ASTM D4808 Standard Test Methods for Hydrogen Content of Light Distillates, Middle Distillates, Gas Oils, and Residua by Low-Resolution Nuclear Magnetic Resonance Spectroscopy
3. Summary of Test Methods
3.1 A test specimen is compared in a continuous wave, low-resolution nuclear magnetic resonance (NMR) spectrometer with a reference standard sample. The spectrometer records in a nondestructive fashion the absolute concentration of hydrogen atoms in the reference standard and test sample. The absolute hydrogen concentrations reported by the integrator on the NMR instrument for the standard and test specimens are used as a means of comparing the theoretical hydrogen content of the standard with that of the sample, the result being expressed as the hydrogen content (on a mass % basis) of the sample.
3.2 To ensure an accurate measure of the absolute hydrogen content of the reference standard and sample, it is necessary to ensure that the measured hydrogen integrator counts are always directly proportional to the absolute hydrogen content of the standard and sample.
3.3 Undercounting of the reference standard with respect to the sample is avoided in Test Methods B and C by dilution of the standard with a relaxation reagent solution. Undercounting of highly viscous or solid test samples is avoided by dissolving the sample in a non-hydrogen containing solvent, which ensures that all of the weighed sample is in a fluid and homogeneous solution at the time of measurement. An elevated sample temperature at the time of measurement also ensures a homogeneous liquid-phase sample.
4. Significance and Use
4.1 The hydrogen content represents a fundamental quality of a petroleum product that has been correlated with many of the performance characteristics of that product.
4.2 This test method provides a simple and more precise alternative to existing test methods, specifically combustion techniques (Test Methods D5291) for determining the hydrogen content on a range of petroleum products.
