We apply the following principles for all our reference materials which are laid down in our accredited quality system that is based on ISO 17034 and ISO Guide 35:
Planning
Starting point for the planning of each reference material are the final characteristics the material must fulfill to be fit for purpose: the type of material (pure substance/solution or matrix material, which matrix), which measurands and level and uncertainty of the measurands. All subsequent studies are then planned in a way so that these requirements can be met. While it is possible that a material is less homogeneous or stable than expected, this planning prevents that we are unable to say whether a material is sufficiently homogeneous or stable.
Processing
Processing is the activity that turns the raw material (e.g. a 5 litres of human serum, 10 litres of bovine urine, 200 kg of polyethylene granulate, 20 kg of cucumbers etc.) into a candidate reference material (the material in the vials). Like the measurements for the subsequent studies, this processing can be done by ourselves or can be outsourced to other organisations. Take a Virtual tour through our processing hall to see how we turn the raw material into the candidate reference materials. After this first step, the homogeneity and stability studies and the characterisation study can start.
Homogeneity
Homogeneity testing is carried out for every reference material produced, even for types of material for which experience has shown that they can be produced with negligible inhomogeneity. The outcome is the quantification of the variation between the various reference material units. This variation is an integral part of the assigned uncertainties.
For each measurand a minimum sample intake is established, either by performing a dedicated study or using a sample intake that has shown to be representative for the whole samplein the homogeneity, stability or characterisation studies.
Stability
We assess for each measurand with certified or indicative values the stability during storage and transport.
Only materials where it has been shown that no significant degradation occurs for one week at +40 °C or +60 °C are shipped without further precautions; all other materials are shipped cooled or on dry ice.
All materials undergo storage stability studies that assess and confirm the stability during storage at our warehouse.
Stability monitoring is performed for all reference materials distributed that are subject to potential instability.
The uncertainty of potential degradation (even if not statistically significant) is an integral part of the uncertainties of the certified values.
Characterisation
We recognise that even the best laboratories can make mistakes. We therefore never rely on results from one laboratory using one method only for assigning certified values. We insist that even results from a primary method of measurement are confirmed by an independent method.
In most cases we rely on a network of six or more laboratories for the characterisation. These laboratories have demonstrated their competence before the start of the characterisation study and have also demonstrated their adherence to ISO/IEC 17025.
We never exclude outliers on statistical grounds. If outliers are present that, even after consideration of the respective uncertainties, are in disagreement with the other values, we do not certify.
The uncertainties of our assigned values include contributions from the characterisation, stability assessment and homogeneity assessment, even if no significant degradation or inhomogeneity has been detected.
Traceability
Only if the characterisation study has demonstrated that different methods give the same result, we assign values that are independent of the measurement method. If this is not the case, the measurands is operationally defined (“as obtained by method …”). This is clearly communicated in one of the footnotes on the assigned value.
Whenever possible, we make our assigned quantity values traceable to the International System of Units (SI). Whatever the final reference, the traceability of the assigned value is clearly communicated in one of the footnotes to the assigned value.
Commutability
Reference materials used in a measurement need to behave the same way as the samples analysed. Reference material that have undergone processing steps which may change the behaviour or which have a composition differing from the samples should therefore be tested for their commutability. We believe that reference material producers can aid the selection of a matching reference material by transparently reporting about commutability studies or consideration related to the reference material. In the clinical field the assessment of commutability is mandatory before using the reference material. We therefore carry out and publish commutability studies for all our reference materials intended to be used for the calibration of in-vitro diagnostic (IVD) assays.
Transparency
We believe that transparency is an important factor in the trust of certified values. The approaches applied to produce a reference material are reviewed by JRC colleagues and additionally by external experts. We publish for each reference material a comprehensive report that describes processing, the setup, results and evaluation of the homogeneity and stability studies, the selection of participants, the setup, results, technical and statistical evaluation of the characterisation study, calculation of assigned values and associated uncertainties and, where relevant, the commutability studies.
The reports are available as free downloads on this website.