monograph of cetrimide

(Ph Eur monograph 0378)




8044-71-1
Action and use
Antiseptic detergent.
Preparations
Cetrimide Cream
Cetrimide Emulsifying Ointment
Ph Eur
DEFINITION
Cetrimide consists of trimethyltetradecylammonium bromide and may contain smaller amounts of dodecyl- and hexadecyl-trimethylammonium bromides.
Content
96.0 per cent to 101.0 per cent of alkyltrimethylammonium bromides, calculated as C17H38BrN (M r 336.4) (dried substance).
CHARACTERS
Appearance
White or almost white, voluminous, free-flowing powder.
Solubility
Freely soluble in water and in alcohol.
IDENTIFICATION
A. Dissolve 0.25 g in alcohol R and dilute to 25.0 ml with the same solvent. At wavelengths from 260 nm to 280 nm, the absorbance ( 2.2.25 ) of the solution has a maximum of 0.05.
B. Dissolve about 5 mg in 5 ml of buffer solution pH 8.0 R. Add about 10 mg of potassium ferricyanide R. A yellow precipitate is formed. Prepare a blank in the same manner but omitting the substance to be examined: a yellow solution is observed but no precipitate is formed.
C. Solution S (see Tests) froths copiously when shaken.
D. Thin-layer chromatography ( 2.2.27 ).
Test solution. Dissolve 0.10 g of the substance to be examined in water R and dilute to 5 ml with the same solvent.
Reference solution. Dissolve 0.10 g of trimethyltetradecylammonium bromide CRS in water R and dilute to 5 ml with the same solvent.
Plate. TLC silica gel F254 silanised plate R.
Mobile phase. Acetone R, 270 g/l solution of sodium acetate R, methanol R (20:35:45 V/V/V).
Application. 1 ml.
Development. Over a path of 12 cm.
Drying. In a current of hot air.
Detection. Allow to cool; expose the plate to iodine vapour and examine in daylight.
Result. The principal spot in the chromatogram obtained with the test solution is similar in position, colour and size to the principal spot in the chromatogram obtained with the reference solution.
E. It gives reaction (a) of bromides ( 2.3.1 ).
TESTS
Solution S
Dissolve 2.0 g in carbon dioxide-free water R and dilute to 100 ml with the same solvent.
Appearance of solution
Solution S is clear ( 2.2.1 ) and colourless ( 2.2.2 , Method II).
Acidity or alkalinity
To 50 ml of solution S add 0.1 ml of bromocresol purple solution R. Not more than 0.1 ml of 0.1 M hydrochloric acid or 0.1 M sodium hydroxide is required to change the colour of the indicator.
Amines and amine salts.
Dissolve 5.0 g in 30 ml of a mixture of 1 volume of 1 M hydrochloric acid and 99 volumes of methanol R and add 100 ml of 2-propanol R. Pass a stream of nitrogen R slowly through the solution. Gradually add 15.0 ml of 0.1 M tetrabutylammonium hydroxide and record the potentiometric titration curve ( 2.2.20 ). If the curve shows 2 points of inflexion, the volume of titrant added between the 2 points is not greater than 2.0 ml.
Loss on drying ( 2.2.32 )
Maximum 2.0 per cent, determined on 1.000 g by drying in an oven at 100-105 °C for 2 h.
Sulphated ash ( 2.4.14 )
Maximum 0.5 per cent, determined on 1.0 g.
ASSAY
Dissolve 2.000 g in water R and dilute to 100.0 ml with the same solvent. Transfer 25.0 ml of the solution to a separating funnel, add 25 ml of chloroform R, 10 ml of 0.1 M sodium hydroxide and 10.0 ml of a freshly prepared 50 g/l solution of potassium iodide R. Shake, allow to separate and discard the chloroform layer. Shake the aqueous layer with 3 quantities, each of 10 ml, of chloroform R and discard the chloroform layers. Add 40 ml of hydrochloric acid R, allow to cool and titrate with 0.05 M potassium iodate until the deep brown colour is almost discharged. Add 2 ml of chloroform R and continue the titration, shaking vigorously, until the colour of the chloroform layer no longer changes. Carry out a blank titration on a mixture of 10.0 ml of the freshly prepared 50 g/l solution of potassium iodide R, 20 ml of water R and 40 ml of hydrochloric acid R.
1 ml of 0.05 M potassium iodate is equivalent to 33.64 mg of C17H38BrN.
Ph Eur