ISO 6588-1:2020 pdf download – Paper, board and pulps – Determination of pH of aqueous extracts

03-06-2022 comment

ISO 6588-1:2020 pdf download – Paper, board and pulps – Determination of pH of aqueous extracts
1 Scope
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 will 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, e.g. chemically treated river water containing electrolytes, are used. In such cases, ISO 29681 should 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 will give more realistic results related to mill conditions than those obtained with this document. For cellulosic papers used for electrical purposes, the method used should be that given in IEC 60554-2 [4] .
8.3 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 (5.2), 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.

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