Fig. 3.

Conversion of RT to RI enables the normalization of retention data between HPLC and UHPLC format. Metabolite standards were measured on the identical phase system in HPLC format compared to the previously used UHPLC format. Analysis was performed on two different hardware setups differing in column dead volume, extra column dead volume, gradient dwell volume, and gradient mixing system (see “Material and methods”). While RTs (as expected) show a large deviation making a direct comparison not possible, RIs from the different systems are in good agreement. The red dashed lines indicate the diagonal, which represents a perfect fit. The histogram of the relative deviation of RIs from reference RIs in % shows no systematic deviation