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104 1100 Series DAD and MWD User Manual

5 How to optimize the Detector

Ratio Qualifiers for Selective Detection of Compound Classes

Ratio qualifiers can be used where, in a complex sample, only one particular

class needs to be analyzed — a parent drug and its metabolites in a biological

sample, for example. Another example is the selective analysis of derivatives

after pre or postcolumn derivatization. Specifying a signal ratio that is typical

for the sample class is one way of selectively plotting only those peaks that are

of interest. The signal output remains at zero so long as the ratio is out of the

user-specified ratio range. When the ratio falls within the range, the signal

output corresponds to the normal absorbance, giving single, clear peaks on a

flat baseline. An example is shown in Figure 61 and Figure 62.

Figure 60 Peak Suppression Using Reference Wavelength

Hydrochlorothiazide

and caffeine

Wavelength 204 nm

No reference

Hydrochlorothiazide

and caffeine

Wavelength 222 nm

No reference

Hydrochlorothiazide

suppressed

Wavelength 204 nm

Reference 260 nm

Caffeine suppressed

Wavelength 222 nm

Reference 282 nm

Time (min)

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