Overview of Limit Tests
Limit tests are a category of impurity tests in which a solution of an unknown sample is compared to a standard that contains the impurity at the product limit. Generally this definition applies to limit tests that are in widespread use in various pharmacopoeial compendia, such as United States Pharmacopoeia (USP), European Pharmacopoeia (EP), Japanese Pharmacopoeia (JP) and Food Chemicals Codex (FCC). These tests do not give quantitative results, only qualitative “pass/fail” results based on the specified limit.
Typically this category of test relies on the comparison of an unknown sample to a standard solution. Often these tests rely on a visual evaluation by the technician, though some may rely on instrumental analysis of the sample.
The methods are given in the USP, EP and JP. Click here to visit the USP (login required).
The following is a list of the qualitative tests we commonly perform. These examples are of USP methods; the EP and JP have similar corresponding (and sometimes harmonized) methods:
Aluminum <206>, Arsenic <211>, Chloride and Sulfate <221>, Dimethylaniline <223>, Elemental Impurities <232> and <233>, Iron <241>, Lead <251>, Mercury <261>, Readily Carbonizable Substances <271>, Residue on Ignition <281>, Selenium <291>.