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.