A limit test is an analytical method used to determine whether the concentration of a specific impurity or substance in a pharmaceutical product is below a predefined acceptable limit.
It ensures the quality, safety, and efficacy of the drug by controlling potentially harmful impurities.
Types of Limit Tests:
1) Qualitative limit tests:
Provide a pass/fail result, indicating whether the impurity or substance is below or above the specified limit.
Involves comparison with a reference standard, often using visual cues like color intensity or precipitate size.
2) Quantitative limit tests:
Measure the actual concentration of the impurity or substance in the sample.
Uses analytical techniques such as HPLC, GC, or AAS to accurately determine impurity levels.
Common Uses of Limit Tests:
1) Heavy metals:
Ensures that toxic heavy metals (e.g., lead, cadmium, mercury, arsenic) are below acceptable limits to prevent harm.
2) Residual solvents:
Verifies that solvents used during synthesis or purification are within safe limits, as some solvents can be toxic or have undesirable effects.
3) Preservatives and antioxidants:
Confirms that the concentrations of preservatives or antioxidants are within acceptable ranges to ensure product stability and prevent contamination.
4) Microbial contaminants:
Assesses whether the microbial load is within safe limits to ensure the product's safety and efficacy.