Question

Residue on ignition & LoD- if any- of paracetamol ?

Answer 1

The Residue on Ignition is defined as the procedure to measure the amount of residual substance that are not volatilized from a sample when the sample is ignited.

If the sample is ignited in the presence of sulphuric acid then it is known as sulphated ash.The residue left over contain any counter parts of sulphate .

Procedure—

1) Ignite a suitable crucibl either silica or quartz at 600 ± 50 degree for 30 minutes.

2) Allow to cool the crucible in a desiccator and weigh it.

3)Weigh accurately 1 to 2 g of th substance,

or as specified in monograph, in the crucible.

4)Moisten the sample with a small amount (usually 1 mL) of sulfuric acid, then heat gently at a temperature as low as practicable till the sample becomes thoroughlycharred. ,

5)Cool the residue completly and then weigh it.

6) Repeat the process of ignition for 30­minute until two consecutive weighings of the residue do not differ by more than 0.5 mg or until the percentage of residue matches with the limit in the individual monograph.

loss of weight of a substance expressed as percentage w/w resulting from water and volatile matter of any kind that can be driven off under specified conditions.

Loss on drying of paracetamol
1)Drying in oven
1.weigh the sample in room temperature and place it in an oven, the sample is weighed repeatedly following a preset schedule, and the weight loss is recorded.
2.When the weight become constant ,the difference between the initial weight and the final weight is calculated, which is equivalent to the moisture vaporized. This method is used to calculate the percentage of moisture.

The advantages of the drying oven technique include its high reproducibility in results and reliable results. It has the serious disadvantage as it takes a long time for completion.

In paracetamol tablets optimum loos on drying is 2.5-3.5%.