Reference materials (RMs), including NIST Standard Reference Materials (SRMs) are used for quality assurance, traceability of measurements and instrument and method validation. The Cryogenic Reference Material Production Facility (CRMPF) at the Hollings Marine Laboratory houses specialized equipment required to generate fresh-frozen RMs, as well as multiple innovative tools used for processing unique materials. The distinctive ISO Class 5 and 7 clean room settings help eliminate external sources of contamination, an important consideration when generating large batches of homogenous materials. To date, the Biospecimen Science Group staff have assisted stakeholders in the development and production of more than 30 different RMs, including dietary supplements and food products, wood products, sediment, coal dust and many marine species (mussels, kelp, aquacultured seafood and wild-caught seafood) to aid stakeholders in making measurements in complex matrices.
Large-batch cryogenic reference materials are produced using a specialized Palla VM-KT Vibrating Cryomill. The mill is pre-cooled to cryogenic temperatures using liquid nitrogen. Frozen material is fed through the inlet funnel to a vibrating chamber containing 26 titanium rods. The rods pulverize the material into a fine powder. The fresh-frozen product is then extruded from the chamber through the outlet below.
The particle size distribution of the resultant material is evaluated using laser-diffraction. These data help assess homogeneity based on size and are used as a process control indicator to determine if additional milling is required. Laser diffraction particle size analysis (PSA) is also used to assign informational values to existing RMs that require particle size data.
Smaller batches of RMs can be homogenized either cryogenically or at room temperature using polytetrafluoroethylene (PTFE) disk mills. Material is added to the disk mill in small pieces and loaded into a shaker. High force oscillations pulverize the material into a fine powder.
Staff are also developing and implementing protocols for generating custom RMs. Using techniques such as blending of multiple materials or amending matrices with exogenous analytes, in-house RMs can be generated when natural sources of material cannot be procured. These techniques can also be used to develop ‘rapid-response’ RMs to aid the measurement community in the event standardization of a specific measurement is immediately required and there is no time to collect and process large amounts of naturally-incurred material.
*Candidate materials in progress