UOP 981-2014 Trace Nitrogen in Liquid Hydrocarbons by Oxidative Combustion with Chemiluminescence Detection.pdf

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1、 IT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TO DETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH AND SAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS PROCEDURE IN THE MANNER PRESCRIB

2、ED HEREIN CAN BE HAZARDOUS. SAFETY DATA SHEETS (SDS) OR EXPERIMENTAL SAFETY DATA SHEETS (ESDS) FOR ALL OF THE MATERIALS USED IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE). COPYRIGHT 2010, 2011, 2014 UOP LLC. All rights reserved. Nonconfiden

3、tial UOP Methods are available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, USA. The UOP Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at serviceastm.org, 610.832.9555 FAX, or 610.832.9585 PHONE.

4、Trace Nitrogen in Liquid Hydrocarbons by Oxidative Combustion with Chemiluminescence Detection UOP Method 981-14 Scope This method is for determining nitrogen in liquid hydrocarbons at concentrations ranging from 30 to 600 ng/g (mass-ppb). It is applicable to highly volatile samples, such as pentane

5、, through the use of a cooled sampling system. Higher concentrations can be determined by ASTM Methods D4629, “Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection,” D6069, “Trace Nitrogen in Aromatic Hydrocarbons by Oxidative Combusti

6、on and Reduced Pressure Chemiluminescence Detection,” and D7184, “Ultra Low Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced Pressure Chemiluminescence Detection,” using the cooled sampling system described herein for highly volatile matrices. Halogens and sulfur interfere at co

7、ncentrations greater than approximately 1%. References ASTM Method D4052, “Density and Relative Density of Liquids by Digital Density Meter,” www.astm.org ASTM Method D4629, “Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection,” www.a

8、stm.org ASTM Method D6069, “Trace Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced Pressure Chemiluminescence Detection,” www.astm.org ASTM Method D7184, “Ultra Low Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced Pressure Chemiluminescence Detection,” www.a

9、stm.org Jones, B.M. and Daughton, C.G., Anal. Chem., 57, 2320-2325 (1985) UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method A commercial instrument is set up and calibrated with liquid standards. For samples containing volatile components such as pentane, a temper

10、ature control system must be used to stabilize the temperature of the sample tray and the syringe at 15 C. Using an autosampler, the sample is directly injected into the combustion tube where it vaporizes into an argon carrier and is mixed with oxygen at high temperature. The organic material is con

11、verted to carbon dioxide and water. The nitrogen in the sample is converted to nitric oxide. This is further reacted in the detector with ozone to produce 2 of 9 981-14 nitrogen dioxide in an excited state. The excited state nitrogen dioxide molecules relax to the ground state, producing light (chem

12、iluminescence), which is detected by a photomultiplier tube. The signal is proportional to the total nitrogen in the sample. The detector is operated at reduced pressure to decrease the probability of excited state nitrogen dioxide molecules colliding with other molecules before emitting light, thus

13、 increasing sensitivity and signal-to-noise ratio. This procedure has a low sensitivity to diatomic nitrogen (N2), but only during the combustion of the hydrocarbon and has reduced sensitivity to compounds with nitrogen-nitrogen bonds that decompose to produce nitrogen gas. The relative responses of

14、 some nitrogen compounds have been determined and tabulated by Jones and Daughton. Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Balance, analytical, readable to 0.0001 g Flasks, volumetric, Class A, borosilicate

15、glass, 100- and 250-mL, Fisher Scientific, Cat. Nos. 10-210-8C and -8E, respectively Nitrogen Chemiluminescence Analyzer, with attached furnace, autosampler, vacuum pump, controls and computer. This method was developed and validated using the Mitsubishi analyzer, Model TS-100V, with ND-100 Nitrogen

16、 Detector and STC-210 Sample Temperature Controller, Mitsubishi Chemical Analytech, available from COSA Instrument. It has also been validated on the Mitsubishi NSX-2100V, with ND-210 Nitrogen Detector and STC-210 Sample Temperature Controller. The procedure for analysis may be different for other i

17、nstruments and all other instruments need to be validated before using for this method. The Mitsubishi analyzer must be equipped with the following accessories: Autosampler, Mitsubishi Model ASC-150L or ASC-250L, COSA Instrument Autosampler syringes, gas tight, 100-L, Mitsubishi, Cat. No. MSSG10, CO

18、SA Instrument Autosampler vials, rinse, Mitsubishi Cat. No. TX3LSW, COSA Instrument. These are also used as pre-fill vials and wash bottles, see Preparation of Apparatus. Membrane drier, Perma Pure, Model MD-110-24F-4 or Mitsubishi Tube Dryer, Cat. No. TN6RPC, COSA Instrument (see Note 1) Sample tem

