Measurement of bulk composition of hydrocarbon groups and individual compounds in automotive spark-ignition fuels is important for quality control as well as ensuring compliance with various governmental regulations. As such, multiple ASTM methods exist for measuring various aspects of automotive fuel samples. Most of the methods are limited in scope to a subset of hydrocarbon groups or specific compounds of interest, meaning that multiple methods are required for typical production control.
During the December 2016 D02 committee meeting ASTM International approved method D8071 for PIONA compound analysis by GC-VUV, known also as the “Standard Test Method for the Determination of Hydrocarbon Group Types and Select Hydrocarbon and Oxygenate Compounds in Automotive Spark-Ignition Engine Fuel using Gas Chromatography with Vacuum Ultraviolet Absorption Spectroscopy Detection (GC-VUV).” The method uses relatively simple instrumentation: a gas chromatograph, a standard 30 m nonpolar column, and a vacuum ultraviolet (VUV) absorption detector.
VUV absorbance exhibits sensitivity to all major hydrocarbon classes that occur in automotive spark-ignition fuels, has a high degree of speciation capability, but also exhibits the intuitive property that species belonging to similar hydrocarbon groups have similar absorption characteristics. The setup procedure is straight-forward, with no pre-column tuning or valve timing adjustments. The ability to perform library searches and deconvolution using the inherently three-dimensional dataset means that the new method can use a wide retention index window, so it is more forgiving of variations in retention times than are methods that rely solely on retention time for compound identification or classification.
Additionally, since the new method can handle co-elution among various species and hydrocarbon classes, analysis is faster since complete chromatographic separation of all components is not necessary. The new method results in a per-measurement information set that would typically require implementation of multiple ASTM methods, while being inherently more robust and production-worthy than the more comprehensive ASTM automotive fuel methods.