B - 1
IPN 074-397-P1G
HAPSITE Smart Operating Manual
Appendix B
Calibrating Gas Mixtures
B.1 Acquisition, Preparation, and Handling
The HAPSITE (or any GCMS instrument) must be calibrated at one or more
concentration levels of the organic compound(s) of interest for quantitative analysis
of these target compounds. In the case of the HAPSITE, the target compounds
must be supplied to the instrument as a gaseous mixture of known volume/volume
composition (mole/mole % or ppmv levels in air or nitrogen) and at atmospheric
pressure.
There are a number of important factors to consider where attention to detail is
important in acquiring, preparing, and handling gaseous standard calibration
mixtures. These can be organized in three groups:
1 How to establish the desired concentrations of the required compounds. See
section B.1.1 on page B-1.
2 Correct delivery of the mix to the inlet of the HAPSITE See section B.1.2 on
page B-3.
3 Gas cylinder safety, and contamination checks & corrective
steps in the equipment. See section B.1.3 on page B-5.
B.1.1 How to Establish the Desired Concentrations
There are two basic ways to obtain several concentrations of a given mix of
compounds. The most obvious is to buy the compounds, premixed to specification,
in cylinders containing the several concentrations desired. The second is to buy a
master cylinder of the compounds at the highest concentration needed, and dilute
to the lower concentrations required. Each of these options is discussed below.
B.1.1.1 Using Cylinders Charged with Each Concentration
To perform a calibration, have the known gas mixtures on hand. A gas supplier
(such as Scott Specialty Gases
1
) can provide a choice of cylinder sizes with the
compounds of interest mixed in a suitable matrix at the requisite concentrations.
The matrix (or balance gas) for the mixture should be specified as "VOC-free
Nitrogen" or "VOC-free Air", to minimize the level of background VOC's in the
calibration mix.
1.Scott Specialty Gases: (215) 766-8861
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