19、perature controller, Mitsubishi Model STC-210, COSA Instrument Vacuum pump, Vacuubrand, Model MD4CNT and Ulvac GLS-050 vacuum pumps meet this requirement; other vacuum pumps must be evaluated before use, COSA Instrument (see Note 2) Pipet, volumetric, Class A, 0.5-, 1-, 2-, and 5-mL, Fisher Scientif

20、ic, Cat. No. 13-650-2A, -2B, -2C, and -2F, respectively Pipet filler, VWR, Cat. No. 53497-055 Refrigerator, laboratory, explosion proof or flammable storage, Fisher Scientific, Cat. No. 97-950 Regulator, argon, single-stage, with stainless steel diaphragm, delivery pressure range 30-700 kPa (4-100 p

21、si), Matheson Tri-Gas, Cat. No. 3231. This regulator is installed downstream of the two-stage regulator to provide better flow control. Regulator, argon, two-stage, with stainless steel diaphragm, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3104-580 3 of 9 981-14 Regul

22、ator, oxygen, single-stage, with stainless steel diaphragm, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3231. This regulator is installed downstream of the two-stage regulator to provide better flow control. Regulator, oxygen, two-stage, with stainless steel diaphragm,

23、 delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3104-540 Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. The following items are required to perform the analysis. Additional

24、reagents and materials may be required depending on the specific instrument. Air, compressed, dry, oil-free, for membrane drier (if instrument does not purge the drier with argon) Alumina balls, Mitsubishi, Cat. No. TS3CAT, COSA Instrument Argon, compressed gas, 99.99% minimum purity, UHP, local sup

25、ply Autosampler vials, 15x45 mm, Grace Davison Discovery Sciences, Cat. No. 98008 Catalyst, Mitsubishi, Cat. No. TN5CAT, COSA Instrument Isooctane, should be as low in residual nitrogen as possible to minimize the blank value, B&J Brand, Burdick & Jackson, Cat. No. BJ362-1, VWR, or Fisher Pesticide

26、grade, Fisher Scientific, Cat. No. O297-4. Test each new lot of solvent before use. Oxygen, compressed gas, 99.98% minimum purity, UHP, local supply Perfluoropolyether vacuum pump oil (PFPE), Krytox 1525, DuPont Pipet, transfer, disposable plastic, 152-mm length, Fisher Scientific, Cat. No. 13-711-S

27、A Pyridine, 99+%, Sigma-Aldrich, Cat. No. 36,057-0 Quartz wool, Mitsubishi, Cat. No. TNQWL, COSA Instrument Toluene, B&J Brand, Burdick & Jackson, Cat. No. BJ347-4, VWR Procedure The analyst is expected to be familiar with general laboratory techniques, nitrogen analysis, and the equipment being use

28、d. Dispose of used supplies and samples in an environmentally safe manner according to applicable regulations. Preparation of Standards Pyridine stock solution, 1000-g N/mL 1. Tare a clean, dry 250-mL volumetric flask. Dispense 1.41 0.005 g of pyridine and record the mass to the nearest 0.1 mg. 2. D

29、ilute to the mark with toluene. Cap and mix well. 3. Calculate the actual concentration of the stock solution using Equation 1: ( )250 101771.0AmL/g,N6= (1) where: 4 of 9 981-14 A = mass of pyridine, g 0.1771 = N mass-fraction of pyridine (14.01/79.10) 14.01 = molecular mass of nitrogen, g/mol 79.10

30、 = molecular mass of pyridine, g/mol 250 = dilution volume, mL 106 = factor to convert g to g Pyridine stock solution, 10-g N/mL 1. Dispense 1.0 mL of the 1000-g/mL N stock solution using a volumetric pipet into a clean, dry 100-mL volumetric flask. 2. Dilute to the mark with low N isooctane. Cap an

31、d mix well. The actual concentration is 1/100th the concentration of the stock solution above. Calibration standard solution, 50-ng N/mL 1. Dispense 0.5 mL of the 10-g/mL N stock solution using a volumetric pipet into a clean, dry 100-mL volumetric flask. 2. Dilute to the mark with low N isooctane.

32、Cap and mix well. The actual concentration is 1/200th the concentration of the nominal 10-g N/mL stock solution above. Calibration standard solution, 25-ng N/mL 1. Dispense 2 mL of the 50-ng/mL N standard solution using a volumetric pipet into a clean, dry vial, such as an autosampler vial. 2. Dispe

33、nse 2 mL of the low N isooctane into the vial using a volumetric pipet. Cap and mix well. The actual concentration is 1/2 the concentration of the 50-ng N/mL standard solution above. Other volumes can be used with a larger vial, as long as the standard:isooctane ratio remains 1:1. Calibration standa

34、rd solution, 100-ng N/mL 1. Dispense 1.0 mL of the 10-g/mL N stock solution using a volumetric pipet into a clean, dry 100-mL volumetric flask. 2. Dilute to the mark with low N isooctane. Cap and mix well. The actual concentration is 1/100th the concentration of the nominal 10-g N/mL stock solution

