The use of long columns have several advantages. Most important are the increase in peak and sample capacity, collectively enlarging the dynamic range in data dependent MS/MS analysis of complex samples. Long columns allow to perform very shallow gradient runs without sacrificing the separation efficiency and/or peak shape.
Slow gradients provide the opportunity to use longer MS cycle times with more MS/MS experiments and longer dwell times. Longer dwell times allow a low repeat count. In addition one may set the precursor ion back on the inclusion list after a time that corresponds to the FWHM (here 15, 21 and 27 s). Such a strategy increases the probability that MS/MS spectra are obtained at or close to maximum intensity of eluting peptides.