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USP Physicochemical testing may consist of four analyses: buffering capacity, nonvolatile residue (NVR), residue on ignition (ROI), or heavy metals.
The sample is extracted in the required extraction media at 70 ± 2°C (water and alcohol) or 50 ± 2°C (hexanes) for 24 ± 2 hours. Other extraction times and temperatures may be used if requested, but the USP General Chapter 661 limits may not be applicable.
For polyethylene or polypropylene samples, the recommended tests are heavy metals (water extraction only) and NVR (water, alcohol, and hexanes extractions). The buffering capacity test (water extraction only) is also recommended when the samples may be in contact with oral liquids.
For general plastics, all four analyses are recommended using a water extraction. The ROI test is not required when the nonvolatile residue does not exceed 5 mg.
Buffering capacity: This test measures the amount of acid or base that is added to the extract which causes a significant change in ion activity (pH).
Nonvolatile residue (NVR): This test quantifies any substances in the extract which do not volatilize at or above a temperature of 105°C.
Residue on ignition (ROI): This test quantifies any substances from the nonvolatile residue test which do not volatilize at or above 600°C in the presence of sulfuric acid. An NVR test must be performed prior to an ROI test.
Heavy metals: This test detects metallic impurities found in the extract that are colored by the sulfide ion. The metals which normally respond to this test are lead, mercury, bismuth, arsenic, antimony, tin, cadmium, silver, copper, and molybdenum. The total amount of heavy metals cannot exceed 1 part per million (ppm).
If you have additional questions about Physicochemical USP Plastics tests, or would like to consult with the experts at Nelson Labs, just send us a request or call us at +1 (801) 290-7500.