Development and strategy of reference materials for the DNA-based detection of genetically modified organisms.

The enforcement of GMO labeling regulations requires validated analytical methods and certified reference materials (CRMs). The early labeling regulations stipulated that the GMO content should be expressed as percentage, but did not specify what unit this percentage referred to. Two reference systems, using mass fraction and copy number ratio as measurement units, individually, are established for GMO analysis using different metrological traceability chains. Three types of CRMs, powder CRMs certified for mass fractions, genomic DNA CRMs, and plasmid DNA CRMs certified for copy number ratios, were developed for calibration and quality control. The type, certification, and measurement unit commutability of current GMO CRMs are presented and discussed in this paper. Both existing reference systems are facing a metrological challenge, although later EU regulations specified that the measurement unit of GMO content must be expressed in mass fraction and recommended to convert one unit into another by introducing a conversion factor, further efforts are required to explore which reference system is more metrologically sound. The determination of conversion factor per CRM batch is recommended to be based on the pure CRMs produced from pure GM materials, which is expected to be the best choice for calibration of PCR measurement results.