Agilent Technologies 1100 Series Servisní příručka stáhnout pdf (Strana 38)

38 1100 Series DAD and MWD Reference Manual

2 How to optmize the Detector

A wide bandwidth has the advantage of reducing noise by averaging over a

wavelength range — compared to a 4 nm bandwidth, the baseline noise is

reduced by a factor of approximately 2.5, whereas the signal is about 75 % of a

4-nm wide band. The signal-to-noise ratio for a 30 nm bandwidth is twice that

for a 4-nm bandwidth in our example.

Because the detector averages absorbance values that are calculated for each

wavelength, using a wide bandwidth does not negatively impact linearity.

The use of a reference wavelength is highly recommended to further reduce

baseline drift and wander induced by room temperature fluctuations or

refractive index changes during a gradient.

An example of the reduction of baseline drifts is shown in Figure 12 for

PTH-amino acids. Without a reference wavelength, the chromatogram drifts

downwards due to refractive index changes induced by the gradient. This is

almost completely eliminated by using a reference wavelength. With this

technique, PTH-amino acids can be quantified in the low picomole range even

in a gradient analysis.

Figure 11 Influence of Bandwidth on Signal and Noise

Bandwidth

30 nm

12 nm

4 nm

1 2 ... 33 34 35 36 37 38 39 40 41 42 43 ... 317 318

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Agilent Technologies 1100 Series Servisní příručka Strana 38