ASTM D4629 Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons
ASTM D4629 Standard Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection
5. Apparatus
5.1 Furnace, electric, held at a temperature sufficient to volatilize and pyrolyze all of the sample and oxidize the organically bound nitrogen to NO. Furnace temperature(s) shall be as recommended by the manufacturer (typically around 1000°C).

5.2 Combustion Tube, fabricated to meet the instrument manufacturer's specifications.

5.3 Drier Tube - The reaction products include water vapor that must be eliminated prior to measurement by the detector. This can be accomplished with a magnesium perchlorate Mg(ClO4)2 scrubber or a membrane drying tube (permeation drier), or by whatever other means the instrument manufacturer specifies as appropriate for the instrument being used.

5.4 Chemiluminescent Detector, capable of measuring light emitted from the reaction between NO and ozone.

5.5 Totalizer, having variable attenuation, and capable of measuring, amplifying, and integrating the current from the chemiluminescent detector. A built in microprocessor or attached computer system may perform these functions.

5.6 Micro-litre Syringe, of 5, 10, 25, 50, or 250 µL capacity capable of accurately delivering micro-litre quantities is required. The needle should be long enough to reach the hottest portion of the inlet section of the furnace when injecting the sample. The syringe may be part of an automatic sampling and injection device used with the instrument.

5.7 Strip Chart Recorder (Optional).

5.8 Sample Inlet System - One of the following must be used:
5.8.1 Manually Operated Syringe.

5.8.2 Syringe, with a constant rate injector system, capable of delivering a sample at a precisely controlled rate.

5.8.3 Boat Inlet System, to facilitate analysis of samples that would react with the syringe or syringe needle. The pyrolysis tube for boat inlet use may require specific construction to permit insertion of a boat fully into the inlet section of the furnace. The boat inlet system external to the furnace may be cooled to a temperature below room temperature to aid in dissipating the heat from the boat when it is removed from the furnace. Cooling the boat inlet system may also reduce the chances of the sample combusting in the boat before introduction into the furnace and may be necessary when running volatile samples such as naphtha using a boat inlet system.

5.9 Quartz Insert Tube (Optional), may be packed with cupric oxide (CuO) or other oxidation catalyst as recommended by the instrument manufacturer, to aid in completing oxidation. This is inserted into the exit end of the pyrolysis tube.

5.10 Vacuum System (Optional), The chemiluminescence detector may be equipped with a vacuum system to maintain the reaction cell at reduced pressure (typically 20 to 25 mmHg). This can improve the signal to noise ratio of the detector.

5.11 Analytical Balance (Optional), with a precision of ±0.01 mg.

6. Reagents
6.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.

6.2 Magnesium Perchlorate Mg(ClO4)2, for drying products of combustion (if permeation drier is not used.) (Warning - Strong oxidizer, irritant.)

6.3 Inert Gas, argon or helium, ultra-high purity grade (UHP).

6.4 Oxygen, (99.8 % or better, 99.996 % is recommended). (Warning - Vigorously accelerates combustion.)

6.5 Solvents, for diluting and matrix matching such as, toluene, isooctane, xylene, acetone, cetane. (Other solvents similar to those occurring in samples to be analyzed are also acceptable). Solvents should contain less than 0.1 µg N/mL. (Warning - Flammable solvents.)

6.6 Nitrogen Stock Solution, 1000 µg N/mL, Prepare a stock solution by accurately weighing approximately 1.195 g of carbazole or 0.565 g of pyridine to the nearest milligram, into a tared 100-mL volumetric flask. Fifteen millilitres of acetone may then be added when using carbazole to help dissolve it. Dilute to volume with the selected solvent. Calculate the exact concentration of the stock solution based on the actual mass of pyridine or carbazole used and corrected for any known purity factors for the specific lot of pyridine or carbazole. This stock may be further diluted to desired nitrogen concentrations.

NOTE 1 - Pyridine should be used with low boiling solvents (<220°C).

NOTE 2 - Carbazole should be used with high boiling solvents (>220°C).

NOTE 3 - Working standards should be remixed on a regular basis depending upon frequency of use and age. Typically, standards have a useful life of about 3 months, and should be refrigerated when not being used.

6.7 Cupric Oxide Wire, as recommended by instrument manufacturer.

6.8 Quartz Wool.

6.9 Pyridine. (Warning - Flammable, irritant.)

6.10 Carbazole.

7. Hazards
7.1 High temperature is employed in this test method. Exercise care when using flammable materials near the pyrolysis furnace.

8. Sampling
8.1 To preserve volatile components, which may be in some samples, do not uncover samples any longer than necessary. Analyze samples as soon as possible after taking from the bulk supplies to prevent loss of nitrogen or contamination due to exposure or contact with sample container.