In times of rocketing gasoline prices, ethanol fuel - mainly derived from the fermentation of sugar cane (in Brazil) and corn (in 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 sulphate.
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 sulphate.
Recognizing the need for validated methods for quality control, ASTM balloted and approved a sulphate specification for fuel ethanol stipulating a maximum level of sulphate in ethanol of four parts per million (ppm).
The corresponding chloride contamination limit in ethanol is proposed at 40ppm.
In this paper a convenient direct injection suppressed ion chromatographic method for determining chloride and sulphate 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.
The determination of inorganic sulphate and chloride in ethanol samples involves the direct injection of 20ul ethanol into the ion chromatograph.
For determining the potential sulphate, 0.5ml of 30% hydrogen peroxide solution is added to 9.5ml of the ethanol sample.
Quantification of the anions was achieved by integration of the resulting peaks compared with an external calibration curve.
The determination of total and potential sulphate and inorganic chloride in fuel ethanol is the subject of ASTM D 7319.
External calibration curves of peak area versus concentration are linear in the range 0.625-50ppm for chloride and 0.25-20ppm for sulphate.
Corresponding correlation coefficients are higher than 0.9998 and the limits of detection for chloride and sulphate are 0.6 and 0.2ppm, respectively.
Even after 1500 ethanol injections containing denaturants and hydrogen peroxide, the analytical unit still provides stable retention times, repeatable peak areas and consistent concentration values.
The excellent repeatability and reproducibility of the applied trichamber MSM II suppressor demonstrates its ruggedness in long-term use.
For all investigated samples, standards and blanks, both mass spectrometric and conductivity detection provide accurate and precise results.
The presented direct injection IC system is solvent compatible and ensures the accurate and precise determination of sulphate and other anions in ethanol samples in full compliance ASTM D 4806-06c.
For a full poster and literature on this application please contact Gemma Clocherty at Metrohm.
