and precise for tetracycline hydrochloride and 4-epianhydrotetracycline
hydrochloride in the drug substance and oral suspension
monographs. Here, we extend the method validation
to the tetracycline hydrochloride capsule USP monograph.
According to USP, system suitability testing is an integral
part of analytical methods to evaluate chromatographic parameters
of the system.1 Thus, replicate injections of the system suitability
solution and resolution solution were made throughout
the validation process. A system suitability chromatogram performed
prior to method validation measurements is shown in
Fig. 1. The resolution between epitetracycline hydrochloride
and tetracycline hydrochloride was always greater than 7 in
all system suitability chromatograms, and that between tetracycline
hydrochloride and 4-epianhydrotetracycline was greater
than 29. The resolution between 4-epianhydrotetracycline and
anhydrotetracycline was greater than 11. The resolution was
calculated according to the USP guidelines.1 Tailing for the four
peaks was between 0.9 and 1.2 and the precision for the tetracycline
hydrochloride and 4-epianhydrotetracycline hydrochloride
peaks for five replicate injections was less than 0.5% and
2%, respectively. The retention times were 3.4, 3.9, 6.1 and
7.1 for epitetracycline hydrochloride, tetracycline hydrochloride,
4-epianhydrotetracycline and anhydrotetracycline, respectively.
The results indicate that the system suitability
requirements are passed and, consequently, further chromatographic
parameters can be examined.