Monitoring time-varying concentrations in sample streams by multiple input chromatography

The possibility of monitoring time-varying concentrations with conventional chromatography or correlation chromatography (CC) is restricted. The highers frequency that can be monitored is, due to Shannon, limited for conventional chromatography to (2 x chromatogram length)−1, and for CC, due to a moving average effect, to (sequence lenght)−. A method is presented in which considerable higher frequencies can be monitored. Theoretically the power spectral density of the chromatographical peak shape limits the upper frequency that can be monitored. The method originates from CC. A pseudo-random binary sequence (PRBS) is used as injection pattern. The detector signal however is not correlated or deconvoluted with a PRBS as in CC. The time-varying concentrations of the components are described as functions of time and a number of parameters, e.g. parameters of a Fourier series. These parameters then are optimised in a non-linear fitting procedure. A detector signal is calculated using the parameters, the known PRBS and known peak shapes; and the squared differences with the real detector signal are minimised. The results from simulated experiments and practical experiments are shown.