5.1 Blends of fuel ethanol and hydrocarbon have a limited solvency for water that is dependent upon temperature and the ratio of ethanol to hydrocarbon. Good handling practices are important during the blending, storage, and transportation of fuel to avoid water contamination. High concentrations of water can cause haze or phase separation in ethanol and hydrocarbon blends and lead to freezing problems at low temperatures. Water has also been associated with corrosion and filter plugging.

1.1 This test method covers the determination of water from 0.05 % to 5.0 %  by mass in blends of ethanol, hydrocarbon, and corresponding blends. It is intended for measuring water content of gasoline or other hydrocarbon blendstock, denatured fuel ethanol as cited in Specification D4806, and ethanol fuel blends such as those cited in Specification D5798 and Practice D7794. This test method is not applicable to samples that are phase separated.

1.1.1 Procedure A—For measurement of water up to 2 % by mass in ethanol and hydrocarbon blends using coulometric Karl Fischer titration. This is the referee method for samples containing up to 2 % ethanol.

1.1.2 Procedure B—For measurement of water up to 5.4 % by mass in ethanol and hydrocarbon blends using volumetric Karl Fischer titration.

1.2 This method measures mass percent water and allows for the alternative reporting of volume percent. This test method recommends the use of pyridine-free reagents.

1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 8.