BS ISO 6588-1:2021 pdf download – Paper, board and pulps — Determination of pH of aqueous extracts Part 1: Cold extraction
This document specifies a method for the determination of the pH-value defined by the electrolytes extractable by cold water from a sample of paper, board or pulp. This document is applicable to all types of paper, board and pulp.
As the quantity of extractable ionic material approaches zero, as in the case of highly purified pulps, the precision of the method becomes poor because of the difficulties encountered in making pH measurements on water containing little electrolytic material. Since the extraction in this document is performed with distilled or deionised water, the pH‑value measured can sometimes be different (e.g. for fully bleached pulp) from the pH‑value measured under mill process conditions, in which various types of process waters, such as chemically treated river water containing electrolytes, are used.
In such cases, ISO 29681 can be used instead, as it is specifically applicable to bleached pulps from virgin fibres and to pulp samples having a low ionic strength for which the pH value gives more realistic results related to mill conditions than those obtained with this document. For cellulosic papers used for electrical purposes, the method used can be that given in IEC 60554‑2 [5] .
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 186, Paper and board — Sampling to determine average quality ISO 7213, Pulps
— Sampling for testing 3? Terms? and? definitions No terms and definitions are listed in this document.
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4 Principle Extraction of a sample of 2 g for 1 h with 100 ml of cold water of high purity. Filtration of the extract and addition of a salt solution. Measurement of the pH‑value of the extract at a temperature between 20 °C and 25 °C.
8.2 Weighing Weigh 2,0 g ± 0,1 g of air‑dry sample (7.2) in a 250 ml flask (6.1). NOTE Since the amount of sample is not critical, there is no need to determine the dry matter content to adjust for minor differences in moisture content.
8.3 Extraction Add 100 ml of water (5.1) to the flask (6.1) containing the sample pieces. Check that all pieces are soaked. Seal the flask with its ground-glass stopper and leave it to stand for 1 h at a temperature between 20 °C and 25 °C. Shake the flask at least once during this time. Filter the extract through a coarse, fritted glass filter into a small beaker (6.1). Immediately add 2 ml of potassium chloride solution (5.3) and continue with the measurement.
8.4 Determination of pH Operate the pH‑meter in accordance with the manufacturer’s instruction. Wash the electrodes with water (5.1); allow the water to drain from the electrodes, but do not wipe them. Calibrate the pH‑meter (6.2), at a temperature between 20 °C and 25 °C, with two different buffer solutions (5.2) having pH‑ values such that the pH of the extract is between the pH-values of the buffer solutions.
The first buffer solution shall be chosen so that the pH‑value of the buffer solution is in the same region as the electric zero point of the pH‑meter (usually = 7). The reading for the second buffer solution should agree with its correct value to within 0,1 pH‑unit. If the pH‑meter fails to show the correct pH‑value for the second buffer solution, consult the manufacturer’s manual. A deviation of, or exceeding, 0,2 pH‑units, rounded to the nearest 0,1 pH unit, indicates a faulty electrode.
In addition, a slow but continuous increase or decrease in the reading indicates a faulty electrode. After calibration, rinse the electrodes several times with water (5.1) and once in a small quantity of the extract. Check that the temperature of the extract is between 20 °C and 25 °C. Immerse the electrodes in the extract. Record the pH when there is no measurable drift, within 30 s. Before measuring the next sample, rinse the electrodes carefully with water (5.1) to remove any traces of sample or buffer solution. At the end of a series of measurements, check the electrodes with the same buffer solutions. The results for both solutions should agree with their correct value to within 0,1 pH unit. Otherwise, repeat the procedure in 8.3.
9 Calculation
Calculate the mean of the duplicate determinations. Report the pH‑value to the nearest 0,1 pH‑unit. The individual results should not differ by more than 0,2 pH‑unit; if they do, repeat the determination with two additional extracts, and report the mean and the range of all measurements.BS ISO 6588-1 pdf download.