1、May 2015DEUTSCHE NORM English price group 10No part of this translation may be reproduced without 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).ICS 71.040.40!%KBg“2403168w
2、ww.din.deDIN 19266pH measurement Reference buffer solutions for the calibration of pH measuring equipment,English translation of DIN 19266:2015-05pHMessung Referenzpufferlsungen zur Kalibrierung von pHMesseinrichtungen,Englische bersetzung von DIN 19266:2015-05Mesure du pH Solutions tampons de rfren
3、ce pour ltalonnage des appareils de mesure du pH,Traduction anglaise de DIN 19266:2015-05SupersedesDIN 19266:200001www.beuth.deDocument comprises 15 pagesDDIN-Normenausschuss Materialprfung (NMP)DIN-Sprachendienst06.16a DIN 19266:2015-05 2 A comma is used as the decimal marker. Contents Page Forewor
4、d . 3 1 Scope 4 2 Normative references 4 3 Terms and definitions 4 4 Fundamentals . 5 4.1 General 5 4.2 pH values of primary reference buffer solutions . 5 4.3 pH values of secondary reference buffer solutions. 6 5 Preparation of primary and secondary reference buffer solutions 9 5.1 General 9 5.2 R
5、eference buffer solution A, pH(S) = 1,679(25 C), Potassium tetraoxalate 9 5.3 Reference buffer solution B, pH(S) = 3,557(25 C), Potassium hydrogen tartrate . 9 5.4 Reference buffer solution C, pH(S) = 4,005(25 C), Potassium hydrogen phthalate 9 5.5 Reference buffer solution D, pH(S) = 6,865(25 C), P
6、hosphate . 9 5.6 Reference buffer solution E, pH(S) = 7,413(25 C), Phosphate 9 5.7 Reference buffer solution F, pH(S) = 9,180(25 C), Borax . 9 5.8 Reference buffer solution G, pH(S) = 12,454(25 C), Calcium hydroxide. 10 5.9 Reference buffer solution H, pH(S) = 3,776(25 C), Potassium dihydrogen citra
7、te . 10 5.10 Reference buffer solution I, pH(S) = 10,012(25 C), Sodium carbonate/sodium hydrogen carbonate 10 6 Storage and shelf life 10 7 Examples of pH(S) values of reference buffer solutions . 10 8 Additional properties of reference buffer solutions 10 Annex A (informative) Examples of pH(S) val
8、ues as a function of temperature at temperatures from 55 C to 95 C . 12 Annex B (informative) Volumetric method . 13 Bibliography . 15 DIN 19266:2015-05 3 Foreword This document has been prepared by DIN-Normenausschuss Materialprfung (DIN Standards Committee Materials Testing), Working Committee NA
9、062-09-21 AA pH-Messtechnik. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. DIN shall not be held responsible for identifying any or all such patent rights. Amendments This standard differs from DIN 19266:2000-01 as follows: a) t
10、he standard has been technically and editorially revised; b) Clause 5 has been completely revised and volumetric values have been replaced by gravimetric values. The advantage is that temperature does not play a role when preparing the solutions. As compared to the previous edition of this standard,
11、 there are minor changes in the resulting concentrations prepared (up to approximately 1 %); c) the volumetric values from Clause 5 of the previous edition have now been included in Annex A)(informative); d) Table 1 has been restructured to contain typical values for primary and secondary reference
12、buffer solutions. Previous editions DIN 19266: 1971-10, 1979-08, 2000-01 )Translators note. Error in German original. It should read “Annex B”. Corrigenda (2017-05) The English version of DIN 19266:2015-05 has been corrected as follows: In the explanation of the symbol “k” in Equation 4, “Nernst slo
13、pe” has been changed to “Nernst voltage”. In 5.10, “disodium hydrogen phosphate” has been corrected to “sodium hydrogen carbonate”. DIN 19266:2015-05 4 1 Scope This standard specifies reference buffer solutions for the calibration of pH measuring equipment. 2 Normative references The following docum
14、ents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. DIN 19261, pH measurement
15、Measuring methods with potentiometric cells Terms and definitions DIN 19268, pH measurement pH measurement of aqueous solutions with pH measuring chains with pH glass electrodes and evaluation of measurement uncertainty ISO 4793:1980, Laboratory sintered (fritted) filters Porosity grading, classific
16、ation and designation 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 pH value negative logarithm to base 10 of the ratio of the hydrogen ion activity, H, to the standard molality, 01 pH = lgH0 (1) with H= HHwhere His the activity of the hydr
17、ogen ion, in mol/kg; 0is the standard molality (1 mol/kg); His the activity coefficient of the hydrogen ion; His the molality of the hydrogen ion, in mol/kg. SOURCE: DIN 19260:2012-10, term 2.3, modified the definition has been shortened to one sentence, Notes 1 and 2 have not been included, and the
