Limit tests

• 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.

Illustration of a student conducting a limit test on a pharmaceutical product

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.