1、CEN EN825bb3 93 3404589 0052808 TT2 EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 25663 September 1993 UDC 628.U.3 : 620.1 : 546.17 Descriptors: Water tests, potable water, sewage, quality, water pollution, chemical analysis, determination of content, nitrogen, Kjeldahl method, mineralization
2、, selenium English version Water quality - Determination of Kjeldahl nitrogen - Method after mineralization with selenium (IS0 5663 : 1984 ) Qualit de l?eau - Dosage de l?azote Kjeldahl - Mthode aprs minralisation slnium Aufschlug mit Selen (IS0 5663 : 1984) Wasserbeschaffenheit - Bestimmung von Kje
3、ldahl-Stickstoff - Verfahren nach (IS0 5663 : 1984) This European Standard was approved by CEN on 1993-09-10. CEN members are bound to comply with the CENKENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any altera
4、tion. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by transla
5、tion under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg,
6、 Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels O 1993 Copyright reserved to CEN members Ref. No. EN 25663
7、: 1993 E CEN EN*25bb3 93 W 3r104589 0052809 939 W Page 2 EN 26663 : 1993 Foreword This European Standard has been taken over by CEN/TC 230 Water quaiity from the wqrk of ISO/Tc 147 Water quaiity of the InteniPtional organization for Standardization (ISO). CENm 230 decided to submit this Final Draft
8、to the CEN members for voting by Unique Acceptance Procedure (UAP) . The result of the Unique Acceptance Procedure was positive. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by March 1994, and con
9、flicting national standards shail be withdrawn at the latest by March 1994. In accordance with the CENKENELEC Internal Regulations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg,
10、 Netherlands, Norway, Portuga, Spain, Sweden, Switzerland and United Kingdom. CEN EN*25bb3 93 m 3404589 0052830 650 m Page 3 EN 25663 : 1993 Water quality - Determination of Kjeldahl nitrogen - Method after mineralization with selenium 1 Scope and field of application 1.1 Substance determined This I
11、nternational Standard specifies a method for the deter- mination of nitrogen by a Kjeldahl-type method. Only trivalent negative nitrogen is determined. Organic nitrogen in the form of azide, azine, azo, hydrazone, nitrite, nitro, nitroso, oxime or semicarbazone is not determined quantitatively. Nitr
12、ogen may be incompletely recovered from heterocyclic nitrogen com- pounds. 1.2 Type of sample This method is applicable to the analysis of raw, potable and waste waters. 1.3 Range A Kjeldahl nitrogen content, N, of up to 10 mg, in the test por- tion may be determined. Using a 10 ml test portion, thi
13、s cor- responds to a sample concentration of up to N = 1 o00 mg/l. 1.4 Limit of detection A practically determined (4 degrees of freedom) limit of detec- tion, using a 100 ml test portion, is Q = 1 mg/l. 1.5 Sensitivity Using a 100 ml test portion, 1,0 ml of 0.02 mol/l hydrochloric acid is equivalen
14、t to N = 2,8 mg/l. 2 Reference IS0 7150/1, Water quality - Determination of ammonium - hrt I: Manual spectrometric method. 3 Definition For the purpose of this International Standard, the following definition applies: Kjeldahl nitrogen: The content of organic nitrogen and am- moniacal nitrogen in a
15、sample determined after mineralization. It does not include nitrate and nitrite nitrogen, and does not necessarily include all organically bound nitrogen. 4 Principle Mineralization of the sample to form ammonium sulfate, from which ammonia is liberated and distilled for subsequent deter- mination b
16、y titration. Conversion of the nitrogen compounds responding to the test to ammonium sulfate by mineralization of the sample with sulfuric acid, containing a high concentration of potassium sulfate in order to raise the boiling point of the mixture, in the presence of selenium which acts as a cataly
17、st. 1) Liberation of ammonia from the ammonium sulfate by the addi- tion of alkali and distillation into boric acid/indicator solution. Determination of ammonium ion in the distillate by titration with standard acid. Alternatively, direct determination of ammonium ion in the mineralizate by spectrom
18、etry at 655 nm. (See clause 11 .I 5 Reagents During the analysis, use only reagents of recognized analytical grade, and only distilled water prepared as described in 5.1. 5.1 ing methods. Water, ammonium-free, prepared by one of the follow- 5.1.1 Ion exchange method Pass distilled water through a co
19、lumn of strongly acidic cation exchange resin (in the hydrogen form) and collect the eluate in a glass bottle provided with a well-fitting glass stopper. Add about 10 g of the same resin to each litre of collected eluate for storage purposes. 1) Selenium has been selected as the catalyst in preferen
