Two main resolution problems were observed when the first
gradient elution program was applied. The colorants E 128 and
E 142 were co-eluted and, although they were determined in
different wavelengths, a mutual interference appeared. The resolution
of colorants E 122 and E 133 was also unsatisfactory.
However, in this case, only E 133 interfered with the determination
of E 122. These conclusions were also verified from the
low peak purities values of E 128, E 142 and E 122, the high
peak purity value of E 133 and the unsatisfactory Rs values for
these two couples of colorant (0.30 and 0.49, respectively).