7. Sampling
7.1 Take a homogeneous sample in accordance with Practice D4057. Mix the sample prior to taking a representative aliquot as the test specimen. Middle distillates, gas oils, and residue can require heating to facilitate mixing to obtain a homogeneous test specimen, as described in 8.2.2.2 and 8.3.2.
8. Preparation of Test Specimen and Standard
8.1 Test Method A - Light Distillates
8.1.1 Take a clean and dry test cell and PTFE plug, and weigh them together to the nearest 0.001 g and record the weight. Add 30 +/- 1 mL of the reference standard or test specimen to the tube, taking extreme care to prevent splashing the liquid above the line inscribed on the tube. Use a pipet for this operation.
8.1.2 Using the insertion rod, push the PTFE plug into the tube until it is about 3 cm above the liquid surface, being careful to keep the tube upright. A gentle twisting or rocking of the plug as it is inserted usually aids the escape of air from the test cell and ensures that the lip of the PTFE plug is turned up around the entire circumference. Take care to ensure that this is so, since a plug that is not properly inserted allows sample evaporation and gives rise to erroneous results.
NOTE 3 - If difficulties are encountered in the insertion of the PTFE plug, this operation is facilitated by inserting a length of thin (less than 0.2-mm diameter) and clean copper wire down the inside surface of the test cell until it is approximately 4 cm from the graduation mark, and then pushing the PTFE plug down past the wire which is then removed.
8.1.3 Unscrew the insertion rod carefully and remove without disturbing the plug and without contacting the liquid with the under surface of the plug.
8.1.4 Weigh the test cell containing the test specimen or standard and plug. Record this mass as MS or MR , respectively, to the nearest 0.001 g.
8.1.5 Place the test cell in the sample conditioning block to equilibrate.
8.1.6 Use procedures 8.1.1 through 8.1.5 to prepare both the reference and sample test cells.
8.2 Test Method B - Middle Distillates, Gas Oils
8.2.1 Reference Standard Preparation:
8.2.1.1 Take a clean and dry test cell with PTFE plug and a 150-mL beaker with glass rod. Weigh the test cell with plug and beaker with glass rod to the nearest 0.001 g and record as tare masses.
8.2.1.2 Add 20 g of the reference standard, n-dodecane, to the beaker. Record this mass to the nearest 0.001 g as SM.
8.2.1.3 To the beaker add 8.6 g TCE and 4.7 g of relaxation reagent solution, as described in 6.3, consisting of TCE and Fe(C5H7O2)3 (40 % dilution of reference standard with 1 mg relaxation reagent/mL). Mix thoroughly using the glass stirring rod.
NOTE 4 - Burets can also be used to aid the addition of TCE and relaxation reagent solutions.
8.2.1.4 Transfer this solution from the beaker to the test cell, using the glass rod to prevent splashing the liquid above the line inscribed on the test cell. Fill the test cell to the prescribed level, just below this mark.
8.2.1.5 Continue as in 8.1.2 and 8.1.3.
8.2.1.6 Weigh the test cell containing the reference solution and plug. Record the mass of the reference solution to the nearest 0.001 g as M1.
8.2.1.7 Weigh the beaker and glass rod containing the unused solution, and record the mass of the remaining solution to the nearest 0.001 g as M2.
8.2.1.8 Place the test cell containing reference solution into the conditioning block to equilibrate.
8.2.2 Test Specimen Preparation:
8.2.2.1 Take a clean and dry test cell with PTFE plug and a 150-mL beaker with glass stirring rod. Weigh the test cell with plug and the beaker with glass rod to the nearest mg, and record as tare masses.
8.2.2.2 Add 20 g of the test specimen to the beaker. Record this mass to the nearest 0.001 g as SM. All samples shall be homogeneous prior to sampling. If the sample is viscous or contains waxy materials, heat the sample in its container to approximately 60°C and mix with a high-speed shear mixer prior to sampling.
8.2.2.3 To the beaker containing sample, add 13.3 g of TCE (40 % dilution of the test sample with TCE). Mix the solution thoroughly, using the glass rod.
NOTE 5 - For some samples, it is necessary to heat and stir until the sample is completely homogeneous. Maintain the liquid level with additional TCE during heating if necessary.
8.2.2.4 Continue as in 8.2.1.4 through 8.2.1.8.
8.3 Test Method C - Residue
8.3.1 Take a clean and dry test cell with PTFE plug, a 150-mL beaker, and a glass rod. Weigh each of them to the nearest 0.001 g, and record as tare weights.
8.3.2 Add 15 g of reference standard or test specimen to the beaker. Record this mass to the nearest 0.001 g as SM. All samples shall be homogeneous prior to sampling. If the sample is viscous or contains waxy materials, heat the sample in its container to approximately 60°C and mix with a high-speed shear mixer prior to sampling.
8.3.3 To the beaker, add 17.2 g of TCE and 5.3 g of relaxation reagent solution (60 % dilution with 1 mg of relaxation reagent per 1 mL). Mix thoroughly using the glass stirring rod (see 6.4).
8.3.4 Continue, as described in 8.2.1.4 through 8.2.1.8.
9. Preparation of Apparatus
9.1 Read and follow the manufacturer's instructions for preparing the instrument to take measurements. Take special care to prevent the instrument and conditioning block from experiencing rapid temperature fluctuations; for example, avoid direct sunlight and drafts resulting from air conditioning or fans.
9.2 Adequate temperature equilibration of the instrument probe assembly after adjustment to an elevated temperature is essential. Due to the size of test specimen and probe assembly specified by these methods, adequate thermal equilibration may require several hours.
9.3 The results obtained during the use of the instrument are susceptible to error arising from changes in the local magnetic environment. Exercise care to ensure that there is a minimum of metallic material in the immediate vicinity of the instrument and keep this constant throughout the course of a series of determinations.
9.4 Set the instrument controls to the following conditions:
9.5 Place a test cell containing typical test specimen in the coil and ensure that the tuning of the instrument results in two coincident resonance curves on the oscilloscope. Recheck this condition after changing samples.
9.6 Remove the test cell from the coil, and observe that the signal readout from the instrument integrator is now 0 +/- 3 units. Check this condition periodically to ensure that no contamination of the coil with hydrogen-containing material has occurred.