BS EN ISO 3071:2020 pdf – Textiles – Determination of pH of aqueous extract

BS EN ISO 3071:2020 pdf – Textiles – Determination of pH of aqueous extract.
1 Scope This document specifies a method for determining the pH of the aqueous extract of textiles. The method is applicable to textiles in any form (e.g. fibres, yarns, fabrics). 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 3696, Water for analytical laboratory use — Specification and test methods 3? Terms? and? definitions For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https://www.iso.org/obp — IEC Electropedia: available at http://www.electropedia.org/ 3.1 pH co-logarithm of the hydrogen ion concentration in an aqueous extract 4 Principle The pH-value of an aqueous extract of a textile is measured electrometrically at room temperature by means of a glass electrode. 5 Reagents All reagents used shall be of recognized analytical grade. 5.1 Distilled or deionized water, of at least grade 3 as defined in ISO 3696, having a pH between 5,0 and 7,5. The pH shall be verified the first time the water is used. If it is not within the specified range, the water shall be redistilled using chemically resistant glassware. Acid or organic matter can be removed by distilling water from a solution of 1 g/l potassium permanganate and 4 g/l sodium hydroxide. Alkalinity (e.g. the presence of ammonia) can be removed by distilling the water from a solution of dilute sulfuric acid. If the distilled water is not grade 3, boil 100 ml of distilled water in a beaker at a moderate rate for (10 ± 1) min and allow the covered beaker to cool to room temperature. 5.2 Potassium chloride solution, 0,1 mol/l, prepared using distilled or deionized water (5.1).
Immerse the electrode several times in the KCl solution used to prepare the extract until the indicated pH-value stabilizes. Decant a portion of the first extract into a beaker, immediately immerse the electrode to a depth of at least 10 mm and stir gently with a rod until the pH-value stabilizes (do not record the pH-value of this solution). Decant the remaining first into another beaker, immediately immerse the electrode, without washing, in the beaker to a depth of at least 10 mm and allow to stand without stirring until the pH-value stabilizes. Record this value as the first measurement. Decant the second extract into another beaker, immediately immerse the electrode, without washing, in the beaker to a depth of at least 10 mm and allow to stand without stirring until the pH-value stabilizes. Record this value as the second measurement. 9 Calculation If the difference between the two pH-values, expressed to the nearest 0,1 pH-units, is greater than 0,2, repeat the procedure with other test specimens. When two valid measurements have been obtained, calculate the mean value. 10 Precision Interlaboratory trials were carried out between nine laboratories measuring seven samples. Statistical analysis was carried out and the following result was obtained: Using KCl solution (5.2) as the extracting solution: Reproducibility limit R = 1,1 pH-units. NOTE The statistical analysis was carried out in accordance with ISO 5725-2. 11 Test report The test report shall include the following information: a) a reference to this document, i.e. ISO 3071:2020; b) the mean pH-value, to the nearest 0,1 pH-units; c) the pH of the extracting solution; d) the temperature of the extracting solution; e) any factor likely to have had an effect on the results, including any resistance to wetting out of the test samples; f) the date of the test.