Interferometer-based spectrometry

This is an analysis frequently conducted on oil lubricants. Generally, the additive is known and its concentration can be followed by direct comparison of the oil with additive and the base stock. For example, concentrations of a few ppm of dithiophosphates or phenols are obtained with an interferometer. However, additive oils today contain a large number of products their identification or their analysis by IR spectrometry most often requires preliminary separation, either by dialysis or by liquid phase chromatography. 

Non-dispersive spectrometry is an alternative to the classic, dispersive technique where monochromators are used, as depicted schematically in Fig. 2.67. Non-dispersive techiuques, used mainly in infrared spectroscopy, are based generally on interferometry. The sample is irradiated by polychromatic radiation. After transmitting the sample, the fight forms an interference pattern, which contains aU pieces of information that could be obtained alternatively by dispersive methods. Several types of interferometers can be built in integrated optics having miiuature dimensions. They are useful for chemical sensors. 

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