1、DEUTSCHE NORM Februarv 2001 German standard methods for the examination of water, waste water and sludge Anions (group D) Determination of iodide by photometry (D 33) DIN 38405-33 - ICs 13.060.50 Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung - Anionen (Gruppe D) - Teil 33
2、: Bestimmung von Iodid mittels Photometrie (D 33) In keeping with current practice in standards published by the International Organization for Standardization (ISO), a comma has been used throughout as the decimal marker. Foreword This standard has been prepared by the Normenausschuss Wasserwesen (
3、Water Practice Standards Com- mittee) jointly with Study Group Wasserchemie (Water Chemistry) of the Gesellschaft Deutscher Chemiker (German Chemists Society) (see Explanatory notes). Expert assistance and specialized laboratories will be required to perform the analyses specified in this standard.
4、Existing safety instructions shall be observed. Depending on the objective of the analysis, a check shall be made on a case-by-case basis as to whether and to what extent additional conditions will have to be specified. Introduction Since natural water contains iodide ions only in trace amounts, the
5、 concentration of iodine depends mainly on the hydrogeological conditions. However, higher concentrations may occur in natural mineral water, natural brine and some types of waste water. 1 Scope The method specified in this standard serves to determine iodide ions in water and waste water in concen-
6、 trations ranging from 0,5 mg/i to 1 O0 mg/i. Higher concentrations can also be determined if the water sample is diluted. 2 Normative references This standard incorporates, by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate pla
7、ces in the text, and the titles of the publications are listed below. For dated references, subsequent amendments to or revisions of any of these publications apply to this standard only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication r
8、eferred to applies. DIN 12331 Beakers for laboratory use DIN 12650-2 Piston-operated pipettes for laboratory use DIN 12691 Class AS fast delivery one-mark bulb pipettes, with a waiting time of 15 seconds, for laboratory use DIN 38402-1 2 German standard methods for the examination of water, waste wa
9、ter and sludge - General information (Group A) - Sampling from stagnant waters (A 12) DIN 38402-1 3 German standard methods for the examination of water, waste water and sludge - General information (Group A) - Sampling from aquifers DIN 38402-1 4 German standard methods for the examination of water
10、, waste water and sludge - General information (Group A) - Sampling of untreated water and drinking water (A 14) Continued on pages 2 to 5. Translation by DI N-Sprachendienst. In case of doubt, the German-language original should be consulted as the authoritative text No pari of this translation may
11、 be reproduced without the prior permission of V Deutsches Institut fur Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany, s the exclusive right of sale for German Standards (DIN-Normen). Ref. No. DIN 38405-33 : 2001 -0 English price group 06 Sales No. 0106 10.01 Page 2 DIN 38405-33 :
12、2001 -02 DIN 38402-1 5 DIN 38402-1 6 DIN 38402-1 7 DIN 38402-1 8 DIN 38402-1 9 DIN 38402-20 DIN 58960-2 DIN EN IS0 1042 DIN EN IS0 8467 IS0 1773:1997 German standard methods for the examination of water, waste water and sludge - General information (Group A) - Sampling from flowing waters (A 15) Ger
13、man standard methods for the examination of water, waste water and sludge - General information (Group A) - Sampling of seawater (A 16) German standard methods for the examination of water, waste water and sludge - General information (Group A) -Sampling from precipitation in or after return to the
14、liquid state (A 17) German standard methods for the examination of water, waste water and sludge - General information (Group A) - Sampling of water from mineral springs and spas (A 18) German standard methods for the examination of water, waste water and sludge - General information (Group A) - Sam
15、pling of water from bathing facilities (A 19) German standard methods for the examination of water, waste water and sludge - General information (Group A) - Sampling of tidal waters (A 20) Photometers for analytical tests - Design - Concepts, classification and components Laboratory glassware - One-
16、mark volumetric flasks (IS0 1042 : 1998) Water quality - Determination of permanganate index (IS0 8467 : 1993) Laboratory glassware - Narrow-necked boiling flasks 3 Principle After arsenite ions have been oxidized with excess cerium(1V) ions in a reaction catalysed by iodide ions (Sandell-Kolthoff r
17、eaction): 2 Ce4+ + As043- + H,O + 2 Ces+ + As043- + 2H+, the unconsumed cerium(1V) ions are determined photometrically at 436 nm after a specified reaction time. By choosing various reaction times, it is possible to cover iodide concentration ranges extending from 0,5 pg/i to 1 O pg/i and from 5 pg/
