BS EN ISO 4045:2018 pdf download – Leather – Chemical tests – Determination of pH and difference figure
This document specifies a method for determining the pH value and the difference figure of an aqueous leather extract. It is applicable to all types of leather.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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 2418, Leather — Chemical, physical and mechanical and fastness tests — Sampling location
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4044, Leather — Chemical tests — Preparation of chemical test samples
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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difference figure
difference between the pH value of a solution and that of its tenfold dilution
Note 1 to entry: The difference figure is a measure of the strength of acids and bases and can never exceed a value of 1. The difference figure amounts to 0,70 to 1,00 when a solution contains a free strong acid (or a free strong base). The ionization of weak acids and bases increases with greater dilution, and therefore the difference figure can only act as a criterion for the presence of free strong acid or base in aqueous extracts with pH values below 4 or above 10.
4 Principle
Preparation of an aqueous extract from a test portion of the leather and measurement of the pH of the extract, using a pH meter. In cases where the pH value obtained is below 4,00 or above 10,00, the pH value of a tenfold dilution of the aqueous extract is also determined.
5 Reagents
5.1 Water, minimum grade 3 in accordance with ISO 3696.
8.2 Calibration of the pH meter Calibrate the pH meter with a minimum of two buffer solutions: at least one below the expected value and at least one above the expected value. Both these buffer readings shall be within 0,02 pH units of the correct reading when the pH meter is standardized.
8.3 Determination of the pH value Ensure that the extract (8.1) is at (20 ± 2) °C. Immediately after stirring, immerse the electrode in the extract solution and determine the pH value with the pH meter (6.2), to the nearest 0,05 pH unit, as soon as a steady reading has been reached. The reading should be taken within 30 s to 60 s. The result of the pH value is either
— the mean value of the two individual determinations, or
— the value for a single sample. The figures shall be given to the nearest 0,05 pH unit.
8.4 Determination of the difference figure If the pH value is below 4,00 or over 10,00, the difference figure shall be determined, except if precluded by the client or specification. For this determination, using the pipette (6.7), transfer 10 ml of the extract solution into the volumetric flask (6.6) and fill up to the mark with water (5.1). Rinse the electrodes with approximately 20 ml of the diluted solution and then measure the pH value, as in 8.3.BS EN ISO 4045 pdf d0wnload.