ASTM D4808 Standard Test Methods for Hydrogen Content of Light Distillates, Middle Distillates, Gas Oils, and Residua by Low-Resolution Nuclear Magnetic Resonance Spectroscopy
5. Apparatus
NOTE 1 - This test method has been written around the Newport Analyzer Mark IIIF or its replacement version, the Newport 4000 (Oxford Analytical Instruments, Ltd., Oxford, England), and the details of the test method are to be read in conjunction with the manufacturer's handbook. These instruments have demonstrated statistically indistinguishable performance in these standard test methods and in Test Method D3701. Any similar instrument is acceptable, provided that the new instrument is adequately correlated and proved to be statistically similar. As of the mid-1990s, however, the Newport 4000 instrument is no longer being manufactured by the vendor. No newer models are currently being manufactured as replacements for the Newport 4000 instrument.
5.1 Nuclear Magnetic Resonance Spectrometer:
5.1.1 A low-resolution, continuous wave instrument capable of measuring a nuclear magnetic resonance signal due to hydrogen atoms in the sample and includes an excitation and detection coil of suitable dimensions to contain the test cell; an electronic unit, to control and monitor the magnet and coil, and containing: circuits, to control and adjust the radio-frequency level and audio-frequency gain; and integrating counter, with variable time period in seconds.
5.1.2 Test Methods B and C also require that the instrument has the ability to equilibrate samples within the probe at an elevated temperature (50°C).
5.2 Conditioning Block - A block of aluminum alloy drilled with holes of sufficient size to accommodate the test cells with the mean height of the sample being at least 20 mm below the top of the conditioning block, capable of holding the sample at the given test temperature (see Fig. 1).
5.3 Test Cells - Nessler-type tubes of approximately 100-mL capacity with a nominal external diameter of 34 mm and a nominal internal diameter of 31 mm marked at a distance of 51 mm above the bottom of the tube by a ring around the circumference. The variation between the internal diameters of the test cells used for the sample and reference material should not be greater than +/- 0.5 mm.
NOTE 2 - To avoid potential difficulties with tightness when the test cell is introduced into the magnet coil, users are cautioned to avoid test cells that have nominal external diameters that are greater than 34.2 mm.
5.4 Polytetrafluoroethylene (PTFE) Plugs, for closing the test cells and made from pure PTFE.
5.5 Insertion Rod - Ametal rod with a threaded end used for inserting and removing the PTFE plugs from the test cells (see Fig. 1).
5.6 Analytical Balance - A top pan-type balance, capable of weighing the test cells in an upright position to an accuracy of at least 0.001 g.
5.7 Beakers, 150 mL and 50 mL with pour spouts.
5.8 Glass Stirring Rod, approximately 250-mm length.
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 Reference Standard - n-Dodecane. (Warning - Flammable.)
6.3 Relaxation Reagent Solution, prepared from ferric acetylacetonate (Fe(C5H7O2)3 - MW = 353.16, reagent grade) - Prepare a fresh 0.02 M Fe(C5H7O2)3 solution by dissolving 1.77 g of Fe(C5H7O2)3 in 250 mL TCE. If any of the Fe(C5H7O2) remains undissolved, filter the solution, and use the filtrate in subsequent steps.
6.4 Tetrachloroethylene (TCE). (Warning - Cancer-suspect agent.)
