Accurate absorbance and wavelength measurements can only be achieved if due consideration is given to the resolution of the monochromator in use. In modern instruments with grating monochromators, the resolution relates directly to the slit width chosen.
The smaller the slit and associated spectral bandwidth, the greater the resolution, but the corresponding reduction in energy means the signal-to-noise ratio falls. When measuring an absorbance band in a high-resolution instrument, it is recommended that the spectral bandwidth (SBW) should not exceed 10% of the natural bandwidth (NBW) of the band.
Therefore, simple checks on the resolution power of a spectrophotometer will ensure, for example that adjacent peaks will be fully resolved and not be blended into a combination peak with the associated wavelength, and absorbance errors.
For the measurement and checking of this fundamental parameter, Starna® offers you the choice of either a sealed liquid cell (0.02% v/v solution of toluene in hexane), or a sealed benzene vapour cell. |
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Toluene in Hexane
Product Description: (see MSDS)
This formulation is described and used in the European Pharmacopoeia where the ratio of the peak maximum at 269 nm to the minimum at 266 nm gives a measure of the resolution of the instrument.
Ratio table:
SBW (nm): |
0.5 |
1.0 |
1.5 |
2.0 |
3.0 |
Ratio: |
2.5 |
2.1 |
1.6 |
1.4 |
1.0 |
Suggestions for Use:
Resolution determinations are run against the hexane blank supplied with each Certified Reference Material, and the procedure is similar for all spectral
bandwidths.
Scan the 265-270 nm region, and calculate the peak maxima and minima.
Calculate the peak/trough ratio and compare to the reference values |
