ASTM D7795 Standard Test Method for Acidity in Ethanol and Ethanol Blends by Titration
4. Summary of Test Method
4.1 Samples are purged with nitrogen prior to and during titration for the elimination of carbon dioxide and then a known amount of ethanol or ethanol blend sample is analyzed potentiometrically either using a monotonic or dynamic end point titrant addition, as specified in Test Method A, or by color end point titration, as specified in Test Method B, using a base (NaOH) solution. Acid content is calculated as milligrams of acetic acid per kilogram of sample.
5. Significance and Use
5.1 This test method measures acidity in ethanol or ethanol blends quantitatively. Denatured fuel ethanol may contain additives such as corrosion inhibitors and detergents as well as contaminants from manufacturing that can affect the acidity of finished ethanol fuel. Very dilute aqueous solutions of low molecular mass organic acids, such as acetic acid, are highly corrosive to many metals. It is important to keep such acids at a very low level.
5.2 Acceptable levels of acidity in Ethanol or Ethanol blends can vary with different specifications but in general it is below 200 mg/kg (ppm). Knowledge of the acidity can be required to establish whether the product quality meets specification.
6. Interferences
6.1 Basic solutions will absorb carbon dioxide from the air to produce carbonate ions in the titrant and change the concentration of the titrant. Care should be taken to minimize exposure of basic titrants to the air as much as possible. Verify the concentration of the titrant (standardize the titrant) frequently enough to detect concentration changes of 0.0005 M and especially if prolonged exposure to the air occurs.
6.2 Minimize exposure of the ethanol or ethanol blend samples to the air to avoid contamination by carbon dioxide.
7. Hazards
7.1 Each analyst shall be acquainted with the potential hazards of the equipment, reagents, products, solvents and procedures before beginning laboratory work. Sources of information include: instrument manuals, MSDS, various literature, and other related sources. Safety information should be requested from the supplier. Disposal of waste materials, reagents, reactants, and solvents shall comply with all the laws and regulations from all applicable governmental agencies.
7.2 Ethanol or ethanol blend products are intended for industrial use only.
7.3 The following hazards are associated with the application of this test method and the use of an automatic titrator.
7.3.1 Chemical Hazard:
7.3.1.1 A solution of potassium hydroxide or sodium hydroxide is corrosive and shall be handled with the appropriate personal protective equipment such as gloves, chemical goggles, and lab coat or chemical-resistant apron. Always add the base to water when diluting 50 % NaOH.
7.3.1.2 Ethanol is a flammable and toxic solvent that is used to prepare the lithium chloride electrolyte solution for the reference electrode. When handling a flammable solvent, work in a well-ventilated area away from all sources of ignition.
