1、Designation: D7184 12Standard Test Method forUltra Low Nitrogen in Aromatic Hydrocarbons by OxidativeCombustion and Reduced Pressure ChemiluminescenceDetection1This standard is issued under the fixed designation D7184; the number immediately following the designation indicates the year oforiginal ad
2、option or, in the case of revision, 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.1. Scope*1.1 This test method covers the determination of totalnitrogen in aromati
3、c hydrocarbons, such as benzene, toluene,and xylene.1.2 This test method is applicable for samples containingnitrogen from 0.38 to 1.2 mg N/kg. For higher nitrogenconcentrations refer to Test Method D6069 or D4629.1.3 In determining the conformance of the test results usingthis method to applicable
4、specifications; results shall berounded off in accordance with the rounding-off method ofPractice E29.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, i
5、f 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. For specific hazardstatements, see Section 9.2. Referenced Documents2.1 ASTM Standards:2D
6、3437 Practice for Sampling and Handling Liquid CyclicProductsD4629 Test Method for Trace Nitrogen in Liquid PetroleumHydrocarbons by Syringe/Inlet Oxidative Combustion andChemiluminescence DetectionD6069 Test Method for Trace Nitrogen in Aromatic Hydro-carbons by Oxidative Combustion and Reduced Pre
7、ssureChemiluminescence DetectionD6809 Guide for Quality Control and Quality AssuranceProcedures for Aromatic Hydrocarbons and Related Ma-terialsE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE691 Practice for Conducting an Interlaboratory Study toDe
8、termine the Precision of a Test Method2.2 Other Documents:OSHA Regulations, 29 CFR paragraphs 1910. 1000 and1910.120033. Terminology3.1 Definitions:3.1.1 oxidative pyrolysis, na process in which a sampleundergoes combustion in an oxygen rich environment attemperatures greater than 900C.3.1.2 pyrolyt
9、ic decomposition, ncombusting a compoundto decompose it to carbon dioxide, water and elemental oxides.3.1.3 reduced pressure chemiluminescence, na chemicalreaction at pressure less than 760 mm mercury (Hg) in whichlight is emitted.4. Summary of Test Method4.1 A specimen is introduced into a carrier
10、gas stream, at acontrolled rate, and incorporated into a high temperaturefurnace (900 to 1150C) where an excess of oxygen is added.Pyrolysis converts hydrocarbons in the specimen to carbondioxide and water. Organic nitrogen and inorganic nitrogencompounds, present in the specimen, are converted to n
11、itricoxide (NO). Nitric oxide reacts with ozone in the detectorproducing nitrogen dioxide molecules in an excited state. Asthe excited nitrogen dioxide molecules relax to ground state,light is emitted. This light is detected by a photomultiplier tubeor by a photodiode with the resulting signal propo
12、rtional to theconcentration of nitrogen in the sample. Operating the detectorat a reduced pressure lowers the probability of the excited1This test method is under the jurisdiction of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct responsibility ofSubcommittee D16.
13、04 on Instrumental Analysis.Current edition approved Dec. 1, 2012. Published January 2013. Originallyapproved in 2007. Last previous edition approved in 2007 as D7184 07. DOI:10.1520/D7184-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at ser
14、viceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from U.S. Government Printing Office Superintendent of Documents,732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http:/www.access.gpo.gov.*A Sum
15、mary 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 States1nitrogen dioxide molecule colliding with other moleculesbefore it undergoes chemiluminescence. Thus, reduced pres-sure provides
16、 improved sensitivity and lower noise.5. Significance and Use5.1 This test method is useful to detect and quantifynitrogen-containing compounds at a concentration of 0.03 to 1mg N/kg in light aromatic hydrocarbons used or produced inmanufacturing process. These nitrogen-containing compoundsare undes
17、irable in finished aromatic products and may be usedin setting specification for determining the total nitrogencontent in aromatic hydrocarbons.5.2 This test method requires the use of reduced pressure atthe detector. Loss of vacuum or pressure fluctuations impactthe sensitivity of the detector and
18、the ability to determinenitrogen concentrations less than 1 mg N/kg.6. Interferences6.1 Chlorides, bromides, and iodides can interfere if any oneor all of these elements are present in a sample in concentra-tions greater than 10 % by total weight of halogen in thesample.6.2 Moisture in the sample pr
