Single boundary measurements in flow analysis

Single boundary measurements using a stream-switching valve in a single-channel manifold, where a large volume injection produces two discrete reaction zones at the extremities of the sample bolus, have been studied. When monitoring with both diode-array and double beam spectrophotometers, refractive index (RI) effects could be compensated for satisfactorily by subtracting measurements made at a second wavelength. This was less effective with a single beam spectrophotometer. For larger volume flow-cells the indicated flow direction should be followed to obtain undistorted signals, but with an 8 μl flow-cell the direction of flow was immaterial. RI correction was possible with all three flow-cells studied, but the use of the 8 μl cell reduced the contribution of the flow-cell to the overall dispersion. [Continues.]