1、BSI Standards PublicationBS ISO 18191:2015W a t e r q u a l i t y D e t e r m i n a t i o n of pHtin sea water Method using the indicator dyem-cresol purpleBS ISO 18191:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 18191:2015.The UK participation in its
2、preparation was entrusted to Technical Committee EH/3/2, Physical chemical and biochemical methods.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are resp
3、onsible for its correct application. The British Standards Institution 2015.Published by BSI Standards Limited 2015ISBN 978 0 580 79390 5 ICS 13.060.50 Compliance with a British Standard cannot confer immunity from legal obligations.This British Standard was published under the authority of the Stan
4、dards Policy and Strategy Committee on 30 September 2015.Amendments/corrigenda issued since publicationDate T e x t a f f e c t e dBS ISO 18191:2015 ISO 2015Water quality Determination of pHt in sea water Method using the indicator dye m-cresol purpleQualit de leau Dtermination du pHt dans leau de m
5、er Mthode utilisant lindicateur color au pourpre de m-crsolINTERNATIONAL STANDARDISO18191First edition2015-09-01Reference numberISO 18191:2015(E)BS ISO 18191:2015ISO 18191:2015(E)ii ISO 2015 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2015, Published in SwitzerlandAll rights reserved. Unless
6、 otherwise specified, 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 add
7、ress below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 18191:2015ISO 18191:2015(E)Foreword ivIntroduction v1 Scope . 12 Terms and defin
8、itions . 13 Principle 24 Reagents 25 Apparatus . 36 Sampling 47 Procedure. 48 Calculation and expression of results . 48.1 Correction of measured absorbances 48.2 Calculation of the pHtof the sea water and indicator . 58.3 Correction for pHtchange resulting from addition of the indicator . 6Annex A
9、(informative) Performance data . 7Annex B (informative) Storage stability 8Bibliography .10 ISO 2015 All rights reserved iiiContents PageBS ISO 18191:2015ISO 18191:2015(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO memb
10、er 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, government
11、al 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 a
12、re 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
13、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
14、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 on the meaning of ISO specific terms and expressions related to conformity assess
15、ment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 147, Water quality, Subcommittee SC 2, Physical, chemical and biochemical
16、methods.iv ISO 2015 All rights reservedBS ISO 18191:2015ISO 18191:2015(E)IntroductionThe greenhouse effect induced by anthropogenic carbon dioxide, CO2, in the atmosphere is one of the serious global environmental issues. A key factor controlling the atmospheric CO2is its absorption into the ocean.
17、As a result of the absorption, the pH in the upper layer of the ocean is observed to have fallen gradually, and its influence on the living organisms is a matter of concern all over the world.On the other hand, carbon capture and storage (CCS) technology is considered as a useful means of reducing t
18、he CO2emissions from fossil fuel. When ocean environment such as sub-seabed aquifer is selected as a storage site, the monitoring of carbonate system including pH in sea water becomes very important. The analytical method for pHtin sea water (the total hydrogen ion concentration pH scale) samples re
19、quires specific conditions and techniques essential to the precise and accurate determination. This International Standard describes a method for the determination of pHtin sea water with the repeatability less than 0,003.This method will provide international communities accurate data sets on pHtin
20、 sea water being compatible with each other. This is the base of national and international operational observation or monitoring programs of the oceanic carbonate system as well as individual research works. ISO 2015 All rights reserved vBS ISO 18191:2015BS ISO 18191:2015Water quality Determination
21、 of pHt in sea water Method using the indicator dye m-cresol purpleWARNING Persons using this International Standard should be familiar with normal laboratory practice. This International Standard does not purport to address all of the safety problems, if any, associated with its use. It is the resp
