ISO 6588-2:2020 specifies a method for the determination of the pH-value defined by the electrolytes extractable by hot water from a sample of paper, board or pulp.

This document is applicable to all kinds 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. 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 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 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 can be that given in IEC 60554-2^[4].