19、oduced during the combustionstep can interfere if not removed prior to the gas entering thedetector cell.7. Apparatus7.1 Pyrolysis FurnaceA furnace capable of maintaining atemperature sufficient to volatilize and pyrolyse the sample andoxidize organically bound nitrogen to NO. The actual tempera-tur
20、e should be recommended by the specific instrument manu-facturer.7.2 Quartz Pyrolysis TubeCapable of withstanding 900 to1200C.7.3 Chemiluminescence DetectorCapable of operation atreduced pressure (less than 760 mm mercury) and able tomeasure light emitted from the reaction between NO andozone.7.4 Mi
21、croliter Syringe5 to 250 L or as recommended byinstrument manufacturer.7.5 Constant Rate Injector SystemIf the sample is to beintroduced into the pyrolysis furnace via syringe, use aconstant rate injector or a liquid introduction module or asrecommended by instrument manufacturer.7.6 Liquid Auto-Sam
22、plerCapable of injecting 5 to 250 Lof sample or as recommended by instrument manufacturer.7.7 Boat Inlet System (Optional)If the instrument isequipped with a boat inlet system, care must be taken to ensurethe boat is sufficiently cooled between analyses to prevent thesample from vaporizing as it is
23、injected into the boat. Thesample should start vaporizing as it enters the furnace. It iscritical that the sample vaporize at a constant and reproduciblerate.7.8 Automatic Boat Drive SystemIf the instrument isequipped with a boat inlet system the boat should be introducedinto the furnace at a contro
24、lled rate.7.9 Membrane DryerRemoves moisture of combustionbefore the detector.8. Reagents48.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. It is intended that all reagents shall conform tothe specifications of the Committee on Analytical Reagents ofthe American Chemical Socie
25、ty, where such specifications areavailable, unless otherwise indicated. Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.8.2 Inert GasEither argon (Ar) or helium (He) may beus
26、ed. The purity shall be no less than 99.99 mol %.8.3 Oxygen GasThe purity shall be no less than 99.99mol %.8.4 SolventThe solvent of choice should be capable ofdissolving the nitrogen sample. The solvent of choice shouldhave a boiling point similar to the sample being analyzed. Thesolvent should con
27、tain less than 0.05 mg N/L. The blank valuemust be determined for each new bottle of solvent. Suggestedpossibilities include, but not limited to methanol, iso-octaneand p-xylene.NOTE 1A quick screening can be conducted by injecting the solventand sample once or twice and comparing relative area coun
28、ts.8.5 Nitrogen Stock Solution, approximately 1000 mg N/LPrepare a stock solution by weighing, to the nearest 0.1 mgapproximately 0.57 g of pyridine into a 100 ml volumetricflask. Dilute to the mark with solvent. Calculate the actualconcentration of nitrogen using Eq 1. This standard may alsobe purc
29、hased.mgN/L 5Wt. of pyridine in grams! 3 .1771! 3 106!100 ml of solvent(1)where:% nitrogen in pryridine = 17.718.6 Nitrogen Working Standard SolutionCalculate the cor-rect concentration obtained from the nitrogen stock solutionprepared in 8.5 and prepare the working standards by dilutingthe stock so
30、lution with the solvent. Prepare approximately 10.0mg N/L standard by accurately pipeting 1.0 mL of the stocksolution into a 100 ml volumetric flask and dilute to mark withsolvent. This Standard is further diluted to 0.05, 0.10, 0.5 and1.0 mg N/L by accurately pipeting 0.5, 1.0, 5 and 10.0 mL ofstan
31、dard into four separate 100 mL volumetric flasks and diluteto the mark with solvent. The working standards will beapproximately blank, 0.05, 0.1, 0.5, and 1.0 mg N/L. Calculatethe correct concentrations using the calculation:mg N/L 5 mg N/L in working standard! 3 ml pipeted!/100 ml!(2)or4Reagent Che
32、micals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. for suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd. Poole Dorset, U.K., and the United States Pharmacopeial andNationa
33、l Formulary, U.S. Pharamacopeial Convention, Inc. (USPC) Rockville,MD.D7184 122mg N/Kg 5 mg N/L in working standard!3 ml pipeted!/100 ml!*Density of solution g/ml! (3)Alternate volumes of solutions may be prepared so long asthe preparation meets the concentration specified.NOTE 2Working standards sh
34、ould be prepared on a regular basisdepending upon the frequency of use and age. The stock solution can beretained, if refrigerated, for up to three months. Do not refrigerate stocksolution if prepared in benzene as the benzene will freeze and cause erraticresults.8.7 Cupric Oxide (CuO or Platinum (P
