Gow-Mac 580 series, Operating Manual

Page: 38 / 68

GOW-MAC Instrument Co. 38
C. Sampling Corrosive Materials
When dealing with harsh samples, such as chlorine gases and wet acid, valves made of Tantalum
or Hastelloy C-276 are recommended.
Corrosion Resistance of Tantalum
to Some Common Chemicals
Excellent Slow Attack Not Recommended
Sulfuric Acid Strongly alkaline Hydofl uoric acid
Hydrochloric acid compounds Fluorine gas
Nitric Acid
All organic corrosive chemicals
Corrosion Resistance of
Hastelloy C-276 to Some Common Chemicals
Excellent Good 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
D. Gas Sampling 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 stream. Valves are also
used to back-fl ush column, column selection, sample selection and detector switching.
Since the most common use of the valve is for sample injection, 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 changed easily. (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 carries it
through the column. The valve is then returned to the CCW position.
NOTE
)
The sample is released to atmosphere in either valve position.