High performance capillary electrophoresis - T.E.A.M.

Figure 62
Photograph of a dye front passing through
the extended light path capillary detection
region
(across the capillary) to fill the increased volume, it contracts
longitudinally (along the capillary). Thus the sample
concentration remains constant but the path length increases.
Figure 62 shows a photograph of the zone front of
a dye in the expanded region of the bubble cell.
Instrumentation/Operation
mAU
60
40
20
0
2 3 4 5 6
60
b)
40
20
0
2 3 4 5 6
Time [min]
Figure 63
Peptide analysis using: a) the extended
light path capillary, and b) a normal
straight capillary
Conditions: a) id = 50 µm with 150 µm
detection cell; b) id = 50 µm
a)
The use of the bubble cell is illustrated in figure 63 for the
separation of neuropeptides. Here the bubble is three times
larger than the inner diameter (150-µm id bubble in a 50-µm
id capillary). This yields nearly a 3-fold increase in signal
relative to a straight capillary. Importantly there is nearly no
measurable band broadening. In addition, the lower limit of
detection and linear detection range are also improved due
to the increased light throughput of the bubble cell.
4.3.7 Diode-array detection
Diode-array detection (DAD) is an alternative to single
or multiple wavelength detection. Instrumentally a DAD
consists of an achromatic lens system to focus
105