A: Thin-Layer Chromatographic Identification Test 201—

B: The retention times of the peaks for silydianin, silychristin, silybin A, silybin B, isosilybin A, and isosilybin B in the chromatogram of the Test solution correspond to those in the chromatogram of Milk thistle standard solution, as obtained in the test for Content of silymarin.

pH 7.5 Phosphate buffer— Dissolve 27.6 g of monobasic sodium phosphate and 6.08 g of sodium hydroxide in water, and dilute with water to 4000 mL.

Medium: pH 7.5 Phosphate buffer containing 2% lauryl sulfate; 900 mL.

Apparatus 2: 100 rpm.

Time: 45 minutes.

Tolerances— Not less than 75% of the labeled amount of silymarin as silybin (C25H22O10) is dissolved in 45 minutes.

Solution A, Solution B, Mobile phase, Silybin standard solutions, and Chromatographic system— Proceed as directed in the test for Content of silymarin under Milk Thistle.

Milk thistle standard solution— Dissolve an accurately weighed quantity of USP Powdered Milk Thistle Extract RS in methanol, sonicate for 20 minutes, and dilute with methanol to obtain a solution having a known concentration of about 0.7 mg of extract per mL.

Test solution— Weigh and finely powder the contents of not fewer than 20 Capsules. Transfer an accurately weighed amount of the powder, equivalent to about 100 mg of silymarin, to a 100-mL volumetric flask, add 90 mL of methanol, and sonicate for 20 minutes with occasional shaking. Cool to 20, and dilute with methanol to volume. Filter through a membrane having a 0.45-µm or finer porosity.

Procedure— Proceed as directed in the test for Content of silymarin under Milk Thistle, except to separately calculate the amount, in mg, of each relevant component of silymarin as silybin (C25H22O10) in the portion of Capsules taken by the formula: in which the term, C, is as defined therein. Calculate the content of silymarin, in mg, in the portion of Capsules taken by adding the individual amounts.