The view from a clinical laboratory
Specialty gas purity requirements for basic gases such as zero air, helium, hydrogen, and nitrogen for instrument calibrations and instrument/process purges are specified by instrument vendors and/or assay protocols. While these do not differ on the surface from gases in nonclinical labs, composition and purity may vary.
Similarly in pathology and diagnostic cell culture, no special precautions need be considered for cryopreservative gases such as liquid nitrogen, which do not come into contact with samples. Users must, however, follow Good Clinical Practices and Good Laboratory Practices, as appropriate, for certifying quality and validating the freezing protocol. Even more leeway is available for cryogenic liquid helium and liquid nitrogen for cooling components of magnetic resonance imaging probes, X-ray devices, lasers, and computerized tomography imagers in diagnostics.
Specialty gas quality and composition become more challenging as clinical or diagnostic processes become more complex or move closer to living, breathing patients. Mixtures of carbon dioxide, oxygen, and nitrogen for calibrating blood gas analyzers must meet both purity and composition specifications, while incubator gases must provide specific oxygen levels to assure growth of cells or organisms. Test gas mixtures for measuring lung function require near depletion of carbon dioxide, the measurand in these tests.
Kim Myers, global product manager at Parker Hannifin (Cleveland, OH), notes that while most lab managers would recognize the gases used in clinical lab operations, and to a lesser degree instrumentation, clinical settings are more demanding. “They’re looking for traceability, that they’ve delivered the right gas at the right purity for the specified period of time.” As with GxP settings, labs must be prepared to demonstrate quality back to their suppliers.
Myers believes that the most effective way to assure gas quality with a minimum of documentation and validation effort is to generate routine lab gases like zero-grade air, nitrogen, and hydrogen at the point of use. A periodic calibration and quality check, which is part of most on-site generator contracts, satisfies the need to document purity. Managers need to trace the quality of gases delivered through conventional tanks by the tank. Gas suppliers will provide a certificate of purity, but these must be individually entered into compliance or quality records.
“If you have twenty cylinders, you need twenty certificates,” Myers says. Parker provides gas generator certification through Mettler Toledo.
Every vendor of on-site generators provides the advantages of very high purity gas (especially hydrogen), safer operation minus heavy tanks, no need to switch out tanks, and a return on investment ranging from one and a half to three years.
On purity and composition
Specialty gas requirements among industries differ more in terms of composition than purity, cylinder type (e.g., materials of construction, lining), or delivery system (valves, regulators). The former are specified by the instrument or protocol, while the latter are standardized by the gas industry. Vendors denominate purity of pure gases as a percentage, say 99.9999%, while composition for gas mixtures is certified at the generating plant up to +/- 1% for individual components. Regardless of end user, specialty gas vendors follow ISO 9002 for quality standards.
Best-in-class manufacturers stock common specialty gas mixtures at recommended composition and purity levels, as well as container size, and tens of thousands of recipes for on-demand mixtures. While commercial clinical and diagnostic labs dealing with patients are unlikely to request nonstandard mixtures, instrument developers and protocol researchers have the opportunity to tweak gas mixtures in ways that further their science.
For additional resources on specialty gases, including useful articles and a list of manufacturers, visit www.labmanager.com/gases