1、DEUTSCHE NORM March 200453125Document comprises 6 pages. No part of this translation may be reproduced without the prior permission ofDIN Deutsches Institut fr Normung e.V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).Determining
2、 the chloride content of aqueousextracts of paper and boardTranslation by DIN-Sprachendienst.In case of doubt, the German-language original should be consulted as the authoritative text.ICS 85.040; 85.060Prfung von Papier und Pappe Bestimmung des Chloridgehaltes inwssrigen ExtraktenIn keeping with c
3、urrent practice in standards published by the International Organization for Standardization(ISO), a comma has been used throughout as the decimal marker.ForewordThis standard has been prepared by Technical Committee Chemisch-technologische Prfverfahren frPapier, Pappe, Halbstoff und Chemiezellstoff
4、 of the Normenausschuss Materialprfung (Materials TestingStandards Committee).AmendmentsThis standard differs from the August 1985 edition in that a reference to cold water extracts has been addedto clause 4 and the standard has been editorially revised.Previous editionsDIN 53125: 1964-02, 1985-08.1
5、 ScopeThis standard specifies a method of determining the chloride content of aqueous extracts of paper andboard, excluding electrical insulating papers. It may be used by analogy for the analysis of pulp.The method is particularly suitable for determining traces of water-soluble chlorides, but high
6、er chloridecontents can be determined if the titrant concentration is suitably increased.2 Normative referencesThis standard incorporates, by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text, and the titles of t
7、he publications arelisted below. For dated references, subsequent amendments to or revisions of any of these publicationsapply to this standard only when incorporated in it by amendment or revision. For undated references, thelatest edition of the publication referred to applies.Supersedes August 19
8、85edition.English price group 7www.din.dewww.beuth.de11.04 9595155Page 2DIN 53125 : 2004-03DIN 12242-1 Conical ground joints on laboratory glassware Dimensions and tolerancesDIN 53114 Determining the conductivity of aqueous extracts of paper, board and pulp (ISO 6587 : 1980,modified)DIN 53124 Determ
9、ining the pH of aqueous extracts of paper, board and pulpDIN EN 645 Paper and board intended to come into contact with foodstuffs Preparation of a cold waterextractDIN EN 20187 Paper, board and pulps Standard atmosphere for conditioning and testing and procedurefor monitoring the atmosphere and cond
10、itioning of samples (ISO 187 : 1990)DIN EN ISO 186 Paper and board Sampling to determine average quality (ISO 186 : 2002)ISO 719 : 1985 Glass Hydrolytic resistance of glass grains at 98 C Method of test and classification3 ConceptWater-soluble chlorides contentThe chloride content that can be extrac
11、ted with water and potentiometrically determined under the conditionsspecified in this standard.4 PrincipleA sample is reduced in size and 5 g of it are extracted for one hour with 100 ml of hot water. The extract is filteredoff, cooled to ambient temperature and, after adding acetone, its chloride
12、content is determined potentiometri-cally by titration with aqueous silver nitrate solution.For very low chloride contents, back-titration with a sodium chloride solution of the same amount-of-substanceconcentration after adding a known volume of silver nitrate solution is recommended.Cold water ext
13、racts as specified in DIN EN 645 may also be used to determine the chloride content by thismethod.5 ApparatusIn addition to standard laboratory equipment, the following shall be used.a) Analytical balance, capable of being read to an accuracy of 0,1 mg.b) Extraction vessel (e.g. round bottom or coni
14、cal flask), made of glass of hydrolytic resistance grain classISO 719 HGB 1, of nominal volume 100 ml to 500 ml (depending on sample size), fitted with a refluxcondenser, made of glass of hydrolytic grain resistance class ISO 719 HGB 1, having ground glass joints(e.g. DIN 12242 V 29/32 joints) or a
15、riser tube of outside diameter 9 mm with a ground cone and 750 mmlong. Before use, new glassware shall be thoroughly rinsed several times with boiling distilled or deionizedwater.c) Water bath.d) Nutsch filter, fitted with a filter plate of porosity grade 4 and a filter flask.e) Magnetic stirrer.f)
16、Microburette, having 0,01 ml scale intervals and finely drawn tip.g) pH meter, capable of measuring to an accuracy of 1 mV.h) Glass bottle, having a ground glass joint and a soda-lime glass tube.i) Electrodes, for potentiometric titration (e.g. silver/silver chloride mercury/mercury(I) sulfate elect
