. Quantification of tretinoin and isotretinoin
Stock solutions containing 1 mM of tretinoin or 1 mM
isotretinoin were prepared in acetonitrile and diluted appropriately
to provide standards for quantification. A standard curve
was constructed by injecting samples containing tretinoin or
isotretinoin at concentrations ranging from 0.0002 to 0.5 mM
(0.01 to 25 nmol injected). The peak area was determined and
plotted versus the concentration of tretinoin or isotretinoin. For
the recovery studies, known volumes of tretinoin and isotretinoin
standard solutions were analyzed, and the absolute recovery was
calculated by comparing the peak area obtained from cream or
gel with the peak area of samples derived from the standard
solutions