Thermal Biosensors in Biotechnology - Advances in Biochemical Engineering Biotechnology - page 53

has a tremendous advantage in that there is no electrical contact between pa-
tient and analyzer.In the case ofenzyme exhaustion,the column is removed and
a fresh one installed.Thus,urease columns are cheap throw-away articles.Urea
analysis is performed in the dialysis buffer and not in the patient's blood.
Therefore,sterile conditions are not necessary.
Figure 12 shows a possible set-up for hemodialysis monitoring. Patients
blood is pumped through a dialysis cell, and low molecular weight substances
including urea are removed by a semipermeable membrane (cut off:10 kD) and
dialysis buffer. The urea enriched dialysate passes through an injection valve
and enters a waste container. Due to switching the valve, a defined sample
volume is pumped to the ET.Here,enzymatic conversion takes place via immo-
bilized urease and provides information about the current urea concentration.
Thus,the hemodialysis effect is automatically monitored via urea analysis and
makes an individual treatment possible.
The set-up of a hemodialysis simulation is shown in Figure 13 (Lammers,
1996). Here, typical changes of urea concentrations in the dialysis buffer were
monitored.Within 5.2 h a urea standard of 12 mmol/l was diluted to 2 mmol/l.
The dilution process was monitored by a computer-controlled FIA system in-
cluding an ET.Figure 14 shows the result of a simulation experiment.Obviously
the ET is suitable for recording the whole concentration range.Danielsson (1995)
observed similar curve shapes in measurements that were performed in real-
Fig.12. Hemodialysis set-up