17、rodesystem or combination electrode). The silver/silver chloride electrode shall be stored in a 1 % potassiumchloride solution.NOTE: If the response of the combination electrode is still poor after being thoroughly cleaned in hot water,leave it for a short time in dilute nitric acid and then rinse i
18、t thoroughly with distilled water. If necessary,activate the electrode by silver plating it, preferably using a 5 % potassium silver cyanide solution,KAg(CN)2, and a direct voltage of 2 V, the electrode to be silver-plated being connected as the cathode anda silver wire as the anode.Top up the 1 mol
19、/l potassium nitrate solution from time to time and store the electrode in a 1 mol/l potassiumnitrate solution to protect the diaphragm.6 Reagents6.1 GeneralOnly analytical grade reagents shall be used and the water used shall be distilled water or fully deionized watermeeting the requirements of DI
20、N 53114 and DIN 53124.The following reagents shall be used.Page 3DIN 53125 : 2004-036.2 Acetone, CH3COCH3, taken from the same stock for the sample and blank tests to allow for any chloridecontent.6.3 0,0025 mol/l sodium chloride solution, prepared by dissolving 0,5845 g of sodium chloride, NaCl, in
21、water, making the solution up to the mark with water in a 100 ml volumetric flask, shaking and then pipetting25 ml of this stock solution into a 1000 ml volumetric flask, making up to the mark with water and mixing.6.4 Nitric acid solution, prepared by mixing one part by volume of nitric acid having
22、 a density of 1,40 g/mlwith one part by volume of water.6.5 0,0025 mol/l silver nitrate solution, prepared by dissolving 1,699 g of silver nitrate, AgNO3, in water,pipetting 25 ml of this stock solution into a volumetric flask and making up to 1 l with water. The solution shallbe stored in the dark.
23、1 ml of 0,0025 mol/l silver nitrate solution is equivalent to 0,0886 mg of chloride.7 Sampling and sample preparationCollect an average sample as specified in DIN EN ISO 186, choosing the sample size to suit the batch size andthe mass of sample material per unit area. Analyse at least ten samples re
24、presentative of the batch if the massper unit area is 50 g/m2or greater, and at least twenty samples if it is less, each sample having a surface areaof about 300 cm2.Cut the samples diagonally into narrow strips, then cut the strips into pieces measuring about 5 mm 5mmusing scissors, and mix thoroug
25、hly. From this mixture, test at least two specimens, each weighing about 50 g,in parallel.Condition the samples in standard atmosphere at a temperature of (23 t 1) C and a relative humidity of(50 t 2) %, as specified in DIN EN 20187.8 Procedure8.1 Determination of dry matter contentCarry out the tes
26、t at least in duplicate.8.2 ExtractionWeigh, to an accuracy of 0,001 g, about 5 g of oven dry sample and transfer it to an extraction vessel. Add100 ml of water using a pipette, fit the reflux condenser or the riser tube and place the aqueous suspension ona water bath maintained at boiling point for
27、 one hour. Extract two specimens taken from the same sample inparallel and, at the same time, perform a blank test. Filter the extract through a sintered glass filter into acarefully rinsed glass bottle, seal the bottle immediately using a soda-lime tube and cool to ambient tempera-ture.8.3 Titratio
28、n8.3.1 Direct titrationPipette 50 ml of aqueous extract into a 400 ml beaker, add 250 ml of acetone and a few drops of nitric acidsolution as in subclause 6.4 and then introduce the magnetic follower and the electrodes or combinationelectrode into the solution. Connect the electrodes to the voltmete
29、r and switch on the magnetic stirrer to runat a speed that does not cause a funnel in the liquid. Using a microburette, titrate with the 0,0025 mol/l silvernitrate solution in steps of about 0,1 ml to 0,2 ml with the tip of the burette immersed in the sample solution.Measure the potential every time
30、 silver nitrate solution is added and wait for it to stabilize before proceedingto the next step. Determine the end point either graphically or by calculation.NOTE: For routine analyses, only a few potential values in the vicinity of the equivalence point need be noted.8.3.2 Back titrationFor chlori
31、de contents of less than 0,5 mg/100 ml, it is preferable to back-titrate. To do this, add 50 ml of acetoneto 50 ml of extract and acidify the solution with a few drops of (1 + 1) nitric acid. After adding a known volumeof 0,0025 mol/l silver nitrate solution, n3, immerse the combination electrode in
