2.5. Standard solutions
A standard solution of tetracycline hydrochloride (0.1 mg/mL)
was prepared in a 100 mL measuring flask by dissolving an
accurately weighed 10 mg of USP tetracycline hydrochloride
RS in 50 mL diluent and completing the flask to mark with
the diluent. The standard solution for the limit procedure
had a concentration corresponding to that for the limit procedure
stated in the USP-relevant monograph. The limit for tetracycline
hydrochloride capsule monograph is 3.0%, so the
standard solution concentration was 3.0 lg/mL of 4-epianhydrotetracycline
hydrochloride.