Determination of Sulphate in Denatured Ethyl Alcohol by Direct Injection Ion Chromatography and Suppressed Conductivity

In times of skyrocketing gasoline prices, ethanol fuel – mainly derived from the fermentation of sugar cane (in Brazil) and corn (in the USA and Canada) – is a promising renewable high-octane vehicular fuel. A major drawback, however, is the contamination with inorganic salt ions such as chloride, nitrate and sulfate. These ions can affect the engine performance because precipitating salts clog filters fuel injector nozzles. Furthermore, these ions enhance corrosion in the vehicle components in contact with the fuel. Hence there is an urgent need for standards defining quality specification and test methods.

While the analysis of sulphate is specified in a number of ASTM norms, until recently, the ASTM D 4806-06b standard – the specification for denatured fuel ethanol – provided no guidelines for total and potential sulfate.
Recognizing the need for validated methods for quality control, ASTM balloted and approved a sulphate specification for fuel ethanol stipulating a maximum level of sulfate in ethanol of 4 parts per million (ppm). The
corresponding chloride contamination limit in ethanol is proposed at 40 ppm. In this paper a convenient direct injection suppressed ion chromatographic method for determining chloride and sulfate in denatured ethanol
samples is presented. The described method is the subject to the recent ASTM D 7319 and the results obtained fully comply with ASTM D 4806-06c.
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