ASTM D6417 Estimation of Engine Oil Volatility by Capillary Gas Chromatography
9. Procedure
9.1 Analysis Sequence Protocol - Define and use a predetermined schedule of analysis events designed to achieve maximum reproducibility for these determinations. Include in the schedule: cooling the column oven and injector to the initial starting temperature, equilibration time, sample injection and system start, analysis, and final temperature hold time. See Table 2 for typical conditions.
9.1.1 After chromatographic conditions have been set to meet performance requirements, program the column temperature upward to the maximum temperature to be used and hold that temperature for the selected time. Following the analysis sequence protocol, cool the column to the initial starting temperature.

9.1.2 During the cool down and equilibration time, ready the integrator/computer system. If a RT calibration is being performed, use the peak detection mode. For samples and baseline compensation (with or without solvent injection), use the area slice mode operation. This is not necessary if the calculations are done using peak integration software as in 10.3.2. The recommended slice rate for this test method is 1.0 Hz (1 slice per second). Other slice rates may be used if within the limits of 0.02 and 0.2 % of the RT of the final calibration component (C60). Other slice rates may be used, as may be required for other reasons, if provision is made to accumulate (bunch) the slice data to within these limits prior to determination of the boiling range distribution.

9.1.3 At the exact time set by the schedule, inject either the calibration mixture, solvent, or sample into the chromatograph; or make no injection (baseline blank). At the time of injection, start the chromatograph time cycle and the integrator/computer data acquisition. Follow the analysis protocol for all subsequent repetitive analyses or calibrations. Since complete resolution of sample peaks is not expected, do not change the sensitivity setting during the analysis.

9.2 Baseline Blank - Perform a blank analysis (baseline blank) at least once per batch of samples. The blank analysis may be without injection or by injection of an equivalent solvent volume as used with sample injections, depending upon the subsequent data handling capabilities for baseline/solvent compensation. The blank analysis is typically performed prior to sample analyses, but may be useful if determined between samples or at the end of a sample sequence to provide additional data regarding instrument operation or residual sample carry-over from previous sample analyses.

9.3 Solvent Blank Run - Since not all of the material contained in fully formulated engine oil sample elute from the column, it is recommended that base oil samples without an additive package not be run in the sample batch as engine oils. Run a solvent blank after each batch of engine oil samples.

NOTE 8 - If automatic baseline correction (see Note 1) is provided by the gas chromatograph, further correction of area slices may not be required. However, if an electronic offset is added to the signal after baseline compensation, additional area slice correction may be required in the form of offset subtraction. Consult the specific instrumentation instructions to determine if an offset is applied to the signal. If the algorithm used is unclear, examine the slice area data to determine if further correction is necessary. Determine if any offset has been added to the compensated signal by examining the corrected area slices of those time slices that precede the elution of any chromatographic unretained substance. If these corrected area slices (representing the true baseline) deviate from zero, subtract the average of these corrected area slices from each corrected area slice in the analysis.

9.4 Retention Time Versus Boiling Point Calibration - A RT versus boiling point calibration must be performed with each batch of samples analyzed. Inject an appropriate aliquot (0.2 to 2.0 µL) of the calibration mixture (7.6) into the chromatograph, using the analysis sequence protocol. Obtain a normal (peak detection) data record to determine the peak RTs and the peak areas for each component. Collect a time slice area record if a boiling range distribution report is desired. Fig. 1 illustrates a graphical plot of a calibration analysis.
9.4.1 Inspect the chromatogram of the calibration mixture for evidence of skewed (non-Gaussian shaped) peaks. Skewness is often an indication of overloading the sample capacity of the column, which will result in displacement of the peak apex relative to nonoverloaded peaks. Distortion in RT measurement and, hence, errors in boiling point temperature calibration will be likely if column overloading occurs. The column liquid phase loading has a direct bearing on acceptable sample size. Reanalyze the calibration mixture using a smaller sample size or a more dilute solution to avoid peak distortion.

9.4.2 Prepare a calibration table based upon the results of the analysis of the calibration mixture by recording the time of each peak maximum and the boiling point temperature in degrees Celsius (or Fahrenheit) for every component in the mixture. n-Paraffin boiling point temperatures are listed in Table 1. An example of a typical calibration report, showing RTs and boiling points for each n-paraffin, is found in Table 3.

9.5 Sample Preparation - Introduce sample aliquots into the gas chromatograph as a solution in a suitable solvent (for example, CS2 or cyclohexane).
9.5.1 Place approximately 0.1 to 1 g of the sample aliquot into a screw-capped or crimp-cap vial.

9.5.2 Dilute the sample aliquot to approximately 2 mass % with the solvent.

9.5.3 Seal (cap) the vial, and mix the contents thoroughly to provide a homogeneous mixture.

9.6 Sample Analysis - Using the analysis sequence protocol, inject a sample aliquot into the gas chromatograph. Collect a contiguous time slice record of the entire analysis (area slice mode).
9.6.1 Be careful that the injection size chosen does not exceed the linear range of the detector. The typical sample size ranges from 0.2 to 2.0 µL of the diluted sample. The maximum sample signal amplitude should not exceed the maximum calibration signal amplitude found in 9.4.1.

10. Calculation
10.1 Tabulate the RTs observed for the calibration standard (n-paraffin blend) versus their respective boiling points. Calculate the RT equivalent to 371°C (700°F), using linear regression and interpolation.
10.1.1 Descriptions of how to apply linear regression can be found in many mathematical textbooks. Scientific hand calculators and software programs may also be used to perform the calculations.

10.2 Subtract the blank analysis (see 9.3) from the sample analysis (see 9.6). If automatic baseline compensation (see Note 8) has been used, skip this step.

10.3 Determine total sample area and area up to the retention time corresponding to 371°C (700°F). This may be done using either area slice summation or peak integration routines in commercial chromatography data systems. See Fig. 2 for baseline definition of fully formulated engine oil sample.
10.3.1 If using area slice summation, use the calculation procedure in Test Method D2887 to find start of sample elution and end of sample elution.
10.3.1.1 Sum the area slices from start of sample to end of sample. This is the total sample area, C.

10.3.1.2 Sum the area slices from start of sample to the slice corresponding to the RT corresponding to 371°C (700°F) found in 10.1. This is the area of sample up to 371°C, B.

10.3.2 If using peak integration software, set integration parameters to determine total sample area, C.
10.3.2.1 Set integration parameters to determine the total area from the start of sample elution to the RT corresponding to 371°C found in 10.1, using a horizontal baseline. This is the area of sample up to 371°C, B.

10.4 Determine the percentage of engine oil volatilized to 371°C, using Eq 3 as follows:
A = 100 x B/C
where:
A = engine oil volatilized to 371°C, area %,
B = area of the engine oil up to 371°C,
C = area of total engine oil sample, and
100 = factor to convert area/area to %.

10.5 Report results as the area percent oil volatilized to 371°C (700°F) to the nearest 0.1 %. Fig. 3 shows typical report showing calculated volatility and chromatogram of a fully formulated engine oil.