1、Designation: E258 07 (Reapproved 2015)Standard Test Method forTotal Nitrogen in Organic Materials by Modified KjeldahlMethod1This standard is issued under the fixed designation E258; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 This test method co
3、vers the determination of totalnitrogen in nitrogen-containing organic compounds. This testmethod is not applicable for use on materials containing N-O,N-N linkages.1.2 The values stated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.1.3 This stand
4、ard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 1Another method of restr
5、icted application is given in TestMethod D1013.2. Referenced Documents2.1 ASTM Standards:2D1013 Test Method for Determining Total Nitrogen inResins and Plastics (Withdrawn 2007)3D1193 Specification for Reagent WaterE200 Practice for Preparation, Standardization, and Storageof Standard and Reagent So
6、lutions for Chemical Analysis3. Summary of Test Method3.1 The sample is digested in a mixture of concentratedsulfuric acid, potassium sulfate, and mercuric oxide. Theamounts of organic matter, potassium sulfate, and sulfuric acidpresent during the digestion step are critical. The organicmaterial is
7、oxidized and the nitrogen converted to ammoniumsulfate. Sodium sulfide is added to the digested mixture toprecipitate the mercury after which the solution is madestrongly alkaline with sodium hydroxide solution and theammonia which is liberated is distilled into a measured volumeof standard acid. Th
8、e amount of acid neutralized by theammonia is determined by titrating the excess acid withstandard sodium hydroxide solution.4. Significance and Use4.1 This test method may be used to determine the totalnitrogen content of certain unknown organic samples, or toassay known nitrogen containing organic
9、 compounds.4.2 This test method may be used on organic materials inwhich the complete conversion of nitrogen to ammoniumsulfate can be accomplished by digestion in a mixture ofsulfuric acid, potassium sulfate, and mercuric oxide. It cannotbe used on materials containing NO, NN linkages.4.3 This test
10、 method assumes that ammonia can be quanti-tatively measured by distillation from an alkaline solution intoa measured volume of standard acid.5. Apparatus5.1 Kjeldahl Flasks of moderately thick, well-annealedborosilicate glass for digestion and distillation, 500 or 800-mLcapacity.NOTE 2The usual fla
11、sk and connecting bulb commercially availableare made to be assembled by means of a rubber stopper. To minimizelacerations from broken flasks while assembling the apparatus, it isrecommended that the flask have an outer spherical 35/25 joint and thebulb have an inner spherical 35/25 joint. This type
12、 apparatus is heldtogether by a spring clamp.5.2 Connecting Bulbs of the Willits-John type, or a scrubberbulb equally effective in preventing mechanical carry-over ofthe contents of the distillation flask to the condenser (Note 2).5.3 Digestion and Distillation Equipment consists of anadjustable hea
13、ter, water-cooled condenser, receiver support,and fume disposal unit. Any of the well-known commercial1This test method is under the jurisdiction of ASTM Committee E15 onIndustrial and Specialty Chemicalsand is the direct responsibility of SubcommitteeE15.01 on General Standards.This test method has
14、 been adopted from Method 2.054 of the Official Methodsof Analysis of the Association of Official Agricultural Chemists, 13th Edition, 1980.Current edition approved June 1, 2015. Published June 2015. Originallyapproved in 1965. Last previous edition approved in 2007 as E258 07. DOI:10.1520/E0258-07R
15、15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is
16、referenced onwww.astm.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Kjeldahl digestion and distillation units are suitable. The unitsmay be heated either electrica
17、lly or by gas burner but must beadjusted after an initial warm-up period to bring 250 mL ofwater to a rolling boil in 4 to 6 min. Before testing the unit,preheat for 10 min if a gas heater or 30 min if an electric heater.For the test add three to four boiling chips to prevent superheating.5.4 Delive
18、ry Tubes made of moderately heavy-wall glasstubing, 150 to 200 mm (6 to 8 in.) in length, for conducting thedistillate from the condenser to the receiver.5.5 Receiver Flask, 500-mL capacity, wide-mouth Erlen-meyer flask.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tes
19、ts. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.4Other grades may beused, provided it is first ascertained that the reagent is ofsuffi
