An internal standard for 11-deoxycortisol, also known as cortodoxone. An immediate precursor to cortisol,11-deoxycortisol is measured in whole blood by LC-MS/MS for newborn screening of congenital adrenal hyperplasia (CAH) and in serum or plasma by LC-MS/MS for determination of several diseases including Cushing’s syndrome, pituitary tumor, and Addison’s disease.