ASTM D2163 Standard Test Method for Determination of Hydrocarbons in Liquefied Petroleum (LP) Gases and Propane/Propene Mixtures by Gas Chromatography
6. Apparatus
6.1 Gas Chromatograph (GC) - Any gas chromatographic instrument provided with a linear temperature programmable column oven. The temperature control must be capable of obtaining a retention time repeatability of 0.05 min (3 s) throughout the scope of this analysis.
6.2 Detector - A flame ionization detector (FID) having a sensitivity of 0.5 ppm (mole) or less for the compounds listed in Table 1 is strongly recommended (see Practice E594).
6.2.1 Other detectors may be used (alone or in series) provided that they have sufficient response, linearity, and sensitivity to measure the components of interest at the concentration levels required.
6.3 Data Acquisition - Any commercial integrator or computerized data acquisition system may be used for display of the chromatographic detector signal and peak area integration. The device should be capable of calibration and reporting of the final response corrected results.
6.4 Sample Introduction - Whether liquid or vapor sampling, the combination of valve injection size and split ratio must be selected such that the required sensitivity is achieved and also that no component concentration in a sample is greater than the detector upper linearity limit.
6.4.1 If capillary columns will be used, then the GC must include a heated splitting type injector that is operated isothermally. Split ratios in the range of 5:1 to 200:1, with a typical value of 100:1, will be used dependent upon the sample injection volume and sensitivity required. If packed columns will be used, then a splitting type injector is not required and a suitable packed inlet port may be used.
6.4.2 Liquid Sampling (recommended) - The GC should be equipped with a liquid sampling valve for introduction of the sample aliquot to the splitting injector. Liquid sampling valves with an internal fixed sample volume between 0.2 to 0.5 µL or a size to provide the minimum detection limits given in 1.1 have been used satisfactorily. The valve shall be rated for at least 1380 kPa (200 psi) above the vapor pressure of the sample at the valve operating temperature. A shut-off valve shall be provided at the exit of the sampling valve waste port. A 2 to 7 µm packed-screen type filter should be provided at the sample inlet port of the sampling valve to remove possible particulate material from the sample. The valve shall provide for a repeatability of at least 2% relative sample volume introduction. The sampling valve shall be located at the GC such that it can be operated at ambient temperature. The use of floating piston sample cylinders is encouraged to minimize or eliminate the volatilization of lighter components into the headspace. Common 80% filled LPG storage cylinders should be pressurized with an inert gas such as helium to facilitate liquid transfer and accurate liquid injections. A minimum pressure of 200 psi above sample vapor pressure is recommended. A pressure gauge may be used to make this determination. Before pressurization, verify that the sample cylinder, transfer lines and valves are rated to safely contain the pressurized sample. It is customary to add a check valve between the helium cylinder and the sample cylinder to prevent contamination in the event the sample cylinder is higher in pressure than the pressurizing cylinder.
6.4.3 Vapor Sampling (optional) - A six-port gas sampling valve or a ten-port sampling/column switching valve with 1.6 mm (1/16 in.) fittings and a 200 µL fixed sampling loop may be provided. This valve shall be contained in a heated enclosure and operated at a temperature above the boiling point of the highest boiling component in the sample. The use of a 2 to 7 µm frit or packed-screen type filter ahead of the sample introduction port is recommended. The valve shall provide for a repeatability of at least 2% relative sample volume introduction.
6.5 Gas Controls - The GC shall be provided with suitable facilities for delivery and control of carrier gas and the detector gases. This will consist of the appropriate tank and downstream regulators and supply tubing as well as the mass or pressure controls for the precise regulation of the instrument operation.
NOTE 1 - Most GC suppliers will provide these devices or recommend the proper supplies.
6.6 Column Series/Reversal Switching Valve - If desired, a multi-port valve mentioned may be used to provide the C5 olefin/C6+ determination for this analysis. The back-flush configuration should be configured according to the manufacturer's recommendations.
