1、Designation: D7184 12D7184 13Standard 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 ofori
2、ginal adoption 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 total nitrogen i
3、n aromatic hydrocarbons, such as benzene, toluene, and xylene.1.2 This test method is applicable for samples containing nitrogen from 0.38 to 1.2 mg N/kg. For higher nitrogen concentrationsrefer to Test Method D6069 or D4629. With careful analytical technique, this method can be used to successfully
4、 analyzeconcentrations below the current scope (see Appendix X1).1.3 In determining the conformance of the test results using this method to applicable specifications; results shall be roundedoff in accordance with the rounding-off method of Practice E29.1.4 The values stated in SI units are to be r
5、egarded as standard. No other units of measurement are included in this standard.1.5 This standard does not purport to address all of the safety concerns, if any associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and det
6、ermine the applicability of regulatorylimitations prior to use. For specific hazard statements, see Section 9.2. Referenced Documents2.1 ASTM Standards:2D3437 Practice for Sampling and Handling Liquid Cyclic ProductsD4629 Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inl
7、et Oxidative Combustion andChemiluminescence DetectionD6069 Test Method for Trace Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced PressureChemiluminescence DetectionD6809 Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related MaterialsE
8、29 Practice for Using Significant Digits in Test Data to Determine Conformance with SpecificationsE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method2.2 Other Documents:OSHA Regulations, 29 CFR paragraphs 1910. 1000 and 1910.1200 33. Terminology3.1 Defin
9、itions:3.1.1 oxidative pyrolysis, na process in which a sample undergoes combustion in an oxygen rich environment at temperaturesgreater than 900C.3.1.2 pyrolytic decomposition, ncombusting a compound to decompose it to carbon dioxide, water and elemental oxides.3.1.3 reduced pressure chemiluminesce
10、nce, na chemical reaction at pressure less than 760 mm mercury (Hg) in which lightis emitted.1 This test method is under the jurisdiction of ASTM Committee D16 on Aromatic Hydrocarbons and Related Chemicals and is the direct responsibility of SubcommitteeD16.04 on Instrumental Analysis.Current editi
11、on approved Dec. 1, 2012July 1, 2013. Published January 2013July 1, 2013. Originally approved in 2007. Last previous edition approved in 20072012 asD7184 07.12. DOI: 10.1520/D7184-12.10.1520/D7184-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service
12、 at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from U.S. Government Printing Office Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http:/www.access.gpo.
13、gov.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior
14、 editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*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
15、-2959. United States14. Summary of Test Method4.1 A specimen is introduced into a carrier gas stream, at a controlled rate, and incorporated into a high temperature furnace(900 to 1150C) where an excess of oxygen is added. Pyrolysis converts hydrocarbons in the specimen to carbon dioxide and water.O
16、rganic nitrogen and inorganic nitrogen compounds, present in the specimen, are converted to nitric oxide (NO). Nitric oxidereacts with ozone in the detector producing nitrogen dioxide molecules in an excited state. As the excited nitrogen dioxidemolecules relax to ground state, light is emitted. Thi
17、s light is detected by a photomultiplier tube or by a photodiode with theresulting signal proportional to the concentration of nitrogen in the sample. Operating the detector at a reduced pressure lowersthe probability of the excited nitrogen dioxide molecule colliding with other molecules before it
18、undergoes chemiluminescence.Thus, reduced pressure provides improved sensitivity and lower noise.5. Significance and Use5.1 This test method is useful to detect and quantify nitrogen-containing compounds at a concentration of 0.03 to 1 mg N/kgin light aromatic hydrocarbons used or produced in manufa
19、cturing process. These nitrogen-containing compounds are undesirablein finished aromatic products and may be used in setting specification for determining the total nitrogen content in aromatichydrocarbons.5.2 This test method requires the use of reduced pressure at the detector. Loss of vacuum or p
