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ASI was founded in 2005 and is located in Foster City, California, in the San Francisco Bay Area.
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>>What is Electron Spin Resonance (ESR)?

Electron spin resonance is an electronic technique to measure the type and concentration of highly reactive free radicals in a sample. The sample could be a liquid, such as oil, fuel, blood or saliva, a solid such as a crystal, or even a gas (for example, measurement of suspended soot particulates in air). Free radicals are highly reactive molecules that, among other functions, govern the rate of breakdown of oil.

For online or offline oil analysis, ESR has three important advantages when compared to many competing sensor technologies. It is quantitative, unambiguous and thermally stable.

Looking at this in more detail:

1. Quantitative vs. Qualitative
Micro-ESR™ gives a quantitative reading of the condition of your lubricating oil. This means that you can flow any type of oil through the Micro-ESR™ sensor and the sensor will immediately tell you the amount of oxidation, the amount of soot in the oil, the percentage of water (both free and dissolved) and in the case of marine engine oil, the concentration of certain metal and sulfur compounds. No information about the 'new' condition of the oil is required for Micro-ESR™ to measure this data.

Many competing sensor technologies (for example, electrical impedance, dielectric permittivity, or viscosity) operate by comparing their sensor's output to stored data obtained from an unused oil sample and laboratory modeling of oil breakdown or contamination. With these types of sensors, just looking at the sensor readout without first knowing the properties of the new oil doesn't give you any concrete information about the present condition of the oil.
Take the case of a viscosity sensor. Suppose the viscosity sensor gives a reading of 12 cSt at 100°C. Is that high or low? Is the oil on the verge of breakdown, is there excess water or fuel dilution, is soot building up, or is everything just fine? Its impossible to tell without first knowing the viscosity of new oil, and second, looking at the trend in viscosity changes, and third, having a complete model of how the oil's viscosity varies with different types of contaminants and oil breakdown products.

A further complication with these other types of sensors, is that without doing substantial laboratory analysis, the remaining life of the oil cannot be determined. We characterize these types of sensors as being 'qualitative' because they don't give you any absolute information about the oil, only information relative to a stored baseline or set of laboratory tests.

2. Unambiguous
The second very important characteristic of Micro-ESR™ is that it gives detailed, unambiguous information about the composition of free radicals and impurities in the sample. Since electron spin resonance is highly selective -- only free radicals can be detected -- our sensor is not confused by the presence of unexpected contaminants (for example, water and diesel fuel together).
Each free radical is characterized by its "g-value," a number often close to 2.0000. For example, the peroxy radical (RO2.) which causes oil oxidation has a g-value of 2.0100 +/- 0.005 (which varies slightly depending on the molecular weight of the oil). The carbon radical due to soot has two signals, a broad signal with a g-value of approximately 2.1, and a narrow signal at g=2.0026. The g-value of the narrow signal varies slightly depending on the origin of the soot.
Transition metal ions, for example, iron, vanadium, manganese and others, as well as sulfur compounds such as iron sulphides (Fe(III)S) also have characteristic ESR spectra. (See the sample Marine Engine Oil spectrum as an example of peroxy, soot, iron sulphide and Iron(III) ions in ESR spectra of cylinder lube oil.)

3. Thermal Stability
A third benefit is temperature stability-- since the electron spin resonance signal is a quantum mechanical effect, it is only weakly dependant on temperature. Therefore, the g-value of a free radical does not vary depending on the measurement temperature, and the intensity of the ESR signal is also independent of temperature. The Micro-ESR™ sensor does not require any temperature compensation!
Contrast that to measurements of viscosity, which is an exponential function of temperature! Proponents of conventional sensor technologies will tell you "we can correct for that in software." Software fixes to bad data will often fail in the field in the presence of unknown contaminants and unexpected operating conditions.
more information
Free radicals also occur in the human body and are associated with many disease processes such as cancer and heart disease -- follow this link for a great article on free radicals and antioxidantS. On of the most common uses of electron spin resonance is to measure short-lived free radicals using a method called spin-trapping. A spin-trap is a molecule designed to bond to short-lived free radicals (like hydroxide and superoxide radicals) and convert these to a stable, ESR visible form. The spin-trapping method is frequently used in biomedical research to measure oxidative stress. Common spin-traps include the compounds PBN, POBN, and DMPO.

Conventional electron spin resonance spectroscopy (also called electron paramagnetic resonance) is discussed in detail here. Notice the size of the conventional instrumentation compared to our tiny 2.25" diameter (hockey puck)