1). In US the fatalities from air pollution, totaling over 70,000 lives in 2002, are twice the number of automobile fatalities
and are equal to deaths from breast cancer and prostate cancer combined (2). Hundreds of scientific studies conducted worldwide
have provided evidences that polluted air has alarming adverse effects on health (3). Clearly, the exposure to air pollution needs
to be dramatically reduced or at least monitored for individuals. While the air pollutants include various chemical compounds, such
as ozone, nitrogen oxides, and sulfur dioxide, Volatile Organic Compounds (VOCs) cover the largest number of >100 pollutants
and are the most common pollutants exposed to humans who spend a significant amount of time indoors. Another report from
EPA states that the indoor air pollution caused by VOCs is ten times higher than outdoor regardless of the building location in rural
or highly industrial areas (4). VOCs are also found to have strong correlation with allergies and asthmas, and each individual has
different levels of responses to specific VOCs (5, 6). Thus, the development of a personal ‘wearable’ warning system against a wide
range of VOCs is much needed to prevent significant harm to public health from nearly inevitable exposure. Currently there are no
viable options for such needs.
MICRO GAS CHROMATOGRAPHY SYSTEM
A micro gas chromatography system (μGC) can be a best option as a ‘wearable’ VOC measurement tool. Compared to commercial
gas sensors that have narrowly-limited detection targets (e.g. carbon monoxide sensor), a gas chromatography (GC) system could
provide much higher detection capacity of >10’s species and seems a more feasible option for miniaturization than mass spectrometry
(MS), because of its ‘less’ requirements for supporting equipments (no vacuum pumps or carrier gases). Indeed a GC is the most
widely used tool in analytical chemistry. Currently MS has proven to be more difficult to miniaturize due to the vacuum pumping
requirements as well as the need to purifying samples before analysis. The state-of-the-art “portable” MS still weighs over 11kg,
consumes >42W, and has the size of a backpack. Note that the miniature GCs also hold significant advantages of high-speed & highresolution
detection, tiny volume, reduced power, as well as the possible ‘wearable’ portability.
Operation Principle: A micro gas chromatograph enables the detection of complex mixtures of ~100 airborne compounds by first
spatially separating and then detecting them along fluidic migration. To do so, it incorporates additional components than the standalone
gas sensor, including a pre-concentrator, a separation column and a fluidic pump (Figure 1). The pre-concentrator collects
targets into high concentration for better sensitivity; the column provides a race track where target species are separated in space
and time to enhance selectivity at the detection sensor; and the micropump forces the target samples to flow at the optimal speed
for efficient separation as well as the rapid detection. Specifically, the spatial separation among compounds is achieved in the column
where special coating inside, called as a stationary phase, adsorbs and releases the different target molecule groups at different
speeds. Resultantly each group of gas molecules becomes apart as they pass through the column. Thus, each group passes by a sensor
at different times and produces a train of peak signals at a micro sensor for detection.
Figure 1. The operation principle of the gas chromatography system: Spatial separation ahead of detection
reduces the burdens on the sensor’s selectivity and sensitivity.
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KSEA LETTERS Vol. 40 No. 3 April 2012