ASTM D4951 for additive elements in lubricating oils by ICP-AES
ASTM D4951 standard test method for determination of additive elements in lubricating oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
10. Preparation of Apparatus
10.1 Instrument - Design differences between instruments, ICP excitation sources, and different selected analytical wavelengths for individual spectrometers make it impractical to detail the operating conditions. Consult the manufacturer's instructions for operating the instrument with organic solvents. Set up the instrument for use with the particular dilution solvent chosen.
10.2 Peristaltic Pump - If a peristaltic pump is used, inspect the pump tubing and replace it, if necessary, before starting each day. Verify the solution uptake rate and adjust it to the desired rate.
10.3 ICP Excitation Source - Initiate the plasma source at least 30 min before performing an analysis. During this warm up period, nebulize dilution solvent. Inspect the torch for carbon build-up during the warm up period. If carbon build-up occurs, replace the torch immediately and consult the manufacturer's operating guide to take proper steps to remedy the situation.
NOTE 2 - Carbon that accumulates on the tip of the torch injector tube can be removed by using nebulizer gas that consists of approximately 1 % oxygen in argon.
10.3.1 Generally, carbon build-up can be minimized by increasing the intermediate argon flow rate or lowering the torch, or both, relative to the load coil.
NOTE 3 - Some manufacturers recommend even longer warm up periods to minimize changes in the slopes of the calibration curves.
10.4 Wavelength Profiling - Perform any wavelength profiling that is specified in the normal operation of the instrument.
10.5 Operating Parameters - Assign the appropriate operating parameters to the instrument task file so that the desired elements can be determined. Parameters to be included are element, wavelength, background correction points (optional), interelement correction factors (refer to 5.1), integration time, and internal standard compensation (required). Multiple integrations (typically three) are required for each measurement. A typical integration time is 10 s.
11. Preparation of Test Specimens
11.1 Diluent - Diluent refers to the dilution solvent containing the internal standard (refer to 8.2).
11.2 Test specimen solutions are prepared in the same way that calibration standards are prepared (refer to 12.2). The mass % oil in diluent must be the same for calibration standards and test specimen solutions.
11.2.1 Lubricating Oil Specimens - Weigh appropriate amount of the test specimen to the nearest 0.001 g. The weight of the test specimen taken will vary depending upon the metal concentration of the specimen. Dilute by mass with the diluent. Mix well.
11.2.2 Additive Packages - The concentrations of additive elements in additive packages are typically ten times the concentrations in lubricating oils. Therefore, additive packages are first blended with base oil before adding diluent.
11.2.2.1 Weigh appropriate amount of the additive package to the nearest 0.001 g. The weight of the test specimen taken will vary depending upon the metal concentration in the specimen. Add approximately ten times this amount of base oil, weighed to the nearest 0.001 g. Dilute this mixture by mass with diluent. Mix well.
11.3 Record all weights and calculate dilution factors by dividing the sum of the weights of the diluent, sample, and base oil (if any) by the weight of the sample.
12. Preparation of Calibration Standards and Check Standards
12.1 Diluent - Diluent refers to the dilution solvent containing the internal standard (refer to 8.2).
12.2 The user of this test method has the option of selecting the dilution factor, that is, the relative amounts of sample and diluent. However, the mass % sample in diluent (for calibration standards and test specimens) must be constant throughout this test method, and the mass % sample in diluent must be in the range of 1 to 5 mass %.
12.2.1 All references to dilute and diluting in this test method refer to the user-selected dilution.
12.3 Blank - Prepare a blank by diluting the base oil or white oil with the diluent.
12.4 Working Standards - Weigh to the nearest 0.001 g, approximately 1 to 3 g of each multi-element standard (refer to 7.4) into separate bottles. Dilute by mass with the diluent.
12.5 Check Standard - Prepare instrument check standards in the same manner as the working standards such that the concentrations of elements in the check standards are similar to the concentrations of elements in the test specimen solutions. It is advisable to prepare the check standard from alternative sources of certified organometallic standards.