18、 term “unit of molality” has been replaced by “standard molality” DIN 19266:2015-05 5 4 Fundamentals 4.1 General Reference buffer solutions are prepared using primary or secondary reference materials. The pH values of the reference buffer solutions are determined using the methods described in 4.2 a
19、nd 4.3. The pH value of a reference buffer solution and the associated uncertainty of measurement are documented in a calibration certificate as the result of calibration. pH values of primary reference buffer solutions form the basis of pH measurements in practice and are generally determined by na
20、tional metrology institutes, such as the Physikalisch-Technische Bundesanstalt (PTB) in Germany or the National Institute of Standards and Technology (NIST) in the United States. Secondary reference buffer solutions are commercially available. The reference buffer solutions prepared according to the
21、 methods described in Clause 5 serve as a material measure of the pH value. 4.2 pH values of primary reference buffer solutions By its very nature, the pH value based upon the activity of single ions according to Equation (1) is not able to be measured. pH is therefore determined using reference buf
22、fer solutions, listed in Table 1. This is achieved using an electrochemical method of measurement that is based on the thermodynamic dependence of the potential of the platinum/hydrogen electrode on the hydrogen ion activity. Through the use of cells without transference, diffusion voltages are mini
23、mized and do not need to be considered when calculating the voltage of the cell. The cell (I) for this purpose shall consist of a platinum/hydrogen and a silver/silver chloride electrode, immersed in the reference buffer solution to which chloride in a low concentration (Cl) has been added, Pt|Ag|Ag
24、Cl(sat.)|reference buffer solution, pH(S), Cl(Cl)|Pt, H2(H2= 101 325 Pa). (I) The pH value of the reference buffer solution is calculated according to Equation (2): pH = Cl0(0)+ lg Cl0+ lgCl(2) where is the cell voltage; 0is the standard electrode potential; is the Nernst slope ( = (ln10)/); 0is the
25、 standard molality (1 mol/kg); Clis the molality of the chloride ions in the solution; Cl is the activity coefficient of the chloride ion. Chloride is added to the reference buffer solution in a minimum of three different molalities less than or equal to 0,02 mol/kg. To calculate the pH value, Cl 0
26、is extrapolated according to Equation (2). The activity coefficient of the chloride ions is estimated according to Equation (3) for solutions with an ionic strength of less than or equal to 0,1 mol/kg 2. lgCl= 1 21+1,5(/0)1 2(3) DIN 19266:2015-05 6 where is the Debye-Hckel constant; Cl is the activi
27、ty coefficient of the chloride ion; 0is the standard molality (1 mol/kg); is the ionic strength. pH values of primary reference buffer solutions are often referred to as pH(S) (S = Standard). The expanded uncertainty of measurement U(pH) when determining a pH(S) value has been shown to be 0,002 to 0
28、,005 at 25 C depending on the primary reference buffer solution. As agreed, this uncertainty of measurement does not take into consideration the uncertainty of the Bates-Guggenheim convention for estimating the ionic activity of the chloride ion (Equation (3) 3. The expanded measurement uncertainty
29、of many pH(S) value measurements of primary reference buffer solutions prepared according to Clause 5 is U(pH) = 0,005 at 25 C and U(pH) = 0,008 at 50 C, depending on the buffer solution, due to the method of measurement and the purity and homogeneity of the materials used for different batches. Acc
30、ordingly, the pH(S) values of each batch can vary. Therefore, the pH(S) value is only valid for an individual batch with a corresponding calibration certificate, e.g. issued by PTB. For buffer solution G, the expanded uncertainty of measurement of the pH(S) values is U(pH) = 0,006 at 25 C and U(pH)
31、= 0,01 for temperatures higher than 25 C. The data has been taken from 4. Contributions to uncertainty are a result of the method of measurement used as well as the purity and homogeneity of the material used. Typical pH values of reference buffer solutions for the temperature range of 0 C to 50 C a
32、re given in Table 1. 4.3 pH values of secondary reference buffer solutions The differential potentiometric method 5 is suitable for determining the pH values of secondary reference buffer solutions against primary reference buffer solutions with the same chemical composition. The isothermal cell use
33、d for this purpose (II) shall consist of two electrodes separated by a P 40 glass frit according to ISO 4793:1980, and containing the primary and secondary standard buffer solutions and identical platinum hydrogen electrodes at exactly the same hydrogen pressure, i.e. Pt, H2(H2)|prim. ref. buffer, p
