Abstract:
The effects of sample solvent composition and the
injection volume, on the chromatographic peak profiles of two
carbamate derivatives, methyl 2-benzimidazolecarbamate (MBC)
and 3-butyl-2,4-dioxo[1,2-a]-s-triazinobenzimidazole (STB),
were studied using reverse phase high performance liquid
chromatograph. The study examined the effects of acetonitrile
percentage in the sample solvent from 5 to 50%, effects of
methanol percentage from 5 to 50%, effects of pH increase from
4.42 to 9.10, and effect of increasing buffer concentration
from ° to 0.12M. The effects were studied at constant and
increasing injection mass and at four injection volumes of
10, 50, 100 and 200 uL. The study demonstrated that the
amount and the type of the organic solvents, the pH, and the
buffer strength of the sample solution can have a pronounced
effect on the peak heights, peak widths, and retention times
of compounds analysed. MBC, which is capable of intramolecular
hydrogen bonding and has no tendency to ionize, showed a
predictable increase .in band broadening and a decrease in
retention times at higher eluting strengths of the sample
solvent. STB, which has a tendency to ionize or to strongly
interact with the sample solvent, was influenced in various
ways by the changes in ths sample solvent composition.
The sample solvent effects became more pronounced as the injection volume increased and as the percentage of organic
solvent in the sample solution became greater. The peak height
increases for STB at increasing buffer concentrations
became much more pronounced at higher analyte concentrations.
It was shown that the widely accepted procedure of
dissolving samples in the mobile phase does not yield the most
efficient chromatograms. For that reason samples should be
dissolved in the solutions with higher aqueous content than
that of the mobile phase whenever possible. The results
strongly recommend that all the samples and standards,
regardless whether the standards are external or internal,
be analysed at a constant sample composition and a constant
injection volume.
