Estimation of the minimum uncertainty of DNA concentration in a genetically modified maize sample candidate certified reference material

Homogeneity testing and the determination of minimum sample mass are an imp ortant part of the certification of reference materials. The smallest theor etically achievable uncertainty of certified concentration values is limite d by the concentration distribution of analyte in the different particle si ze fractions of powdered biological samples. This might be of special impor tance if the reference material is prepared by dry mixing, a dilution techn ique which is used for the production of the new and third generation of ge netically modified (GMO) plant certified reference materials. For the produ ction of dry mixed PMON 810 maize reference material a computer program was developed to calculate the theoretically smallest uncertainty for a select ed sample intake. This model was used to compare three differently milled m aize samples, and the effect of dilution on the uncertainty of the DNA cont ent of GMO maize was estimated as well. In the case of a 50-mg sample mass the lowest achievable standard deviation was 2% for the sample containing 0 .1% GMO and the minimum deviation was less than 0.5% for the sample contain ing 5% GMO.