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Dirt and residue from the field often plug the syringe and/or needle. Clean the caps of sample vials with a clean compressed air source (not from a can containing difluoroethane) prior to loading the vials into the autosampler tray.Calibration and check standards are made from a certified primary standard manufactured by Airgas.Blanks are run with the calibration standards. Check standards should be placed at a minimum frequency of every twenty samples. Two sets on the front end and two sets at the end of each sample sequence. Prepare analytical run to include four sets of calibration standards.Ensure that applicable steps in the System Maintenance schedule below have been performed prior to initiating an analytical run of samples.The regulator on the nitrogen tank is set to 80psi, P10 to 45psi, air to 60psi, and hydrogen to 80psi. There should be no needle pulse on the gauges. Linear velocities of each gas at the regulator are checked monthly.It is recommended that traps be changed every two years or earlier if the GC detector baseline rises dramatically. Traps on UHP or Ultra Zero grade gas purities last for dozens of cylinders in our application.
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Traps are also employed as an additional step to ensure gas purity.For most cylinders, this means the cylinder should be replaced at no lower than 200 psi remaining. Gas purity is certified down to 10% of the starting pressure. The carrier and standard gas purity in the Robertson GHG Lab meet or exceed all Agilent specifications.CO 2 is analyzed using a Licor-820 infrared gas analyzer with nitrogen carrier gas. N 2O is analyzed with the ECD (350° C) using argon/methane (90/10, P10) as a carrier gas. CH 4 is analyzed with the FID (300 degrees C) using nitrogen as a carrier gas. The CVs of 12-15 atmospheric samples collected in the field and measured with this instrument commonly range between 1-3% for each of the trace gases.ĬH 4 and N 2O are determined by GC after separation on a Porapak Q column (1.8 m, 80/100 mesh) at 80° C. Instrument sensitivity is calculated by the coefficient of variation (CV) and is acceptable when less than 10% for each trace gas analyzed. Each GC is coupled to a Gerstel MPS2XL autosampler with a custom sampling tray using Agilent Chemstation and Gerstel Maestro software, which outputs results to a. The Robertson GHG Lab has two of these instrumental setups for a combined analytical capacity of approximately 50,000 samples (three gases per sample) per sampling season (April through November). Greenhouse gases (N 2O, CH 4, and CO 2) are analyzed simultaneously from a single sample using an Agilent 7890 Gas Chromatograph (GC) equipped with a flame ionization detector ( FID), a 63Ni electron capture detector ( ECD), and a Licor 820 – Infrared Gas Analyzer coupled to the GC via an analog/digital signal transfer. Agilent 7890 Gas Chromatography - Analysis of Greenhouse Gases