Advantages

• A properly operated and programmed ICP-OES can average one sample per minute. This speed, along with the amount of data generated (twenty or more elements), makes this perhaps the most cost-effective test of all.
  
• NIST standards are readily available for calibration curve generation.
  
• Accuracy is usually within acceptable limits.
  
• Results are easily used for trend analysis.
  
• Results include some contaminant and additive metals as well as wear metals.
  

Disadvantages
The major disadvantage of the ICP-OES is the particle size limitation. Usable detection efficiency is limited to an average of 10 microns, thus large 50 and 100 micron particles will not be seen as easily by the detection system. The limitation on the detection efficiency size will vary with each metal, along with such things as the thickness of the metal oxide layer on the particle's surface and the melting point of each metal. Usually, however, when the number of large particles increases in a sample, so does the number of smaller particles (1-10 microns in size). This is one of the reasons that trending becomes so important when looking at emission spectrometer data. Also, this size limitation can be overcome by acid digestion of the sample which reduces the metals particles to an ionic state so they can be easily seen by the spectrometer. This is done at the sacrifice of speed and efficiency, however.

The heart of most lube oil analysis programs is a check for metals. With today's technology, this is usually a quick, simple, and cost-effective test. The two most common instruments used for this are the ICP-OES, Inductively Coupled Plasma-Optical Emission Spectrometer, and the Rotating Disk Electrode-Optical Emission Spectrometer (RDE-OES). Either of these two instruments can be set up to analyze twenty-four or more single metal elements simultaneously. This section is focused on the ICP-OES.

The ICP-OES operates on the fact that both atoms and ions can absorb energy to move electrons from a ground state to an excited state. The energy, in this instance, is the heat provided by an argon plasma that operates at 10,000 Kelvin. As the atoms are excited, they release light at specific wavelengths and then converted to parts per million, or ppm. This is the value you will see on your reports. The spectrographic metals reported fall into three categories. Some of the metals can fall into multiple categories as well.

OPTICAL emission spectrometer

* These elements are available upon request