Frans_M_Everaerts_Isotachophoresis_378342.pdf

W ABSORPTION METER
230 240 2% m zm 280 EC GO 30 m 330
wovelength (nm)
Fig.6.27. Optical filters used for the UV absorption measurements on the various zones. A combina-
tion of an interference filter and an end filter (coloured glass filter) was always used. From this figure,
an estimation of the band width can be made for the experiments included in this book.
impedance, the circuit must be surrounded with a metal frame in order to prevent
disturbances. Special care must be taken in selecting the 104-Ma resistor, which is
basically responsible for a bad signal-to-noise ratio and drift.
In the PTFE narrow-bore tube (I.D. 0.45 mm, O.D. 0.75 mm), in combination with
a slit width of 0.3 mm*, the difference in signal (uv) between dark and light is approxi-
mately 100 mV, which is the normal value if a non-absorbing component is inside the
narrow-bore tube with water as the solvent and the combination of interference filter
and coloured glass filter (end filter) is chosen, as shown in Fig.6.27. This value of 100 mV
is chosen arbitrarily and depends mainly on the sensitivity of the potential recorders
available.
6.5.4. UV detector in combination with a modulated UV source
In the UV detector, the alternating current, due to the alternating influx of W
quanta, in the phototube is changed to an alternating voltage, which is then detected
synchronously.
*Later experiments learn that with a slit of 0.1 mm and a narrow-bore tube (I.D. 0.2 mm, O.D.
0.4 mm), sharper boundaries could be detected between the various zones.
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