CombiFlash Torrent® User Manual - Isco

Section 4 User Help Reference
4.4.7 Monitoring the Wavelength Ratio
When using two peak detection options, such as 1 with 2 or
All Wavelength Detection with External, a ratio of the
detection sources can also be displayed, which at times can
provide the best indication of compound purity. Refer to the
following discussion.
If a pure compound is eluting, the absorbance is linearly
related to the concentration of the compound in the solvent. If
the compound absorbs differently at different wavelengths,
the absorbance at each wavelength may be different, but still
linearly related. For example, assume a compound eluting
from the module has an absorbance equal to 2 times the
concentration at 254 nm. This same compound at 220 nm has
an absorbance of 1.5 times the concentration. The ratio of
these signals will be 1.33. Since the relationship of absorbance
to concentration is not variable, the ratio remains steady while
the concentration changes from the beginning to the end of the
peak. During the duration of the peak, the ratio will be 1.33
and this constant value is displayed as a horizontal line.
Now assume a case where there is a second compound eluting,
only slightly shifted in time from the original compound. It is
possible that the detection absorbance trace alone would
indicate a single, valid chromatographic peak. In reality, it is a
combination of two peaks. By monitoring a second wavelength,
it may be possible to reveal the second compound. Because of
the slight shift in time and the different absorbance properties
of the two compounds, the changing ratio during the detected
peak would reveal the impurity. Therefore, one can therefore
assume that if the ratio is not constant for the entire duration
of the peak, the compound eluting may not be pure.
To display the ratio, open the METHOD EDITOR [4.3.2] window
and select the Show Ratio option.
4.4.8 Bypassing the Solid Load Cartridge
Occasionally, impurities precipitate in the solid load cartridge
as compounds are purified. This may cause high back
pressures resulting in reduced flow rates and long run times.
Clicking this button changes the injection valve position,
which removes the solid load cartridge from the solvent path
and relieves the back pressure.
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