Medical Device Link.

Originally Published EMDM November/December 2002

SPECIAL REPORT

For manufacturers that do not already conduct chemical characterization, ISO 10993 part 18 may mean incorporating new tests and investing in new equipment for their biological safety assessment procedures. For many manufacturers, the best solution will be to contract with a testing laboratory that already has the expertise and equipment to handle the requirements. Even those manufacturers that do intend to contract with testing laboratories, however, need to know which tests will be required for their devices. Testing requirements depend on the material used and the type of body contact expected.

David Albert of NAMSA has recently written an article for Medical Device & Diagnostic Industry magazine detailing the type of tests that are needed for chemical characterization. His article can be accessed at www.devicelink.com/mddi/archive/02/03/003.html. NAMSA also provides a Chemical Characterization Matrix, which lists the tests needed for particular materials and clinical uses. The matrix can be obtained at www.namsa.com/select/char_matrix.htm.

The following are brief descriptions of the major types of chemical characterization tests described in Albert's article.

Infrared analysis. Since the infrared spectrum of a chemical compound or polymer is perhaps its most characteristic physical property, infrared analysis finds extensive application in fingerprinting, or identifying, materials. Small differences in the structure and constitution of a molecule result in significant changes in the distribution of absorbance peaks in the fingerprint region of the spectrum.

Aqueous and nonaqueous physicochemical tests. Aqueous physicochemical tests are designed to determine the presence of water-soluble substances without regard to their identity. The aim of these tests is to ensure that the materials will not release water-soluble chemicals into the drug products or tissue fluids that they contact. The tests also help detect surface contaminants that may find their way into raw materials during manufacturing. The United States Pharmacopeia prescribes isopropyl alcohol for conducting nonaqueous physicochemical tests of elastomeric closures used for pharmaceutical containers.

High-performance liquid and gas chromatography. In gas chromatography (GC), the sample is vaporized and injected onto the head of a chromatographic column. GC can be used to separate and quantitate volatile and semivolatile chemicals found in polymeric materials. Like GC, high-performance liquid chromatography (HPLC) can be performed using different types of detectors to identify and quantitate analytes. For the most part, ultraviolet/visible light detectors have been the universal type for liquid chromatography, but light detectors based upon refractive index, infrared absorbance, evaporative light scattering, and fluorescence, as well as on mass spectrometry, have also been widely used. HPLC using mass spectrometer detectors has seen considerable growth owing to the substantial analytical strength and sample-compound identification capabilities using automated search libraries available with the technique.

Atomic absorption spectroscopy and inductively coupled plasma spectroscopy. To fully characterize trace metals, atomic absorption spectroscopy (AAS) and inductively coupled plasma (ICP) spectroscopy are frequently used. AAS can determine the amount of specific metals present in a material or its extract, while ICP spectroscopy permits simultaneous determinations of all the periodic-table elements, and has a lower limit of detectability in the parts-per-billion range.

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