A Review of “Use of an Accelerometer and a Microphone as Gas Detectors in the Online
Quantitative Detection of Hydrogen Released from Ammonia Borane by Gas
Chromatography”
He, Y., Chen, K., Lin, C., Lin, M., Chen, C., Lin, C. Use of an Accelerometer and a Microphone
as Gas Detectors in the Online Quantitative Detection of Hydrogen Released from Ammonia
Borane by Gas Chromatography. Journal of Analytical Chemistry. 2013. 88(4), 1-6.
Caitlin Verhalen 2 March, 2013
This article discussed the use of an accelerometer as a gas detector in gas
chromatography (GC). An accelerometer is a device that measures the acceleration due to its
weight by any test mass in the frame of reference. It can measure the g-force acceleration rather
than just a rate of change of velocity. Many different detectors are used for various mechanisms
such as flame ionization, thermal conductivity, electron capture, and surface acoustic wave are
known detectors used in gas chromatography, however the most commonly used detector is mass
spectrometry. All of these detectors are used for various sensitivity and simplicity of use. The
proposed method in this study was using the milli-whistle/GC system with an accelerometer and
a microphone to record the frequencies of sound. The frequency shifts and the hydrogen
concentration relationships are discussed to determine the best method store and carry and
produce hydrogen.
The milli-whistle is connected to the outlet of the GC capillary, and the GC eluted and
carrier gases passing through the capillary together produces the sound as they pass through the
milli-whistle. A specific frequency can be observed once applying a Fast Fourier transform
which is a built-in program. Qualitative results can be determined based on retention times with
various GC elutants. The concentration levels of these analytes should be able to be determined
based on the frequency changes in relation to the fundamental frequency of the carrier gas. Many
methods for the storage of hydrogen are being studied to find the best technique. This study used
ammonia borane (AB) as a source of hydrogen fuel and hydrogen storage medium because it is
able to release hydrogen on heating. This is basically a better technique because it is more
hydrogen-dense than liquid hydrogen and can be stored at normal temperatures and pressures
which makes it relatively safer than known techniques. The storage and delivery service for this
technique is based on the substrate of microtube array membrane (MTAM), a microcomposite of
AB/PC with which the AB was encapsulated within the PC (polycarbonate) MTAM which is an
overall lightweight and effective use for hydrogen storage and carrier device. The point of this
study was based on the current difficulty in monitoring an online quantitative result at the
microliter level.
The online quantitative detection of hydrogen released from ammonia borane was found
to be successful. They found the frequency of the whistle vibration and the sound frequency to
be identical so that components of the GC elutes could be detected using the accelerometer or the
microphone depending on which frequencies change. The limit of detection was the same for
both detectors and this milli-whistle/accelerometer system was applied to the online quantifying
detection of hydrogen released from ammonia borane. This method for an online quantitative
data collection is successful. The amount of ammonia that they used is able to produce hydrogen
in a significant quantity.
They discussed the dimensions of the pan-flute pipe having a major effect on the results
that they received. Factors that could influence the results included pipe width, air density and
temperature. It is possible that the data could have been swayed depending on these factors. The
specific sound produced may vary depending on the shorter the pipe or width. They used
dimensions of 5 mm in length and 1 mm in width with a tunnel diameter of 0.3 for gas blown in
and a 0.8mm mouthpiece for gas out. It is debatable whether or not these dimensions would be
the optimal size for the most accurate production of sound or not. Various other studies could be
performed with different dimensions of width, length, temperature, air density and it is
reasonable to believe that these changes would sway the results.
There are many variables that could also have been changed to possibly result in different
data for this particular experiment. They could have tested different derivatives of ammonia
borane as a storage medium for hydrogen to see if any result in retaining more hydrogen than
others. A big component of the production of hydrogen deals with the loss of it when they are
storing and carrying it, so perhaps a microtube array membrane that is encapsulated with another
polymer that could prove more amendable in different conditions may be helpful.