ASTM D4808 Standard Test Methods for Hydrogen Content of Light Distillates, Middle Distillates, Gas Oils, and Residua by Low-Resolution Nuclear Magnetic Resonance Spectroscopy
10. Procedures
10.1 Test Methods A, B, and C:
10.1.1 Leave the reference standard and the test specimens in the conditioning block for at least 0.5 h, to ensure that they reach the specified test temperature. The temperature of the conditioning block shall be maintained at the same temperature required for the NMR measurement as specified in 9.4.
10.1.2 Read the following instructions in conjunction with the procedure provided in the manufacturer's handbook for analyzing samples. Specific steps may vary with instrument manufacturer and model. In cases where the manufacturer's instructions differ from the following steps, follow the manufacturer's instructions.
10.1.3 Take the reference standard and place it carefully into the instrument sample probe (coil), being careful that the liquid does not splash onto the under side of the PTFE plug. When fully inserted, the top of the test cell is just above the cover of the instrument unit.
10.1.4 Check that the peaks on the oscilloscope are coincident, and if this is not so, adjust the tuning, as described by the manufacturer's instructions, until they are.
10.1.5 After the reference standard is in the magnet unit for at least 3 s, push the reset button to begin a measurement.
10.1.6 After a count time of 128 s, the digital display stops at its final value. Record the integrator counts, and reset the instrument to take a second measurement. Record a total of seven readings, averaging the last five.
10.1.7 Remove the test cell containing reference standard from the instrument and reweigh after it has cooled to room temperature. If this mass differs significantly from the mass obtained in 8.1.4 or 8.2.1.6, the PTFE plug need not have sealed properly and the result is considered suspect. This additional weighing step is required due to the presence of the TCE diluent in some samples.
10.1.8 Replace the reference standard in the conditioning block, and make similar readings on the test specimen to be tested.
NOTE 6 - Measurements are affected by temperature variations in the sample and reference standard so these test cells are always returned to the conditioning block ifadditional measurements are anticipated on the same sample.
11. Calculation
11.1 Determination of the mass of test specimen or reference material delivered to the NMR test cell. This calculation accounts for the dilution with TCE and the loss of material during the transfer to the test cell.
11.1.1 Test Method A - Not applicable.
11.1.2 Test Methods B and C:
MR or MS = SM x (M1) / (M1 + M2)
where:
MR or MS = mass of reference material or test specimen in the test cell,
SM = mass of standard or test specimen in the preparation beaker,
M1 = mass of solution in the NMR test cell, and
M2 = mass of solution remaining in the preparation beaker.
11.2 Hydrogen Content:
11.2.1 Calculate mass % hydrogen content as follows:
Hydrogen Content (mass)
(S/R) x (MR/MS) x (15.39)
where:
S = mean of integrator counts on test specimen under test,
R = mean of integrator counts on reference standard,
MR = mass of reference standard in the test cell,
MS = mass of test specimen in the test cell, and
15.39 = mass hydrogen in the reference sample, n-dodecane.
