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1、 Reference number ISO 15705:2002(E) ISO 2002 INTERNATIONAL STANDARD ISO 15705 First edition 2002-11-15 Water quality Determination of the chemical oxygen demand index (ST-COD) Small-scale sealed-tube method Qualit de leau Dtermination de lindice de demande chimique en oxygne (ST-DCO) Mthode petite c
2、helle en tube ferm ISO 15705:2002(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 computer performing th
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5、at at the address given below. ISO 2002 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
6、 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.ch Web www.iso.ch Printed in Switzerland ii ISO 2002 All rights reserved ISO 15705:2002(E) ISO 2002 All rights reserved
7、iii Contents Page Foreword iv Introduction. v 1 Scope 1 2 Normative references 1 3 Terms and definitions. 2 4 Principle . 2 5 Interferences 2 6 Reagents 2 7 Apparatus. 5 8 Sample collection and preservation 6 9 Preparation of tubes and instrument set-up 6 10 Analytical procedure for measurement of s
8、amples 7 11 Calculation of results 8 12 Expression of results 9 13 Test report 9 14 Precision 9 Annex A (informative) Comparison between the COD method according to ISO 6060 and the method described in this International Standard 10 Annex B (informative) Hazards 11 Annex C (informative) Information
9、on the use of commercial small-scale ST-COD test kits utilizing photometric detection. 12 Annex D (informative) Low-range sealed-tube photometric method (up to 150 mg/l) 13 Annex E (informative) Low-range sealed-tube titrimetric method (up to 150 mg/l) 14 Annex F (informative) Screening test for sam
10、ples with high chloride concentrations. 15 Annex G (informative) Precision data. 16 Bibliography 18 ISO 15705:2002(E) iv ISO 2002 All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work
11、 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-governmen
12、tal, 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 3. The ma
13、in 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. At
14、tention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 15705 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC
15、2, Physical, chemical and biochemical methods. Annexes A to G of this International Standard are for information only. ISO 15705:2002(E) ISO 2002 All rights reserved v Introduction The chemical oxygen demand, ST-COD value, of water as determined by this dichromate method can be considered as an esti
16、mate of the theoretical oxygen demand, i.e. the amount of oxygen consumed in total chemical oxidation of the organic constituents present in the water. The degree to which the test results approach the theoretical value depends primarily on how complete the oxidation is. The ST-COD test is an empiri
17、cal test and the effects of any oxidizing or reducing agents are included in the result. Under the conditions of the test, many organic compounds and most inorganic reducing agents are oxidized to between 90 % and 100 %. For waters that contain these compounds, such as sewage, industrial waste and o
18、ther polluted waters, the ST-COD value is a realistic measure of the theoretical oxygen demand. However, for waters that contain large quantities of other substances that are difficult to oxidize under the conditions of the test, such as nitrogenous and heterocyclic compounds (e.g. pyridine and alip
19、hatic and aromatic hydrocarbons), the ST-COD value is a poor measure of the theoretical oxygen demand. This may be the case for some industrial effluents. The significance of an ST-COD value thus depends on the composition of the water studied. This should be borne in mind when judging results obtai
20、ned by the method specified in this International Standard. Detailed testing has shown good comparison between this method and the method of ISO 6060. However, it should not be assumed that this method is comparable in all cases to that of ISO 6060 without testing, particularly when there is a probl
