ISO-6588-2-2005.pdf

Reference number ISO 6588-2:2005(E) © ISO 2005 INTERNATIONAL STANDARD ISO 6588-2 First edition 2005-05-15 Paper, board and pulps Determination of pH of aqueous extracts Part 2: Hot extraction Papier, carton et pâtes Détermination du pH des extraits aqueux Partie 2: Extraction à chaud ISO 6588-2:2005(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. © ISO 2005 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii © ISO 2005 All rights reserved -,-,- ISO 6588-2:2005(E) © ISO 2005 All rights reserved iii Contents Page Forewordiv Introduction v 1 Scope1 2 Normative references .1 3 Principle.1 4 Reagents2 5 Apparatus and equipment2 6 Sampling and preparation of sample2 7 Procedure.2 8 Calculation.3 9 Precision3 10 Test report4 Annex A (informative) Preparation of some standard buffer solutions5 Bibliography .6 -,-,- ISO 6588-2:2005(E) iv © ISO 2005 All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 6588-2 was prepared by Technical Committee ISO/TC 6, Paper, board and pulps. This first edition of ISO 6588-2, together with ISO 6588-1, cancels and replaces ISO 6588:1981, which has been technically revised. The work within ISO/TC 6 has shown that the results obtained with the two parts of ISO 6588 are equivalent to those obtained in ISO 6588:1981. There are four major differences compared with the previous edition of ISO 6588:1981: a) ISO 6588 has been divided into two parts: one dealing with cold extraction and the other with hot extraction; b) the determination is now carried out on an air-dry sample without determination of dry matter content, as the amount of sample is not critical; c) the extract is filtered; d) a salt solution is added to speed up the measurement. ISO 6588 consists of the following parts, under the general title Paper, board and pulps Determination of pH of aqueous extracts: Part 1: Cold extraction Part 2: Hot extraction -,-,- ISO 6588-2:2005(E) © ISO 2005 All rights reserved v Introduction Kraft fibre is well known to contain ionisable groups that are fixed to or in the fibre wall. In order to fulfil the electro-neutrality, these groups are balanced by an equivalent number of positive charges, which can be either protons or various metal ions. Especially in pulp suspensions at low ionic strengths, this can give rise to a marked uneven distribution of mobile ions between the volume held by the fibre wall and the bulk suspension liquor. This means that the fibre acts as an ion exchanger. These ion-exchange phenomena can be modelled very well with the Donnan theory 2, 3. If a relatively clean pulp fibre sample, as for example bleached dried pulp, is diluted in deionised water, the result will be a pulp suspension with a very low ionic strength. In such a system, most of the cations present, including protons, will be concentrated in the water volume held by the fibre wall. If the pH is measured, it will be measured in the bulk suspension liquor. By adding salt to this kind of system, the ion exchange phenomena will be decreased and the concentration of different cations will be the same in the water held by the fibre wall and in the bulk suspension liquor. Since the process waters always contain a certain amount of ions, such a salt addition will give a more realistic environment when measuring the pH of relatively clean pulp samples. It is necessary to be aware of these effects when interpreting the measured pH-values of highly purified pulps. -,-,- INTERNATIONAL STANDARD ISO 6588-2:2005(E) © ISO 2005 All rights reserved 1 Paper, board and pulps Determination of pH of aqueous extracts Part 2: Hot extraction 1 Scope This part of ISO 6588 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 part of ISO 6588 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 part of ISO 6588 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. ISO 6588-1 differs from this part of ISO 6588 only as regards the extraction conditions. No general guidance can be given as to which of the two procedures (hot or cold) is best suited in a particular situation. For cellulosic papers used for electrical purposes, the method used should be that given in IEC 60554-2 (see 4 in the Bibliography). 2 Normative references The following referenced documents are indispensable for the application 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 3696, Water for analytical laboratory use Specification and test methods ISO 7213, Pulps Sampling for testing 3 Principle Extraction of a sample of 2 g for 1 h with 100 ml of boiling 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. -,-,- ISO 6588-2:2005(E) 2 © ISO 2005 All rights reserved 4 Reagents 4.1 Water, distilled or deionised water shall be used throughout the test. The conductivity of the water must not exceed 0,1 mS/m after boiling for 1 h and cooling in an acid-free atmosphere (e.g. free of CO2, SO2, H2S) to a temperature between 20 °C and 25 °C. The pH of the water should be in the range of 6,8 to 7,3. Instructions for the determination of conductivity are specified in ISO 3696. 