API MPMS 22.6:2015 pdf free download.Manual of Petroleum Measurement Standards Chapter 22.6 Testing Protocol for Gas Chromatographs
6.2.3 Verification GC A GC separate from the units under test shall be used to verify the composition of each of the calibration gases and test gases before tests of any GC begin under this testing protocol. This “verification GC” may also be used to check the gas compositions during testing. The verification GC shall be capable of analyzing all components listed in the certificate of analysis of the calibration gases and test gases, without reporting listed components as combined fractions. The verification GC should be one in which the investigator has confidence and prior record of good performance, such as a GC that has been utilized in an interlaboratory comparison to identify and eliminate biases. The verification GC shall be calibrated on a different gas blend than the gas blend(s) used to calibrate the GCs under test, preferably on a gas blend from a different supplier, so as to establish a separate traceability chain. If any discrepancy is observed in the compositions of the calibration or test gases, another GC (such as one of the test units) shall be used to confirm that the discrepancies are in the gas blend certificate of analysis, and not with the verification GC.
6.2.4 Equipment Cleaning and Leak Testing Before tests begin, the manifold and other equipment used to transfer gases to the GCs shall be cleaned with reagent-grade acetone or shall be steam cleaned. The equipment shall then be leak-tested with helium before first use. A thermal conductivity detector (TCD) or similar gas leak detector should be used to check system integrity during leak tests. Checks should ensure that each test GC is venting helium to atmosphere, and that its discharge pressure is equal to ambient atmospheric pressure.
6.2.5 Carrier Gas Analysis After equipment cleaning is complete, and before tests are performed, each GC shall be used to analyze a sample of the carrier gas supply to be used with the GC. The carrier gas analysis should produce a flat baseline, except for any expected valve switching effects. A successful carrier gas analysis from each test GC may be used as a baseline chromatogram for comparison with later test results. If the carrier gas is a gas other than nitrogen, the appearance of nitrogen in the carrier gas analysis may indicate an air leak in the manifold or test installation.
If leaks have been eliminated, yet nitrogen or other contaminants appear after repeated system purges, the carrier gas supply shall be analyzed as an unknown gas using the verification GC and a separate carrier gas supply. If contaminants are found in the suspect carrier gas supply, that supply shall be replaced.
6.2.6 Test Gases and Calibration Gases Certified test gases shall be used to evaluate the performance of each GC. Multiple test gas blends are required for mandatory baseline (ideal condition testing) and mandatory non-ideal condition testing to evaluate the response of the GCs at different component concentrations, as well as the measurement error, repeatability and response linearity of the GCs.
The test gases shall be chosen to represent gas compositions that the GCs are expected to analyze in actual use. Test gas compositions should also consider each GC’s lower limit of detection for components of interest. Users are encouraged to consult with the GC manufacturer to determine the limits of detection for components of interest. Calibration gas blends separate from the test gas blends shall be used for GC calibration. Each component in a GC calibration gas shall have a concentration between one-half and twice its concentration in the test gases to be analyzed. If necessary, more than one calibration gas shall be used to meet this requirement for all test gases.
The calibration gas blend for the verification GC should be obtained from a different supplier than the test gas so as to establish a separate traceability chain and eliminate possible biases related to the blend supplier.API MPMS 22.6 pdf download.API MPMS 22.6:2015 pdf free download
