Shape-Based Peak Identity Confirmation in Liquid Chromatography

Chromatography is used to separate analytes in a mixture. In the absence of a detector providing analyte-specific information, the retention time is used to identify the analyte, typically by comparing the retention time of the unknown with that of a standard. This is the simplest of identification routines, but it remains the most widely used. The challenge is that analyte retention times can and do shift; sole reliance on retention time for identification is not prudent. Retention time is influenced by the total sample concentration, elution of components near the peak of interest, aging of a column, and so on, complicating time window-based identification. We propose a sameness threshold (ST) that is based on numerical comparison of shapes of chromatographic peaks for identification confirmation. We demonstrate shape-based identification confirmation or lack thereof of an unconfirmed peak by comparison with a shape library of standards. In numerous cases we look at, only one analyte in the shape library fits the putative identity. ST can be based on r², the commonly used coefficient of determination used in regression analysis, or on an "index of width mismatch" that compares the widths of the peaks throughout the available height range.