20、ce to mercury because of concern in many countries about the toxicity of mercury. However, the toxicity of selenium must not be overlooked. See 11.2 for a suggested procedure for removal of selenium from mineralization residues. page 4 EN 26663 : 1993 5.1.2 Distillation method Add 0.10 f 0,Ol ml of
21、sulfuric acid (5.3) to 1 O00 f 10 ml of distilled water and redistil in all glass apparatus. Discard the first 50 ml of distillate, and then collect the distillate in a glass bottle provided with a well-fitting glass stopper. Add about 10 g of strongly acidic cation exchange resin (in the hydrogen f
22、orm) to each litre of collected distillate. 5.2 Hydrochloric acid, Q = 1.18 g/ml. 5.8 Catalyst mixture. WARNING - This mixture is toxic. Inhalation of any dust resulting from its preparation or use shall be avoided. All residues containing selenium shall be collected for selenium recovery (11.2) or
23、controlled disposal. Thoroughly mix 1 O00 f 20 g of potassium sulfate and 10.0 f 0,2 g of selenium pellets. 5.9 Anti-bumping granules. 5.3 Sulfuric acid, e = 1,M giml. 6 Apparatus WARNING - This reagent causes severe burns. The highest purity sulfuric acid shall always be used. Pay par- ticular atte
24、ntion to the manufacturers specification with respect to its nitrogen content. 5.4 Sodium hydroxide, approximately 500 g/l solution. WARNING - This reagent causes severe burns. Dissolve 500 f a) g of sodium hydroxide in about 800 ml of water. Cool to room temperature and dilute to 1 litre with water
25、 in a measuring cylinder. 5.5 Hydrochloric acid, standard volumetric solution, dHCH = 0.10 mol/l. This solution shall be prepared by dilution of hydrochloric acid (5.2) followed by standardization by normal analytical pro- cedures. Alternatively, a commercial solution of guaranteed concentration may
26、 be used. 5.6 Hydrochloric acid, standard volumetric solution, cHCI) = 0.02 mol/l. This solution shall be prepared by dilution of hydrochloric acid (5.2 or 5.5) followed by standardization by normal analytical procedures. Alternatively, a commercial solution of guaranteed concentration may be used.
27、5.7 Boric acid/indicator, solution. 5.7.1 Dissolve 0,5 f 0,l g of methyl red in about 800 ml of water and dilute to 1 litre with water in a measuring cylinder. 5.7.2 Dissolve 1,5 f 0,l g of methylene blue in about 800 ml of water and dilute to 1 litre with water in a measuring cylinder. 5.7.3 Dissol
28、ve 20 f 1 g of boric acid (H3B03) in warm water. Cool to room temperature. Add 10 f 0.5 ml of methyl red solu- tion (5.7.1) and 2,O f 0,l ml of methylene blue solution (5.7.2) and dilute to 1 litre with water in a measuring cylinder. Ordinary laboratory apparatus and : 6.1 Kjeldahl mineralization fl
29、asks, specially designed, of sufficient capacity to accommodate the test portion volume to be used in the analysis, and in any event not exceeding 500 mi. They should preferably be suitable for direct attachment to the distillation apparatus (6.2). 6.2 Distillation apparatus, incorporating an anti-s
30、plash distillation head and a vertical condenser whose outlet can be submerged in the absorbent solution. If the Kjeldahl flasks (6.1) are not suitable for direct attachment to the distillation apparatus, separate distillation flasks are necessary. NOTE ON PRELIMINARY CLEANING OF THE DISTILLATION AP
31、PARATUS Carry out the following procedure whenever the apparatus has been out of use for more than a few days. Add about 350 mi of water (5.1) to the distillation flask. Add a few anti-bumping granules (5.91, assemble the apparatus, and distil at least 100 mi. Discard the distillate and the residue
32、in the distillation flask. 7 Sampling and samples Laboratory samples shall be collected in polyethylene or glass bottles. They should be analysed as quickly as possible, or else stored at between 2 and 5 OC until analysed. Acidification with sulfuric acid (5.3) to pH 2 may also be used as an aid to
33、preservation, provided that possible contamination of the acidified sample by absorption of any atmospheric ammonia is avoided. 8 Procedure 8.1 Test portion If the approximate nitrogen concentration of the sample is known, the test portion volume can be selected from table 1. CEN EN825bb3 93 3404569
34、 0052832 423 Kjeldahl nitrogen concentration, eN Page 5 EN 25663: 1993 Volume of the test portion* Table 1 - Selection of test portion up to 10 loto 20 20 to 50 50 to 100 * When using the 0,02 mol/l hydrochloric acid standard volumetric solution (5.6) for titration. 8.2 Blank test Proceed as describ
