Temperaturewas varied between 15 and 25 C (data not shown).
When temperature was decreased up to 20 C, B1 peak comigrated
with vitamin C peak, while at 15 C both vitamins comigrated with
B5 vitamin; moreover, analysis time increased while peak efficiency
decreased; thus, a temperature of 25 C was selected for
further studies.
Next, voltage was varied between 20 and 10 kV. When the
voltage was reduced up to 15 kV (data not shown), resolution of
some peak pairs (caffeine-B12 and B2-B6) increased, while other
peak pairs (C-B5 and IS-sorbic acid) comigrated. Moreover, analysis
time increased and peak efficiency largely decreased. The same
tendency, although more pronounced, was observed at 10 kV. Thus,
a voltage of 25 kV was selected for further studies.
On the other hand, injection time was next varied between 2
and 10 s. Sensitivity increased when injection time was increased.
However, more than 8 s resulted in no separation of C and B5 peaks.
Consequently, an injection time of 8 s was selected as the optimum
value.