ISO/DIS 11265:2024(en)

ISO TC 190/SC 3/WG 14

Secretariat: DIN

Date: 2024‑08-05

Environmental solid matrices — Determination of the specific electrical conductivity

© ISO 2024

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of the requester.

ISO copyright office

CP 401 • Ch. de Blandonnet 8

CH-1214 Vernier, Geneva

Phone: +41 22 749 01 11

Email: copyright@iso.org

Website: www.iso.org

Published in Switzerland

Contents

Foreword iv

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Principle 1

5 Reagents 1

6 Apparatus and glassware 2

7 Laboratory sample 2

8 Procedure 2

8.1 Extraction 2

8.2 Checking of the cell constant 3

8.3 Measurement of the electrical conductivity of the filtrates 3

9 Interferences 3

10 Repeatability 4

11 Test report 4

Annex A (informative) Results of an interlaboratory trial for the determination of the specific electrical conductivity of soils 5

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.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

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. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical and physical characterization.

This second edition cancels and replaces the first edition (ISO 11265:1994), which has been technically revised.

The main changes compared to the previous edition are as follows:

— change of temperature criteria during extraction.

— merger with CEN/TS 15937

— the distinction between solid and sludge like matrices is added.

Annex A of this International Standard is for information only.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Environmental solid matrices — Determination of the specific electrical conductivity

This International Standard specifies an instrumental method for the routine determination of the specific electrical conductivity in an aqueous extract of soil, sludge, biowaste and waste. The determination is carried out to obtain an indication of the content of water-soluble electrolytes in a sample.

This International Standard is applicable to all types of air-dried samples of soil, sludge, biowaste and waste.

The following documents are referred to in the text in such a way that some or all 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 7888:1985, Water quality — Determination of electrical conductivity

ISO 11464:2006, Soil quality — Pretreatment of samples for physico-chemical analysis

EN 15002, Characterization of waste — Preparation of test portions from the laboratory sample

EN 16179, Sludge, treated biowaste and soil — Guidance for sample pretreatment

No terms and definitions are listed in this document.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

Air-dried solids are extracted with water at 22 °C ± 3 °C at an extraction ratio of 1:5 (m/V), to dissolve the electrolytes. The specific electrical conductivity of the extract or fresh liquid sludge is measured and the result is corrected to a temperature of 25 °C.

NOTE For definitions of the concepts used, see ISO 7888.

Use only reagents of recognized analytical grade.

5.1 Water, demineralized, with a specific electrical conductivity not higher than 0,2 mS/m at 25 °C.

5.2 Potassium chloride solution, c(KCl) = 0,1 mol/l.

Dissolve 7,456 g of potassium chloride, previously dried for 2 h at 105 °C ± 5 °C in water (5.1), and dilute to 1 000 ml at 20 °C. The specific electrical conductivity of this solution is 1 288 mS/m at 25 °C.

5.3 Potassium chloride solution, c(KCl) = 0,020 0 mol/l.

Pour 200,0 ml of the potassium chloride solution (5.2) into a 1 000 ml volumetric flask and dilute to volume with water at 20 °C. The specific electrical conductivity of this solution is 277 mS/m at 25 °C.

5.4 Potassium chloride solution, c(KCl) = 0,010 0 mol/l.

Pour 100,0 ml of the potassium chloride solution (5.2) into a 1 000 ml volumetric flask and dilute to volume with water at 20 °C. The specific electrical conductivity of this solution is 141 mS/m at 25 °C.

All the potassium chloride solutions (5.2, 5.3 and above) used for calibration shall be stored in tightly sealed bottles which do not release sufficient alkali or alkali-earth cations to affect the electrical conductivity of the solutions.

NOTE 1 Plastics bottles may be suitable.

NOTE 2 For bottles containing potassium chloride solutions, plastics seals are recommended as glass will weld to the bottle.

NOTE 3 The use of commercially available conductivity standards is permitted.

6.1 Conductivity meter, fitted with a conductivity cell, equipped with an adjustable measuring range setting and (automatic) temperature correction and having an accuracy of 1 mS/m at 20 °C. Preferably, the conductivity meter should also be equipped with a cell-constant control.

6.2 Analytical balance, with an accuracy of at least 0,01 g.

6.3 Thermometer, capable of measuring to the nearest 0,1 °C.

6.4 Shaking machine, with a horizontal movement sufficiently vigorous to produce and maintain a 1:5 soil: water suspension, placed in a environment where the temperature adjusted is maintained at (22 ± 3) °C.

NOTE Machines with a speed of about 180 cycles per minute and a stroke of about 5 cm have been found suitable.

6.5 Filter paper, with low ash and high retentive properties.

6.6 Shaking bottle, of capacity 250 ml, made of plastics (e.g., polyethylene or polypropylene).

NOTE Borosilicate glass bottles can be used.

6.7 Usual laboratory glassware.

This determination can be performed on dried and un-dried samples.

Pretreat samples according to e.g., ISO 11464, EN 15002 or EN 16179 as appropriate.

NOTE For biowaste samples with particles > 10 mm reference is made to EN 13038.

Use the fraction of particles smaller than 2 mm of air-dried soil samples pretreated according to ISO 11464.

Depending on the origin, nature and appearance of the sample different procedures stated in e.g. EN 15002 or EN 16179 can be used:

Solid (bio)waste samples shall be comminuted and reduced to a particle size less than 2 mm. The drying temperature of the air-drying shall not exceed 40 °C.

