The following terms are used here and in literature elsewhere to discuss reference materials.
There are currently 11 names in this directory beginning with the letter C.
Certified Reference Materials (CRMs)
Reference materials that are characterised by metrologically valid procedures for one or more specified properties and which are accompanied by a certificate providing the value of the specified property, its associated uncertainty, and a statement of metrological traceability. ISO Guide 30:2015
recommends terms and definitions that should be assigned to them when used in connection with reference materials, with particular attention to terms that are used in reference material certificates and corresponding certification reports. The certificate must contain a statement of traceability indicating the principles and procedures on which the property values (together with their measurement uncertainties) are based. In the case of mineral CRM's this will be method specific, by inter-laboratory testing, with operationally defined property values using a network of competent laboratories employing methods which have been independently validated (ISO 17034:2016
The Canadian Institute of Mining, Metallurgy and Petroleum (CIM). The CIM Definition Standards for Mineral Resources and Mineral Reserves are one of the CRIRSCO-style reporting Codes. It was originally based on the Australasian JORC Code . It is the document underlying the Canadian Stock Exchanges NI 43-101.
Coefficient of Variation
Measures the spread of a set of results as a proportion to its mean (SD/mean). Also known as one relative standard deviation (1RSD).
Reference material producers should ensure that a reference material is suited for its intended use. For calibrators and quality control materials this usually includes verification that the raw material selection and processing procedures result in a material with the same behaviour as routine samples in the relevant measurement procedures. The assessment of commutability is part of the demonstration that such a reference material is fit for the intended use. Non-commutability of a reference material can be caused by a matrix alteration or by the presence of different analyte host minerals (eg. refractory minerals). A matrix effect or a matrix bias is often caused by differences in sample matrix between the reference material and the routine 'field' samples.
A range of values within which the Recommended Value is expected to lie. The magnitude of the confidence interval is inversely proportional to the number of participating laboratories and inter-laboratory agreement. It is a measure of the reliability of the recommended value; the narrower the confidence interval the greater the certainty in the recommended value.
The quality of agreement in measurements of the same parameter in the same RM between different laboratories in a certification program.
Schewart or Levey-Jennings control charts are used to monitor analytical processes. In the context of monitoring QC data for CRMs, these charts contain a centreline and the CRM’s ±2 and ±3 SD window control limits are plotted. The user’s own data obtained for the CRM by a laboratory being monitored is then progressively plotted and the data should follow a normal distribution. By definition, 4.5% of data falls outside the 2SD window and 0.3% of data will fall outside the 3SD window. This means approx. 1 in 22 analyses will naturally fall outside 2SDs and approx. 1 in 333 analyses will naturally fall outside 3SDs. Westgard Rules can be used to determine when intervention should be instigated due to QC failures.
A CRMs statistics quoted in certificates is linked to the round robin program and is at best, a first principle guide to what a laboratory may be able to perform within. Each laboratory has its own unique operators, equipment, reagents and processes all of which contribute to a repeatable and reproducible level of variability. This means each laboratory has its own inherent SD linked to the particular method carried out and this may or may not be a good match to the SD quoted in a CRM’s certificate. For this reason, some CRM producers prefer not to provide SD’s in certificates and recommend that users monitor the precision over time and attribute their own empirically derived SD. The obvious weakness of this is that it takes a while to accumulate a critical mass of analyses (in order to calculate a meaningful SD) and if the analytical process has poor precision or bias the laboratory won’t be held accountable. At the very least, empirically derived SD's should be compared to those published in the certificate as in indication of the general performance of their laboratory and whether their data has sufficient process control.
A window of acceptability for results obtained by a laboratory for a reference material and generally calculated from multiples of the standard deviation (SD) of the certification data. The SD for each analyte’s certified value reported in OREAS’ certificates is calculated from the same filtered data set used to determine the certified value, i.e. after removal of any individual, lab dataset (batch) and 3SD outliers (single iteration). These outliers can only be removed after the absolute homogeneity of the CRM has been independently established, i.e. the outliers must be confidently deemed to be analytical rather than arising from inhomogeneity of the CRM. The standard deviation is then calculated for each analyte from the pooled accepted analyses generated from the certification program.
In the application of SD’s in monitoring performance it is important to note that not all laboratories function at the same level of proficiency and that different methods in use at a particular laboratory have differing levels of precision. Each laboratory has its own inherent SD (for a specific concentration level and analyte-method pair) based on the analytical process and this SD is not directly related to the round robin program.
The majority of data generated in the round robin program was produced by a selection of world class laboratories. The SD’s thus generated are more constrained than those that would be produced across a randomly selected group of laboratories. To produce more generally achievable SD’s the ‘pooled’ SD’s provided in this report include inter-lab bias. This ‘one size fits all’ approach may require revision at the discretion of the QC manager concerned following careful scrutiny of QC control charts.
The International Reporting Template, first published in 2006, is a document that represents the best of the CRIRSCO-style codes, previously referred to as JORC-style codes; reporting standards that are recognised and adopted world-wide for market-related reporting and financial investment.
Custom Reference Materials
Synonymous with Matrix-Matched CRMs (MMCRMs also mine-matched or site-specific CRMs) manufactured out of source materials supplied by clients; usually for mines and advanced reserve-definition stage projects but can also be made from materials sourced from exploration projects or downstream metallurgical products (feed, tails and concentrate). Matrix-Matched Reference Materials provide the highest degree of assurance of the entire analytical process being in control and completely avoid issues of commutability.