20、ciently high purity to permit its use without lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean Type II or III reagentwater conforming to Specification D1193.6.3 Indicator Solution (either may be used):6.3.1 Methy
21、l Purple Indicator SolutionCommerciallyavailable.6.3.2 Methyl Red Indicator SolutionDissolve1gofmethyl red in 200 mL of ethyl alcohol (denatured alcohol,formula 2B, 3A, or 30A of the U.S. Bureau of InternalRevenue, may be used).6.4 Mercuric Oxide (HgO).NOTE 3Packaged units available commercially, co
22、ntaining the re-quired weight of mercuric oxide and potassium sulfate are satisfactory.6.5 Potassium Sulfate (K2SO4), anhydrous (Note 3).6.6 Sodium Hydroxide Solution (450 g/L)Dissolve 450 gof sodium hydroxide (NaOH) in water and dilute to 1 L.Alternatively a 50 % sodium hydroxide solution can be di
23、lutedwith water to give a solution having a specific gravity of 1.36or higher.6.7 Sodium Hydroxide, Standard Solution (0.1 or 0.5meq/mL (N)Prepare and standardize in accordance withPractice E200.6.8 Sulfide SolutionDissolve 40 g of potassium sulfide orsodium sulfide in water and dilute to 1 L.6.9 Su
24、lfuric Acid (sp gr 1.84)Concentrated sulfuric acid(H2SO4).NOTE 4In the analysis of samples containing nitrile or cyanategroups, which are easily hydrolyzed, the concentrated sulfuric acid mustcontain essentially no water. The acid should be taken from a freshlyopened bottle, or boiled just prior to
25、use, or preferably, a small amount ofphosphorus pentoxide should be added to the acid.6.10 Sulfuric Acid, Standard (0.1 or 0.5 meq/mL (N)Prepare in accordance with the Precision and Bias Section inthe portion of Practice E200 pertaining to hydrochloric acid,0.02 to 1.0 me1/mL (N). An exact standardi
26、zation of thisreagent is not necessary.6.11 Zinc, granular.7. Procedure7.1 Place the sample, weighed to 0.0001 g, in a Kjeldahldigestion flask. The weight of sample will depend uponwhether 0.1 or 0.5 meq/mL (N) H2SO4is used as the standardacid; if 0.1 me1/mL (N) acid is used, the sample should conta
27、inbetween 14 and 56 mg of nitrogen and if 0.5 N acid is used thesample should contain between 70 and 280 mg of nitrogen, butthe sample weight taken should normally be less than 2.2 g.NOTE 5The optimum weight of sample to be digested, if of unknowncomposition, must be determined by a trial determinat
28、ion. Since the natureand amount of the sample will affect the amount of acid consumed in thedigestion, the preferred weight of sample is one that will give the largestamount of nitrogen within the prescribed range while using the smallesttotal weight of sample and adhering to the prescribed maximum.
29、7.2 To the flask add 0.7 g of HgO, 15 g of K2SO4, and 25mL of H2SO4(sp gr 1.84) (Note 3, Note 6). Place the flask inan inclined position and heat gently until frothing ceases, thenboil briskly causing the condensate to be formed approximatelyhalf way up the neck of the flask. Continue boiling until
30、thesolution clears and then for 2 h longer (Note 7).NOTE 6The temperature of the digestion mixture is critical and isregulated by the ratio of salt to acid (free acid at the completion of thedigestion period). The ratio must be kept close to 1:1 (weight:volume)K2SO4-to-free acid in weight from the w
31、eight of acid initially added, andconverting weight of acid to a volume basis. If a sample weight in excessof 2.2 g is used, increase the volume of acid by 10 mL for each1ginexcess.NOTE 7For easily digested materials a digestion period of 30 minafter clearing may be adequate.7.3 Add exactly 50 mL of
32、 the standard acid (see 7.1 forconcentration to be used) and 5 to 7 drops of indicator solutionto the receiving flask. Connect the delivery tube to thecondenser and place the receiver under the condenser with thedelivery tube extending to the bottom of the flask.7.4 Cool the digestion mixture in the
33、 Kjeldahl flask toapproximately room temperature. Add approximately 200 mLof water, and swirl (Note 8). Cool the contents of the flask tobelow 25C, add 25 mLof the sulfide solution to precipitate themercury, and swirl. Add a few zinc granules to preventbumping, tilt the flask, and add an excess (Not
34、e 9) of the NaOHsolution (450 g/L) down the inclined neck of the flask withoutagitation to form two layers. Immediately connect the flask tothe connecting bulb attached to the condenser, and mix thecontents of the flask thoroughly by swirling (Note 10).NOTE 8Before addition of the water, the content