4.2 Standard buffer solutions, with known pH-values of about 4, 7 and 9. Such buffer solutions are commercially available. Some examples of suitable buffer solutions are given, and their preparation is described, in Annex A. 4.3 Potassium chloride solution, about 1M. Dissolve about 7,4 g of KCl, analytical grade, in 100 ml of freshly boiled, distilled water. Prepare a fresh solution every week. 5 Apparatus and equipment Use the following, in addition to ordinary laboratory apparatus and equipment. 5.1 Glassware of chemically resistant glass, flasks with ground-glass joints, stoppers, beakers, reflux condenser and fritted glass filter. All glassware shall be cleaned with an acid cleaning solution, without the use of soap or detergent, and they shall be carefully rinsed with water (4.1) and allowed to dry before use. 5.2 pH-meter, fitted with glass and calomel electrodes or with a combined electrode, capable of being read to at least 0,05 pH-unit. 6 Sampling and preparation of sample 6.1 Sampling The sampling procedure to be followed depends on the particular circumstances in each case. If the analysis is being made to evaluate a lot or a consignment of pulp, paper or board, the sample shall be taken in accordance with ISO 7213 or ISO 186, as relevant. If the analysis is made on another type of sample, report the origin of the sample and, if possible, the sampling procedure. Wear clean protective gloves when handling the sample. NOTE Some gloves are powdered to prevent them from sticking to one another, and this powder can cause contamination of the sample. 6.2 Preparation of sample Do not touch the sample with bare hands and ensure that it has been placed only on clean surfaces. Cut or tear the sample into pieces approximately 1 cm2 in size with a clean knife or a cutter. Split samples of heavy board. Mix the pieces thoroughly. Store the pieces in clean, covered containers. 7 Procedure Run the procedure in duplicate. -,-,- ISO 6588-2:2005(E) © ISO 2005 All rights reserved 3 7.1 Weighing Weigh 2,0 g ± 0,1 g of air-dry sample (6.2). 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. 7.2 Extraction Add 100 ml of water (4.1) to a 250 ml flask (5.1) and heat to boiling. Add the weighed sample, attach the reflux condenser (5.1) fitting the flask, and continue boiling gently for 1 h ± 5 min on an electric heater. Cool the flask rapidly to a temperature between 20 °C and 25 °C with the condenser in place. Filter the extract through a coarse, fritted glass filter into a small beaker (5.1). Immediately add 2 ml of potassium chloride solution (4.3) and continue with the measurement. 7.3 Determination of pH Operate the pH-meter in accordance with the manufacturers instruction. Wash the electrodes with water (4.1); 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 (4.2) having pH-values such that the pH of the extract is between the pH-values of the buffer solutions. The first buffer solution should 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 manufacturers manual. A deviation exceeding 0,2 pH-units indicates a faulty electrode. Also a slow but continuous increase or decrease in the reading indicates faulty electrodes. After calibration, rinse the electrode several times with water (4.1) 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 (4.1) to remove any traces of sample or buffer solution. At the end of a series of measurements, check the electrodes with buffer solutions. 8 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. 9 Precision 9.1 Repeatability The pH-values of four different samples were determined in one laboratory according to this part of ISO 6588. Ten determinations were made in each case. Mean values and coefficients of variation for each type of sample are shown in Table 1. -,-,- ISO 6588-2:2005(E) 4 © ISO 2005 All rights reserved Table 1 Repeatability of this method Sample pH Coefficient of variation, % Copy paper 10,0 0,21 Paperboard 8,7 0,64 Bleached pulp 5,2 0,50 Unbleached pulp 8,0 0,54 9.2 Reproducibility The pH-values of four different samples were determined in five different laboratories according to this part of ISO 6588. Mean values and coefficients of variations, for each type of sample, based on the results of five laboratories, are shown in Table 2. Table 2 Reproducibility of this method Sample pH Coefficient of variation, % Copy paper 9,7 2,6 Paperboard 8,5 1,8 Bleached pulp 5,6 9,6 Unbleached pulp 8,0 4,9 10 Test report The test report shall include the following information: a) reference to this part of ISO 6588; b) the date and place of testing; c) all the information necessary for complete identification of the sample; d) the result, expressed as indicated in Clause 8; e) any unusual features observed in the course of the test; f) any departure from the procedure described in this part of ISO 6588, or any other circumstances which may have affected the result. -,-,- ISO 6588-2:2005(E) © ISO 2005 All rights reserved 5 Annex A (informative) Preparation of some standard buffer solutions All the reagents used shall be of recognized reagent grade. The buffer solutions shall be renewed at least once a month. The a