What is herein hypothesized is that the four-stage process enables more time for the analyte to reach a more uniform intra loop concentration distribution. A further important consideration can be made observing Fig. 1a and b: the retention time shift (one modulation period delay in Fig. 1b)is certainly due to the additional accumulation/re-injection process inside the loop.What remains to be explained is why the shape of the first modulated peak is nearly always good.