01/2008:0825

FENNEL, SWEET
Foeniculi dulcis fructus

DEFINITION
Dry cremocarps and mericarps of Foeniculum vulgare Miller sp. vulgare var. dulce (Miller) Thellung.
Content:
— essential oil: minimum 20 mL/kg (anhydrous drug);
— anethole: minimum 80.0 per cent in the essential oil.

CHARACTERS
Sweet fennel is pale green or pale yellowish-brown.

IDENTIFICATION
A. The fruit of sweet fennel is a cremocarp of almost cylindrical shape with a rounded base and a narrowed summit crowned with a large stylopod. It is generally 3-12 mm long and 3-4 mm wide. The mericarps, usually free, are glabrous. Each bears 5 prominent, slightly carenated ridges. When cut transversely, 4 vittae on the dorsal surface and 2 on the commissural surface may be seen with a lens.

B. Reduce to a powder (355) (2.9.12). The powder is greyish-brown or greyish-yellow. Examine under a microscope using chloral hydrate solution R. The powder shows the following diagnostic characters: yellow fragments of wide secretory canals, often made up of yellowish-brown-walled polygonal secretory cells, frequently associated with a layer of thin-walled transversely elongated cells 2-9 pm wide, having a parquetry arrangement; reticulate parenchyma of the mesocarp; numerous fibre bundles from the ridges, often accompanied by narrow spiral vessels; very numerous endosperm fragments containing aleurone grains and very small calcium oxalate microrosette crystals, as well as some fibre bundles from the carpophore.

C. Thin-layer chromatography (2.2.27).
Test solution. Shake 0.3 g of the freshly powdered drug (1400) (2.9.12) with 5.0 mL of methylene chloride R for 15 min. Filter and carefully evaporate the filtrate to dryness on a water-bath at 60 °C. Dissolve the residue in 0.5 mL of toluene R.
Reference solution. Dissolve 60 μL of anethole R in 5.0 mL of hexane R.
Plate: TLC silica gel GF254 plate R.
Mobile phase: hexane R, toluene R (20:80 V/V).
Application: 10 μL, as bands of 20 mm by 3 mm.
Development: over a path of 10 cm.
Drying: in air.
Detection A: examine in ultraviolet light at 254 nm.
Results A: the chromatograms show in the central part a quenching zone due to anethole.
Detection B: spray with sulfuric acid R and heat at 140 °C for 5 min; examine in daylight.
Results B: the chromatograms show in the central part a violet band due to anethole; the chromatogram obtained with the test solution also shows a reddish-brown zone in the upper third (terpenes).

TESTS

Estragole and fenchone. Gas chromatography (2.2.28): use the normalisation procedure.
Test solution. Dilute the mixture of essential oil and xylene R obtained in the assay of essential oil to 5.0 mL with xylene R, by rinsing the apparatus.
Reference solution. Dissolve 5 mg of estragole R and 5 mg of fenchone R in 0.5 mL of xylene R.
Column:
— size: l = 30-60 m, Ø = 0.3 mm;
— stationary phase: macrogol 20 000 R.
Carrier gas: nitrogen for chromatography R.
Flow rate: 0.40 mL/min.
Split ratio: 1:200.

Detection: flame ionisation.
Injection: 1 μL.
Limits:
— estragole: maximum 10.0 per cent in the essential oil;
— fenchone: maximum 7.5 per cent in the essential oil.

Foreign matter (2.8.2): maximum 1.5 per cent of peduncles and maximum 1.5 per cent of other foreign matter.

Water (2.2.13): maximum 80 mL/kg, determined on 20.0 g of the powdered drug (710) (2.9.12).

Total ash (2.4.16): maximum 10.0 per cent.

ASSAY

Essential oil. Carry out the determination of essential oils in herbal drugs (2.8.12). Use a 500 mL round-bottomed flask and 200 mL of water R as the distillation liquid. Reduce the drug to a coarse powder (1400) (2.9.12) and immediately use 10.0 g for the determination. Introduce 0.50 mL of xylene R into the graduated tube. Distil at a rate of 2-3 mL/min for 2 h.

Anethole. Gas chromatography (2.2.28) as described in the for estragole and fenchone with the following modification.
Reference solution. Dissolve 5 mg of anethole R in 0.5 mL xylene R.

STORAGE
Protected from moisture.