Agilent Technologies 1100 Series Manual de Serviço descarregar pdf (Página 44)

44 1100 Series DAD and MWD Reference Manual

2 How to optmize the Detector

Optimizing Selectivity

Quantifying Coeluting Peaks by Peak Suppression

In chromatography, two compounds may often elute together. A conventional

dual-signal detector can only detect and quantify both compounds

independently from each other if their spectra do not overlap. However, in

most cases this is highly unlikely.

With a dual-channel detector based on diode-array technology, quantifying

two compounds is possible even when both compounds absorb over the whole

wavelength range. The procedure is called peak suppression or signal

subtraction. As an example, the analysis of hydrochlorothiazide in the

presence of caffeine is described. If hydrochlorothiazide is analyzed in

biological samples, there is always a risk that caffeine is present which might

interfere chromatographically with hydrochlorothiazide. As the spectra in

Figure 15 show, hydrochlorothiazide is best detected at 222 nm, where

caffeine also shows significant absorbance. It would therefore be impossible,

with a conventional variable wavelength detector, to detect

hydrochlorothiazide quantitatively when caffeine is present.

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Agilent Technologies 1100 Series Manual de Serviço Página 44