Assay Method for Paracetamol and Diphenhydramine HCl Tablets

 Tablets contains following Active Ingredients:

Paracetamol 500mg
Diphenhydramine HCl 25mg

Chromatographic Conditions: 
Column : 150 × 4.6 mm, 5µm C18 
Detector : 220 nm 
Injection volume : 10µl 
Flow rate : 1 ml/ minute 
Column temperature : 30ºC 
Mobile phase : Buffer : Acetonitrile (50 : 50, v/v) 

Buffer Preparation: 
Mix 260 mg of sodium Hexane Sulfonate in 500 ml water, and adjust pH 2.0 with Orthophosphoric acid.

Standard Preparation I:

Transfer 250 mg Paracetamol SRS in to 50 ml volumetric flask, add 35 ml water, sonicate 20 minutes and make up to volume with same.

Standard Preparation II:

Transfer 25 mg Diphenhydramine HCl SRS in to 100 ml volumetric flask, add 70 ml water, sonicate 20 minutes and make up to volume with same.

Standard Preparation III:

Transfer 1 ml of Standard – I and Standard – II in to 10 ml volumetric flask, and dilute with water.

Sample Preparation:

Weigh and powder 20 tablets. Weigh accurately about 327 mg of powder tablets for coated tablet and 322 mg tablet powder for core in to a 50 ml volumetric flask and add 35 ml water, sonicate for 30minutes, dilute up to the mark with same. Dilute 1 ml of resulting solution to 10 ml with water.

System suitability

The % RSD for 5 replicate injection of standard preparation should NMT 2.0 %


Inject standard preparation in five replicate and record the chromatogram. It should comply with the system suitability criteria as mention above. Inject sample preparation in duplicate, record the chromatogram and calculate the percent of assay by using the following formula:


                          At = Average area of Sample solution 
                          As = Average area of Standard solution 
                          Ws = Weight of Standard 
                          Wt = Weight of Sample 
                          ATW = Average Tablet Weight 
                          L = Label Claim 
                          P = Potency of Standard

NOTE: Analysts have to perform Method Validation as per Regulatory Guidelines.

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