20、ressure fluctuations impact thesensitivity of the detector and the ability to determine nitrogen concentrations less than 1 mg N/kg.6. Interferences6.1 Chlorides, bromides, and iodides can interfere if any one or all of these elements are present in a sample in concentrationsgreater than 10 % by tot
21、al weight of halogen in the sample.6.2 Moisture in the sample produced during the combustion step can interfere if not removed prior to the gas entering thedetector cell.7. Apparatus7.1 Pyrolysis FurnaceA furnace capable of maintaining a temperature sufficient to volatilize and pyrolyse the sample a
22、ndoxidize organically bound nitrogen to NO. The actual temperature should be recommended by the specific instrumentmanufacturer.7.2 Quartz Pyrolysis TubeCapable of withstanding 900 to 1200C.7.3 Chemiluminescence DetectorCapable of operation at reduced pressure (less than 760 mm mercury) and able to
23、measurelight emitted from the reaction between NO and ozone.7.4 Microliter Syringe5 to 250 L or as recommended by instrument manufacturer.7.5 Constant Rate Injector SystemIf the sample is to be introduced into the pyrolysis furnace via syringe, use a constant rateinjector or a liquid introduction mo
24、dule or as recommended by instrument manufacturer.7.6 Liquid Auto-SamplerCapable of injecting 5 to 250 L of sample or as recommended by instrument manufacturer.7.7 Boat Inlet System (Optional)If the instrument is equipped with a boat inlet system, care must be taken to ensure the boatis sufficiently
25、 cooled between analyses to prevent the sample from vaporizing as it is injected into the boat. The sample should startvaporizing as it enters the furnace. It is critical that the sample vaporize at a constant and reproducible rate.7.8 Automatic Boat Drive SystemIf the instrument is equipped with a
26、boat inlet system the boat should be introduced into thefurnace at a controlled rate.7.9 Membrane DryerRemoves moisture of combustion before the detector.8. Reagents48.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. It is intended that all reagents shall conform to thespecifi
27、cations of the Committee onAnalytical Reagents of theAmerican Chemical Society, where such specifications are available,unless otherwise indicated. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening the accura
28、cy of the determination.8.2 Inert GasEither argon (Ar) or helium (He) may be used. The purity shall be no less than 99.99 mol %.8.3 Oxygen GasThe purity shall be no less than 99.99 mol %.4 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. for sug
29、gestions on the testing of reagents not listed by theAmerican Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd. Poole Dorset, U.K., and the United States Pharmacopeial and National Formulary,U.S. Pharamacopeial Convention, Inc. (USPC) Rockville, MD.D7184 1328.4 SolventThe sol
30、vent of choice should be capable of dissolving the nitrogen sample. The solvent of choice should have aboiling point similar to the sample being analyzed. The solvent should contain less than 0.05 mg N/L. The blank value must bedetermined for each new bottle of solvent. Suggested possibilities inclu
31、de, but not limited to methanol, iso-octaneiso-octane andp-xylene.p-xylene.NOTE 1A quick screening can be conducted by injecting the solvent and sample once or twice and comparing relative area counts.8.5 Nitrogen Stock Solution, approximately 1000 mg N/LPrepare a stock solution by weighing, to the
32、nearest 0.1 mgapproximately 0.57 g of pyridine into a 100 ml volumetric flask. Dilute to the mark with solvent. Calculate the actual concentrationof nitrogen using Eq 1. This standard may also be purchased.mg N/L5Wt. of pyridine in grams!3.1771!3106!100 ml of solvent (1)where:% nitrogen in pryridine
33、 = 17.718.6 Nitrogen Working Standard SolutionCalculate the correct concentration obtained from the nitrogen stock solutionprepared in 8.5 and prepare the working standards by diluting the stock solution with the solvent. Prepare approximately 10.0 mgN/L standard by accurately pipeting 1.0 mL of the
34、 stock solution into a 100 ml volumetric flask and dilute to mark with solvent.This Standard is further diluted to 0.05, 0.10, 0.5 and 1.0 mg N/L by accurately pipeting 0.5, 1.0, 5 and 10.0 mL of standard intofour separate 100 mL volumetric flasks and dilute to the mark with solvent. The working sta
35、ndards will be approximately blank,0.05, 0.1, 0.5, and 1.0 mg N/L. Calculate the correct concentrations using the calculation:mg N/L 5mg N/L in working standard! 3ml pipeted!/100 ml! (2)ormg N/Kg5mg N/L in working standard! 3ml pipeted!/100 ml!*Density of solution g/ml! (3)Alternate volumes of solut
