Methods of testing petroleum and associated products Standard test method for the identification of components in automotive gasoline using gas chromatography

This test method is a standard procedure for the determination of paraffins, olefins, naphthenes, aromatics and unknowns (P.O.N.A.U.) in automotive gasolines using gas chromatography and flame ionization detection (GC/FID). Group types greater than or equal to 0.01% by mass are determined by summing individual components.  Individual hydrocarbon components greater than or equal to 0.01% by mass are determined.

Oxygenated components greater than or equal to 0.01% by mass, including alcohols and ethers, may be determined by this test method. See Annex A, Table A2 for example of retention times and response factors for oxygenates at concentrations typically found in automotive gasoline.

This method applies to automotive gasoline, ethanol-blended gasoline and denatured ethanol. Liquefied petroleum gas (LPG), naphtha, reformate, alkylate, blendstocks, and typical petroleum or petrochemical product may also be analyzed, however precision may not apply.

The final boiling point of samples as defined by ASTM D86 should not exceed 225°C, however individual hydrocarbons eluting to nC15 can be determined.

Components such as water which do not elute from the gas chromatograph or which have little or no response in a FID are not determined. The water content can be determined by using ASTM D6304, Procedure A.

The separation of individual hydrocarbons and oxygenated compounds by the procedure described in this test method is not absolute and will result in some peaks that represent coeluting components (see Annex A, Table A2).

Due to the possibility of coeluting peaks, the user is cautioned in the interpretation of the data.

Toluene and 2,3,3-trimethylpentane may coelute. If isooctane (2,2,4-trimethylpentane) and 2,3,4-trimethylpentane are present in the gasoline sample, it is probable that the sample contains 2,3,3-trimethylpentane. The concentration of 2,3,3-trimethylpentane is almost certain to be less than the  concentration of 2,3,4-trimethylpentane. When determining the concentration of toluene and 2,3,3-trimethylpentane, it is essential that the gas chromatographic integrator has individual peak processing capabilities including peak expansion and perpendicular drop. To detect 2,3,3-  and toluene, it is essential for these components to be within a 5:1 ratio of each other with either component having the greater concentration. If these components are present in a greater than 5:1 ratio, the toluene and 2,3,3-trimethylpentane may appear as a coeluted peak, thus causing the component in the smallest concentration to be integrated with the more concentrated component.

Typically forty components with concentrations greater than 1% by mass constitute an average of approximately 80% by mass of automotive gasoline. From these forty components, this method identifies coeluting peaks for toluene, 2-methylhexane, methylcyclopentane and n-hexane (see Annex A, Table A1). The forty components are identified in Table 5 by an asterisk beside its identification number.

The number of coeluting peaks depends on the total number of individual components and the number of olefinic components present. The possibility of coeluting components increases with the increase of components detected after n-octane. Supplementary analytical techniques such as ASTM D1319 for olefins, D5580 and D5769 for aromatic components, D4815 and D5599 for oxygenates may assist in interpretation of data obtained by this method.

The testing and evaluation of a product against this method may require the use of materials and/or equipment that could be hazardous. This document does not purport to address all the safety aspects associated with its use.

Anyone using this method has the responsibility to consult the appropriate authorities and to establish appropriate health and safety practices in conjunction with any applicable regulatory requirements prior to its use.