Optimizing For Sensitivity, Selectivity, Linearity And Dispersion; Flow Cell Path Length - Agilent Technologies InfinityLab LC Series User Manual

5 Optimizing the Detector

Optimizing for Sensitivity, Selectivity, Linearity and Dispersion

Optimizing for Sensitivity, Selectivity, Linearity
and Dispersion

Flow Cell Path Length

Lambert-Beer's law shows a linear relationship between the flow cell path length
and absorbance.
where
T is the transmission, defined as the quotient of the intensity of the transmitted
light I divided by the intensity of the incident light, I
 is the extinction coefficient, which is a characteristic of a given substance under
a precisely-defined set of conditions of wavelength, solvent, temperature and
other parameters,
C [mol/L] is the concentration of the absorbing species, and
d [m] is the path length of the cell used for the measurement.
The detector can now output the signal in two forms:
1 In Absorbance divide by the path length AU/cm, that is then similar to [ x C].
2 In AU that is equal to  x C x d like normal done in the past: now for
Therefore, flow cells with longer path lengths yield higher signals. Although noise
usually increases little with increasing path length, there is a gain in
signal-to-noise ratio.
When increasing the path length, the cell volume could increase. Depending on
the peak volume, this could cause more peak dispersion.
Agilent InfinityLab LC Series Diode Array Detectors User Manual
Advantage: samples with same concentration have same peak height also at
cells with different path lengths.
The upper limit of concentration: the linearity limit of the detector is then seen
at about 2 AU/path length, so for the 6 cm Max-Light Cartridge Cell the
linearity limit is 333 mAU/cm].
recalculation to your concentration C the path length must be considered.
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