ASTM D5599 Determination of Oxygenates in Gasoline
ASTM D5599 Standard Test Method for Determination of Oxygenates in Gasoline by Gas Chromatography and Oxygen Selective Flame Ionization Detection
7. Apparatus
7.1 Gas Chromatograph - Any gas chromatograph can be used having the following performance characteristics:
7.1.1 Column Temperature Programmer - The chromatograph must be capable of reproducible linear temperature programming over a range sufficient for separation of the components of interest.
7.1.2 Sample Introduction System - Any system capable of introducing a representative 0.1 to 1.0-µL liquid sample into the split inlet device of the gas chromatograph. Microlitre syringes, autosamplers, and liquid sampling valves have been used successfully. The split injector should be capable of accurate split control in the range from 10:1 to 500:1.
7.1.3 Carrier and Detector Gas Control - Constant flow control of carrier and detector gases is critical to optimum and consistent analytical performance. Control is best provided by the use of pressure regulators and fixed flow restrictors. The gas flow rates are measured by any appropriate means. The supply pressure of the gas delivered to the gas chromatograph must be at least 70 kPa (10 psig) greater than the regulated gas at the instrument to compensate for the system back pressure. In general, a supply pressure of 550 kPa (80 psig) will be satisfactory.
7.2 OFID Detector System, consisting of a cracking reactor, methanizer, and FID. A schematic of a typical OFID system is shown in Fig. 1.
7.2.1 The detector must meet or exceed the typical specifications given in Table 1 of Practice E 594 while operating in the normal FID mode as specified by the manufacturer.
7.2.2 In the OFID mode, the detector shall meet or exceed the following specifications: (a) equal to or greater than 103 linearity, (b) less than 100-ppm mass oxygen (1-ng O/s) sensitivity, (c) greater than 106 selectivity for oxygen compounds over hydrocarbons, (d) no interference from coeluting compounds when 0.1 to 1.0-µL sample is injected, (e) equimolar response for oxygen.
7.3 Column - A 60-m by 0.25-mm inside diameter fused silica open tubular column containing a 1.0-µm film thickness of bonded methyl silicone liquid phase is used. Equivalent columns which provide separation of all oxygenates of interest may be used.
7.4 Integrator - Use of an electronic integrating device or computer is required. The device and software should have the following capabilities:
7.4.1 Graphic presentation of the chromatogram,
7.4.2 Digital display of chromatographic peak areas,
7.4.3 Identification of peaks by retention time,
7.4.4 Calculation and use of response factors, and
7.4.5 Internal standard calculation and data presentation.
8. Reagents and Materials
8.1 Purity of Reagents - Reagents grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall 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.
8.2 Calibrant Materials - The following compounds may be used for calibrating the detector: methanol, ethanol, n-propanol, iso-propanol, n-butanol, tert-butanol, sec-butanol, iso-butanol, tert-pentanol, methyl tert-butylether (MTBE), tert-amylmethylether (TAME), ethyl tert-butylether (ETBE), di-iso-propylether (DIPE). (Warning - These materials are very flammable and may be harmful or fatal when ingested, inhaled, or allowed to be absorbed through the skin.)
8.3 Internal Standard - Use one of the compounds listed in 8.2 that is not present in the sample. If all of the materials in 8.2 are likely to be present in the test sample, use another organic oxygenate of high-grade purity that is separated from all other oxygenates present (for example, 1,2-dimethoxyethane).
8.4 Dopant - If the OFID is so designed, reagent-grade pentane is used as a hydrocarbon dopant for the cracking reactor. (Warning - Pentane is extremely flammable and harmful when inhaled.)
8.5 Instrument Gases - The gases supplied to the gas chromatograph and detector are:
8.5.1 Air, zero grade. (Warning - Compressed air is a gas under high pressure and supports combustion.)
8.5.2 Hydrogen, pure grade, 99.9 mol %. (Warning - Hydrogen is an extremely flammable gas under high pressure.)
8.5.3 Helium or nitrogen as column carrier gas, 99.995 mol % minimum purity, or a blend of 95 % helium/5 % hydrogen, depending on the instrument's manufacturer. (Warning - Helium and nitrogen are compressed gases under high pressure.)
8.5.4 Additional purification of the carrier, air, and hydrogen is recommended. Use molecular sieves, Drierite, charcoal, or other suitable agents to remove water, oxygen, and hydrocarbons from the gases.
8.6 Sample Container - Glass vials with crimp on or screwdown sealing caps with self-sealing polytetrafluoroethylene (PTFE)–faced rubber membranes are used to prepare calibration standards and samples for analyses.
