A microfluidic microchip includes a channel structure having a delivery channel connected in a substance conductive manner to a separation channel. Laterally offset discharge channels are at connection points displaced from a connection point between the delivery and separation channels. Between the connection points on the one hand and the connection point on the other are channel sections having concordant channel lengths. By imposing suitable electrical potentials along these channel sections, the filling volumes present in the channel sections are satisfactorily homogenous after a certain period of time to form a representative part of a substance specimen. Substance volume units are formed in these channel sections. The lengths of the volume units are determined exclusively by the lengths of the channel sections. Pulse-shaped substance volume sequences are injected into the separation channel. The signal-to-noise ratio of the measurement results is substantially improved by generating substance volume sequences on the basis of pseudo-randomly scattered binary digit sequences similar to Hadamard sequences, and by a cross-correlation analysis of spectra measured on the basis of such substance volume sequences.