Goldbeater’s skin test: Goldbeater’s skin is a membrane produced from the intestine of Ox. It behaves just like untanned animal hide.
CHEMICAL TESTS
1. Goldbeater’s
skin test:
Goldbeater’s skin is a membrane produced
from the intestine of Ox. It behaves just like untanned animal hide. A piece of
goldbeaters skin previously soaked in 2% hydrochloric acid and washed with
distilled water is placed in a solution of tannin for 5 minutes. It is then
washed with distilled water and transferred to 1% ferrous sulphate solution. A
change of the colour of the goldbeater’s skin to brown or black indicates the
presence of tannin.
2. Hydrolysable and condensed tannins
both give the positive goldbeater’s test, whereas pseudotannins show very
little colour or negative test.
3. Phenazone
Test: To 5 ml of
aqueous solution of tannin containing
drug, add 0.5 g of sodium acid phosphate. Warm the solution, cool, and filter.
Add 2% phenazone solution to the filtrate. All tannins are precipitated as
bulky, coloured precipitate.
4. Gelatin
Test: To a 1%
gelatine solution, add little 10% sodium
chloride. If a 1% solution of tannin is added to the gelatine solution, tannins
cause precipitation of gelatine from solution.
5. Test
for Catechin (Matchstick Test): Catechin test is the modification of the well-known
phloroglucinol test for lignin. Matchstick contains lignin. Dip a matchstick in
the dilute extract of the drug, dry, moisten it with concentrated hydrochloric
acid, and warm it near a flame. Catechin in the presence of acid produces
phloroglucinol which stains the lignified wood pink or red.
6. Test
for chlorogenic acid:
A dilute solution of chlorogenic acid containing extract, if treated with
aqueous ammonia and exposed to air, slowly turns green indicating the presence
of chlorogenic acid.
7. Vanillin-hydrochloric
acid test: Drug
shows pink or red colour with a mixture of vanillin: alcohol : dilute HCl in
the ratio 1:10:10. The reaction produces phloroglucinol which along with
vanillin gives pink or red colour.
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