In uv spectroscopy, quartz cuvettes are used and not glass cuvettes. Why?
Answers
In order to acquire a UV-Vis spectrum, the solid has to be completely dissolved in a suitable solvent. Note that not every solvent is suitable for UV-Vis spectroscopy. Generally, spectrograde solvents are used that have undergone special purification steps to remove trace impurities of aromatic and other compounds (see link below for solvent cutoffs). For instance, 95 % ethanol is generally not suitable as solvent for UV-Vis measurements because it often contains aromatic compounds as denaturing agents.
2. Cuvettes also have limited optical windows. While cuvettes made from fused quartz allow measurements as far down as ~200 nm, Pyrex cuvettes already show a significant absorption around 260 nm. Cuvettes made from acrylic plastic or ordinary glass absorb already at higher wavelengths. In addition, many of the plastic cuvettes are not compatible with most organic solvents (the windows are not translucent anymore or they are plainly dissolved, for details see link below). If you use a quartz cuvette, please keep in mind that it is very expensive (~$150 each). If you break it, you will have to pay for it since your lab material fee does not cover this kind of loss. So be careful when you handle them.
Absorption Characteristics of various cuvette materials
3. Since UV-Vis spectroscopy is an absorption technique, Beer's Law can be applied. It is only valid at low concentrations (<10-4 mol/L). At higher concentrations, a negative deviation is observed due to association of the molecules and other effects. Another critical factor is the detector of the UV-Vis instrument that only works linear within a certain range as well. A meaningful absorbance reading should be between A=0.1 and A=1.0. In essence, the concentration has to be low enough, so that the maximum absorbance does not exceed A=1. And yes, you do need to know the exact concentration of your sample in order to determine the molar extinction coefficient (e). Just preparing a solution that gives you a good reading is not enough to obtain all thr relevant information (l and e-value!).