C₂₆H₂₉NO,C₆H₈O₇

Relative molecular mass. 563.6

Chemical name. (Z)-2-[p-(1,2-Diphenyl-1-butenyl)phenoxy]-N,N-dimethylethylamine citrate (1:1); (Z)-2-[4-(1,2-diphenyl-1-butenyl)phenoxy]-N,N-dimethylethanamine 2-hydroxy-1,2,3-propanetricarboxylate (1:1); CAS Reg. No. 54965-24-1.

Description. A white or almost white, crystalline powder.

Solubility. Slightly soluble in water and acetone R; soluble in methanol R.

Category. Antiestrogen.

Storage. Tamoxifen citrate should be kept in a well-closed container, protected from light.

Requirements

Tamoxifen citrate contains not less than 99.0% and not more than the equivalent of 101.0% of C₂₆H₂₉NO,C₆H₈O₇, calculated with reference to the dried substance.

Identity tests

• Either tests A and D or tests B, C, and D may be applied.

A. Carry out the examination as described under 1.7 Spectrophotometry in the infrared region. The infrared absorption spectrum is concordant with the spectrum obtained from tamoxifen citrate RS or with the reference spectrum of tamoxifen citrate.

B. Carry out the test as described under 1.14.1 Thin-layer chromatography, using silica gel R4 as the coating substance and a mixture of 9 volumes of toluene R and 1 volume of triethylamine R as the mobile phase. Apply separately to the plate 5 μl of each of two solutions in methanol R containing (A) 10 mg of Tamoxifen citrate per ml and (B) 10 mg of tamoxifen citrate RS per ml. After removing the plate from the chromatographic chamber, allow it to dry in air, and examine the chromatogram in ultraviolet light (254 nm).

The principal spot obtained with solution A corresponds in position, appearance, and intensity with that obtained with solution B

C. To 10 mg add 4 ml of pyridine R and 2 ml of acetic anhydride R, and shake; a yellow colour is immediately produced. Heat on a water-bath for 2 minutes; a light pink to red colour is produced.

D. Melting temperature, about 142 °C with decomposition.

Heavy metals. Use 1.0 g for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 3; determine the heavy metals content according to Method A; not more than 10 μg/g.

Sulfated ash. Not more than 2.0 mg/g.

Loss on drying. Dry to constant mass at 105 °C; it loses not more than 5.0 mg/g.

E -isomer and related substances. Carry out the test as described under 1.14.4 High-performance liquid chromatography, using a stainless steel column (20cm × 5mm) packed with particles of silica gel, the surface of which has been modified with chemically bonded octadecylsilyl groups (5μm). As the mobile phase, use a mixture of 400 volumes of acetonitrile R and 600 volumes of water containing 0.9g/l of sodium dihydrogen phosphate R and 4.8g/l of N,N-dimethyloctylamine R adjusted to pH 3.0 with phosphoric acid (~105 g/l) TS.

Prepare the following solutions in the mobile phase: for solution (A) use 1.0mg of Tamoxifen citrate per ml; for solution (B) use 1.0 mg of tamoxifen citrate E-isomer RS per ml; for solution (C) dilute 1 volume of solution A to 100 volumes with the mobile phase; and for solution (D) dilute 1 volume of solution B to 100 volumes with the mobile phase.

Operate with a flow rate of 1.0 ml per minute. As a detector use an ultraviolet spectrophotometer set at a wavelength of about 240 nm, the instrument being fitted with a low volume flow cell (10μl).

Equilibrate the column with the mobile phase at a flow rate of 1.0 ml per minute for about 30 minutes.

Make three replicate injections of 10μl each of solution D, adjusting the sensitivity of the system so that the height of the peak is not less than 40% of the full scale of the recorder.

Inject alternately 10μl each of solutions A, C, and D. The test is not valid unless the peak obtained with solution D elutes prior to that for solution C, and with solution A there is baseline separation between all the peaks.

Measure the areas of the peak responses obtained in the chromatograms from solutions A, C, and D, and calculate the content of the related substances as a percentage. Calculate the content of E-isomer comparing the peaks obtained with solutions A and D; not more than 10 mg/g. In the chromatogram obtained with solution A, the area of any peak, other than the peak due to the E-isomer obtained with solution D, is not greater than half that of the peak obtained with solution C (0.5%). Furthermore, the sum of the areas is not greater than the peak obtained with solution C (1%).

Assay. Dissolve about 1 g, accurately weighed, in 150 ml of glacial acetic acid R1, add 0.25 ml of 1-naphtholbenzein/acetic acid TS, and titrate with perchloric acid (0.1 mol/l) VS as described under 2.6 Non-aqueous titration, Method A.

Each ml of perchloric acid (0.1 mol/l) VS is equivalent to 56.36 mg of C₂₆H₂₉NO,C₆H₈O₇.