DIAGNOSIS AND RESOLUTION OF MULTIWAVELENGTH CHROMATOGRAMS BY RANK MAP, ORTHOGONAL PROJECTIONS AND SEQUENTIAL RANK ANALYSIS

Cases with unresolved chromatographic peaks, where the diagnosis and s ubsequent resolution using common procedures from evolutionary factor analysis fails, are investigated and discussed in some detail. A new p rocedure is then developed. Local principal component analysis is firs t performed using a window procedure called eigenstructure tracking an alysis. This evolving and dynamic procedure provides the best possible sensitivity for assessment of the number of coeluting analytes at a p articular retention time as the method adapts the window size to the n umber of coeluting analytes. The result is a rank map in retention tit le direction, showing, in any retention time interval, the number of e luting analytes. The information in the rank map is subsequently used to define a set of n orthogonal projection matrices (n is the total nu mber of detected analytes in the chromatogram). Each projection matrix is constructed from n - 1 loading vectors obtained, e.g., from princi pal component analysis of the zero-concentration window for a particul ar analyte. This procedure enables unambiguous identification of the p eak pattern in an unresolved region. Resolution of the chromatographic peaks can then be accomplished by the combined use of orthogonal proj ections and a procedure called sequential rank analysis to solve the p roblem of embedded peaks. Sequential rank analysis assumes local symme try around peak: maxima and uses first-order differentiation for uniqu e resolution of embedded peaks. The approach is demonstrated on some s imulated chromatographic systems.