# Preparation and standardization of 0.004 M Benzethonium Chloride BP Volumetric Solution

## 1.  PREPARATION:

Dissolve 1.792 g of Benzethonium chloride previously dried to constant weight at 100° to 105°, in sufficient water to produce 1000 ml.

## 2. STANDARDISATION:

Calculate the Molarity of the solution from the content of C27H42ClNO2 in the dried Benzethonium chloride in the following manner:

Dissolve 0.35 g of the dried Benzethonium chloride in 30 ml of anhydrous Acetic acid, add 6 ml of Mercury (II) acetate solution. Carry out non-aqueous titration against 0.1 M Perchloric acid using 0.05 ml of Crystal violet solution as an indicator (T.R.). Perform a blank determination (B.R.) in the same way excluding sample and make any necessary correction.

When the temperature (t2) of the titrant at the time of the assay differs from the temperature (t1) of the titrant when it was standardized, multiply the volume of the titrant required by [1+0.0011(t1 – t2)] and calculate the result of the assay from the corrected volume.

1 ml of 0.1 M Perchloric acid is equivalent to 44.81 mg of C27H42ClNO2.

Calculation:

Purity of C27H42ClNO= [(T.R. – B.R.) x Molarity of 0.1 M HClO4 x 0.04481 x 100]/[ 0.1 x Weight of Benzethonium chloride (in g) ]

Molarity (M) = [0.004 x Purity of Benzethonium chloride]/ 100

Limit: 0.004 M ± 5 % (0.0038 M – 0.0042 M)

## 3. PREPARATION OF INDICATORS / REAGENTS:

a. Mercury (II) acetate solution:

A 3.19 % w/v solution of Mercury (II) acetate in anhydrous acetic acid. Neutralize, if necessary, with 0.1 M Perchloric acid VS using 0.05 ml of Crystal violet solution as indicator.

b. 0.1 M Perchloric acid:

Preparation and standardization as per Doc. Ref. No. D/VS/BP/001.

c. Crystal violet solution:

A 0.05 % w/v solution of Crystal violet in anhydrous Acetic acid.

It should comply with the following test:

Sensitivity: A mixture of 0.1 ml of the solution and 50 ml of anhydrous Acetic acid is bluish purple. Add 0.1 ml of 0.1 M Perchloric acid; the colour of the solution changes to bluish green.

## 4. STORAGE CONDITION:

Store in glass -stoppered bottles.

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