Analyte concentration, optical measurement approaches

Combustion diagnostics today relies on a number of analytical and optical techniques, depending on the species under investigation. For the detection of molecular components with more than two or three atoms, mass spectrometry is usually applied with different ionization techniques. For smaller reactive intermediates, optical techniques are the methods of choice because of their non-invasive natme. One of the most widespread experimental approaches to combustion chemistry is through the measurement of the spatial concentration profiles of the intermediate products of combustion the results from such measurements are then compared with model calculations. 

For an optical probe that displays a wavelength shift in absorption or emission on binding, the analyte concentration may be determined from a ratio of intensities at two wavelengths. This is known as a wavelength-ratiometric approach and avoids some of the limitations mentioned above for intensity-based sensing, since, the measurements are independent of probe concentration. Absorption-, excitation-and emission-based ratiometric measurements are all possible. 

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