21、em in obtaining a 2 ml representative sample (e.g. samples with high content of suspended solids). -,-,- INTERNATIONAL STANDARD ISO 15705:2002(E) ISO 2002 All rights reserved 1 Water quality Determination of the chemical oxygen demand index (ST-COD) Small-scale sealed-tube method WARNING Persons usi
22、ng this 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 appropriate safety and health practices and to ensure compliance with any nati
23、onal regulatory conditions. 1 Scope This International Standard specifies a method for the determination of the chemical oxygen demand (ST-COD) using the sealed tube method. The test is empirical and is applicable to any aqueous sample, which includes all sewage and waste waters. The method is appli
24、cable to undiluted samples having ST-COD values up to 1 000 mg/l and a chloride concentration not exceeding 1 000 mg/l. Samples with higher ST-COD values require predilution. For samples with a low COD, the precision of the measurement will be reduced and the detection limit will be poorer. Samples
25、with a high chloride concentration will need to be prediluted to give a chloride concentration of approximately 1 000 mg/l or less before analysis. The method oxidizes almost all types of organic compounds and most inorganic reducing agents. It has a detection limit (4,65 times the within-batch stan
26、dard deviation of a blank or very low standard) of 6 mg/l for photometric detection at 600 nm, and 15 mg/l for titrimetric detection as reported by one laboratory comparing the photometric and titrimetric techniques using a commercial test kit with a range up to 1 000 mg/l. The titrimetric part of t
27、his International Standard is applicable to samples exhibiting an atypical colour or turbidity after the digestion stage. NOTE A comparison between the full-scale method (ISO 6060) and the method of this International Standard is given in annex A. A discussion of possible hazards is given in annex B
28、. Information on commercial small-scale test kits is given in annex C. The method can be used over a reduced range (see annexes D and E). For checking the chloride concentration, see annex F. 2 Normative references The following normative documents contain provisions which, through reference in this
29、 text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most
30、 recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 3696:1987, Water for analytical laboratory use Specificatio
31、n and test methods ISO 5667-3:1994, Water quality Sampling Part 3: Guidance on the preservation and handling of samples ISO 15705:2002(E) 2 ISO 2002 All rights reserved 3 Term and definition For the purposes of this International Standard, the following term and definition applies. 3.1 chemical oxyg
32、en demand ST-COD mass concentration of oxygen equivalent to the amount of dichromate consumed by dissolved and suspended matter when a water sample is treated under the conditions specified in this International Standard NOTE 1 Adapted from ISO 6060. NOTE 2 1 mol of dichromate (Cr2O72) is equivalent
33、 to 3 mol of oxygen (O). 4 Principle 4.1 Samples are oxidized in a standard manner by digesting with sulfuric acid and potassium dichromate in the presence of silver sulfate and mercury(II) sulfate. Silver acts as a catalyst to oxidize the more refractory organic matter. Mercury reduces the interfer
34、ence caused by the presence of chloride ions. The amount of dichromate used in the oxidation of the sample is determined by measuring the absorbance of the Cr(III) formed at a wavelength of 600 nm 20 nm for a range up to 1 000 mg/l. Absorbance measurements are made in the digestion tube, which acts
35、as a cuvette, and are converted to an ST-COD value. 4.2 For the reduced calibration range up to 150 mg/l, an alternative wavelength 440 nm 20 nm may be used (see annexes D and E). For a further reduced calibration range up to 50 mg/l, an alternative wavelength of 348 nm 15 nm may be used. At 348 nm
36、and 440 nm, the absorbance of the remaining chromium(VI) is measured. 4.3 For turbid and atypically coloured digested samples, titration with standardized ammonium iron(II) sulfate is used. 5 Interferences 5.1 High concentrations of chloride give a positive bias caused by the oxidation of chloride i
