Combi Flash 7650 Series Manual de usuario descargar pdf (Pagina 125)

Section 4 User Help Reference

4-45

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 M

ETHOD 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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Combi Flash 7650 Series Manual de usuario Pagina 125