SIMPLE-MODEL OF FLOW-INJECTION SAMPLE TRANSPORT FOR PREDICTION OF PEAK HEIGHTS

A model of the flow characteristics of a simple single-line flow-injection manifold is described and evaluated for the effects of various operating conditions on peak parameters, in particular peak height. The model is based on the mechanism for dispersion of diffusion across concentration gradients generated by laminar flow in a closed circular pipe. The flow conduit is considered to be divided into a number of segments both radially and longitudinally. The number of the segments in both dimensions is calculated from an empirically derived relationship from the initial input parameters of length, internal diameter, sample volume, detector volume and flow-rate. An iterative procedure assigns whole number values to the number of segments. Both normal and reverse procedures can be modelled. Diffusion is modelled by averaging the concentration of any one segment over those with which it has a common boundary and flow by transport of a proportion of the contents of a segment according to a parabolic velocity profile. The performance of the model was evaluated from the predicted peak heights for manifolds in which injector volume, flow-rate and tube length were varied. The predicted effect of changing the volume of the detector was examined. The model indicates that detector volume has little effect on peak shape unless the injected volume is less than the detector volume.