36、ions may be prepared so long as the preparation meets the concentration specified.NOTE 2Working standards should be prepared on a regular basis depending upon the frequency of use and age. The stock solution can be retained,if refrigerated, for up to three months. Do not refrigerate stock solution i
37、f prepared in benzene as the benzene will freeze and cause erratic results.8.7 Cupric Oxide (CuO or Platinum (Pt)May be used as an oxidation catalyst in the combustion tube, as recommended bythe instrument manufacturer.8.8 Quartz WoolMay be needed if recommended by the instrument manufacturer.9. Haz
38、ards9.1 Consult current OSHA regulations, chemical suppliers Material Safety Data Sheets, and local regulations for all materialused in this test method.9.2 High temperature is employed in this test method. Extreme care should be exercised when using flammable materials nearthe pyrolysis furnace.9.3
39、 Ozone can be hazardous so use of good vented room is necessary.10. Sample Handling10.1 Collect the sample in accordance with Practice D3437.10.2 To preserve sample integrity and prevent the loss of volatile components, which may be in some samples, do not exposesamples to the atmosphere any longer
40、than necessary. Analyze specimen as soon as possible after transferring from the samplecontainer to prevent loss of nitrogen or contamination.10.3 Since this procedure is intended for trace level analysis, care must be taken to ensure that the sample container, andworking standards containers are cl
41、ean and do not contaminate the sample.11. Instrument Assembly and Preparation11.1 Setup the instrument in accordance with the instrument manufacturers instructions.11.2 Set instrument parameters in accordance with instrument manufacturers recommendations.11.3 Adjust gas flows and pyrolysis temperatu
42、res to the operating conditions as recommended by the instrument manufacturer.11.4 The actual operation of injecting a sample will vary depending upon the instrument manufacturer and type of inlet systemused (see 7.5-7.8).12. Calibration and Standardization12.1 Prepare the working calibration standa
43、rds using the stock solution as described in and 8.5 and 8.6.D7184 13312.2 Before injecting a standard or blank, refer to the procedures (Section 13), to ensure proper technique for either the directinjection system or the boat inlet system.12.3 A calibration based on the four gravimetrically prepar
44、ed standards works well within the limited scope of this procedure.This type of calibration can be used to quantitate nitrogen at the 0.03 to 1.0 mg N/kg concentration range.12.4 Run a calibration program for linear regression in accordance with the instrument manufacturers recommendations. Thecorre
45、lation coefficient should be a minimum of 0.99.12.5 Inject each standard and blank at least 3 times.NOTE 3The calibration corrects for residual nitrogen content of the solvent used to make the standards (often greater than 0.05 mg N/L) by generatingthe regression line as a standard addition to the s
46、olvent blank. The slope generated is used to create a calibration line starting at the origin, that is, zerosignal for nitrogen.13. Procedure13.1 Sample size from 5 to 250 L is acceptable.13.2 When using a constant rate injector always flush the syringe several times with the material to be injected
47、 to preventcontamination. Do not return the first few flushes back into the specimen bottle.13.3 If using an auto-sampler set the program to the instrument manufacturers recommendations.NOTE 4Follow instrument manufacturers recommendations for sample size.13.4 Set the automatic boat control to the i
48、nstrument manufacturers recommendations. Cycle the empty boat in and out of thecombustion furnace to remove any residual contamination until you see a minimum peak on your baseline as a result of the cyclingof the empty boat.13.5 Fill the auto-sampler vials with the samples and place the vials into
49、the rack.13.6 Using a constant rate injector fill the syringe past the desired volume to be injected, (that is, if you are going to inject 50L fill the syringe to 60 L and then back to 50 L), taking care not to pull air bubbles into the syringe with the sample. With thesyringe needle pointed up, push the plunger to the desired volume, tap the last drop off the needle point, and pull the plunger backuntil air can be seen in the syringe barrel.NOTE 5The inherent accuracy of this technique is dependent upon the ability of the anal