34、H(S) | sec. ref.buffer, pH|Pt, H2(H2). (II) The cell voltage E of cell (II) is a measure of the difference in the pH values of the solutions and enables the pH value of the secondary reference buffer solution to be determined using Equation (4), provided the absolute difference is |pH(S)-pH 0,02| an
35、d the pH of the solutions is between 3 and 11. The diffusion voltage is then less than 10 % of the measured cell voltage E and the cell is virtually without transference. pH = pH(S) / (4) where is the Nernst voltage ( = (ln10)/); is the cell voltage. Measured cell voltages are in the order of magnit
36、ude of a few hundred microvolts (V). Consequently, pH differences down to 0,001 can be determined. The expanded uncertainty of measurement U of the pH value of the secondary reference buffer solution ranges from 0,003 to 0,006 at 25 C when determining a single pH value depending on the type of secon
37、dary reference buffer solution, and is only slightly greater than that of the pH(S) values of primary reference buffer solutions determined using cell (I). DIN 19266:2015-05 7 Table 1 Typical values of primary and secondary reference buffer solutions Reference buffer solution A B C D E F G H I Buffe
38、r material Potassium tetraoxalate dihydrate KH3(C2O4)22 H2O Potassium hydrogen tartrate KHC4H4O6Potassium hydrogen phthalate KHC8H4O4Potassium dihydrogen phosphate + Disodium hydrogen phosphate KH2PO4 + Na2HPO4Potassium dihydrogen phosphate + Disodium hydrogen phosphate KH2PO4 +Na2HPO4Disodium tetra
39、borate decahydrate Na2B4O710 H2O Calcium hydroxide Ca(OH)2Potassium dihydrogen citrate KH2C6H5O7Sodium carbonate + Sodium hydrogen carbonate Na2CO3 + NaHCO3Molality mol/kg 0,05 saturated at 25 C 0,05 0,025 (KH2PO4) + 0,025 (Na2HPO4) 0,008695 (KH2PO4) + 0,03043 (Na2HPO4) 0,01 saturated at 25 C 0,05 0
40、,025 (Na2CO3) + 0,025 (NaHCO3) Temperature C pH(S) values 0 1,666 4,000 6,984 7,534 9,464 3,863 10,317 5 1,668 3,998 6,951 7,500 9,395 13,207 3,840 10,245 10 1,670 3,997 6,923 7,472 9,332 13,003 3,820 10,179 15 1,672 3,998 6,900 7,448 9,276 12,810 3,802 10,118 20 1,675 4,000 6,881 7,429 9,225 12,627
41、 3,788 10,062 25 1,679 3,557 4,005 6,865 7,413 9,180 12,454 3,776 10,012 DIN 19266:2015-05 8 Table 1 (continued) Temperature C pH(S) values 30 1,683 3,552 4,011 6,853 7,400 9,139 12,289 3,766 9,966 35 1,688 3,549 4,018 6,844 7,389 9,102 12,133 3,759 9,926 37 3,548 4,022 6,841 7,386 9,088 3,756 9,910
42、 38 1,691 12,043 40 1,694 3,547 4,027 6,838 7,380 9,068 11,984 3,754 9,889 45 11,841 50 1,707 3,549 4,050 6,833 7,367 9,011 11,705 3,749 9,828 NOTE The data for buffers A and G were taken from 4 and the data for the buffers B, C, D, E, F, H and I were taken from 6. Working-reference buffer solutions
43、 for use in daily practice are measured according to DIN 19268 and characterized with regard to measurement uncertainty. DIN 19266:2015-05 9 5 Preparation of primary and secondary reference buffer solutions 5.1 General The reference buffer solutions in Table 1 form the basis of practical pH measurem
44、ents. They are prepared gravimetrically according to the following instructions using reference materials appropriate for use in making pH reference buffer solutions. The pH value of reference buffer solutions prepared according to 5.2 to 5.10 shall be determined with one of the methods given above
45、(see 4.2 and 4.3) or a similar method. The numbers given for pH(S) values are designations of the particular reference buffer solutions and are to be understood as names. Consequently, they can differ from those given in Table 1. The values stated on the certificates of the reference materials are b
46、inding. When preparing the saturated solutions (see 5.3 and 5.8) care is to be taken that a temperature of (25,0 0,5) C is maintained. 5.2 Reference buffer solution A, pH(S) = 1,679(25 C), Potassium tetraoxalate Dissolve 12,74 g of potassium tetraoxalate dihydrate, KH3(C2O4)22 H2O, in 1 000 g water.
47、 5.3 Reference buffer solution B, pH(S) = 3,557(25 C), Potassium hydrogen tartrate Add 6,40 g of potassium hydrogen tartrate, KHC4H4O6, to 1 000 g water. After shaking or stirring vigorously until the solution is saturated, filter off the excess salt.)5.4 Reference buffer solution C, pH(S) = 4,005(2
48、5 C), Potassium hydrogen phthalate Dry potassium hydrogen phthalate, KHC8H4O4, for two hours at 110 C. Dissolve 10,21 g of this material in 1 000 g water. The solution has a shelf life of approximately 6 weeks. Solutions affected by fungal infestation shall not be used. 5.5 Reference buffer solution D, pH(S) = 6,865(25 C), Phosphate Dry anhydrous potassium dihydrogen phosphate, KH2PO4, and anhydrous disodium hydrogen phosphate, Na2HPO4, for two hours at 110 C. Dissolve 3,40 g of potassium dihydrogen phosphate and 3,55 g of disodium h
