ASTM D4815 for elements in gasoline by gas chromatography
ASTM D4815 Standard Test Method for Determination of MTBE, ETBE, TAME, DIPE, tertiary-Amyl Alcohol and C1 to C4 Alcohols in Gasoline by Gas Chromatography
6. Apparatus
6.1 Chromatograph - While any gas chromatographic system, which is capable of adequately resolving the individual ethers and alcohols that are presented in Table 1, can be used for these analyses, a gas chromatographic instrument, which can be operated at the conditions given in Table 2 and has a column switching and backflushing system equivalent to Fig. 1, has been found acceptable. Carrier gas flow controllers shall be capable of precise control where the required flow rates are low (see Table 2). Pressure control devices and gages shall be capable of precise control for the typical pressures required.
6.1.1 Detector - A thermal conductivity detector or flame ionization detector can be used. The system shall have sufficient sensitivity and stability to obtain a recorder deflection of at least 2 mm at a signal-to-noise ratio of at least 5 to 1 for 0.005 volume % concentration of an oxygenate.
6.1.2 Switching and Backflushing Valve - A valve, to be located within the gas chromatographic column oven, capable of performing the functions described in Section 11 and illustrated in Fig. 1. The valve shall be of low volume design and not contribute significantly to chromatographic deterioration.
6.1.2.1 Valco Model No. A 4C10WP, 1.6-mm (1/16-in.) fittings. This particular valve was used in the majority of the analyses used for the development of Section 15.
6.1.2.2 Valco Model No. C10W, 0.8-mm (1/32-in.) fittings. This valve is recommended for use with columns of 0.32-mm inside diameter and smaller.
6.1.2.3 Some gas chromatographs are equipped with an auxiliary oven, which can be used to contain the valve and polar column. In such a configuration, the nonpolar column is located in the main oven and the temperature can be adjusted for optimum oxygenates resolution.
6.1.3 An automatic valve switching device must be used to ensure repeatable switching times. Such a device should be synchronized with injection and data collection times.
6.1.4 Injection System - The chromatograph should be equipped with a splitting-type inlet device if capillary columns or flame ionization detection are used. Split injection is necessary to maintain the actual chromatographed sample size within the limits of column and detector optimum efficiency and linearity.
6.1.4.1 Some gas chromatographs are equipped with on-column injectors and autosamplers, which can inject small samples sizes. Such injection systems can be used provided that sample size is within the limit of the column and detectors optimum efficiency and linearity.
6.1.4.2 Microlitre syringes, automatic syringe injectors, and liquid sampling valves have been used successfully for introducing representative samples into the gas chromatographic inlet.
6.2 Data Presentation or Calculation, or Both:
6.2.1 Recorder - A recording potentiometer or equivalent with a full-scale deflection of 5 mV or less can be used to monitor detector signal. Full-scale response time should be 1 s or less with sufficient sensitivity and stability to meet the requirements of 6.1.1.
6.2.2 Integrator or Computer - Means shall be provided for determining the detector response. Peak heights or areas can be measured by computer, electronic integration, or manual techniques.
6.3 Columns, Two as Follows:
6.3.1 Polar Column - This column performs a preseparation of the oxygenates from volatile hydrocarbons in the same boiling point range. The oxygenates and remaining hydrocarbons are backflushed onto the nonpolar column in 6.3.2. Any column with equivalent or better chromatographic efficiency and selectivity to that described in 6.3.1.1 can be used. The column shall perform at the same temperature as required for the column in 6.3.2, except if located in a separate auxiliary oven as in 6.1.2.3.
6.3.1.1 TCEP Micro-Packed Column, 560 mm (22 in.) by 1.6-mm (1/16-in.) outside diameter by 0.76-mm (0.030-in.) inside diameter stainless steel tube packed with 0.14 to 0.15 g of 20 % (mass/mass) TCEP on 80/100 mesh Chromosorb P(AW). This column was used in the cooperative study to provide the precision and bias data referred to in Section 15.
6.3.2 Nonpolar (Analytical) Column - Any column with equivalent or better chromatographic efficiency and selectivity to that described in 6.3.2.1 and illustrated in Fig. 2 can be used.
6.3.2.1 WCOT Methyl Silicone Column, 30-m (1181-in.) long by 0.53-mm (0.021-in.) inside diameter fused silica WCOT column with a 2.6-µm film thickness of cross-linked methyl siloxane. This column was used in the cooperative study to provide the precision and bias data referred to in Section 15.
7. Reagents and Materials
7.1 Carrier Gas - Carrier gas appropriate to the type of detector used. Helium has been used successfully. The minimum purity of the carrier gas used must be 99.95 mol %.
7.2 Standards for Calibration and Identification - Standards of all components to be analyzed and the internal standard are required for establishing identification by retention time as well as calibration for quantitative measurements. These materials shall be of known purity and free of the other components to be analyzed. (Warning - These materials are flammable and can be harmful or fatal if ingested or inhaled.)
7.3 Methylene Chloride, used for column preparation, reagent grade, free of nonvolatile residue. (Warning - Harmful if inhaled. High concentrations may cause unconsciousness or death.)
