ASTM D2163 Standard Test Method for Determination of Hydrocarbons in Liquefied Petroleum (LP) Gases and Propane/Propene Mixtures by Gas Chromatography
8. Preparation of Apparatus
8.1 Set up the instrumentation in accordance with the manufacturer's instructions or as specified herein.
8.2 Install and condition the column according to manufacturer's instructions. See Practice E1510 for recommended installation and conditioning procedures.
8.3 Set the GC instrument to the operating parameters. Allow the instrument to stabilize before proceeding with calibration and sample injections. Typical operating conditions for both PLOT and 100% dimethylpolysiloxane columns are provided in Table 2. The conditions provided for the dimethylpolysiloxane column are equivalent to those described in Test Method D6729.
8.4 Obtain duplicate chromatograms of the standard or sample, or both. Ensure that none of the peaks obtained have exceeded the upper range limit of the data handling device (at full scale on the data handling device, all peaks are on scale and display symmetrical, Gaussian shapes as opposed to flat peak tops). Peak areas of like components shall agree within 2%. Use the same sample size (split ratio) and range for all runs. Example chromatograms are provided in Figs. 1 and 2.
8.5 Liquid Sampling Valve (recommended) - Set valve on and off times to comply with manufacturer's instructions.
8.6 Gas Sampling Valve (optional) - Set valve on and off times to comply with manufacturer's instructions.
8.7 Switching (Backflush) Valve (optional) - The valve rests in the "off" state, allowing a continuous back flush flow through the pre-column. Before or upon injection of the sample, the valve should be rotated to the "on" position so that the pre-column is placed at the head of the flow path from the sample valve. At a time which must be empirically determined and which is dependant upon the length and type of pre-column used, the valve must be returned to the "off" position, causing the flow to back flush through the pre-column and flush to the detector ahead of components eluting from the analytical column. Determining this switch time may require iterative attempts and interpolation. However, once the time has been determined, it should remain repeatable for all samples of similar composition.
9. Calibration and Standardization
9.1 Qualitative - Determine the retention times of components by analyzing known reference mixtures in the same manner as the samples (Section 10). Typical retention times are given in Table 1.
9.2 Quantitative, Hydrocarbons - Use response factors for correction of the detector response of hydrocarbons determined by this test method. Experimental or theoretical response factors may be used.
9.2.1 Experimental Response Factors - Determine the experimental response factor of components by analyzing known calibration mixtures under the same conditions of pressure and temperature as the samples (Section 10). For each component present in the calibration standard, calculate the response factor according to Eq 1. (Note that some integrators or computer data systems may use another formula (inverse of the formula given, in some cases) for calculating response factors.) After determining the response factors for each component, analyze a secondary standard as a sample and verify that the concentrations agree with the values for the standard within the precision and bias for this test method as determined by interlaboratory testing.
RFi = Ci/Ai
where:
RFi = the response factor for component i,
Ci = the known concentration of i, and
Ai = the integrated area of peak i.
9.2.2 Theoretical Response Factors - If the samples to be assayed contain only hydrocarbons and a FID is employed for the determination of those components, then theoretical response factors may be applied. The results shall then be normalized to 100%.
9.2.2.1 Table 3 provides theoretical mass response factors relative to methane (RRF). Use of these response factors will produce results in mass percent units, which may be converted to other units (liquid volume percent or mole percent) by the user as needed. Alternately, the theoretical response factors may be converted to other units prior to quantification. Individually eluting C5 olefins or hexane-plus components, or both, may be quantified using the same RRF as the C5 =/C6+ composite peak.
9.2.2.2 It is necessary to compare calculated results to the certified values for a known standard before adopting the calibration. The standard should contain all of the components typically observed in the samples. Results should agree within 5% of the certified value. Failure to compare may result from lack of injection split linearity or use of a standard that has not been maintained under pressure.
9.3 Quality Monitoring - The primary or secondary standard should be analyzed at least once a week to verify system accuracy, when the test method is in regular use. If the test method is used only occasionally, analyze a primary or secondary standard before each set of analyses.
