ASTM D7624 Standard Test Method for Condition Monitoring of Nitration in In-Service Petroleum and Hydrocarbon-Based Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry
10. Procedure
10.1 Collect a background spectrum according to the procedure specified in Practice D7418.
10.2 Differential Trend Analysis Only - Collect the spectrum of a reference oil sample, according to the procedure specified in Practice D7418.
10.3 Collect the spectrum of an in-service oil sample according to the procedure specified in Practice D7418.
10.4 Data Processing - All data are normalized to a pathlength of 0.100 mm according to the procedure specified in Practice D7418.
11. Calculation of Nitration Values
11.1 Procedure A (Direct Trend Analysis) - Nitration by the direct trending method is calculated from the oil sample spectrum using the measurement peak and baseline points listed in Table 1.
11.2 Procedure B (Differential Trend Analysis) - Nitration by the differential trending method is calculated from the differential spectrum using the measurement peak and baseline points listed in Table 1. Fig. 1 illustrates the band used in the measurement of nitration in the differential spectrum of diesel crankcase oil.
11.3 Reporting:
11.3.1 Procedure A (Direct Trend Analysis) - Values are reported in units of absorbance per centimetre (Abs/cm), calculated as follows:
Nitration in Abs/cm = Nitration in Abs/0.100 mm*100
11.3.2 Procedure B (Differential Trend Analysis) - Values are reported in units of absorbance per centimeter (Abs/cm), calculated as follows:
Nitration in Abs/cm = Nitration in Abs/0.100 mm*100
11.4 Sample Carryover - To ensure the minimum amount of sample-to-sample cross-contamination or carryover, either a minimum volume of the subsequent sample or a solvent rinse is used to flush out the previous sample. The efficacy of the flushing protocol may be assessed by consecutively analyzing an oil having a low (or zero) nitration level (L1, for example, a fresh oil) and a used oil sample having a high nitration level (H1) followed by a second run of the oil sample having a low nitration level (L2) and then calculating the percent carryover (PC) as follows:
PC = [(L2 - L1)/H1] x 100
where L1, H1, and L2 are the values measured for nitration (using the parameters given in Table 1) for the samples run in the indicated sequence. The calculated PC should be <5 %.
