Full Description
This test method is a standard procedure for the determination of paraffins, olefins, napthenes, aromatics and unknowns (P.O.N.A.U.) in automotive gasollines using gas chromatography.
The final boiling point of samples should not exceed that of nC15.
Individual hydrocarbon components or groups of coeluting components greater than or equal to 0.01% by mass are determined.
The separation of individual hydrocarbons by the procedure described in this test method is not absolute and will result in some peaks that represent coeluting compounds (Table 1).
A limitation of the method is that 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 contans 2,3,3-trimethylpentane. The conentration of 2,3,3-trimethylpentane is almost certain to be less than the concentration of 2,3,4-trimethylpentane. When determining the conentration 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-trimethylpentane and toluene, these compounds must be within a 5:1 ratio of each other with either compound 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, this causing the component in the smallest concentration to be integrated with the more concentrated component.
The data obtained from analyzing three hundred and sixty-nine Canadian automotive gasolines were used to develop this test method. These data, excluding toluene and 2,3,3-trimethylpentane, did not indicate the presence of coeluting peaks, which would have a significant influence on the final interpretation of the information.
From the gasolines analyzed, forty compounds with concentrations greater than 1% by mass have been found. These possible forty compounds constitute an average of 79% by mass of automotive gasoline. From these forty compounds which may be found in gasoline, this method identifies coeluting peaks for toluene, 2-methylhexane, methylcyclopentane and n-hexane (Table 1). The forty compounds are identified in Table 5 by an asterisk beside its identification number.
The number of coeluting peaks depends on the total number of individual compounds and the number of olefinic compounds present. The possibility of coeluting compounds increases with the increase of compounds detected after n-octane.
Oxygenated compounds may be determined by this test method. To analyze for oxygenated compounds, insert oxygenated compounds of interest (Table 2) in the hydrocarbon data table (Table 5). Due to the possibility of coeluting peaks in other areas, the user is cautioned in the interpretation of the data.
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.