18、i to 1 O0 pg/i. 4 Interferences The following ions may interfere with the analysis if the following concentrations are exceeded: a) nitrate: 80 mg/i; b) phosphate: 8 mg/i; c) fluoride: 0,5 mg/i; d) free chlorine: 0,3 mg/i. Since reducing constituents in the water may simulate an iodide content as a
19、result of reduction of the cerium(1V) ions, their concentration shall not exceed an oxygen consumption of 2 mg/i, as determined from the perman- ganate index (see DIN EN IS0 8467). Other catalytically active iodine compounds (e.g. iodate) will also affect the analysis. 5 Designation Designation of t
20、he method of determining iodide by photometry (D 33): Method DIN 38405 - D 33 6 Apparatus Immediately before use, glassware shall be cleaned with hot dilute nitric acid and then rinsed with water. The following equipment shall be used. 6.1 Piston-operated pipettes, having volumes varying between 0,2
21、5 mi and 10 mi (e.g. DIN 12650-2 pipettes). 6.2 One-mark bulb pipettes, of nominal capacity 1 O0 mi (e.g. DIN 12691 - VPAS 1 O0 pipettes). 6.3 Spectrophotometer or filter photometer and filter, suitable for measurements at 436 nm (e.g. as in 6.4 Glass cells, with a path length of 1 O mm. 6.5 Stopwat
22、ch. 6.6 Volumetricflasks, of nominal capacities 500 mi and 1 O00 mi (e.g. DIN EN IS0 1042 -A 500 - C volumet- ric flasks). 6.7 Beakers, of nominal capacity 600 mi (e.g. DIN 12331 - HF 600 beakers). DIN 58960-2). Page 3 DIN 38405-33 : 2001 -02 6.8 Conical flasks, of nominal capacities 25 mi and 500 m
23、i (e.g. IS0 1773 conical flasks). 6.9 Magnetic stirrer, with polytetrafluoroethane-coated magnetic follower. 7 Reagents 7.1 General Only analytical grade reagents shall be used and the water used shall be double-distilled water or water of equivalent purity. The iodide concentration of the water and
24、 the reagents shall be negligible compared with the lowest concentration to be determined. The following reagents shall be used. 7.2 1,84 g/ml sulfuric acid, H,SO,. 7.3 1,61 g/ml sulfuric acid, prepared by transferring about 150 mi of water to a 500 mi conical flask, slowly adding 306 mi of 1,84 g/m
25、i sulfuric acid while swirling and, after cooling, making up to 500 mi with water. 7.4 1,16 g/ml hydrochloric acid, HCi. 7.5 3,6 moM hydrochloric acid, prepared by transferring 250 mi of water to a 500 mi volumetric flask, adding 190 mi of 1,16 g/mi hydrochloric acid, mixing and, after cooling, maki
26、ng up to 500 mi with water. 7.6 Cerium(1V) sulfate tetrahydrate, Ce(SO,), . 4 H,O. 7.7 0,016 moM cerium(1V) sulfate solution, prepared by transferring 400 mi of water to a 600 mi beaker, mixing with 35 mi of 1,61 g/mi sulfuric acid, cooling, dissolving 3,2 g of cerium(1V) sulfate tetrahydrate in thi
27、s mixture using a magnetic stirrer and follower, transferring the solution without heating to a 500 mi volumetric flask and making the contents of the flask up to the mark with water. This solution will be stable for at least one month. 7.8 Sodium hydroxide, NaOH. 7.9 Arsenic trioxide, As,O,. 7.10 0
28、,015 mol/l sodium arsenite solution, prepared by introducing water into a 500 mi volumetric flask, dissolving 2 g of sodium hydroxide, adding 3,71 g of arsenic trioxide, dissolving it by heating on a water bath, adding 200 mi of water, cooling, while swirling, slowly adding 53 mi of 1,61 g/mi sulfur
29、ic acid, cooling and making up to the mark with water. 7.1 1 7.12 a 1 O00 mi volumetric flask, dissolving in water and making up to the mark with water. If stored in the dark, this solution will be stable for four weeks. 7.13 1 O00 mi volumetric flask and making up to the mark with water. If stored
30、in the dark, this solution will be stable for at least 24 hours. 7.14 into a 1 O00 mi volumetric flask and making up to the mark with water. Always use a freshly prepared solution. 7.15 a 1 O00 mi volumetric flask and making up to the mark with water. Always use a freshly prepared solution. 7.16 Ref
31、erence solutions To suit the expected iodide concentration range, prepare a minimum of seven reference solutions, proceeding as follows for an expected range of 5 pg/i to 1 O0 pg/i. Pipette 0,25 mi, 0,5 mi, 1 mi, 2 mi, 3 mi, 4 mi and 5 mi, respectively, of standard iodide solution No. 1 into a serie
32、s of seven 25 mi conical flasks and make up all but the seventh flask to 5 mi with water. Use 5 mi of water as a blank. For an expected range of 0,5 pg/i to 1 O pg/i, proceed as follows. Pipette 0,25 mi, 0,5 mi, 1 mi, 2 mi, 3 mi, 4 mi and 5 mi, respectively, of standard iodide solution No. 2 into a
33、series of seven 25 mi conical flasks and make up all but the seventh flask to 5 mi with water. Use 5 mi of water as a blank. Always use freshly prepared reference solutions. Potassium iodide, KI, dried at 105 “C. 100 mg/l iodide stock solution No. 1, prepared by weighing 0,1308 g of dried potassium
