Thus, vitamins B2, B3 (nicotinic acid), B5, B6 and C were all
were negatively charged at pH 8.5, and their migration velocity
depended on their degree of ionization and molecular size. On the
other hand, vitamins B3 (nicotinamide) and B12 were non-charged
analytes at this pH, and a comigration with EOF peak was evidenced.
It should be noted that thiamine (B1) was the only vitamin
that has a positive charge at this pH, and therefore migrated faster
than EOF peak. As shown in Fig. 2, the resolution between C and B5
vitamin peaks increased when increasing borate content. Thus, as a
compromise between resolution and analysis time, a 40mMborate
buffer was chosen for the next studies.
Next, the effect of pH in the BGE was investigated. The pH values
were varied between 8.0 and 9.5. However, no significant differences
were observed when pH was changed within this range (data
not shown). Thus, a pH of 8.5 was selected for the following
experiments.