BS ISO 3771:2011 pdf download – Petroleum products — Determination of base number — Perchloric acid potentiometric titration method
1 Scope
This International Standard specifes a method for the determination of basic constituents in petroleum products by potentiometric titration with perchloric acid in glacial acetic acid. The constituents that can be considered to have basic characteristics include organic and inorganic bases, amino compounds, salts of weak acids (e.g. soaps), basic salts of polyacid bases, and salts of heavy metals. The ranges of base number values for which precision values for the method have been established are:
— unused oils: base numbers from 3 to 45;
— additive concentrates: base numbers from 5 to 45;
— used oils: base numbers from 3 to 30. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3696, Water for analytical laboratory use — Specifcation and test methods
3 Terms and defnitions
For the purposes of this document, the following terms and defnitions apply.
3.1 base number w BN quantity of perchloric acid, expressed in terms of the equivalent number of milligrams of potassium hydroxide, required to titrate 1 g of sample dissolved in the specifed solvent to a well-defned infection point, as specifed in this International Standard
4 Principle
The test sample is dissolved in an essentially anhydrous mixture of toluene, acetone and glacial acetic acid, and titrated with a standard volumetric solution of perchloric acid in glacial acetic acid using a potentiometric titrimeter. A combination pH-Ag/AgCl glass electrode (6.2) is used. The meter readings are plotted against the corresponding volumes of titrating solution, and the endpoint is taken as the last infection in the resulting curve.
5 Reagents During the analysis, use only reagents of recognized analytical grade, and water equivalent to Grade 3 of ISO 3696.
5.1 Acetic acid (CH 3 COOH), glacial.
5.2 Acetic anhydride [(CH 3 –CO) 2 O].
5.3 Toluene.
5.4 Acetone.
5.5 Tris (hydroxymethyl)-aminomethane (Tris) (C 4 H 11 NO 3 ).
5.6 Potassium hydrogen phthalate (KHC 8 H 4 O 4 ).
5.7 Tetraethylammoniumbromide 0,4 mol, electrolyte. Use an appropriate non-aqueous electrolyte in the electrode. Tetraethylammoniumbromide (TEABr in ethylene glycol, 0,4 mol/l) is an example of such an electrolyte. In general, follow the manufacturer’s instructions for electrolyte use in the electrode. Prepare a solution (0,4 mol/l) of TEABr in ethylene glycol.
5.8 Lithium chloride (LiCl): electrode manufacturers recommend alternatively a saturated solution of LiCl in ethanol (96 % denatured). Dissolve 70 g LiCl in 500 ml ethanol at ambient temperature, stirring for several hours.
5.9 Titration solvent: add six volumes of toluene (5.3) to three volumes of acetic acid (5.1) to one volume of acetone (5.4).
5.10 Perchloric acid (HCIO 4 ), 0,1 mol/l standard volumetric acetous solution.
5.10.1 A 0,1 mol/l acetic acid perchloric acid mixture may be obtained commercially. If necessary this may be prepared using concentrated perchloric acid (HClO 4 ), acetic acid and acetic anhydride. Perchloric acid is available in different concentrations, the amount of acetic anhydride required depends on the concentration. Three typical possibilities are found in Table 1. When preparing the mixture, initially dissolve the appropriate amount of perchloric acid in 500 ml of acetic acid, add the appropriate amount of acetic anhydride and dilute to 1 l with acetic acid. Store this solution for at least 24 h before standardization. WARNING — This perchloric acid solution is not harmful under the test conditions, but concentrated perchloric acid is a powerful oxidant when dry or heated. Take great care to avoid contact with organic matter under conditions that may result in subsequent drying or heating. Wash spills immediately and thoroughly with water. NOTE Avoid adding excess acetic anhydride to prevent acetylation of any primary or secondary amines which may be present in the sample being tested.
5.10.2 Standardization may be conducted using either tris (hydroxymethyl)-aminomethane (5.5) or potassium hydrogen phthalate (5.6), as described below. Commercially available certifed solutions may be used in place of standardization.