Gow-Mac 400 Series, Operating Manual

Page: 36 / 64

GOW-MAC Instrument Co. Series 400 / 402 Gas Chromatograph Operating Manual
May 2017, Rev. 7
36
Corrosion Resistance of Hastelloy to Some Common Chemicals
Excellent Slow Attack Not Recommended
Acetic Acid Bromine Gas Fluorine
Amines Chlorine (wet) Hydrofl uoric Acid
Ammonia Hydrochloric Acid Hydrofl uoride
Chlorine (dry) Nitric Acid
Formic Acid Phosphoric Acid
Hydrogen Chloride (dry)
Hydrogen Sulfi de
Phosgene
Sulfur Dioxide
6.4 Gas Sample Valve
The gas sample valve is used to introduce gas samples into the chromatograph on a
reproducible basis. The sample may be taken from a static system or from a fl owing system.
Valves are also used for column back-fl ush, column selection, sample selection and detector
switching.
Since the most common use of the valve is for sample introduction, only that application will
be discussed here in general terms. The valve may be installed in place of, or in series with
the injection port. The valve may be permanently connected to a sample source or the sample
may be passed through by means of a pump or other sample container.
The size of the sample loop is fi xed but can be easily changed (see below).
The valve is fi rst placed in the counter clockwise (CCW) position, that is, the valve handle is
as far counter clockwise as it will go. At this time, the sample is purged through the loop and
the carrier gas merely passes through the valve to the column. When the valve handle is
placed in the clockwise (CW) position, the carrier gas purges the sample from the loop and
carrier it through the column. The valve is then returned to the CCW position.
NOTE
&
The sample is released to atmosphere in either valve
position.
Care must be exercised to allow suffi cient time for the sample loop to be fi lled with the sample
before injection. This is easily calculated from the carrier gas fl ow and size of the sample loop.
The same holds true for time allowed for the sample to enter the column.
6.5 Sample Loops
A. Sizes
Sampling valves are supplied with a 2 mL loop if not otherwise specifi ed on the order.
Other sample loops are available, including: 0.25 mL, 0.50 mL, 1.0 mL, 2.0 mL, 3.0 mL,
4.0 mL, 5.0 mL, 10.0 mL, and 20.0 mL.