ISO 22719-2008 Water quality - Determination of total alkalinity in sea water using high precision potentiometric titration《水质 用高精度电位滴定仪测定海水总碱度》.pdf

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1、 Reference number ISO 22719:2008(E) ISO 2008INTERNATIONAL STANDARD ISO 22719 First edition 2008-03-15 Water quality Determination of total alkalinity in sea water using high precision potentiometric titration Qualit de leau Dtermination de lalcalinit totale dans leau de mer en utilisant une titratio

2、n potentiomtrique de haute prcision ISO 22719:2008(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes 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 compu

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5、Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT ISO 2008 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 permis

6、sion in writing from either ISO at the address below or ISOs 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 2008 All rights reserv

7、edISO 22719:2008(E) ISO 2008 All rights reserved iiiContents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 4 Principle. 2 5 Apparatus 2 6 Reagents 3 7 Procedure 3 8 Calculation and expression of results 6 Annex A (informative) Theoretical backgroun

8、d and calculation of alkalinity in sea water 9 Annex B (informative) Quality assurance 14 Annex C (informative) Data from a comparability test . 15 Bibliography . 16 ISO 22719:2008(E) iv ISO 2008 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide fede

9、ration 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 commi

10、ttee. 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 accordan

11、ce 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

12、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 22719 was prepared by Technical Co

13、mmittee ISO/TC 147, Water quality, Subcommittee SC 2, Physical, chemical and biochemical methods. ISO 22719:2008(E) ISO 2008 All rights reserved vIntroduction The greenhouse effect, induced by anthropogenic carbon dioxide, CO 2 , in the atmosphere is a serious global environmental issue. A key facto

14、r controlling the concentration of atmospheric CO 2is its absorption into the ocean. Since the volume of ocean water is huge, the change in the oceanic carbonate system from year to year is slight, and it is necessary to measure its components continuously with great precision over a long period. Fu

15、rthermore, the oceanic carbonate system is related to many components such as water temperature, salinity, dissolved oxygen, and nutrient elements. The oceanic carbonate system can be depicted by measuring at least two parameters of four: total inorganic carbon; total alkalinity; fugacity of CO 2 ;

16、and pH of sea water. At the time of publication, it is possible to determine the first two parameters more precisely for subsurface water. Analytical methods for sea water samples, however, require specific conditions and techniques essential to the precise and accurate determination. This Internati

17、onal Standard describes a method for the determination of total alkalinity in sea water with an error of less than 0,1 %. This method is designed to provide international compatibility of accurate data sets on total alkalinity in sea water, which are collected by various communities. Such compatibil

18、ity is the basis for national and international operational observation and monitoring programs of the oceanic carbonate system, as well as individual research work. INTERNATIONAL STANDARD ISO 22719:2008(E) ISO 2008 All rights reserved 1Water quality Determination of total alkalinity in sea water us

19、ing high precision potentiometric titration WARNING Persons using this International Standard should be familiar with normal laboratory practice. This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user to establish a

20、ppropriate safety and health practices and to ensure compliance with any national regulatory conditions. IMPORTANT It is absolutely essential that tests conducted according to this International Standard be carried out by suitably trained staff. 1 Scope This International Standard specifies an open-

21、cell potentiometric titration determination of total alkalinity in sea water. The results are expressed in moles per kilogram of sea water. The method is suitable for assaying oceanic levels of total alkalinity (2 000 mol kg 1to 2 500 mol kg 1 ) for normal sea water of practical salinity ranging fro

22、m 30 to 40. 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 5667-1, Wa

23、ter quality Sampling Part 1: Guidance on the design of sampling programmes and sampling techniques 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 total alkalinity A Tsea water number of moles of hydrogen ion equivalent to the excess of proto

24、n acceptors (bases formed from weak acids with a dissociation constant, K u 10 4,5at 25 C and zero ionic strength) over proton donors (acids with K 10 4,5 ) in 1 kg of sample NOTE This definition is taken from Reference 5. 3.2 practical salinity S sea water the ratio K 15of the electrical conductivi

25、ty of the sea water sample at the temperature of 15C and the pressure of one standard atmosphere, to that of a potassium chloride (KCl) solution, in which the mass fraction of KCl is 32,435 6 10 3 , at the same temperature and pressure NOTE This definition is taken from Reference 6, p. 12, and was f

26、ormulated and adopted by the UNESCO/ICES/SCOR/IAPSO Joint Panel on Oceanographic Tables and Standards, Sidney, B.C., Canada, September 1-5, 1980, and endorsed by those international bodies. As a ratio, the practical salinity has no unit. ISO 22719:2008(E) 2 ISO 2008 All rights reserved4 Principle A

27、known amount of sea water is placed in an open cell where it is titrated in a two stage procedure with a solution of hydrochloric acid. The acid solution also contains sodium chloride to compensate for the sodium ion concentration of the sea water and to maintain approximately constant activity coef

28、ficients during the titration. An open cell is used so that, in subsequent data processing, it can be assumed that the total dissolved inorganic carbon (and hence the residual bicarbonate ion concentration) is approximately zero between pH 3,0 and pH 3,5. The progress of the titration is monitored u

29、sing a pH glass-reference cell, and the total alkalinity is computed from the titrant volume and electromotive force (EMF) measurements using a non-linear least-squares approach allowing for the reactions of hydrogen ion with sulfate and fluoride ions. 5 Apparatus The setup of apparatus specified in

30、 5.2 and 5.4 is shown in Figure 1. Usual laboratory equipment, and in particular the following. 5.1 Sampling equipment. 5.1.1 For laboratory use. 5.1.1.1 Calibrated balance, capable of weighing 200 g to within 0,01 g. 5.1.1.2 Plastic screw-cap bottle, of capacity 125 ml, with cap. 5.1.2 For use on b

