ASTM E2412 Condition Monitoring of In-Service Lubricants by Trend Analysis
ASTM E2412 Standard Practice for Condition Monitoring of In-Service Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry
7. Sampling and Sample Handling
7.1 Sample Acquisition - The objective of sampling is to obtain a test specimen that is representative of the entire quantity. Thus, laboratory samples should be taken in accordance with the instructions in Practice D4057.
7.2 Sample Preparation - No sample preparation is required. Laboratory samples should be shaken or agitated to ensure a representative sample is taken from the bottle.
8. Instrumentation Preparation
8.1 Spectral Acquisition Parameters:
8.1.1 Spectral Resolution - 8 cm(-1) or better (lower numeric value).
8.1.2 Data Point Spacing Resolution - 4 cm(-1) or better (lower numeric value).
8.1.3 Typical Range - 4000 to 550 cm(-1) (see 6.1.2).
8.1.4 Spectral Format - Absorbance as a function of wave-number.
8.1.5 Other Optical, Electronic Filtering and Interferogram Computational Parameters - These parameters should be as recommended by the manufacturer or as determined necessary for adequate measurement quality. Individual parameters and settings will vary depending on instrument manufacturer but most FT-IR spectrometers should be able to collect an adequate spectrum in less than one minute.
NOTE 2 - Identical scanning acquisition parameters should be used for all samples to be trended.
8.2 Background Collection:
8.2.1 The single-beam background collection (empty system reference scanned and stored on an FT-IR spectrometer) should be performed frequently enough such that ambient changes in atmospheric water vapor levels and other changing ambient conditions do not significantly affect the sample results (see Practice E1421). The frequency of background checks should be determined by the individual laboratory conditions and sampling technique; for example, at the completion of each run when an autosampler is used.
8.2.2 Note that changing water vapor levels will have the strongest effect, as water vapor is a strong infrared absorber. A water vapor check may be included in the software to monitor the intensity of the water vapor in the single-beam background spectrum. For example, the water vapor bands superimposed on the single-beam spectrum at 1540, 1559, and 1652 cm(-1) may be measured relative to the average of baseline points at 1609 to 1582 cm(-1). Acceptable limits for operation can be set; for example, measured peaks due to water vapor superimposed on the single-beam background should not be more than 10 % of the single-beam intensity.
8.2.3 Most of the research and development work used in the development of this practice used a background collection at least every 2 h. Individual parameters and settings will vary depending on instrument manufacturer but most FT-IR spectrometers should be able to collect an adequate spectrum in less than one minute.
8.3 Cell Pathlength Check - A cell pathlength check is needed to verify the pathlength consistency of the cell. Results are referenced to 0.100 mm as mentioned in 6.1.2. This check is particularly important for water-soluble salt cell windows (for example, KBr). For systems using a fixed flow cell, the check can be performed at the same time as the background collection. Different instrument manufacturers may use different techniques for cell pathlength checks that may require the use of a reference or calibration fluid(s). A fringe-based method for determining cell pathlength is discussed in the appendix. Manufacturers' instructions and recommendations should be considered.