ASTM D5762 Test Method for Nitrogen in Petroleum and Petroleum Products
ASTM D5762 Standard Test Method for Nitrogen in Petroleum and Petroleum Products by Boat-Inlet Chemiluminescence
8. Preparation of Apparatus
8.1 Assemble apparatus in accordance with the manufacturer's instructions.
8.2 Adjust the oxygen flow for the ozone generator in accordance with the manufacturer's instructions. Adjust the combustion tube gas flows and the pyrolysis temperature to the desired operating conditions using the following guidelines for each furnace type.(Warning - Ozone is extremely toxic. Make sure that appropriate steps are taken to prevent discharge of ozone within the laboratory work area.)
8.2.1 For the single-zone furnace without the ability to change to a pure oxygen carrier gas flow after the boat has been fully extended into the furnace, adjust the combustion tube gas flows to the following values: pyrolysis oxygen, 360 mL/min; inlet oxygen, 60 mL/min; and inert carrier inlet, 155 mL/min. Set the furnace temperature to 1100 ± 25°C. Adjust the boat drive mechanism to obtain a drive rate of 150 ± 10 mm/min. Refer to the manufacturer's instructions for descriptions of these settings.
8.2.2 For the two-zone furnace without the ability to change to a pure oxygen carrier gas flow after the boat has been fully extended into the furnace, adjust the combustion tube gas flows to the following values: combustion oxygen, 165 mL/min; inlet inert carrier, 85 mL/min; and boat inert carrier, 50 mL/min. Set the inlet furnace temperature to 1050 ± 25°C, and the outlet furnace temperature to 925 ± 25°C. Adjust the boat drive mechanism to obtain a drive rate of 150 ± 10 mm/min (boat speed number 4). Refer to the manufacturer's instructions for the description of these settings. (Warning - High temperature is employed in this test method. Use flammable materials with care near the pyrolysis furnace.)
8.2.3 For the two-zone furnace with the ability to change to a pure oxygen carrier gas flow after the boat has been fully extended in to the furnace, adjust the combustion tube gas flows to the following values: main oxygen, 400 mL/min; inlet argon carrier, 0.4 L/min, and inlet oxygen carrier, 0.4 L/min. Set the inlet furnace temperature to 600 ± 25°C, and the outlet (catalyst) temperature to 950 ± 25°C. Set the automatic boat control as follows: 1 Fuc FWD 125 speed 10 time 30, 2 Fuc 285 speed 05 time 30, 5 Fuc time 30, 6 Fuc time 90, A Fuc time 60. Refer to manufacturer's instructions for a description of these settings.
8.3 Insert boat into furnace for a minimum of 2 min to remove any residual nitrogen species.
9. Calibration and Standardization
9.1 Prepare calibration standards containing 1, 5, 10, 50, and 100 ng nitrogen/µL in xylene by volumetric dilution of the 500-ng nitrogen/µL nitrogen stock solution.
9.2 Five microlitres of the material to be analyzed (see Note 2) shall be quantitatively placed in the sample boat for measurement of chemiluminescence response. There are two alternative injection procedures available, the volumetric and the gravimetric procedures.
NOTE 2 - The formation of NO and NO2 from oxidative combustion of nitrogen containing hydrocarbons is dependent on combustion conditions such as temperature and oxygen concentration. Injection of a constant solution volume, and dilution of all test specimens and standards with a common solvent, maintain consistent combustion conditions for test specimens and standards.
9.2.1 For volumetric measurement of the material by microlitre syringe, flush the microlitre syringe several times with the material, discarding the flushed liquid each time. Fill the 10-µL syringe to the 5-µL level. Retract the plunger so that the lower liquid meniscus falls on the 10 % scale mark. When bubbles are present within the liquid column, flush the syringe and withdraw a new aliquot of the liquid. Record the volume of liquid in the syringe. Immediately inject the liquid into the boat, being careful to displace the last drop by touching the edge of the boat, or the quartz wool if present, with the syringe needle. After the injection, again retract the plunger so that the lower liquid meniscus falls on the 10 % scale mark and record the volume of liquid in the syringe. The difference between the two volume readings is the volume of liquid injected.
NOTE 3 - An automatic sampling and injection device can be used in place of the described manual injection procedure.
9.2.2 For gravimetric measurement of the solution, fill the syringe as indicated in 9.2.1. Weigh the microlitre syringe and its contents, and record the mass to the nearest 0.01 mg. Immediately inject the liquid into the boat, being careful to displace the last drop by touching the edge of the boat, or quartz wool if present, with the syringe needle. After the injection, remove the syringe and again weigh the syringe and its contents. Record the mass to the nearest 0.01 mg. The difference between the two weighings is the mass of liquid injected. The gravimetric procedure is more precise than the volumetric procedure, provided a balance with a precision of ±0.01 mg is used.
9.3 Activate the boat drive mechanism to insert the boat into the furnace. The instrument baseline should remain stable until the boat approaches the furnace and volatilization of injected material begins. After the measurement is complete, retract the boat. The instrument baseline should reestablish before the boat has completely emerged from the furnace. Record the integrated chemiluminescence response. Allow the boat to cool for at least 1 min before the next injection.
9.4 Calibrate the instrument using one of the following two techniques.
9.4.1 Perform measurements for the calibration standards and blank using the procedure described in 9.2 and 9.3. Measure the calibration standards and blank three times each, and determine the average integrated chemiluminescence response for each. Construct a curve plotting average integrated detector response (y-axis) versus nanograms of nitrogen injected (x-axis).
9.4.2 If the system features an internal calibration routine, measure the calibration standards and blank three times each using the procedure described in 9.2 and 9.3. Calibrate the analyzer in accordance with the manufacturer's instructions using the average of the three measurements for each standard and blank.
9.5 If analyzer calibration is performed using only a subset of the calibration standards listed in 9.1, the calibration standards closest in concentration to the measured solution(s) must be included in the subset (that is, if the concentration of the test specimen solution is 20 ng nitrogen/µL, include the 10 and 50-ng nitrogen/µL standards in the calibration). System performance must be checked with the calibration standards at least once per day.
10. Quality Assurance
10.1 A sample of known nitrogen content will be run after each calibration. The sample can also be analyzed periodically throughout a series of analyses to check the functioning of the instrument and the validity of the calibration curve. This sample can be a National Institute for Standards and Technology Standard Reference Material (SRM) material, an acridine in xylene standard prepared to have a nitrogen value not used to calibrate the instrument, or any other material that has been analyzed repeatedly such that sufficient data are available to determine a statistical mean. The results of the analysis of the known sample will be within 10 % of the certified or accepted value for the operation and calibration of the instrument to be considered acceptable. If the results are not within 10 % of the accepted value, perform appropriate corrective maintenance on the instrument and repeat the calibration procedure described in 9.4.
