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What is Gas Chromatography?
Chromatography
is the separation of a mixture of compounds (solutes) into separate
components
so that they can be identified and
quantified. By separating the sample into individual components, it is
easier to identify (qualitative))
and measure
the amount (quantitative)
of the various sample components. There are numerous chromatographic
techniques and corresponding instruments. Gas chromatography (GC)
is one of these techniques. In gas chromatography (GC), a
moving gas (the mobile phase) carries the sample across a stationary phase
(the solid support found within a GC column). It is estimated that 10-20% of the known
compounds can be analyzed by GC. To be suitable for GC analysis, a
compound must have sufficient volatility and thermal stability.
GC is normally used when the sample can be vaporized below 400-450°C.
It was
nearly 50 years from Mikhail Tswett's description of chromatography. The
suggestion to use a gas as the mobile phase was made by
Martin and
Synge in 1941, but it was not implemented until the work of
James and Martin (1952) on gas-liquid chromatography and the work of Cremer
and Prior (1951) and Cremer and Müller (1951) on gas-solid chromatography.
Since then, gas chromatography has developed rapidly, particularly during
the 1960s and the use of the technique has been applied in almost every area
of analytical and biochemical researches. The introduction of
chemically bonded fused silica capillary
columns was a very recent innovation in gas chromatography,
more commonly referred to high resolution gas chromatography (HRGC).
Every gas chromatograph includes the
following key components: flow controller, a sample introduction device,
column, oven, detectors, and data handling system. A powerful and widely
used combination is to couple a GC to a mass spectrometer (MS) to form a
GC/MS system. A mass spectrometer measures the molecular weight of a
compound to provide data for both quantitation and qualitative
identification. It usually provides greater sensitivity and far more
specificity than most other LC detectors. At GMI,
you will find knowledgeable staff to guide you through proper
instrumentation choice with respect to your application and budget.
In gas
chromatography (GC), the sample is vaporized and injected onto
chromatographic columns and then separated into many components. The elution
is brought about by the flow of an inert gaseous mobile phase. In decent
decade the development of gas chromatographic skill and its applications
have been phenomenal. It has been estimated that as many as 200,000 gas
chromatographs are currently in use throughout the world.
The
carrier gas serves as the mobile phase that elutes the components of a
mixture from a column containing an immobilized stationary phase. In
contrast to most other types of chromatography, the mobile phase dose not
interact with molecules of the analytes.
Carrier
gases, the mobile phase
of GC include helium, argon and nitrogen which are chemically inert. The
stationary phase in gas-solid chromatography is a solid that has a large
surface area at which adsorption of the analyte species (solutes) take
place. In gas-liquid chromatography, a
stationary phase is
liquid that is immobilized on the surface of a solid support by adsorption
or by chemical bonding. Gas chromatographic separation occurs because of
differences in the positions of adsorption equilibria between the gaseous
components of the sample and the stationary phases.
In GC
the distribution ratio is dependent on the component vapor pressure, the
thermodynamic properties of the bulk component band and affinity for the
stationary phase. The equilibrium is temperature dependent. Hence the
importance of selecting the stationary phase of column and column
temperature programming in optimizing a separation.

Why HP / Agilent?
While there is choice in the marketplace it is GMI's opinion that the
simplest, highest value, most rugged / durable choice with least risk and
downtime...ie., lowest cost of ownership is an HP (Hewlett Packard) /
Agilent system.
Historically
speaking:
HP
defined the market.
1965
HP enters the analytical instrumentation field with the acquisition of GC
manufacturer F&M Scientific Corporation of Avondale, Pennsylvania.
The acquisition allows HP to further expand its measuring and testing
expertise into the area of chemical analysis.
1973
HP introduces first microprocessor controlled GC, the 5830.
1976
HP introduces world’s first benchtop GC/MS system, the 5992.
1979
HP introduces fused silica capillary columns for gas chromatography.

1984
HP introduces the 5890,
the best-selling
GC
in history.
1984
HP introduces electronic pneumatics control. EPC
1994
HP introduces first version of ChemStation software.
Simplicity AND horsepower
1995
GMI is incorporated to provide
laboratories alternative service options for instrumentation and a
venue to purchase pre-owned laboratory instrumentation certified to meet
original manufacturer specifications
1996
HP introduces the 5973 MSD.
1997
HP introduces the Micro-ECD for the 6890. The detector incorporates the
first major design changes in any ECD in the last 20 years.
AGILENT leads the pack (still)...
Jun 2005
Agilent introduces the 5975 inert MSD
January 2007
"GMI CERTIFIED" defines value in the "previously experienced"
laboratory instrumentation market.
GMI formally introduces "GMI CERTIFIEDTM"
an industry leading methodology for reconditioning previously owned
laboratory instrumentation AND providing a comprehensive documentation of
work performed to ensure instrument fully meets original specifications and
ships 'defect free'.

January 2005 GMI
introduces inert ion sources for HP / Agilent
mass specs. Superior in sensitivity AND simpler to maintain !
With proprietary modifications GMI can provide superior technology solutions
at a fraction of the price. Call today and find out how.
email: tfagrelius@gmi-inc.com
At
GMI...its instrumental
!
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