ASTM D5292 Standard Test Method for Aromatic Carbon Contents of Hydrocarbon Oils by High Resolution Nuclear Magnetic Resonance Spectroscopy
6. Apparatus
6.1 High-Resolution Nuclear Magnetic Resonance Spectrometer - A high-resolution continuous wave (CW) or pulse Fourier transform (FT) NMR spectrometer capable of being operated according to the conditions in Table 1 and Table 2 and ofproducing peaks having widths less than the frequency ranges of the majority of chemical shifts and coupling constants for the measured nucleus.
6.1.1 1H NMR spectra can be obtained using either CW or pulse FT techniques but 13C measurements require signal averaging and, therefore, currently require the pulse FT technique. Low resolution NMR spectrometers and procedures are not discussed in this test method (see Test Method D3701 for an example of the use of low resolution NMR).
6.2 Tube Tubes - Usually a 5 or 10 mm outside diameter tube compatible with the configuration of the CW or pulse FT spectrometer.
7. Reagents and Materials
7.1 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.
7.2 Chloroform-d - For 1H NMR, chloroform-d must contain less than 0.2 vol % residual chloroform. Care must be taken not to contaminate the solvent with water and other extraneous materials. (Warning - Health hazard. Highly toxic. Cancer suspect agent. Can be fatal when swallowed and harmful when inhaled. Can produce toxic vapors when burned.)
7.3 Tetramethylsilane, American Chemical Society (ACS) reagent internal chemical shift reference for 1H and 13C NMR spectra. (Warning - Flammable liquid.)
7.4 Chromium (III) 2,4-Pentanedionate , relaxation reagent for 13C NMR spectra, typically 97 % grade.
8. Sampling
8.1 It is assumed that a representative sample acquired by a procedure ofPractice D4057 or equivalent has been received in the laboratory. If the test is not to be conducted immediately upon receipt of the sample, store in a cool place until needed.
8.2 A minimum of approximately 10 mL of sample is required for this test method. This should allow duplicate determinations, if desired.
8.3 All samples must be homogeneous prior to subsampling. If any suspended particles present are attributable to foreign matter such as rust, filter a portion of the sample to be tested through a small plug of glass wool, contained in a clean small funnel, into a clean and dry vial or NMR sample tube containing chloroform-d.
8.4 If the sample contains waxy materials, heat the sample in the container to approximately 60°C and mix with a high-shear mixer prior to sampling. It may be necessary to transfer a portion of the sample to an NMR tube containing chloroform-d by means of a pipet which has been heated to approximately 60°C to maintain the homogeneity of the sample.
8.5 For a valid test result, samples must be completely soluble in chloroform-d. Check to ensure that the final solution is homogeneous and free of undissolved particles.