34、iodide into 1 mg/l iodide stock solution No. 2, prepared by pipetting 1 O mi of iodide stock solution No. 1 into a 100 pg/l standard iodide solution No. 1, prepared by pipetting 100 mi of iodide stock solution No. 2 10 mg/l standard iodide solution No. 2, prepared by pipetting 1 O mi of iodide stock
35、 solution No. 2 into Page 4 DIN 38405-33 : 2001 -02 8 Sampling Follow the instructions given in DIN 38402-12 to DIN 38402-20 and collect water samples in glass or plastic bottles. 9 Pretreatment Filter the sample through a membrane filter having a pore size of 0,45 pm and, especially in the case of
36、mineral water, remove dissolved carbon dioxide and hydrogen carbonate by acidifying with sulfuric acid to a pH value of 3 (test with indicator paper) and then outgassing in an ultrasonic bath. 10 Procedure Pipette 5 mi of test solution into a 25 mi conical flask and then add 5 mi of sodium arsenite
37、solution, 1 mi of 1,16 g/mi hydrochloric acid and 5 mi of cerium(1V) sulfate solution in that order while mixing. After adding the cerium(1V) sulfate solution, start the stopwatch and, after a reaction time of 35 minutes for the 0,5 pg/i to 1 O pg/i iodide range or after a reaction time of ten minut
38、es for the 5 pg/i to 1 O0 pg/i iodide range, respectively, determine the transmittance at a wavelength of 436 nm in cells having a path length of 1 O mm, using water as a reference. Since the analysis is dependent on the kinetics of the reaction, temperature and reaction time have a crucial effect o
39、n sensitivity, as is indicated by the slope of the calibration graph. Experience has shown that it is best to perform the determination and calibration in a room at a constant temperature of 21 “C, making up reference and test solutions at intervals of 30 seconds and then performing measurements at
40、exactly equal intervals ten minutes after making up the first solution. Use a stopwatch for all the time measurements. Alternatively, the test and reference solutions may be brought to a constant temperature of 25 “C. 11 Calibration Treat the reference solutions and blank (prepared as specified in s
41、ubclause 7.1 6) in the same way as the test solution. Use a stopwatch to ensure that the reaction times are exactly the same for the test and reference solutions and measure the solutions at the same temperature. 12 Evaluation Determine the regression line from the calibration data, checking that th
42、e value found for the blank does not deviate significantly from that found for the intercept on the vertical axis. Calculate the iodide concentration in the test solution, e, in pg/i, from the transmittance obtained from the calibration graph, using the following equation: T-a e= - b where T is the
43、transmittance of the sample; a is the intercept on the vertical axis; b is the slope of the calibration function, in i/pg. If other aliquots have been used, make allowance for this in the calculation. 13 Expression of result All results are subject to a certain degree of uncertainty, this often bein
44、g greatest for lower concentrations. In this standard the concentration range from 17,8 pg/i to 73 pg/i has been chosen for the determination of the uncertainty of measurement (expressed as the reproducibility coefficient of variation). As can be seen from the values in table 1, the uncertainty is b
45、etween 3,6 YO and 13,4 YO. For a different concentration range, the uncertainty can be estimated from laboratory quality control data (e.g. range control cards for duplicate determinations), another method being interlaboratory testing. The uncer- tainty of measurement may vary considerably with the
46、 type of sample. Report the values to the nearest 0,l pg/i, but not to more than two significant places. EXAMPLE: Iodide: 15 pg/i or 5,4 pg/i. 14 Test report The test report shall refer to this method and include the following details: a) designation of method; b) identification of sample; c) expres
47、sion of results as specified in clause 13; Page 5 DIN 38405-33 : 2001 -02 d) sample pretreatment, if any; e) any deviation from this method and an indication of any circumstances that may have affected the result. 15 Results of interlaboratory testing An interlaboratory test carried out in early 200
48、0 yielded the results shown in table 1. Further details of the interlaboratory test are to be found in the validation document. Table 1: Results of interlaboratory testing Key to symbols: L number of laboratories WFR accuracy of recovery N number of measurements SR reproducibility standard deviation
49、 NAP percentage of outliers VR reproducibility coefficient of variation XSoll conventional true value SI repeatability standard deviation X overall mean VI repeatability coefficient of variation Type of sample 1 2 3 natural mineral water with a high mineral content ozonized natural mineral water with a high mineral content drinking water with iodide added Explanatory notes This standard incorporates the German standard method Determination of iodide by photometry (D33) jointly prepared by the Normenausschuss Wasserwesen of DIN and Study Group Wasserchemie of the Gesellschaft Deutscher C
