AVS-TLGC is the powerful combination of a unique pneumatic
sampling system, known as Atmospheric (or Automated) Vapor Sampling (AVS),
and a high speed capillary gas chromatography approach known as Transfer
Line Gas Chromatography (TLGC). The AVS is a gas phase sampling system
designed to eliminate the sample loss problems of conventional syringe,
sample loop or trap-and-desorb injection systems. The sample handling portions
of the AVS system are constructed from the same materials as capillary
GC columns. There are no intervening valves, pumps or other analyte adsorption
sites in the sample path (see Figure 1.) AVS operation uses pneumatically
controlled carrier and analyte gas flows to control the timing of sample
introduction. This involves periodically exchanging the carrier gas flow
in the second tube for sample flow in the opposite direction, then restoring
the carrier gas flow as a diffusion barrier against additional sample flow.
This approach allows millisecond resolution of injection pulse widths without
additional sample adsorption sites. The GC separation is actually performed
in the capillary flow restrictor of a mass spectrometry system, known as
a "transfer line". The title "Transfer Line Gas Chromatography" indicates
that the GC conditions are optimized (based on both separation and flow
rate considerations) using variations in the column length and radius in
the context of fixed pressure drops from ambient conditions to the detector.
The AVS-TLGC approach was conceived for on-line measurement of ambient atmospheres to protect U.S. soldiers against chemical attack. This approach is naturally extended to measuring hazardous industrial chemicals or environmental pollutants. In addition to sampling local atmospheric chemical environments, the technology can be coupled into a number of on-line applications including:
The technology has been implemented into two FemtoScan products: the Enviroprobe Module and the Enviromental Vapor Monitor (EVM) II.
These products were developed to address a number of real-world analytical problems based on a new analytical paradigm. Simply stated: "every sample handling step and every minute waiting for a result cost you money!" Therefore, the most expeditious way to tackle an analytical problem is to provide on-line or in-situ sampling, thereby paving the way for real-time analytical results to be ready for immediate on-site use. In real-world applications, this is easier said than done. Real-world samples involve mixtures. In order to separate and quantitate mixtures of analytes and interferants, the analytical chemist requires either off-line sample preparation or powerful on-line analytical methods capable of separating the target constituents. AVS-TLGC is designed to apply the latter approach to gas phase analytes in a way that is consistent with the on-line, in-situ, real-time, on-site philosophy.
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Page last updated on 7/19/99