Last Thursday we went to the TU Delft ChemLab for fluid testing with a fluoresence spectrometer. The difference between this type of spectrometry and the type we use in our own home made spectrometer can be found in a previous post.
Our spectrometer is based on absorption spectrometry, which is one way to get a spectrum which clearly differentiates between different materials (conventionally in the case of absorption only materials that let through light can be tested). Other types of spectroscopy include fluorescence spectroscopy which uses a laser to excite the liquid, and emissions are read.
As the absorption spectrometry machine was not available in the Chemical Engineering lab, an alternative was given to us to test various liquids in a fluorescence spectrometer. The results of the fluorescence emission chart shows similarities with the results of our absorption spectrometer.
The principle behind the fluorescence spectrometry testing is to define a region in which the liquid fluorescence is strongest with a particular laser wavelength. There are three steps to getting an accurate liquid emission chart.
The first step is to get a general emissions chart by subjecting the liquid to a fixed excitation wavelength. The output wavelengths can be plotted against the intensity of the output light. Like this a rough emission chart can be retrieved. The second step involves selecting a range of wavelengths the laser will shoot into the liquid to get an excitation chart. This range is generally between the lowest wavelength tested in the emission tests up to the wavelength of the maximum peak. Like this we select a laser wavelength that amplifies our output during an emissions test.
The third step is to apply this laser wavelength that amplifies the output in a second emission test that should ideally look similar to the first emissions test except amplified. This becomes the final emission chart.
Both techniques are appropriate to determine material differences, it is not possible to draw any conclusions. The fluorescence tests are appropriate for more accurate results, while our spectrometer is much more accessible. The accuracy of our spectrometer cannot be determined without comparing it directly to a absorption spectrometer.