37、ons to chlorine. The interference from chloride ions is reduced but not totally eliminated by the addition of mercury(II) sulfate. This binds the chloride ions as a soluble chloromercurate(II) complex. 5.2 Manganese can give a positive bias using photometric detection at 600 nm. Using a 0 mg/l to 1
38、000 mg/l commercial test kit, duplicate analysis of a 500 mg/l manganese solution (as sulfate) gave ST-COD results of 1 080 mg/l and 1 086 mg/l and of a 50 mg/l manganese solution gave ST-COD results of 121 mg/l and 121 mg/l. The effect is much less with lower range (0 mg/l to 150 mg/l) kits at 440
39、nm (5.1). At this wavelength the interference is expressed as a negative bias. For a 0 mg/l to 150 mg/l commercial test kit, duplicate analysis of a 500 mg/l manganese solution (as sulfate) gave ST-COD results of 7 mg/l and 8 mg/l. See also note in C.6. 5.3 Many aromatic hydrocarbons and pyridine ar
40、e not oxidized to any appreciable extent. Some volatile organic substances may escape the oxidation by evaporating. 5.4 Ammonium ions are not oxidized (organic nitrogen is normally converted to ammonium ions). 6 Reagents 6.1 Water, complying with ISO 3696:1987, Grade 3. -,-,- ISO 15705:2002(E) ISO 2
41、002 All rights reserved 3 6.2 ST-COD sealed tubes Whenever possible it is recommended to use ST-COD sealed tubes purchased ready for use. This minimizes the handling of toxic chemicals by laboratory staff. Commercial tubes can be purchased covering different analytical ranges (e.g. up to 50 mg/l, 16
42、0 mg/l, 1 000 mg/l or 1 500 mg/l). If tubes cannot be purchased already prepared, then prepare them within the laboratory as described in 6.7, for an analytical range of up to 1 000 mg/l. In this instance the user shall ascertain the reproducibility of optical transmission of the tubes or transfer t
43、he contents after digestion to a glass cuvette of 10 mm optical path length. The ST-COD concentration range of commercial tubes will be specified by the manufacturer and shall not be exceeded. If this occurs, the sample should be suitably diluted to within the specified concentration range. It is es
44、sential that the purchased sealed tubes contain mercury(II) sulfate for suppression of chloride interference. See note in C.6. 6.3 Standard reference solution of potassium dichromate, c(K2Cr2O7) = 0,10 mol/l (range up to 1 000 mg/l ST-COD). Dissolve 29,418 g 0,005 g of potassium dichromate (dried at
45、 105 C for 2 h 10 min) in about 600 ml of water in a beaker. Carefully add 160 ml of concentrated sulfuric acid (6.4.1) with stirring. Allow to cool and make up to 1 000 ml in a graduated flask. The solution is stable for 6 months. 6.4 Sulfuric acid 6.4.1 Concentrated sulfuric acid, (H2SO4) = 1,84 g
46、/ml. 6.4.2 Dilute sulfuric acid, c(H2SO4) = 4 mol/l. Add to about 500 ml of water (6.1) in a beaker, 220 ml 10 ml of concentrated sulfuric acid (6.4.1) cautiously with stirring. Allow to cool and dilute to 1 000 ml 10 ml in a measuring cylinder. Transfer to a glass bottle. The solution is stable for
47、 12 months. 6.4.3 Dilute sulfuric acid, c(H2SO4) = 1,8 mol/l. Add cautiously, while swirling, 20 ml 1 ml of concentrated sulfuric acid (6.4.1) to 180 ml 2 ml of water in a beaker. The solution is stable for 12 months. 6.5 Mercury(II) sulfate solution, c(HgSO4) = 1,35 mol/l. Dissolve 80 g 1 g of labo
48、ratory grade mercury(II) sulfate in 200 ml 2 ml of dilute sulfuric acid (6.4.3). WARNING: This reagent is very toxic. For hazards, see annex B. The solution is stable for 12 months. 6.6 Silver sulfate in sulfuric acid, c(Ag2SO4) = 0,038 5 mol/l. Dissolve 24,0 g 0,1 g of silver sulfate in 2 litres of
49、 concentrated sulfuric acid (6.4.1). To obtain a satisfactory solution, shake the initial mixture. Allow it to stand overnight and then shake it again in order to dissolve all the silver sulfate. Store in a dark brown glass bottle out of direct sunlight. The solution is stable for 12 months. -,-,- ISO 15705:2002(E) 4 ISO 2002 All rights reserved 6.7 Dispensed