32、 the solution and back-titratethe excess silver nitrate with 0,0025 mol/l sodium chloride solution in steps of 0,1 ml to 0,2 ml while stirring,recording the volume required to reach the equivalence point, n4. Evaluate this titration in the same way as thedirect titration.To determine the blank value
33、, either titrate or, better still, back-titrate 50 ml of the water used for extraction afteradding the same amount of nitric acid solution and acetone.Page 4DIN 53125 : 2004-039 Evaluation9.1 CalculationTo calculate the end point of the titration, determine the second differences of the potentials e
34、quivalent to thesame proportions by volume, DDU (see table 1). Then calculate the volume of the silver nitrate solution, n, inml, required to reach the end point as in the following example:n = 0,4 + 0,2 G31G31G32G38G32G38+= 0,54 (1)Table 1: Calculation of titration end point (example)Volume of silv
35、erPotential, 1stdifference, 2nddifference,nitrate solution,E, DU, DDU,n,in mV in mV in mVin ml0,2 730250,4 735 +28330,6 768 11220,8 790 17251,0 7959.2 Plotting a graphAfter every addition of silver nitrate solution, read off the potential and plot the associated values on graphpaper. This will give
36、a graph like that shown in figure 1. Drop a perpendicular from the centre of the point ofinflection to the x-axis and read off the volume. The equivalence point can also be precisely determined fromthe change in the value of the ratio DU/DV, which reaches a maximum at the end point when plotted on t
37、he x-axis.The end point can also be determined from the first derivative of the curve given by the maximum or by plottingthe second difference ratio DDU/DDV against the volume of silver nitrate solution used.9.3 Titration to direct end pointIf the potential curve is steep (which is indicative of a h
38、igh chloride content), the DU/DV ratio at the end pointwill be very large. In such cases, the end point can be determined without any evaluation. In the vicinity of theend point add the silver nitrate solution in drops and observe the potential jump after each addition. The dropthat causes the great
39、est mV deflection indicates the end of the reaction.Calculate the water-soluble chlorides content, v (Cl), in mg/kg, using the following equation:v (Cl) = 21E)(mG30 8 864 (2)Page 5DIN 53125 : 2004-03Figure 1: Titration curveThe volumes of 0,002 5 mol/l silver nitrate solution used in back titration
40、are equal ton1* = n3 n4n0* = n3 n5If back titration is used, calculate the chlorides content, v(Cl), in mg/kg, using the following equation:v (Cl) = 21E*mG30 8 864 (3)wheren1is the volume of 0,0025 mol/l silver nitrate solution used in titrating the extract, in ml;n1* is the volume of 0,0025 mol/l s
41、ilver nitrate solution required in titrating the extract using the back titrationmethod, in ml;n0is the volume of 0,0025 mol/l silver nitrate solution used in titrating the blank solution, in ml;n0* is the volume of 0,0025 mol/l silver nitrate solution required in titrating the blank solution using
42、the backtitration method, in ml;n2is the volume of aqueous extract used for the titration, in ml;n3is the volume of 0,0025 mol/l silver nitrate solution added during the back titration, in ml;n4is the volume of 0,0025 mol/l sodium chloride solution used in back-titrating the extract, in ml;n5is the
43、volume of 0,0025 mol/l sodium chloride solution used in back titrating the blank solution, in ml;mEis the initial sample mass of the oven dry sample, in g.NOTE: If the amount-of-substance concentration of the silver nitrate solution differs from that given in clause 6,use the following equation to d
44、etermine the water-soluble chlorides content, X, in mg/kg:X= u c 105 e)(m21G30(4)whereu is the atomic mass of chlorine (35,45);c is the amount-of-substance concentration of the silver nitrate solution, in mol/l.9.4 Expression of resultCalculate the mean of two determinations and report the water-sol
45、uble chlorides content of the oven dry samplein mg/kg, to two decimal places (indicating results below 25 mg/kg as less than 25 mg Cl/kg and resultsexceeding 25 mg Cl/kg as greater than 25 mg Cl/kg).Equivalence pointAgNO3solution, in mlPage 6DIN 53125 : 2004-03Variations in the results may indicate
46、a non-uniformity of the chloride content of the sample. This will necessitatethe collection of several samples and a statistical evaluation of test results.10 Test reportThe test report shall refer to this standard and include the following details:a) type and designation of sample;b) chloride content of sample (single values and mean), in mg/kg;c) name of analyst;d) date and place of testing;e) any departure from this method that could have affected the result.
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