Dissolved Gas Analysis Essay

1252 Words 5 Pages
1.0 REFERENCES
1.1 Sample Preparation and Calculations for Dissolved Gas Analysis in Water Samples Using a GC Headspace Equilibration Technique, EPA National Risk Management Research Laboratory, RSKSOP-175, Rev.2, May 2004.
1.2 Light Hydrocarbons in Aqueous Samples via Headspace and Gas Chromatography with Flame Ionization Detection (GC/FID), Pennsylvania Department of Environmental Protection Bureau of Laboratories, PA-DEP 3686, Rev.0, April 2012.
1.3 Lange’s Handbook of Chemistry, 14th edition (1992), McGraw Hill.
1.4 Gas Encyclopedia, Air Liquide, online edition (2009).
2.0 SCOPE AND APPLICATION
2.1 Samples reported using this procedure reference the sample preparation SOP commonly referred to as “RSK-175” for use in West Virginia. The
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Analytes are detected using a Flame Ionization Detector (FID). The amount of gas in the original liquid sample is directly proportional to the amount of gas in the headspace of a closed vessel.
3.2 Standards are prepared by saturating a solution of water with the gases, and making dilutions from that stock.
4.0 INTERFERENCES
4.1 Since these compounds are highly volatile, care must be taken during sampling to prevent agitation, creation of bubbles or headspace during storage. Transfer all samples quickly to the sampler vials while still cold, if possible.
4.2 Results are dependant on the headspace sampler conditions remaining constant.
4.3 Studies have not been done to determine the effect of differing matrices (chlorination, salinity) on solubility of the gases in this procedure. It should have little effect as the gases have a low partition coefficient.
4.4 Methane is a common contaminate and occurs naturally in the atmosphere. Analysis of a blank proves that the system is not
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Each gas is prepared and calibrated separately.
8.3 The chromatography software performs all calculations for determining the calibration model (or fit). Average calibration factor represents the slope of the line between the response for each standard and the origin.
8.3.1 The variation over the range of the calibration must be less than or equal to 20% Relative Standard Deviation (RSD) to be considered linear.
8.3.2 Linear calibration using a least squares regression can also be used. The “goodness of fit” of the linear regression, given as r2 by the software, must be greater than or equal to 0.995.
8.4 Verify the calibration curve with an independent standard for each gas. The second source ICV must be within 20% of its expected value for each analyte.
8.5 Also examine the calculated value of the lowest calibration standard (MRL). This step is used to ensure analytes can be accurately reported at the quantitation limit or to demonstrate bias in the calibration model. If the value exceeds 50% of the expected value, inspect the curve for proper values, proper integration and identification, or ensure proper standards were

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