22、onsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions.IMPORTANT It is absolutely essential that tests conducted in accordance with this International Standard be carried out by suitably qualified staff.1 ScopeThis
23、 International Standard specifies a spectrophotometric determination of the pHtof sea water on the total hydrogen ion concentration pH scale using the indicator dye m-cresol purple. The total hydrogen ion concentration, H+t, is expressed as moles per kilogram of sea water. The method is suitable for
24、 assaying oceanic levels of pHt7,4 to 8,2 for normal sea water of practical salinity ranging from 20 to 40.2 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.2.1total hydrogen ion concentration H+thydrogen ion concentration including the contribution
25、of the hydrogen sulfate ions in the sea waterNote 1 to entry: Total hydrogen ion concentration is defined as: / HH SHHSOtFTS F+ +=+()+14KwhereH+Fis the free concentration of hydrogen ion in sea water;STis the total sulfate concentration HSOSO442+( );KSis the acid dissociation constant for HSO4.The p
26、Htis then defined as the negative of the base 10 logarithm of the hydrogen ion concentration as:pHHmol/kgtt=+log102.2practical salinitySratio K15of the electrical conductivity of the sea water sample at the temperature of 15 C on IPTS-68 and the pressure of one standard atmosphere, to that of a pota
27、ssium chloride (KCl) solution, in which the mass fraction of KCl is 32,435 6 10-3, at the same temperature and pressureINTERNATIONAL STANDARD ISO 18191:2015(E) ISO 2015 All rights reserved 1BS ISO 18191:2015ISO 18191:2015(E)3 PrincipleThe values of pHtare determined by adding an indicator to sea wat
28、er. For the sulfonephthalein indicators such as m-cresol purple, the reaction of interest at sea water pHtis the second dissociation as given in Formula (1):HI aq HaqI aq+()=()+()2(1)where I represents the indicator, which is present at a low level in a sea water sample. The total hydrogen ion conce
29、ntration of the sample can then be determined as given in Formula (2):pH pHIIHIt=()+K log102(2)The principle of this approach uses the fact that the different forms of the indicator have substantially different absorption spectra. Thus the information contained in the composite spectrum can be used
30、to estimate I2-/HI-.At an individual wavelength, , the measured absorbance, A, in a cell with a pathlength L is given by the Beer-Lambert law as:ALB=()+()+ HI HI II e22(3)where Bcorresponds to the background absorbance of the sample and e is an error term due to instrumental noise. Provided that the
31、 values of the extinction coefficients: (HI-) and (I2-) have been measured as a function of wavelength, absorbance measurements made at two or more wavelengths can be used to estimate the ratio I2-/HI-.In the case that only two wavelengths are used, and provided that the background can be eliminated
32、 effectively by a subtractive procedure, Formula (3) can be rearranged to give (assuming no instrumental error):IHIHI HIIHI2121212212=()()() ()AAAA/ 222IHI() ()/(4)where the numbers 1 and 2 refer to the wavelengths chosen. For the best sensitivity, the wavelengths corresponding to the absorbance max
33、ima of the base (I2-) and acid (HI-) forms, respectively, are used. The various terms are the extinction coefficients of the specified species at wavelengths 1 and 2, respectively.4 ReagentsUse only reagents of recognized analytical grade.4.1 m-cresol purple, containing no spectrophotometrical impur
34、ities.NOTE 1 Reference 14 showed that the indicator can be characterized and purified using the HPLC system. The wavelength of isosbestic point for HI-/I2-of the pure m-cresol purple, isos(HI-/I2-) depends on the following formula: isos(HI-/I2-) = 490,6 0,10 t, where t is the temperature in degrees
35、Celsius. That for H2I/HI-, it is also isos(H2I/HI-) = 482,6 0,10 t.NOTE 2 References 14 and 17 describe the purification method of m-cresol purple.2 ISO 2015 All rights reservedBS ISO 18191:2015ISO 18191:2015(E)4.2 Solution of pure m-cresol purple.A concentrated (at least 2 mmol/l) pure indicator so