35、s of the flask shouldhave a syrup-like consistency. If the contents of the flask do not dissolve4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar St
36、andards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.E258 07 (2015)2completely in the water, discard the determination (evidence of impropersalt-acid ratio).NOTE 9To determin
37、e the required volume of alkali, dilute the samevolume of acid used for the determination with water and note the volumeof NaOH solution (450 g/L) required to neutralize the solution to thephenolphthalein end point. This will give an excess since acid is consumedor volatilized during digestion of th
38、e sample.NOTE 10The digestion flask must be connected to the connecting bulband the rest of the apparatus immediately after the alkali has been addedand layered, but before swirling to mix the concentrated acid and alkali.Should any mixing occur before the digestion flask is connected, the heatof ne
39、utralization may be sufficient to volatilize some of the ammoniawhich would be lost, yielding low recoveries.7.5 Promptly heat the flask and collect the distillate in thereceiver containing the standard acid solution (Note 11).Continue the distillation until all of the ammonia has beencollected (a m
40、inimum of 150 mL of distillate).NOTE 11Heat must be applied promptly to prevent sucking thestandard acid into the condenser if the digestion solution cools. The initialdistillation rate must not be too rapid since most of the ammonia isdistilled during the first few minutes and if too large an amoun
41、t is presentit may not be completely trapped in the standard acid.7.6 Remove the receiver and delivery tube from the appa-ratus (preferably just before stopping the distillation). Rinse thedelivery tube with water, collecting the rinsings in the receiver.7.7 Titrate the excess acid in the receiver w
42、ith the standardNaOH solution, using the same (approximate) concentration asthe acid used in the receiver. Record the volume to the nearest0.02 mL.7.8 Conduct a blank determination in parallel, using thesame volume of reagents as used in the determination.NOTE 12Water from the same lot should be use
43、d in the blank as in thedetermination since reagent water tends to contain free ammonia whichwould affect the results of samples having a low nitrogen content.8. Calculation8.1 Calculate the nitrogen content as follows:Nitrogen, % 5 $A 2 B! N 30.01401#/C% 3100 (1)where:A = standard NaOH solution req
44、uired for titration ofthe blank, mL,B = standard NaOH solution required for titration ofthe sample, mL,N = normality of the NaOH solution, meq/mLC = sample used, g, and0.01401 = meq weight of nitrogen.9. Report9.1 Report the nitrogen content to the nearest 0.01 % if thecontent is below 1.0 % and to
45、the nearest 0.1 % if the contentis greater than 1.0 %.9.2 Results from duplicate determinations that agree within0.2 % absolute are acceptable for averaging.10. Precision and Bias10.1 The following criteria should be used for judging theacceptability of the results (Note 13):10.1.1 RepeatabilityThe
46、average difference between tworesults (each the average of duplicate determinations) obtainedby the same analyst on different days will approximate 0.1 %absolute. Two such values should be considered suspect (95 %confidence level) if they differ by more than 0.2 % absolute.10.1.2 ReproducibilityThe
47、average difference betweentwo results (each the average of duplicate determinations)obtained by analysts in different laboratories will approximate0.2 % absolute. Two such values will be considered suspect(95 % confidence level) if they differ by more than 0.5 %absolute.10.2 The bias of this test me
48、thod has not been determined.NOTE 13The precision of various Kjeldahl procedures for determi-nation of nitrogen content has been evaluated in several independentinterlaboratory studies. The precision estimates are based on studies: (a)conducted by the Association of Official Agricultural Chemists in
49、 1955and 1956 in which ten or eleven laboratories analyzed one sample each ofnicotinic acid, a urea-formaldehyde resin, a mixed fertilizer of 8-6-4composition, and a mixed fertilizer of 14-14-14 composition,5and (b)conducted byASTM Committee D-1, Subcommittee XI, in 1958, in whichfive laboratories analyzed two samples of a urea-formaldehyde resin, twosamples of a melamine-formaldehyde resin, one sample each of melamineand of acetanilide (Test Method D1013). The precision statements givenabove should be interpreted as guides rather than as specific valu
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