A practical device and method of performing comprehensive multi-dimensional chemical separation using a first dimension of a two-dimensional chromatograph to generate a chromatogram in a time comparable to or even faster than common practice while the second dimension generates multiple chromatograms each in a time comparable to the fastest prior art chromatography. The transfer of sample portions from the first dimension to the second dimension is by any one of several sample stream modulation techniques. These techniques accumulate portions of sample between the first and the second dimensions transferring them as very sharp concentration pulses analogous to fast injections, without loss of sample and with a substantial improvement in sensitivity.