User manual

76 Agilent 1260 Infinity High Performance Autosampler User Manual

5 Optimizing Performance

How to Achieve Higher Sensitivity

The sensitivity of a separation method is linked to the choice of stationary

and mobile phases as good separation with narrow peaks and a stable

baseline with minimal noise are desirable. The choice of instrument

configuration will have an effect and a major impact is the setup of the

detector. This section considers how sensitivity is affected by:

• Pump mixer volume

• Narrower columns

• Detector flow cell

• Detector parameters

In addition, the discussion on detector parameters also mentions the

related topics of selectivity and linearity.

Columns

Sensitivity is specified as a signal- to- noise ratio (S/N) and hence the need

to maximize peak height and minimize baseline noise. Any reduction in

peak dispersion will help to maintain peak height and so extra- column

volume should be minimized by use of short, narrow internal diameter,

connection capillaries and correctly installed fittings. Using smaller inner

diameter columns should result in higher peak height and is therefore

ideal for applications with limited sample amounts. If the same sample

amount can be injected on a smaller i.d. column, then the dilution due to

column diameter will be less and the sensitivity will increase. For

example, decreasing the column i.d. from 4.6 mm to 2.1 mm results in a

theoretical gain in peak height of 4.7 times due to the decreased dilution

in the column. For a mass spectrometer detector, the lower flow rates of

narrow columns can result in higher ionization efficiencies and therefore

higher sensitivity.