Tolerance analysis of a micro-optical detection system for on-line monitoring of lubricant oils

We present a functional prototype of a micro-optical detection unit for both absorbance andlaser-induced fluorescence analysis in fused silica capillaries. Absorbance detection allowsconcentration measurements ranging from 0.6 micro-M to 12 mM, whereas fluorescence detectionenables concentration measurements from 6 pM up to 0.6 mM. We make use of non-sequentialoptical ray tracing simulations combined with statistical design methodology to perform acomplete tolerance analysis for manufacturability and we demonstrate experimentally that theefficiency of the system is insensitive to reasonable misalignment and fabrication errors of itsbuilding blocks. The possibility of using standard fabrication techniques to prototype andreplicate this miniaturized plastic detection system, as well as its wide measurement rangemake it a good candidate for applications where low-cost and portable systems are needed tomeasure small volumes of liquid samples with low-level concentrations. As an example wedemonstrate the use of the system for the optical characterization and differentiation ofnanoliter volumes of lubricant oils.