Macroscopic— The terrestrial stem is nearly cylindrical,0.5to 3.0cm in diameter,and over 1m in length;it is externally dark brown to red-brown and longitudinally wrinkled.It often has lenticels,small buds,and scaly leaves.The transverse section reveals a rather clear border between the phloem and the xylem,and a radial structure that often has radiating splits.

Microscopic— The transverse section reveals several yellow-brown cork layers,and a layer of phelloderm that is 1to 3cells thick.The cortex exhibits medullary rays,and obliterated sieve portions radiate alternately.The phloem exhibits groups of phloem fibers,which are surrounded by crystal cells,with thick but incompletely lignified walls.The vessels are accompanied by xylem fibers,which are surrounded by crystal cells,and by xylem parenchyma cells.The parenchyma cells contain starch grains and often contain single crystals of calcium oxalate.

Test solution— Add 10mLof a mixture of alcohol and water (7:3)to 2.0g of pulverized Licorice,heat by shaking on a water bath for 5minutes,cool,and filter.

Standard solution— Dissolve 5mg of USP Glycyrrhizic Acid RSin 1mLof a mixture of alcohol and water (7:3).

Application volume: 2µL.

Developing solvent system: a mixture of butyl alcohol,water,and glacial acetic acid (7:2:1).

Procedure— Proceed as directed in the chapter,except to develop the chromatogram in an unsaturated chamber to a length of about 10cm.Examine the plate under UVlight at a wavelength of 254nm.The chromatograms show a dark purple zone,among other spots,due to glycyrrhizic acid at an RFvalue of about 0.4.

Solvent: a mixture of alcohol and water (1:1).

Mobile phase: a filtered and degassed mixture of diluted acetic acid (1in 15)and acetonitrile (3:2).

Standard solution— Dissolve an accurately weighed quantity of USP Glycyrrhizic Acid RSin Solventto obtain a solution having a known concentration of about 0.25mg per mL.

Test solution— Transfer about 500mg of Licorice,reduced to a powder and accurately weighed,to a suitable flask,add 70mLof Solvent,shake for 15minutes,centrifuge,and decant the supernatant into a 100-mLvolumetric flask.Mix the residue with 25mLof Solvent,shake for 15minutes,centrifuge,and add the supernatant to the volumetric flask.Dilute with Solventto volume,mix,and pass through a membrane filter having a 0.45-µm porosity.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains packing L1.The flow rate is about 0.6mLper minute.Chromatograph the Standard solution,and record the peak areas as directed for Procedure:the column efficiency determined from glycyrrhizic acid is not less than 5000theoretical plates;the tailing factor for the glycyrrhizic acid peak is not more than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak areas.Calculate the percentage of glycyrrhizic acid (C42H62O16)in the portion of Licorice taken by the formula: in which Cis the concentration,in mg per mL,of USP Glycyrrhizic Acid RSin the Standard solution;Wis the weight,in mg,of Licorice taken to prepare the Test solution;and rUand rSare the peak areas for glycyrrhizic acid obtained from the Test solutionand the Standard solution,respectively.