This report describes the production of ERM®-BF442, which are cotton powder materials certified for the mass fraction of GHB811 (unique identifier BCS-GH811-4). These materials were produced and certified in accordance with ISO 17034:2016 and ISO Guide 35:2017. ERM BF442 was produced within the scope of ISO 17034 accreditation. Genetically modified (GM) cotton seeds of the GHB811 event and seeds from a non-GM cotton variety were milled to obtain GM and non-GM seed powders with a similar particle size distribution. Mixtures of non-GM and GM cotton seed powder were prepared gravimetrically. The certified reference materials (CRMs) are available in glass vials containing at least 1 g of dried cotton powder, which were sealed under an atmosphere of argon. Between-unit homogeneity was quantified and stability during dispatch and storage was assessed in accordance with ISO Guide 35:2017. The minimum sample size for one measurement is 200 mg. The certified value was obtained from the gravimetric preparations, taking into account the genetic purity of the base materials with respect to the GHB811 cotton and their water mass fractions. The certified values were confirmed by event-specific real-time polymerase chain reaction (PCR) (measurements performed under the scope of ISO/IEC 17025:2017 accreditation). Uncertainties of the certified values were calculated in accordance with ISO 17034:2016 and ISO Guide 35:2017 and include uncertainties related to possible inhomogeneity, instability and characterisation. The materials are intended for the calibration or quality control of quantitative PCR measurements to identify GHB811 cotton and quantify its mass fraction. As with any reference material, they can be used for establishing control charts or validation studies.JRC.F.6 - Reference Material