35、t)May be used asan oxidation catalyst in the combustion tube, as recommendedby the instrument manufacturer.8.8 Quartz WoolMay be needed if recommended by theinstrument manufacturer.9. Hazards9.1 Consult current OSHA regulations, chemical suppliersMaterial Safety Data Sheets, and local regulations fo
36、r allmaterial used in this test method.9.2 High temperature is employed in this test method.Extreme care should be exercised when using flammablematerials near the pyrolysis furnace.9.3 Ozone can be hazardous so use of good vented room isnecessary.10. Sample Handling10.1 Collect the sample in accord
37、ance with Practice D3437.10.2 To preserve sample integrity and prevent the loss ofvolatile components, which may be in some samples, do notexpose samples to the atmosphere any longer than necessary.Analyze specimen as soon as possible after transferring fromthe sample container to prevent loss of ni
38、trogen or contamina-tion.10.3 Since this procedure is intended for trace levelanalysis, care must be taken to ensure that the samplecontainer, and working standards containers are clean and donot contaminate the sample.11. Instrument Assembly and Preparation11.1 Setup the instrument in accordance wi
39、th the instrumentmanufacturers instructions.11.2 Set instrument parameters in accordance with instru-ment manufacturers recommendations.11.3 Adjust gas flows and pyrolysis temperatures to theoperating conditions as recommended by the instrument manu-facturer.11.4 The actual operation of injecting a
40、sample will varydepending upon the instrument manufacturer and type of inletsystem used (see 7.5-7.8).12. Calibration and Standardization12.1 Prepare the working calibration standards using thestock solution as described in and 8.5 and 8.6.12.2 Before injecting a standard or blank, refer to theproce
41、dures (Section 13), to ensure proper technique for eitherthe direct injection system or the boat inlet system.12.3 A calibration based on the four gravimetrically pre-pared standards works well within the limited scope of thisprocedure. This type of calibration can be used to quantitatenitrogen at t
42、he 0.03 to 1.0 mg N/kg concentration range.12.4 Run a calibration program for linear regression inaccordance with the instrument manufacturers recommenda-tions. The correlation coefficient should be a minimum of 0.99.12.5 Inject each standard and blank at least 3 times.NOTE 3The calibration corrects
43、 for residual nitrogen content of thesolvent used to make the standards (often greater than 0.05 mg N/L) bygenerating the regression line as a standard addition to the solvent blank.The slope generated is used to create a calibration line starting at theorigin, that is, zero signal for nitrogen.13.
44、Procedure13.1 Sample size from 5 to 250 L is acceptable.13.2 When using a constant rate injector always flush thesyringe several times with the material to be injected to preventcontamination. Do not return the first few flushes back into thespecimen bottle.13.3 If using an auto-sampler set the prog
45、ram to theinstrument manufacturers recommendations.NOTE 4Follow instrument manufacturers recommendations forsample size.13.4 Set the automatic boat control to the instrument manu-facturers recommendations. Cycle the empty boat in and outof the combustion furnace to remove any residual contamina-tion
46、 until you see a minimum peak on your baseline as a resultof the cycling of the empty boat.13.5 Fill the auto-sampler vials with the samples and placethe vials into the rack.13.6 Using a constant rate injector fill the syringe past thedesired volume to be injected, (that is, if you are going to inje
47、ct50 L fill the syringe to 60 L and then back to 50 L), takingcare not to pull air bubbles into the syringe with the sample.With the syringe needle pointed up, push the plunger to thedesired volume, tap the last drop off the needle point, and pullthe plunger back until air can be seen in the syringe
48、 barrel.NOTE 5The inherent accuracy of this technique is dependent upon theability of the analyst to repeatedly inject the same volume for eachinjection. Air bubbles lodged between the syringe plunger and thespecimen will result in variable volumes and can not be tolerated.NOTE 6If the detector resp
49、onse continuously increases or decreases,this is an indication of contamination. Check with the instrumentmanufacturers recommendations for decontamination of the instrument.13.7 Insert the syringe needle through the inlet septum as faras it will go (the syringe barrel should be touching the septum).Inject the sample in accordance with the instrument manufac-turers recommendations.13.8 Repeat 13.7 and 13.8 analyzing each sample or stan-dard 3 times. Average the 3 results for each sample and recordthe results.D7184 12314. Calcu
