Temporal shifting: A hidden key to the skewed peak puzzle

The recorder-provided peak position for flow-type chemical instruments has been verified mathematically as being comprised of a “spatially-non-existent” shift, which is generated due to the relativity in accounting for the detection at a fixed point. This shift, denoted as Φ, can be approximated by Φ ≈ 0.5 μ t 2 , where μt is the temporal expanding coefficient of the system given. For flow injection analysis, the shift is correlated to a longitudinal dispersion coefficient D and the flow speed u, i.e., Φ ≈ D/u2. For linear chromatography, it is correlated to a dynamic partition ratio k″ and a scaling factor f of the column used, i.e., Φ ≈ 0.5k″f. In combination, the temporal shift can be expressed as Φ ≈ 0.5k″f + D(k″ + 1)2/u2. Although the shift may be small in scale, it provides a clue to decipher the basic parameters from a recorded peak. Under a linear isotherm, this parameter can be estimated readily from an experimental peak following a very simple procedure.