Description of Instrumentation and Procedures - Advances in Biochemical Engineering Biotechnology - page 6

2
Description of Instrumentation and Procedures
2.1
Conventional System
The earlier investigations employed several different types of plexiglas con-
structions containing the immobilized enzyme column. These devices were
thermostated in a water bath, and the temperature at the point of exit from the
column was monitored with a thermistor connected to a commercial Wheat-
stone bridge. The latter was constructed for general temperature measurements
and osmometry. Later, we developed more sensitive instruments for tempera-
ture monitoring indigenously: the water bath was replaced by a carefully tem-
perature-controlled metal block, which contained the enzyme column. The
enzyme thermistor concept has been patented in several major countries.
Such simple plexiglas devices were extremely useful and could be employed
for determinations down to 0.01 mM. An example of such a simple device will
therefore be described here in some detail. (Fig. 1). The plastic column, which
can hold up to 1 ml of the immobilized enzyme preparation, was mounted into
a plexiglas holder, leaving an insulating airspace around the column. The heat
exchanger consisted of acid-proof steel tubing (ID 0.8-1 mm and about 50 cm
long) coiled and placed in a water-filled cup. The whole device was placed in a
water bath with a temperature stability of at least 0.01°C. The cap surrounding
the heat exchanger reduced the temperature fluctuations considerably and
improved the baseline.
Fig. 1. Cross section of a conventional ET system (see text for detailed description)