35、ed in 8.3, but using about 250 ml of water (5.1) instead of a test portion. Record the volume of hydrochloric acid (5.6) added. 8.3 Determination WARNING - The mineralization procedure may evolve toxic sulfur dioxide gas. Hydrogen sulfide and/or hydrogen cyanide may also be liberated from polluted s
36、amples. The mineralization should therefore be carried out under an effective fume extraction system. Place the test portion (8.1) in a Kjeldahl flask (6.1) and add, from a measuring cylinder, 10 ml of sulfuric acid (5.3) and 5,O I 0,5 g of the catalyst mixture (5.8). Add a few anti- bumping granule
37、s (5.9) and boil the flask contents rapidly, under a suitable fume extraction system. The volume of the contents will decrease as water is boiled away, then evolution of white fumes will begin. After fume evolution has ended, periodically observe the mineralizate and, after it has become clear and e
38、ither colourless or light brown in colour, continue heating for a further 60 min. (See note 1.) After mineralization allow the flask to cool to room tempera- ture. Meanwhile, measure 50 * 5 ml of indicator (5.7) into the receiving flask of the distillation apparatus. Ensure that the delivery tip of
39、the condenser is below the surface of the in- dicator solution. Carefully add 250 I 50 ml of water (5.1 ) to the mineralization flask, together with a few anti-bumping granules (5.9). Then add, from a measuring cylinder, 50 ml of sodium hydroxide solution (5.4) and immediately attach the flask to th
40、e distillation apparatus.(See note 2.) Heat the distillation flask so that distillate collects at a rate of about 10 ml/min. Stop the distillation when about 200 ml have been collected. Titrate the distillate to a purple end-point with 0,02 mol/l hydrochloric acid (5.6) and record the volume added.
41、(See note 3). NOTES 1 After water has boiled away, the rate of heating should be sufficient to reflux the acid mixture half-way up the neck of the flask. This en- sures the attainment of a sufficiently high mineralization temperature. 2 Where the flask is not compatible with the distillation apparat
42、us, the contents must be transferred quantitatively to a suitable distillation flask. This may conveniently be done at the water addition stage. 3 0.10 moll1 hydrochloric acid (5.51 may be used for the titration of distillates from samples containing high concentrations of nitrogen. 9 Expression of
43、results 9.1 Method of calculation The Kjeldahl nitrogen Concentration, N, expressed in milligrams per litre, is given by the formula “ - ” x c x 14,Ol x 1 O00 VO where Vo is the volume, in millilitres, of the test portion (see 8.1 1; Vi hydrochloric acid used for titration (see 8.3); is the volume,
44、in millilitres, of the standard volumetric V2 is the volume, in millilitres, of the standard volumetric hydrochloric acid used for the titration in the blank test (see 8.2); c is the exact concentration, expressed in moles per litre, of the hydrochloric acid used for titration; 14,Ol is the relative
45、 atomic mass of nitrogen. The result may be expressed as the mass concentration of nitrogen, eN, in milligrams per litre, or as the amount of substance concentration of nitrogen, cN, in micromoles per litre. TO convert N to cN, multiply N by 71.4. 9.2 Repeatability Repeatability standard deviations
46、have been determined as shown in table 2. 10 Interferences The presence of nitrate and/or nitrite may be a cause of both negative and positive errors. Nitrate and/or nitrite may be reduced under the test conditions to ammonium, leading to falsely high results. Nitrate and/or nitrite may also form am
47、- monium salts with ammonium in the sample. These salts may be decomposed at the temperature of the mineralization, resulting in the loss of nitrogen in gaseous forms and conse- quently low results. If the concentration of nitrate and/or nitrite in the sample seems likely to cause unacceptable bias
48、or loss of precision, separate reduction to ammonium should precede the mineralization process. Falsely low results may also be obtained if the mineralization procedure is over-prolonged. The procedure given in clause 8 must be carefully observed. CEN EN+25bb3 93 340q589 00528L3 3bT Nitrogen concent
49、ration, e., mg/l 2 50 150 79“ 16“ 6.2“ Wge 6 EN 25663 : 1993 Test portion Standard deviation* Degr- Of freedom volume ml mg/l 500 0,027 19 100 0.31 19 100 2.69 19 50 0.68 19 No 0,19 15 100 QM 15 11 Notes on procedure 11.1 Ammonium ion may be determined directly in the mineralizate by spectrometry at 656 nm. The following pro- cedure should be used. After allowing the flask to cool following mineralization, add 50 f 10 ml of water (5.1) to the flask. Add 2 drops of a solu- tion of 4-nitrophenol, 1 g/l. Then, very slowly, add sodium hydroxide solution (5.4) while
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