ASTM D5443 Standard Test Method for Paraffin, Naphthene, and Aromatic Hydrocarbon Type Analysis in Petroleum Distillates Through 200°C by Multi-Dimensional Gas Chromatography
6. Apparatus
6.1 Chromatograph - A gas chromatograph capable of isothermal operation at 130 more or less 0.1°C. The gas chromatograph must contain the following:
6.1.1 A heated flash vaporization sample inlet system capable of operation in a splitless mode.
6.1.2 Associated gas controls with adequate precision to provide reproducible flows and pressures.
6.1.3 A flame ionization detection system optimized for use with packed columns and capable of the following:
Some instruments will produce a non-linear response for benzene, above approximately 5.5 mass %, and for toluene above approximately 15 mass %. The linearity of these components above these concentrations must be verified with appropriate blends. Where non-linearity has been shown to exist, samples, that contain no higher than C13, can be analyzed if the sample is diluted with n-C15 and the instrument is equipped with a prefractionating column. The sample may also be diluted with a component that is not present in the sample and this component will then not be included in the normalized report.
6.2 Sample Introduction System - Manual or automatic liquid sample system operated in a splitless mode. Although this test method is intended primarily for use with syringe sample injection, automatic sampling valves have also been found satisfactory. Devices capable of a reproducible injection volume of 0.1 to 0.5 µL are suitable. The sample introduction system must be capable of heating the sample to a temperature that ensures total sample vaporization. A temperature range of 120 to 180°C has been found suitable.
6.3 Electronic Data Acquisition System - The data acquisition and integration device used for detection and integration must meet or exceed the following specifications:
6.3.1 Capacity for at least 75 peaks for each analysis,
6.3.2 Normalized area percent calculation,
6.3.3 Noise and spike rejection capability,
6.3.4 Sampling rates for fast (<2 s) peaks,
6.3.5 Peak width detection for narrow and broad peaks, and
6.3.6 Perpendicular drop and tangent skimming as required.
6.4 Independent Temperature Control - This test method requires the temperature control of five columns, column switching valves and sample lines. The columns consist of polar, non-polar, Tenax, platinum, and molecular sieve columns. The specifications for these columns are listed in Table 2. The polar column, non-polar column, column switching valves, and sample lines require isothermal operation at a temperature equivalent to the temperature of the gas chromatograph oven. These components may be located in the gas chromatograph oven. The Tenax3 column, platinum column, and molecular sieve column require operation at temperatures other than the gas chromatograph oven temperature. These columns may be temperature controlled by any means that will meet the following specifications:
6.4.1 Ability to control the temperature of the Tenax column within a range from 60 to 280°C, with a tolerance of more or less 5°C at any point. The time required to heat this column between any two points must be no more than 1 min. The time required to cool this column between any two points must be no more than 5 min,
6.4.2 Ability to control the temperature of the molecular sieve column within a range from 100 and 490°C, with a tolerance of more or less 10°C at any point. The time required to heat this column between any two points must be no more than 10 min. The time required to cool this column from 450 to 100°C must be no more than 15 min, and
6.4.3 Ability to control the platinum column within a temperature range of 170 and 350°C. During routine analysis, this column is operated within a temperature range of 170 to 220°C.
7. 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 of the 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 - Extremely flammable gas under high pressure.)
7.1.2 Helium, 99.995 % minimum purity, <0.1 ppm H2O. (Warning - Compressed gas under high pressure.)
7.2 Detector Gases:
7.2.1 Hydrogen, 99.99 % minimum purity. (Warning - Extremely flammable gas under high pressure.)
7.2.2 Air, less than 10 ppm each of total hydrocarbons and water. (Warning - Compressed gas under high pressure.)
7.3 Valve Actuation Gas - This test method permits the use of any type of valve switching or valve actuation. When pneumatic valves are used, air of any grade that will result in no water condensation or will not introduce oil or other contaminates in the switching valves may be used. Air from a piston operated compressor equipped with a water and oil separator has been found suitable. Column switching valves that do not require air to operate do not have this air requirement.
7.4 Columns - Five columns, as described in Table 2. These column specifications are to be considered as guidelines and have been found to be acceptable. Other materials or combinations of materials may also provide acceptable performance. The suitability of each column is determined by test criteria as defined in Section 8.
NOTE 1 - It is not the intention of this test method to include detailed column preparation steps. Columns may be prepared in any way that follows accepted safety practices and results in columns that will meet the performance requirements of Section 9.
7.5 Valves - This test method uses valves for column switching and flow switching. Any commercially available valves may be used that are intended for, or adapted for use in gas chromatography that meet the following specifications:
7.5.1 The column switching valves are generally installed in the gas chromatograph oven. These valves must be capable of continuous operation at the operating temperature of the GC oven.
7.5.2 Materials used in the construction of the valves must be unreactive to hydrocarbons present in the sample under analysis conditions. Stainless steel, PFA, and vespel materials have been found suitable.
7.5.3 Valves must be sized such that they offer little restriction to carrier gas flow under the analysis conditions defined in this test method.
7.5.4 Care must be taken to prevent the introduction of any form of foreign material or contaminant into the valve that may adversely affect its performance.
7.6 Hydrocarbon Test Mixture - A quantitative synthetic mixture of pure hydrocarbons, an example of which is identified in Table 1, is used to tune the instrument analysis conditions and establish that the instrument is performing within specifications. Individual hydrocarbon components, in addition to those listed in Table 1, may be used to aid in the analysis. The concentration level of each component in the hydrocarbon test mixture is not critical as long as the concentration is accurately known. Percentage ranges from 1.0 to 6.0 mass % have been found suitable. Impurities in the individual components may have an adverse effect on the quantitative aspect of the analysis. If an impurity is of the same carbon number and basic molecular structure as the main component itself, it will be correctly grouped and quantitated within the group. As an example, isobutylcyclopentane and isopropylcyclohexane will both be determined as C9 naphthenes. Each of the individual hydrocarbon components used for this test mixture must have a minimum purity level of 99 mol %. Refer to Practice D4307 for instructions on the preparation of liquid blends for use as analytical standards.
7.7 Gas Flows and Pressures:
7.7.1 Carrier Gases:
7.7.1.1 The helium carrier gas through the injection port, polar column, platinum column and molecular sieve column is flow controlled. Flow rates of 16 to 23 mL/min have been found suitable. A helium supply pressure of 620 kDa (90 psi) has been found suitable to meet the helium flow requirement. The helium carrier gas flow will be referred to as the "A" flow within this test method.
7.7.1.2 The helium carrier gas used as the make up gas when the polar column is in stop flow is set to the same flow rate as the helium carrier gas through the injection port.
7.7.1.3 The hydrogen carrier gas flow through the Tenax column and non-polar column is flow controlled. Flow rates of 12 to 17 mL/min have been found suitable. A hydrogen supply pressure of 517 kDa (75 psi) has been found suitable to meet the hydrogen flow requirements. The hydrogen carrier gas flow will be referred to as the "B" flow within this test method.
7.7.1.4 The hydrogen flow to the platinum column is flow controlled. Flow rates of 10 to 15 mL/min have been found suitable.
7.7.2 Detector Gases - The flow rates of the air and hydrogen, as oxidant and fuel gases for the flame ionization detector, must be set according to the instrument manufacturer's instructions.
7.7.3 Valve Actuation Gases - Pneumatic valves require air delivery at pressures and flows adequate to ensure correct actuation. When pneumatic valves are used for this test method, air pressure and flow must be provided in accordance with the valve manufacturer's instructions.