This series of tests is designed to aid in characterizing both the physical and chemical properties of plastics or polymers. This method is intended for homogeneous plastic samples, though it may be applied to other sample types if requested. The procedure is described in the USP <661> and may consist of four analyses:
- Buffering capacity
- Nonvolatile residue (NVR)
- Residue on ignition (ROI)
- Heavy metals
USP <661> also discusses thermal analysis and multiple internal reflectance testing of polymers, specifically polyethylene and polypropylene. Refer to DSC and FTIR.
Study Outline
SAMPLE EXTRACTION: 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 <661> limits may not be applicable.
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. A nonvolatile residue test must be performed prior to a residue on ignition 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).
For polyethylene or polypropylene samples, the recommended tests are heavy metals (water extraction only) and nonvolatile residue (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 residue on ignition test is not required when the nonvolatile residue does not exceed 5 mg.
Sample Requirements
The amount of sample needed for the test(s) is based on the USP <661>/ISO 10993-12 requirements. Please refer to the USP 661 samples requirements table.
Nelson Experts:
- Brent Shelley 801-290-7824, 800-826-2088
