Micro-continuous flow system for wet chemical analysis

A new continuous flow system based on controlled pumping of exact volumes of sample and reagents into a microbore manifold has been designed. The piston type pumps are made of Al2O3 ceramics and driven by a stepper motor with 48 steps per rotation. One pump per liquid (sample, reagents) is used. For each complete rotation a repeatable and exact volume in the range 3-4 mu l is delivered. Samples are introduced sequentially into the system without being separated by any rinsing or conditioning carrier solution. The mixing channels in the manifold are zigzagged in order to promote secondary flow and thereby efficient mixing through inertial effects. Several types of dedicated manifold have been manufactured with volumes in the range 10-30 mu l. Optical measurement is made vertically against the flow direction using a light emitting diode as the light source. The detection volume is 0.25 mu l. When a new sample is introduced into the system, a signal level typical for the analyte concentration in the sample is rapidly obtained. The detector signal oscillates because of the short and stepwise movement of the liquids in the system. The chemical reactions occurring while the liquids are stationary in the system give rise to a signal change thereby contributing significantly to thr: oscillation. Data evaluation can be based on the average of the signal or by merely utilising the signal obtained during a full turn of the pumps, The developed technique is not sensitive to changes in viscosity (density, salt content) between samples. A typical sample throughput can reach 45 h(-1) and the total reagent consumption is about 40 mu l per sample (two reagents). (C) 1997 Elsevier Science B.V.