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
5. Apparatus
5.1 Boat Inlet System, capable of being sealed to the inlet of the combustion tube and swept with inert gas. The boats are fabricated from platinum or quartz. To aid quantitative liquid injection, add a small piece of quartz wool to the boat. The boat drive mechanism should be able to fully insert the boat into the furnace tube inlet section. A drive mechanism that advances and withdraws the sample boat into and out of the furnace at a controlled and repeatable rate is required.
5.2 Chemiluminescence Detector, capable of measuring light emitted from the reaction between nitric oxide and ozone, and containing a variable attenuation amplifier, integrator, and readout.
NOTE 1 - Detectors designed to maintain the chemiluminescence reaction cell at reduced pressure are acceptable for use and were included in the instruments used to determine the precision of this test method.
5.3 Combustion Tube, fabricated from quartz. The inlet end of the tube shall be large enough to accept the sample boat and to have side arms for introduction of oxygen and inert gas. The construction is such that the carrier gases sweep the inlet zone transporting all of the volatilized sample into a high-temperature oxidation zone. The oxidation section should be large enough to ensure complete oxidation of the sample. Combustion tubes recommended for the two furnaces in 5.5.1 and 5.5.2 are described in 5.3.1 and 5.3.2. Other configurations are acceptable if precision and bias are not degraded. 5.3.1 Quartz combustion tube for use with the single-zone furnace is illustrated in Fig. 1. A water-jacket around the inlet section can be used to cool the boat prior to sample injection.
5.3.2 Quartz combustion tube for use with the two-zone furnace is illustrated in Fig. 2. Fig. 3 illustrates a combustion tube for a two-zone furnace that is equipped with the ability to switch to a pure oxygen carrier gas flow after the boat has been fully extended into the furnace (consult the instrument manual to determine if the instrument changes to a pure oxygen carrier gas flow after the boat is inserted). The outlet end of the pyrolysis tube is constructed to hold a removable quartz insert tube. The removable quartz insert tube is packed with an oxidation catalyst as recommended by the instrument manufacturer.
5.4 Drier Tube, for the removal of water vapor. The reaction products include water vapor that shall be eliminated prior to measurement by the detector. This can be accomplished with a magnesium perchlorate, Mg(ClO4)2, scrubber, a membrane drying tube permeation drier, or a chilled dehumidifier assembly.
5.5 Furnace, Electric, held at a temperature sufficient to pyrolyze all of the sample and oxidize the nitrogen to NO. The following furnace designs may be used. All furnace assemblies include a method for gas flow control, such as needle valves, flow restrictors or mass flow controllers. Furnaces that are operated at temperatures below 1050°C shall be capable of switching to 100% oxygen carrier gas flow after the boat has been fully extended into the furnace.
5.5.1 Single-zone tube furnace with temperature controller capable of maintaining a stable furnace temperature of 1100 (± 25°C).
5.5.2 Two-zone tube furnace with temperature controllers capable of maintaining the temperature of each furnace zone independently from 950 to 1050°C (see 5.5). Or two-zone tube furnace equipped with the ability to change to a pure oxygen carrier gas flow after the boat is fully extended in to the furnace and temperature controllers capable of maintaining the temperature of each furnace zone independently to 950°C.
5.6 Microlitre Syringe, of 5 or 10-µL capacity, capable of accurately delivering microlitre quantities.
5.7 Ozone Generator, to supply ozone to the detector reaction cell.
5.8 Recorder (Optional), for display of chemiluminescence detector signal.
6. Reagents and Materials
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 Acridine, C13H9N, molecular weight 179.21, 7.82 mass % nitrogen. (Warning - Irritant.)
6.3 Oxidation Catalyst: Cupric Oxide Wire, CuO, or Platinum Catalyst, PtAl2O3, as recommended by the instrument manufacturer.
6.4 Inert Gas - Argon or Helium only, high-purity grade (that is, chromatographic or zero grade), 99.998 % minimum purity, 5 ppm maximum moisture.
6.5 Anhydrous Magnesium Perchlorate, Mg(ClO4)2, for drying products of combustion (if permeation drier or chilled drier is not used). (Warning - Strong oxidizer, irritant.)
6.6 Nitrogen Stock Solution, 500 ng nitrogen/µL - Accurately weigh (to the nearest 0.1 mg) approximately 0.64 g of acridine into a tared 100-mL volumetric flask. Add xylene to dissolve, then dilute to volume with xylene. Calculate the nitrogen content of the stock solution to the nearest milligram of nitrogen per litre. This stock can be further diluted to desired nitrogen concentrations. (Warning - Remake standard solutions on a regular basis depending upon frequency of use and age. Typically, standards have a useful life of approximately three months.)
6.7 Oxygen, high-purity grade (that is, chromatographic or zero grade), 99.75 % minimum purity, 5 ppm maximum moisture, dried over molecular sieves. (Warning - Vigorously accelerates combustion.)
6.8 Quartz Wool.
6.9 Silver Wool, as recommended by the instrument manufacturer.
6.10 Xylene. (Warning - Flammable, health hazard.)
7. Sampling
7.1 Obtain a test sample in accordance with Practice D4057 or D4177. (Warning - Samples that are collected at temperatures below room temperature can undergo expansion at laboratory temperatures and rupture the container. For such samples, do not fill the container to the top. Leave sufficient air space above the sample to allow room for expansion.) (Warning - To minimize loss of volatile components, which can be present in some test samples, do not uncover any longer than necessary. Test samples should be analyzed as soon as possible after taking from bulk supplies to prevent loss of nitrogen or contamination due to exposure or contact with sample container.)
7.2 If the test sample is not used immediately, then thoroughly mix it in its container prior to taking a test specimen. Some test samples require heating in order to thoroughly homogenize.
