Agilent Technologies 1100 Series Reference Manual page 31

Internal
column
diameter
Figure 5
Flow Cell Path Length
Lambert-Beer's law shows a linear relationship between the flow cell path length and
absorbance.
bsorbance
where
Tis the transmission, defined as the quotient of the intensity of the transmitted light I
divided by the intensity of the incident light, I
is a characteristic of a given substance under a precisely-defined set of conditions of
wavelength, solvent, temperature and other parameters,
Cis the concentration of the absorbing species (usually in g/l or mg/l), and dis the path
length of the cell used for the measurement.
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. For example, in
70 % increase in signal intensity was achieved by increasing the path length from 6 mm
to 10 mm.
When increasing the path length, the cell volume usually increases — in our example
from 5 – 13 µl. Typically, this causes more peak dispersion. As
demonstrates, this did not affect the resolution in the gradient separation in our
example.
As a rule-of-thumb the flow cell volume should be about 1/3 of the peak volume at half
height. To determine the volume of your peaks, take the peak width as reported in the
integration results multiply it by the flow rate and divide it by 3).
1.0 mm 2.1 mm
Choosing a Flow Cell
T C d
Figure 6 on page 30 the noise increased by less than 10 % but a
3.0 mm
How to optimize the detector
I
, εis the extinction coefficient, which
0
Figure 6
4.6 mm
2
on page 30