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          Citrus Hystrix Peel is the dried exocarp and mesocarp of green mature fruit of Citrus hystrix DC.  (C. papeda Miq., C. tuberoides J. W. Benn.) (Family Rutaceae), Herbarium Specimen Number:  DMSC 1459. 

Constituents  Citrus Hystrix Peel contains volatile oil, of which β-pinene, limonene, β-phellandrene, and citronellal are its major components.  It also contains linalool, borneol, camphor, sabinene, germacrene D, aviprin, umbelliferone, β-sitosterol, etc.

Description of the plant  See under Citrus Hystrix Leaf, See also Figs. 1a, 1b.

Description  Odour, characteristic, aromatic; taste, bitter.

     Macroscopical  (Fig. 1)  Citrus Hystrix Peel occurs as strips of dried fruit rind; outer surface dark green to brown, rough with pits of oil glands; inner surface exhibiting whitish spongy part.

     Microscopical  (Figs. 2a, 2b)  Transverse section of the exocarp and mesocarp shows exocarp, a layer of rectangular cells covered by thick cuticle.  Mesocarp, the outer part composed of several layers of thick-walled parenchyma containing chromoplastids; the inner part composed of thick-walled spongy parenchyma; vascular bundles, scattered; vessels, lignified reticulate and spiral.  Prismatic crystals of calcium oxalate and schizolysigenous oil cavities containing oil droplets are also found.
       Citrus Hystrix Peel in powder possesses the diagnostic microscopical characters of the unground drug. 

Additional information Citrus Hystrix Peel in this monograph refers to exocarp with attached unremovable mesocarp.

Packaing and storage Citrus Hystrix Peel shall be kept in well-closed containers, preferably  of metal or glass, protected from light and stored in a cool and dry place.  It should be used within 1 year and air-dried every 2 to 3 months.

Identification

     A. Reflux 1 g of the sample, in powder, with 30 mL of ethanol for 15 minutes, and filter (solution 1).  To 2 mL of solution 1, add a few drops of ammonium molybdate TS:  a bright yellow precipitate is produced.

     B. To 2 mL of solution 1, add a few drops of a freshly prepared 1 per cent w/v solution of iron(III) chloride:  a deep greenish brown colour is produced.

     C. To 2 mL of solution 1, add a few drops of ninhydrin TS and warm on a water-bath for a few minutes:  a reddish purple colour is produced.

     D. Moisten 1 g of the sample, in powder, with 0.5 mL of strong ammonia solution, add 5 mL of chloroform, occasionally shaking for 10 minutes, and filter.  Evaporate the filtrate until dryness and dissolve the residue in 1 mL of ethanol, and add a few drops of modified  Dragendorff TS2:  an orange precipitate is produced.

     E. Extract 1 g of the sample, in powder, with 10 mL of chloroform, shake occasionally for 20 minutes, and filter.  Evaporate 2 mL of the filtrate to dryness, dissolve the residue in 2 mL of acetic anhydride, and add slowly 1 mL of sulfuric acid to make two layers:  a brown colour forms at the zone of contact and the upper layer is green.

    F. Carry out the test as described in the “Thin-Layer Chromatography” (Appendix 3.1), using silica gel GF254 as the coating substance and chloroform as the mobile phase.  Apply to the plate, 5 μL of the test solution prepared by moistening 1 g of the sample, in powder, with 1 mL of strong ammonia solution for a while, extracting with 10 mL of chloroform by occasionally shaking for 15 minutes, filtering, and concentrating the filtrate to 1 mL.  After removal of the plate, allow it to dry in air, and examine under ultraviolet light (254 nm), marking the quenching spots.  Examine the plate under ultraviolet light (366 nm) (Table 1); see also Fig. 3.  Spray the plate with anisaldehyde TS and heat at 105° for 5 minutes.  Several spots of different colours are observed (Table 1); see also Fig. 3. 

           Repeat the same procedure on other two plates but use a mixture of 20 volumes of chloroform and 1 volume of methanol as the mobile phase and allow the solvent front to ascend 12 cm above the line of application.  After removal of the plates, allow them to dry in air, and spray one plate with modified Dragendorff TS2:  two orange spots are observed.  Spray another plate with iodoplatinate TS:  one dark blue spot and one brown spot are observed (Table 1); see also Fig. 4.

Table 1 hR_f Values of Components in Chloroform Extract of the Peels of Citrus hystrix DC

a.      Mobile phase: chloroform

b.       Mobile phase: 20 volumes of chloroform and 1 volume of methanol

Water  Not more than 12.0 per cent v/w (Azeotropic Distillation Method, Appendix 4.12).

Foreign matter  Not more than 2.0 per cent w/w (Appendix 7.2).

Acid-insoluble ash  Not more than 1.0 per cent w/w (Appendix 7.6). 

Total ash  Not more than 9.0 per cent w/w (Appendix 7.7).

Ethanol-soluble extractive  Not less than 11.0 per cent w/w (Appendix 7.12).

Water-soluble extractive  Not less than 23.0 per cent w/w (Appendix 7.12).

Chloroform-soluble extractive  Not less than 8.0 per cent w/w (Appendix 7.12H).

Volatile oil  Not less than 2.0 per cent v/w (Appendix 7.3H).  Use 25 g, in coarse powder, freshly prepared and accurately weighed.  Use 250 mL of water as the distillation liquid and  a 500-mL round-bottomed flask.  Distil at a rate of 2 to 3 mL per minute for 5 hours.  Use 2.0 ml of xylene in the graduated tube.