The Spectral Bandwidth (SBW) of a spectrophotometer
is the basis of establishing it ability to resolve absorbtion lines
seperated by small differences in wavelength. If a substance
that you need to measure has an absorbtion line at 257.4nm
and there is an interfering line at 260.0 nm you need to establish
whether your spectrophotometer can resolve the two lines seperately
or "mixes" the two absorbtion lines into a single line which would
give erroneous results.

Toluene in Hexane is used as a reference for the calculation of SBW.
The ratio of the absorbtion of the solution when read at a maxima
(around 268.7nm) and at a minima (around 267.0nm) relates
directly to the SBW of the instrument being assessed. Regular
use of this technique will assure that the resolution
of your instrument is within the required range for your work

Set your spectrophotometer to a slit width and a scan rate
Make a note of the settings. Place the Hexane call in the blank position and
the Tol/Hex cell in the sample position. Scan from 265 to 270 nm.
Determine the absorbtion values for minima around 267.0nm
and the maxima around 268.7nm. Divide the maxima absorbance value
by the mimima absorbance value. Compare your ratio result to the expected
result in your instrument handbook

After determining the ratio of the Toluene in Hexane as instructed in
your instrument operation handbook, follow the interpertation
of results as specified by the instrument manufacturer. All instruments
use the results differently.

Each time that the ratio is derived you can compare the new ratio
with the previous ratios to check for any variance. If your
instrument needs service because of a change in resolution,
the historical data will greatly assist the service technician.