I took several spectra of glyphosate on alumina. After several hours spectra migrated upwards (peaks stayed the same, but they were elevated above the previous measuremets).
maybe you can help this work,
Adsorption of Glyphosate on Goethite: Molecular Characterization of Surface Complexes
Julia Sheals*, Staffan Sjöberg, and Per PerssonDepartment of Chemistry, Inorganic Chemistry, Umeå University, S-901 87 Umeå, Sweden Environ. Sci. Technol., 2002, 36 (14), pp 3090–3095
Quite often the reference spectrum is not stable for several hours, but drifts. You should take a reference spectrum every once in a while to compensate for that.
The intensity of the ATR spectrum depends on the layer thickness (usually the layer thickness is higher than the penetration legth unless very thin adsorption layer are used) and on the contact area. It may change in time. The best is to select an internal standard.
Thank you for your answers. Thomas Mayerhöfer, does it mean that it is impossible to measure my sample overnight (and compare with earlier results)?
The point is: I try to measure the change in spectra with time (I expect sorption), thus I have a layer of particles and pesticide on them. I.e. I can not take a reference spectra when sorption is in process
I would advise that you first take, say every hour, a spectrum without sample just to see if it is really problem of drift.
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