36、lution of known pH adjusted to be in the range 7,9 0,1 pH units, chosen to match pHtmeasurements from an oceanic profile, is required; this implies that for m-cresol purple A1/A2approximately 1,6.NOTE The absorbance ratio of a concentrated indicator solution can be measured using a cell with a short
37、 pathlength (0,5 mm).4.3 Deionized ultrapure water, of resistivity about 18 M cm.5 ApparatusUsual laboratory equipment and, in particular, the following:5.1 Flexible drawing tubeApproximately 40 cm long, sized to fit snugly over cell port. Silicone rubber is suitable. The drawing tube can be pre-tre
38、ated by soaking in clean sea water for at least one day. This minimizes the amount of bubble formation in the tube when drawing a sample.5.2 Spectrophotometric cellThese should be made of optical glass with a 10 cm pathlength, two ports and polytetrafluoroethylene stoppers. A sufficient number of ce
39、lls are needed to collect all the samples that will be analysed from a particular cast.NOTE A flow through cuvette with a 10 cm pathlength is also available. Sample bottles of at least 200 ml with air tight caps are needed to use the cuvette.5.3 MicropipetteA micropipette is used to add the indicato
40、r to the cell. It should be of 0,1 cm3capacity with a narrow polytetrafluoroethylene (PTFE) tube attached to act as a nozzle.5.4 High-quality spectrophotometerFor work of the highest sensitivity and precision, a double-beam spectrophotometer is desirable. However, good results can be obtained with a
41、 high-quality single-beam instrument.5.5 Temperature-control system for spectrophotometer cellCommercially manufactured, thermostated spectrophotometer compartments that can accommodate 10 cm cells are rarely available and one will probably have to be custom-made. The temperature should be regulated
42、 to within 0,1 C.5.6 System to warm samples to measurement temperatureAlthough, it is possible to warm up the cells containing samples in the sealed bags in a thermostat bath, this is inconvenient. It is much better to build a custom-made thermostated compartment that can hold approximately 12 cells
43、 at once without getting them wet.5.7 Thermostat bathTemperature 0,05 C, to regulate the temperature of the cell compartment and the temperature of the system. ISO 2015 All rights reserved 3BS ISO 18191:2015ISO 18191:2015(E)6 SamplingCollection of water at sea from the water sampler bottle must be d
44、one soon after opening the sampler and before much other water has been removed from it. This is necessary to minimize exchange of CO2with the air space in the sampler which affects all carbon parameters except total alkalinity. It is desirable that the carbon samples be collected before the sampler
45、 bottle is half empty and within 10 min of it being first opened.Rinse the sample bottle If the bottle is not already clean, rinse it twice with 30 cm to 50 cm of sample to remove any traces of a previous sample.Fill the sample bottle Fill the bottle smoothly from the bottom using a drawing tube whi
46、ch extends from the sampler bottle drain to the bottom of the sample bottle. It is critical to remove any bubbles from the draw tube before filling. Overflow the water by at least a full bottle volume. The air space with the sample bottle is kept to a minimum.910It is allowed to draw the sample dire
47、ctly from sampler bottle into the optical cell with two ports.It is recommended that the pH analysis must be performed immediately after sampling, although storage experiments showed that the pH of sea water is stable within 24 h even in the case of coastal water (see Annex B). However, while awaiti
48、ng analysis, store the samples in the refrigerator or icebox (not frozen).7 ProcedureIn the case of optical cell with two ports, warm sample cell to (25,0 0,1) C by placing a number of cells in a thermostated compartment (see 5.6) for a few hours. Place the cell in the thermostated sample compartmen
49、t of the spectrophotometer by cleaning and drying the exterior of the cell.Measure and record the absorbances at three wavelengths: at the wavelengths corresponding to the absorption maxima of the base (I2-) and acid (HI-) forms of the m-cresol purple, 578 nm and 434 nm, respectively, and a non-absorbing wavelength (730 nm).Remove one of the cell caps to inject m-cresol purple. Add approx