Liquid samples with a solid content of less than 200 g/L shall be filtered before measurement.

Foreign bodies or non comminutable material (as metallic parts such as nuts, blots, scrap) should be separated from the sample and the weight and nature of the material recorded.

Weigh 20,0 g of the laboratory sample and transfer to a shaking bottle (6.6). For soil, a minimum of 5,0 g of pretreated laboratory sample, shall be used.

Add 100 ml of water (5.1), or less with respecting the ratio 1:5 (m/V), at a temperature of 22 °C ± 3 °C. Close the bottle and place it in a horizontal position in the shaking machine (6.4). Shake for 30 min. Immediately after shaking, filter through a filter paper (6.5).

Liquid samples shall be filtered directly through a filter paper (6.5).

NOTE 1 The volume of filtrate should be just sufficient to perform the measurements.

NOTE 2 An extraction ratio of 1:5 (m/V) is chosen to ensure that an extract is obtainable from all solids including those with high organic matter contents. Using a smaller ratio, it is hardly possible to obtain an extract for some solids. The Horizontal study [2] showed no significant differences between extraction times of 30 minutes and 3 hours.

NOTE 3 The extraction should be performed at the chosen temperature of 22 °C ± 3 °C, because the solubility of the salts present depends on the temperature. After the filtration, the temperature of the extract is allowed to change. . In automation, settling instead of filtration can be used if the laboratory proves that comparable results are obtained. E.g. acceptable results were obtained with 1 min vigorous stirring, then 30 min settling followed by gentle stirring and measurement, or alternatively with 15 min stirring, then 15 min settling followed by measurement.

The measurement result obtained at the measurement temperature is adjusted to 25 °C either by the apparatus or by correction.

Measurement of the blank is carried out to determine the contribution of the water, glassware and filter paper to the electrical conductivity of the extracts.

NOTE 4 The shaking action should be just sufficient to produce and maintain a suspension. More vigorous shaking may lead to excessive dispersion of mineral parts, difficulty in filtration and consequent adverse effects on conductivity (see also note 3).

8.2.1 Measure the conductivity (x_m) of the potassium chloride solutions (5.2 to 5.4) according to the instruction manual of the instrument.

8.2.2 Calculate, for each potassium chloride solution, a cell constant according to

where

Use the average of the calculated values as the cell constant of the instrument.

The calculated cell constant shall not differ by more than 5 % from the value given by the manufacturer.

8.2.3 Adjust the cell constant on the conductivity meter.

Measure the electrical conductivity of the filtrates (x_m) according to the instructions provided by the manufacturer of the conductivity meter (6.1). Carry out the measurements with the temperature corrected to 25 °C. Conversions to the electrical conductivity at 25 °C, can be made using equation:

(1)

where

Note the results to one decimal place, expressed in millisiemens per metre (mS/m).

Carry out a blank determination in the same way. The value of the blank shall not exceed 1 mS/m. If the value of the blank exceeds this, repeat the extraction.

9.1 The measured values of the electrical conductivity can be influenced by contamination of the electrodes.

This type of interference is very difficult to recognize. Pollution of the electrodes may change the cell constant, and this can be perceived by measuring the conductivity of the potassium chloride solutions.

9.2 Air bubbles on the electrodes, for example formed during warming of the extracts, perturb the measurements.

9.3 Measurements of electrical conductivities less than 1 mS/m are influenced by carbon dioxide and ammonia from the atmosphere. In these cases, measurements shall be carried out in an adapted measuring cell. Such measurements are outside the scope of this International Standard.

The repeatability of the electrical conductivity measurements in two separately prepared filtrates shall satisfy the requirements of Table 1.

Table 1 — Repeatability

The test report shall contain the following information:

a) a reference to this International Standard;

b) all information necessary for complete identification of the sample;

c) the results of the determination in whole numbers, expressed in millisiemens per metre;

d) details of any operations not specified in this International Standard or regarded as optional, and any other factors which may have affected the results.

1. EN 13038:1999 - Soil improvers and growing media - Determination of electrical conductivity Horizontal: Desk study to assess the feasibility of a draft horizontal standard for electrical conductivity, Lars Johnsson, S. Ingvar Nilsson and Per Jennische; https://horizontal.ecn.nl/docs/society/horizontal/Hor_desk_15-2_EC-revised.pdf

1. 
   (informative)
   
   Results of an interlaboratory trial for the determination of the specific electrical conductivity of soils

In 1991, an interlaboratory trial was organized by the Wageningen Agricultural University to test the procedure specified in this International Standard.

For this interlaboratory trial. the determination of the specific electrical conductivity of five soils was carried out by 26 laboratories.

The summary of the results of the interlaboratory trials on soil is presented in Table A.1.

The soil samples 1 and 4 mentioned in Table A.1 were collected in salt-affected areas in Hungary. The fifth sample originates from the Netherlands.

The repeatability, r, and the reproducibility, R, given in this table were calculated according to ISO 5725:1986, Precision of test methods — Determination of repeatability and reproducibility for a standard test method by inter-laboratory tests.

Table A.1 — Results of an interlaboratory trial for the determination of the specific electrical conductivity

An interlaboratory trial was performed on the other matrices mentioned in this standard by the Horizontal project in 2008. The outcome of that study was not satisfactory due to the fact that relatively high standard deviations were observed possibly due to the fact that the proposed ratio of sample intake to extraction volume (m/V) of the standard was not in all cases traceable. Additional validation will be sought.