35、above. Calibration standard solution, 200-ng N/mL 1. Dispense 2.0 mL of the 10-g/mL N stock solution using a volumetric pipet into a clean, dry 100-mL volumetric flask. 2. Dilute to the mark with low N isooctane. Cap and mix well. The actual concentration is 1/50th the concentration of the nominal 1

36、0-g N/mL stock solution above. Calibration standard solution, 500-ng N/mL 1. Dispense 5.0 mL of the 10-g/mL N stock solution using a volumetric pipet into a clean, dry 100-mL volumetric flask. 2. Dilute to the mark with low N isooctane. Cap and mix well. 5 of 9 981-14 The actual concentration is 1/2

37、0th the concentration of the nominal 10-g N/mL stock solution above. The stock solutions can be retained, if refrigerated, for up to six months. The 100-, 200-, and 500-ng N/mL standard solutions can be retained, if refrigerated, for up to four weeks. The 50-ng N/mL standard solution should be made

38、fresh weekly. The 25-ng N/mL standard solution should be made fresh daily. Preparation of Apparatus 1. Set up the instrument according to the manufacturers instructions. New combustion tubes need to be conditioned with catalyst before use, following the manufacturers procedure. For Mitsubishi instru

39、ments, procedure ZINF026 must be followed. Connect the membrane drier in series between the combustion tube and the detector. For the NSX-2100V, the mixing chamber is not used between the membrane drier and the detector. Allow the instrument to warm up and the baseline to stabilize before injecting

40、samples. Suggested Operating Conditions for the Mitsubishi TS-100V analyzer are listed in Table 1 and for the NSX-2100V in Table 2. Table 1 Suggested Operating Conditions for Mitsubishi TS-100V/ND-100 Upper temperature 800 C Lower temperature 900 C Argon main 100 mL/min Oxygen main 400 mL/min Argon

41、auxiliary 50 mL/min Oxygen auxiliary 50 mL/min Ozone 150 mL/min Gain ultra Normal end off Timer start 3 sec Timer end 240 sec Minimum area 5000 Base line 25% Syringe pre-fill 10 L Injection rate 1.2 L/sec Table 2 Suggested Operating Conditions for Mitsubishi NSX-2100V/ND-210 Inlet heater temperature

42、 800 C Outlet heater temperature 900 C Argon 100 mL/min Oxygen 500 mL/min Argon time 30 sec Oxygen time 120 sec Ozone 200 mL/min PMT sensitivity high (for low concentration) Type timer Waiting tme 5 sec Measurement time 250 sec Syringe pre-fill 10 L Injection rate 1.2 L/sec Precedent rinse enable 2.

43、 Set the STC-210 temperature set points to 15 C for both the sample tray and the syringe. Allow at least 30 minutes for the temperature to stabilize before injecting samples. 6 of 9 981-14 3. Fill the rinse and pre-fill vials with low nitrogen isooctane. Empty the waste bottle. Dispose of all materi

44、als in an environmentally safe manner according to local regulations. 4. Before starting to measure either calibration standards or samples, run an instrument program with 3 (or more) injections of isooctane to condition the instrument. The response should be stable before proceeding. Calibration Ca

45、librate weekly when in use. 1. Rinse each autosampler vial with approximately 1 mL of the fill material, dump and then fill the autosampler vial with the sample. 2. Fill several autosampler vials, one each with the solvent used to make the standard solutions (solvent blank) and the 25-, 50-, 100-, 2

46、00-, and 500-ng N/mL calibration standards. Rinse each autosampler vial with approximately 1 mL of the fill material, dump and then fill the autosampler vial with the sample. 3. Cycle the instrument (Step 4 in the Preparation of Apparatus section) while the temperature of the standard solutions equi

47、librates to 15 C. 4. Run a calibration program with multiple 80-L injections of the solvent blank and each standard. It is recommended to inject each standard or blank at least 4 times. The injections contain approximately 0, 2, 4, 8, 16, and 40 ng of added nitrogen. Relative standard deviation (RSD

48、), as calculated by the instrument software for the blank, should be within 25%. The RSD for the standards should be within 10%. If an outlier occurs in one of the four replicates, it may be excluded if it is statistically valid to do so. 5. Create a regression line using the instrument software usi

49、ng the blank and the three standards. Set the regression line to “y=bx+c”. The calibration corrects for the residual diatomic nitrogen content of the solvent used to make the standards. Nitrogen solubility in hydrocarbons will result in a non-zero intercept. Sample Analysis 1. Fill the autosampler vials with sample and place in the cooled sample tray. 2. Enter the sample parameters into the instrument software to create a sample method. Set injection volume to 80 L. Each sample should be injected at least four times. More than four