EXPERIMENT # ___01___


OBJECT:  Preparation of stock solution and serial dilutions of cetrimide (molecular formula: 365.5)



Cetrimide, Weighing balance, water bath, Warm water, pipettes, beaker, stirrer, volumetric flask (100ml, 50ml, 25ml)



These solutions are frequently prepared or purchased by the pharmacists to facilitate dispensing of pharmaceutical preparations. Stock solutions are of higher concentrations which are used to prepare solutions of lower concentration (dilution).


These are solutions of lower concentration which are prepared in series from the stock solution.


Serial dilutions of antibiotics are prepared and their antibacterial activity is observed and MIC (minimum inhibitory concentration) is also determined. During preclinical testing of new investigational drugs, serial dilutions of drugs are prepared and then tested on animals to assess toxicity.

Quaternary ammonium compounds are any of a group of ammonium salts in which organic radicals have been substituted for all four hydrogen’s of the original ammonium cation. They has a central nitrogen atom which is is joined to four organic radicals and one acid radical. They show a variety of physical, chemical, and biological properties and most compounds are soluble in water and strong electrolytes. Such compounds include cetrimide. They have properties of disrupting micro-organisms cell processes and surfactants. These compounds are used as:

·         Active ingredient for conditioners.

·         Antistatic agent.

·         Detergent sanitizers.

·         Softener for textiles and paper products.

·         Antimicrobials.

·         Disinfection agents and sanitizers.

·          Algaecide.

·         Emulsifying agents.

·         Pigment dispersants.

Cetrimide (C19 H42 N+) is an antiseptic agent with detergent properties. It has the wide spectrum of anti-infective agent against bacteria and fungi. It is used as an ingredient of shampoos for treating seborrhea and psoriasis. A very dilute solution can be applied topically for the relief of sore gums. It is a quaternary ammonium compound used as a detergent and, having powerful antiseptic properties, for sterilizing surgical instruments, cleaning wounds a cationic detergent that is a powerful disinfectant.


·         Calculate the amount of cetrimide from the given formula for preparation of normal stock solution in 100ml volumetric flask.

                        Amount = conc.  x  molecular weight   x 100


·         Rinse all glassware with water.

·         Weigh cetrimide and slowly dissolve it in water in a beaker on water bath

·         Transfer the solution in 100ml volumetric flask and make up the volume with warm water up to the mark. Stock solution is prepared.

·         Now for preparing dilutions of different concentrations from the stock, calculate the volume required to make further dilutions from the given formula.


·         Pour the required amounts in the flasks and make up the volumes with warm water.


After producing the stock solution of 100ml in warm water having 0.1 molarity we produces two serial dilutions, one having 0.01 molarity in 50ml warm water and other having 0.001 molarity in 25ml warm water.                                                                                                                                                                                                            











·         To prepare the stock solution we uses this formula

     Amount = conc.  x  molecular weight   x 100


Amount =  0.1  x  336.4  x  100


Amount =  3.364

·         To prepare dilution having normality of 0.01 we use the formula.  

                 n1v2 = n2v2 

                 0.1 v2 = 0.01 x 50

                 v2 = 0.01 x 50


                 v2 = 5ml

·         To prepare dilution having normality of 0.001 we use the formula.

n1v1 = n2v2

0.01 v2 = 0.001 x 25

v2 = 0.001 x 25


v2 = 2.5ml


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