Hi, I would like to know the procedure for studying the uv-absorption of a Langmuir film (peptide) on a glass? I am only familiar with studying the absorption spectra of liquid substances.
glass adsorbs strongly in the UV spectrum so I recommend purchasing polished quartz windows which are transparent in UV. Take a background spectrum using the quartz, then measure the quartz-supported-langmuir film. subract out the background and *boom* you've got your spectra! To self promote I did some of these type of measurments here: DOI: 10.1021/ma5010698
The method of Dr. Janes, may work, but you never can be sure and it also depends if semi-quantitative data may be enough for you or if you have to be as exact as possible. The Maxwell-conform way to do things is to set up the correct optical model, in your case this would be semi-infinite incidence medium/thick layer (incoherent)/thin layer/exit medium (if the order is the other way round, this will not affect the transmittance calculation - it will simply be the same). From the measurement of the substrate without film you can then determine the optical constants of the substrate (semi-infinite incidence medium/thick layer (incoherent)/exit medium), which you can subsequently use to model your layer. Software to do this is available, e.g. SCOUT2 or RefFIT. Is this effort really necessary? We are investigating this situation at the moment in the infrared ( https://www.researchgate.net/project/Fast-and-reliable-Determination-of-the-true-Absorbance ). First results show that the errors can reach up to 30 % concerning the intensities, and the errors depend on frequency range, difference between the index of refraction of substrate and layer (anomalous dispersion...) etc. It is on you to decide if this is ok for the problem at hand...
Thank you Dr Janes and Dr Thomas. I will try your suggestions out.
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