dear michael Päch, I'm follow those discussing; in those question, about the minimum absorption discussed by Dr. Schmitt but the maximize absorption not mentioned.therefore my question is what's the maximize Absorption can be used for quantitative analysis in uv/vis spectroscopy ?
In terms of absorption one needs to be careful with desired region of absorption and the chromophores involved. The solvent effect plays a role too and therefore should not be ignored. If the sample absorbs in the same range as the solvent then definately nothing will be observed. That brings in concentration because of the addition nature of absorption spectra. The linear absorption range of most spectrophotometers is between 0.2 to 2.5 but at around 1.8 absorbance units (au) the curve slowly becomes nonlinear as well as below 0.2 au. Looking at concentration; [conc] x 10-2 have shown to be more concentrated leading to higher absorbance above 2.5 au and [conc] x 10-6 show very low absorbance below 0.2 au these two regions are non linear and therefore not suitable for quantitative work. I would suggest an ideal analytical region as between 0.3 and 1.2 au avoiding solvent absorption effect and addition effect from nearby absorbing solutes. A concetration range of 10-5 to 10-3 would be most ideal for pi and lone pair absorbing systems.
for quantitative analysis use only absorbance (extinction) because this is proportional to concentration up to a value of about 1. If you exceed the linearity range you would be able to do analysis having the calibration data and taking into account nonlinearity. Nevertheless, it is recommended to stay in linearity range by using thinner cells or by dilution.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry