The application of two models based on the stirred mixing tanks, the well stirred tank and the two tanks in parallel models, is discussed, and results are presented for flow manifolds with both flame atomic absorption spectrometric and solution spectrophotometric detectors. Both models can be applied to the description of the dispersion generated by the nebuliser/spray chamber of a flame atomic absorption spectrometer. They can also be applied to flow injection manifolds under conditions giving rise to peaks having exponential-like rise and fall curves