Miniature Sensors for Biological Warfare Agents using Fatty Acid ...

such as air. There have been few investigations, however, that compare the
pyrolysis results of these two atmospheres [62].
There are several types of instrumentation used to perform pyrolysis including gas
chromatographic inlet, infrared, Curie-point, and resistive pyrolyzers. The
characteristics of each type are summarized below, including a brief history of
pyrolysis/methylation, and are listed in Table 13.
2.5.1. Gas Chromatographic inlet pyrolysis.
In this method the sample of interest is injected in liquid form into the inlet, which is
simply a heated glass tube, of a commercial gas chromatograph. The inlet
temperature cannot exceed about 250ºC and is kept constant. Depending on the
volume, the liquid is vaporized within 0.5 seconds. A portion of the sample is
swept by an inert carrier gas into the gas chromatographic separation column.
Because of the limitations of the upper temperature, this method is not practiced
widely.
2.5.2. Infrared pyrolysis.
In this method, infrared laser radiation heats the sample. Various lasers are
available that can be used for this purpose. Their emission is usually pulsed, and
the heating rate depends upon the irradiance or energy per unit area focused upon
the sample during the pulse. As a chromatographic introduction technique, this
technique is rarely used. It is more often used as a sample introduction for a mass
spectrometer.
2.5.3. Curie-point pyrolysis
For this type of pyrolysis, a magnetic metal foil or wire of particular alloy
composition is excited by radio frequency energy. The metal heats until the
characteristic Curie-point temperature of the alloy is reached, at which point the
metal is no longer magnetic and ceases to heat. In this way temperatures from
300 to nearly 1000ºC can be achieved in a matter of 10-20 milliseconds. The
major limitation of the method is that particular alloys are required, limiting the
pyrolysis to discrete temperatures. Available temperatures include 220, 358, 423,
500, 670, 920, and others. The alloys are somewhat specialized, which increases
the cost per sample. There are three manufacturers currently offering Curie-point
pyrolysis instrumentation, GSG Analytical Instruments Ltd. (UK), Japan Analytical
(Japan), and Horizon Instruments (UK). For solids analysis the foil must be
crimped to enclose the sample. Curie point can take 100W (0.5Mhz) to produce a
1-2 second rise to 358, 510, or 610°C [27].
2.5.4. Resistive pyrolysis
This type of pyrolysis is perhaps the simplest, requiring only a metal filament (often
platinum) and a capacitive power supply capable of sending a large current rapidly
through the filament. The filament heats due to its electrical resistance. This
method is more flexible than Curie-point because it is not limited to discrete
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