Spectrographic metals analysis is usually the ‘heart’ of most oil analysis programs. Using either a Rotrode Emission Spectrometer or an Inductively Coupled Plasma Spectrometer (ICP), 20 or more metals can be simultaneously determined. The metals analyzed for include wear, additive, and contaminant metals and are reported in parts per million (ppm).
MRT Laboratories uses a Rotating Disk Emission Spectrometer. The instrument is quick and easy to operate and is accurate within acceptable limits. The Rotrode Spectrometer has a particle size detection limitation of between 3µ and 10µ (depending on the particular metal in question and the amount of surface oxidation on the particle surface) compared to the .5µ – 2µ limitation of the ICP. Results of the Rotrode Spectrometer are accurate to about 1 or 2 ppm. Results of the ICP are accurate to 0.1 ppm. The advantage of the Rotrode Spectrometer is that no dilution of the sample is required, while the advantage of the ICP is its accuracy. With proper sample preparation, an ICP can measure in the 10’s of parts per billion (ppb). Particle size limitations of an ICP are even more severe than a Rotrode Spectrometer because the sample and particles have to be nebulized.
If measuring very low concentrations, the diluent (usually diesel fuel) has to be at least as clean.
For routine lube oil analysis, commonly every three months maximum between tests, accuracy below the 1 ppm level is not required. Assuming that samples are properly and cleanly taken there should be little change in the particles detected in the machine fluid over time. Changes over time can indicate issues.
At MRT Laboratories we analyze for 21 elements, and break them down into three categories of wear, additive, and contaminant.