Macroscopic— Turmeric occurs as ovate, oblong, or pear-shaped primary rhizomes, also known as bulb or round turmeric, about 3 cm in diameter and 4 to 5 cm long, and showing transverse annular leaf scars, and as cylindrical, sometimes short-branched secondary rhizomes, also known as finger or long turmeric, about 1 cm in diameter and 2 to 7 cm long, and showing scars of lateral branches. The cured and dried turmeric of commerce is bright yellow to dull yellow in appearance, with a rough or polished surface, and a characteristic aromatic odor. The texture is hard and uneasily broken, and the fracture is smooth and finely granular. Internally it is orange-yellow to orange, showing a cortex separated from a central cylinder by a distinct endodermis.

histology—

Transverse section of rhizome— It shows a row of thin-walled, flattened epidermal cells; a few layers of thin-walled, brick-shaped parenchyma cells of the cork; a broad cortex consisting of multiple layers of thin-walled parenchyma cells showing scattered vascular bundles; a thin layer of oblong cells of the endodermis; pericycle consisting of 1 to 2 rows of parenchyma cells; and a pith consisting of parenchyma cells showing scattered vascular bundles, most of them forming discontinuous rings near the endodermis and fewer inward. The vascular bundles are of the collateral type; the vessels have mainly spiral thickening, and a few have reticulate and annular thickening. Scattered throughout the parenchyma of the pith and cortex are oleoresin cells containing oil and scattered particles of an orange-yellow pigment, and prisms of calcium oxalate, which are usually obscured due to the bright yellow color of the pigment content. The parenchyma cells are full of starch granules, 15 to 30 mm in size, and flat or disc shaped. Bast fibers are absent.

A: Thin-Layer Chromatographic Identification Test 201—

B: The retention times of the peaks for curcumin, desmethoxycurcumin, and bisdesmethoxycurcumin in the chromatogram of the Test solution correspond to those in the chromatogram of the Standard solution for the appropriate USP Reference Standard, as obtained in the test for Content of curcuminoids.

Mobile phase— Prepare a filtered and degassed mixture of citric acid in water (1 g in 1000 mL) and tetrahydrofuran (6:4). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution 1— Accurately weigh about 20 mg of USP Curcuminoids RS into a 50-mL volumetric flask, add about 30 mL of Mobile phase, and sonicate to dissolve. Dilute with Mobile phase to volume, and mix. Transfer 5 mL of this mixture to a 50-mL volumetric flask, dilute with Mobile phase to volume, mix, and before injection pass through a filter having a 0.45-µm porosity.

note—Curcumin, desmethoxycurcumin, and bisdesmethoxycurcumin Standards can also be prepared as one Standard solution containing the final concentration specified below for each.

Standard solution 2— Dissolve, using sonication, an accurately weighed quantity of USP Curcumin RS in Mobile phase to obtain a solution having a known concentration of about 40 µg per mL. Before injection, pass through a filter having a 0.45-µm porosity.

Standard solution 3— Dissolve, using sonication, an accurately weighed quantity of USP Desmethoxycurcumin RS in Mobile phase to obtain a solution having a known concentration of about 10 µg per mL. Before injection, pass through a filter having a 0.45-µm porosity.

Standard solution 4— Dissolve, using sonication, an accurately weighed quantity of USP Bisdesmethoxycurcumin RS in Mobile phase to obtain a solution having a known concentration of about 2 µg per mL. Before injection, pass through a filter having a 0.45-µm porosity.

Test solution— Pulverize about 5.0 g of Turmeric. Transfer about 0.5 g of the pulverized sample to a 50-mL volumetric flask, add about 30 mL of acetone, and sonicate for 30 minutes. Dilute with acetone to volume, mix, and centrifuge. Transfer 5 mL of the supernatant to a 50-mL volumetric flask, dilute with Mobile phase to volume, mix, and before injection pass through a filter having a 0.45-µm porosity.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 420-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L1. The flow rate is about 1.0 mL per minute. Chromatograph Standard solution 1, and record the peak responses as directed for Procedure: the chromatogram of Standard solution 1 is similar to the Reference Chromatogram provided with USP Curcuminoids RS; the relative retention times are about 1.0 for curcumin, 1.2 for desmethoxycurcumin, and 1.4 for bisdesmethoxycurcumin; the resolution, R, between the curcumin peak and the desmethoxycurcumin peak and between the desmethoxycurcumin peak and the bisdesmethoxycurcumin peak is not less than 2.0; the tailing factor for the curcumin peak, the desmethoxycurcumin peak, and the bisdesmethoxycurcumin peak is not more than 1.5; and the relative standard deviation for replicate injections of the desmethoxycurcumin peak is not more than 2.0%.

Procedure— Inject equal volumes (about 20 µL) of Standard solution 1, Standard solution 2, Standard solution 3, Standard solution 4, and the Test solution into the chromatograph, allow to elute for not less than three times the retention time of curcumin, and proceed as directed for Chromatographic system. Record the chromatograms, and measure all of the peak responses due to curcumin, desmethoxycurcumin, and bisdesmethoxycurcumin. Separately calculate the percentages of curcumin, desmethoxycurcumin, and bisdesmethoxycurcumin in the portion of Turmeric taken by the formula: in which C is the concentration, in mg per mL, of USP Curcumin RS, USP Desmethoxycurcumin RS, or USP Bisdesmethoxycurcumin RS in the corresponding Standard solution; W is the weight, in mg, of Turmeric taken to prepare the Test solution; rU is the peak response of the relevant analyte in the Test solution; and rS is the peak response of the relevant analyte in the corresponding Standard solution. Add the percentages due to curcumin, desmethoxycurcumin, and bisdesmethoxycurcumin: not less than 3% is found.USP32