28. Apparatus
28.1 Headspace Sampler, equipped with an injection loop and a transfer line connected directly to the first column of the gas chromatograph. The sampler must be capable of equilibrating the species of interest in a specific time. The required equilibration time can be minimized by mixing the sample during the equilibration period, and this can be achieved by using a sampler equipped with mechanical shaking.
28.2 Gas Chromatograph, equipped with a bypass valve, an adjustment restrictor, a universal nondestructive thermal conductivity detector (TCD), and a flame ionization detector (FID). The permanent gases H2, O2, and N2 are detected using the TCD, while the FID is used for detection of hydrocarbons and carbon oxides.
28.3 Molecular Sieve, 5 Å PLOT column (30-m by 0.53-mm inside diameter with a film thickness of 50 µm) for the separation of the lighter gases (H2, O2, N2, CH4, and CO).
NOTE 9 - The molecular sieve column used should be able to resolve at the baseline all the gases of interest.
28.4 Carboxen-1006 PLOT Column (30-m by 0.53-mm inside diameter) for the separation of the other compounds (CO2, C2H2, C2H4, C2H6, and C3H8).
NOTE 10 - Packed columns that give adequate peak separation may also be used with this method. In that case, the analytical performance may be somewhat different than that specified in Method C.
28.5 Catalytic Converter, containing powdered nickel installed between the TCD and the FID, for the conversion of CO and CO2 into CH4 for a sensitive recording of the signal by the FID.
28.6 Zero-dead Volume Adapter, for the column connections (0.53-mm inside diameter).
28.7 Headspace Glass Vials, of 20-mL nominal capacity. The exact volume of these vials should be estimated by performing the procedure in accordance with 30.1.
28.8 Crimping System, including crimp head and a decapper head.
28.9 Perforated Aluminum Caps.
28.10 TFE-fluorocarbon Faced Butyl Septa for headspace vials.
28.11 Glass Syringes, 30-mL equipped with three-way plastic stopcocks.
NOTE 11 - The variation in the oil delivery volume of the 30-mL syringes should be verified by the laboratory. The analytical performance of Method C was established with a delivery volume variation of 1.9 % (% RSD over 20 syringes from different batches).
28.12 Needles, 18G1 and 26G 1/2.
28.13 Pressure Regulators, two-stage, with a delivery pressure adjusted at 20.7 Kpa (3 psi) for the cylinders containing the argon and the calibrating gases.
The diagram of the test assembly is shown in Fig. 7 and the instrumental conditions are given in Table 4. The system must be capable of sufficiently separating the component gases at the sensitivity levels in accordance with 11.3 of Method A. An example of the detection limits achieved by one laboratory with a 3-mL injection loop and capillary columns is given in Table 5. Fig. 8 presents a typical chromatogram recorded in accordance with the conditions given in Table 4 for an oil sample collected from an open-breathing transformer with 6.0 % total gas content.
NOTE 12 - The detection limits shown in Table 5 were obtained from the analysis of a dissolved-gas standard of 1 ppm for all gases, except for O2, N2, CO, and CO2, where the concentration was 17, 24, 1.6, and 8.8ppm, respectively. These results were obtained with a headspace sampler coupled with a gas chromatograph of one commercial source; other devices can be used but the analytical performance may be somewhat different than that specified in Method C.