6.7 Columns - Condition all columns used according to the manufacturers' suggestions prior to use.
6.7.1 Analytical Column - The recommended analytical column is a 50 m by 0.53 mm (I.D) Na2SO4 deactivated Al2O3 porous layer open tubular (PLOT) column. Relative retention order is dependent upon the deactivation method for the column. (Warning - Specifically test the column to ensure that the column does not adsorb propadiene and butadienes. This condition can exist depending upon the degree of column deactivation.)
6.7.1.1 Routine re-conditioning of the column may be required to maintain column performance.
6.7.1.2 Alternatively, any column(s) that provides the appropriate component separations may be used. Columns (100 m by 0.25 mm (ID) by 0.5 µm film thickness) employed in standard methods Test Method D6729 and CGSB 3.0 No. 14.3 have been successfully used.
6.7.2 Pre-column (optional) - If an initial back flush of the C5 olefins or hexane plus (C6+) components, or both, through the use of the sequence reversal/back flush valve is desired, a second column is required. Any pre-column that provides separation between the components of interest and the composite heavier components may be used. Choices may include lengths of column such as a 10 to 30 m section of 0.53 mm (I.D.) 1 µm film thickness dimethylpolysiloxane or polyethylene glycol capillary column or a 9 to 15 cm section of the same column material as the analytical column or any pre-column that provides the desired retention of C5 olefins, hexanes, and heavier components. This pre-column acts to keep the heavier components away from the analytical column and to back flush the heavier components as a composite peak to the detector for quantitation. A pre-column that also has the ability to retain water and oxygenated hydrocarbon compounds is recommended to keep those materials from entering the analytical column.
7. Reagents and Materials
7.1 Carrier Gases - For carrier gases, it is recommended to install commercial active oxygen scrubbers and water dryers, such as molecular sieves, ahead ofthe instrument to protect the system's chromatographic columns. Follow supplier instructions in the use of such gas purifiers and replace as necessary.
7.1.1 Hydrogen, 99.995% minimum purity, <0.1 ppm H2O. (Warning - Hydrogen is a flammable gas under high pressure.)
7.1.2 Helium, 99.995 % minimum purity, <0.1 ppm H2O. (Warning - These materials are flammable and may be harmful or fatal if ingested or inhaled.)
7.2 Detector Gases:
7.2.1 Hydrogen, 99.99 % minimum purity. (Warning - Hydrogen is a flammable gas under high pressure.)
7.2.2 Air, less than 10 ppm each of total hydrocarbons and water. (Warning - These materials are flammable and may be harmful or fatal if ingested or inhaled.
7.3 Reference Standards:
7.3.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, all reagents should conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
7.3.2 Reference Gas Mixture - Individual and mixed component reference materials are commercially available and may be used to establish qualitative and quantitative calibration. The calibration standard mixture should be gravimetrically prepared, supplied with both gravimetric and calculated volumetric concentrations, and certified. Due to the high partial pressure exerted by methane and ethylene, it is recommended that these components be limited to no greater than 0.2 vol% of the mixture composition. It is strongly recommended that the calibration standards be contained in floating piston cylinders pressurized to at least 1380 kPa (200 psi) above the vapor pressure of the mixture at all times (a constant pressure source is suggested). Common LPG storage cylinders may also be used provided they can be maintained at the required pressure. Liquid mixtures containing levels of each of the analytes listed in Table 1 in a balance of the type of LPG that is being analyzed should be used to calibrate the instrumentation. (Warning - These materials are flammable and may be harmful or fatal if ingested or inhaled.)
7.3.3 Calibration Gas Mixture - A mixture of known composition similar in concentration to the samples being analyzed may be used to monitor precision and accuracy. For liquid sampling, it is strongly recommended that the mixture be contained in floating piston or other cylinders pressurized to at least 1380 kPa (200 psi) above the vapor pressure of the mixture at all times (a constant pressure source is suggested).