31、oard ship, preferably a volumetric dispensing system, containing a constant volumetric pipette made of glass with valves at each end, maintained at constant temperature by an air bath or a water jacket. The sample water maintained at the same temperature is flushed into the pipette using pressurised

32、 air. A constant volume of water is dispensed by switching the valve. The temperature of the sample water shall be known to within 0,4 C. A manual pipette may be used on condition that the temperature of sample water and room air is strictly controlled. 5.2 Titration cell assembly. 5.2.1 Jacketed be

33、aker, of capacity 200 ml. A glass beaker enclosed by a water jacket (Figure 1), of internal diameter 57 mm. 5.2.2 Calibrated thermometer, readable to 0,01 C, used to confirm that the solution temperature remains constant to within 0,05 C during the titration and to provide the value of solution temp

34、erature for use in subsequent calculations. 5.2.3 Water bath, capable of being maintained at a constant temperature to within 0,05 C. 5.2.4 Magnetic stirrer, of dimensions 38 mm 8 mm. 5.2.5 Holder for burette tip, electrode, and thermometer 5.3 EMF-measuring assembly. 5.3.1 Digital voltmeter, readab

35、le to 0,01 mV. 5.3.2 High-impedance voltage follower amplifier system, used to buffer the EMF of the glass electrode- reference cell so that it can be measured accurately using the digital voltmeter. NOTE A digital pH meter ( 0,1 mV) can be used instead of a digital voltmeter and voltage-follower am

36、plifier, but with a loss in precision. ISO 22719:2008(E) ISO 2008 All rights reserved 35.3.3 pH glass-reference electrode A very rapid response pH glass electrode system in sea water is essentially important. The 90 % response time during a pH change of 0,1 should be less than 10 s when sea water is

37、 titrated by acid titrant. To reduce the sample volume, the combination of a pH glass-reference electrode is more suitable. The performance of the pH electrode is paramount for achieving high quality results. The performance of a new electrode can be assessed by measuring A Ton a sea water reference

38、 material. If the certified value is not obtained, it may be necessary to replace the electrode. 5.4 Burette assembly. A highly reproducible burette ( 0,001 ml) is necessary to obtain the highest quality results. Unfortunately, although the burette is capable of the high reproducibility needed, its

39、accuracy is typically not as good, and the burette system shall be calibrated prior to use. 5.4.1 Automatic burette, of capacity 5 ml 0,002 ml, equipped with an anti-diffusion tip. 5.4.2 Calibrated thermometer, readable to 0,1 C, used to measure acid temperature. 5.5 Miscellaneous. 5.5.1 Transfer de

40、vice for samples by mass, designed to allow dispensation from a bottle with a greased ground-glass joint in a manner that ensures that grease is not transferred to the weighing bottle. Such a system may comprise a rubber stopper to which two rigid plastic tubes are skewered; the rubber stopper is se

41、cured to the sample bottle with a metal clamp. Connected tubes should be chemically inert and acid resistant. One of the tubes is long enough to make contact with the bottom of a 500 ml sample bottle, and the other tube protrudes about 6 mm below the stopper. The shorter tube is attached with about

42、500 mm of tubing to a rubber bulb, which is used to pressurise the system. The other tube is attached to a length of tubing (approx. 500 mm) and is closed with a pinch clamp. This tube is used to dispense the sample. 5.5.2 Basin for waste. 5.5.3 Wash bottle, containing water (6.2). 6 Reagents 6.1 Ti

43、trant, calibrated solution for normal sea water samples, containing hydrochloric acid, 0,1 mol/kg, and sodium chloride, 0,6 mol/kg. Ideally, the hydrochloric acid titrant solution is calibrated with an accuracy of better than 0,02 % using a coulometric titration procedure (see e.g. Reference 7). In

44、addition, the density of this titrant solution should be known as a function of temperature with an accuracy of better than 0,02 % experimentally by using a pyknometer (e.g. ISO 758). However, these procedures are complicated and require a great deal of skill. Furthermore, acid concentration and den

45、sity may be changed by evaporation in several days. It is necessary to recalibrate the acid from time to time. Thus, the calibration of acid titrant using certified reference material (CRM) is recommended (see B.1.3). 6.2 Deionised ultrapure water, of resistivity about 18 M cm. 7 Procedure 7.1 Sampl

46、ing Collect the sea water sample according to the standard method for water sampling of dissolved gases (see ISO 5667-1). It is strongly recommended that the sample is analysed within a few hours. When analysis is not ISO 22719:2008(E) 4 ISO 2008 All rights reservedpossible immediately after samplin

47、g, add mercury(II) chloride. Recommended minimum amount is about 0,02 % by volume of saturated aqueous solution. Store the samples in a cool, dark place (preferably refrigerated, but not frozen) until use. WARNING Dispose of samples containing mercury(II) chloride in accordance with local government

48、 regulations. 7.2 Equipment setup Assemble the apparatus as shown in Figure 1. Use extra caution when assembling the burette glass pieces and tubing. Make all connections finger tight, and do not overtighten. The most common cause of leaks and bubbles is damaged threads and chipped glass. Set the wa

49、ter bath to a suitable temperature (close to room temperature). Mix the hydrochloric acid titrant solution to ensure a consistent temperature and composition. Key 1 automatic burette 2 sensor for thermometer 3 thermometer 4 burette reservoir 5 HCl/NaCl titrant 6 inlet from water bath 7 combination electrode 8 outlet to water bath 9 lead to EMF-measurement system 10 jacketed beaker Figure 1 Open-cell alkalinity measurement setup ISO 22719:2008(E) ISO 2008 All rights res