Certified Reference Materials - A Path to Traceable Chemical Measurements

Transcription

1 Certified Reference Materials - A Path to Traceable Chemical Measurements Paul Armishaw 5 May 2016

2 What I plan to talk about Why traceability so measurements can be compared Traceable to what? SI units other reference CRMs realization of a quantity means of achieving traceability ISO Guide 34 The quality standard for reference material producers ISO Guide 31 good practice for the content of CRM certificates

3 Metrological Comparability of Measurement Results Metrological comparability of measurement results: comparability of measurement results, for quantities of a given kind, that are metrologically traceable to the same reference Why do laboratories make measurements to make comparisons changing with time? different to some other item? complies with a standard? So the measurement result is not interpreted in isolation it has meaning when compared to other results Comparable measurement results must be traceable to a common reference VIM

4 Dieldrin (mg/kg) Example of comparing results Source: <insert source here> Method 1 Method 2 The persistent insecticide dieldrin, measured in beef fat using two methods. Extraneous Residue Limit is 0.2 mg/kg.

5 Making a Comparison is Not Enough Mid-day cannon Expensive watches

6 Metrological Traceability property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty VIM Metrological traceability means measurements can be meaningfully compared. Even when. made at different times at different places by different people using different equipment

7 Traceable to What? Measurement standard: realization of the definition of a given quantity, with stated quantity value and associated measurement uncertainty, used as a reference VIM SI units mole, kilogram, metre, ampere, second, kelvin, candela Other references Standard method for operationally defined measurands eg total petroleum hydrocarbons NOTE 2: A measurement standard is frequently used as a reference in establishing measured quantity values and associated measurement uncertainties for other quantities of the same kind, thereby establishing metrological traceability through calibration of other measurement standards, measuring instruments, or measuring systems.

8 Reference Materials and Certified Reference Material Reference material: material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be fit for its intended use in a measurement procedure. ISO Guide 30 Certified reference material: reference material (RM) characterized by a metrologically valid procedure for one or more specified properties, accompanied by an RM certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability. ISO Guide 30

9 Reference materials carry information: That is what the user pays for NIST SRM 2387 Ash 3.10 Calories 629 Carbohydrates 25.0 Dietary Fiber-Total 5.57 Fat (extracted) 51.6 Protein 22.2 Solids 99.2 Acrylamide Aflatoxins Elements Fatty Acids Tocopherols Vitamins Sum of Fatty Acids (as triglycerides) Amino Acids X X X X X X 49.8 X

10 Quality standards for reference material producers ISO guide 34: General requirements for the competence of reference material producers ISO Guide 35: Reference materials General and statistical principles for certification ISO Guide 31: Reference materials Contents of certificates, labels and accompanying documentation ISO Guide 30: Terms and definitions used in connection with reference materials ISO Guide 32: Uses of certified reference materials

11 ISO Guide 34 Specifies general requirements for reference material producers to demonstrate competency Guidelines for development and implementation of management system quality, administrative and technical based on ISO 9000 series similar to ISO Specifies the quality assurance (QA) requirements for the RM production Specifies requirements for production of reference materials and certified reference materials

12 What is needed in a certified reference material measurement standard: realization of the definition of a given quantity, with stated quantity value and associated measurement uncertainty, used as a reference VIM Certified property value metrologically traceable Stable during storage during transport Homogeneous between units within units minimum sub-sample specified In a useful form pure solid, solution, fresh, freeze dried, etc how far does the light shine?

13 Guide 35: Detailed guidance for preparing and certifying reference materials Assigning property values single primary method several independent reference methods interlaboratory study method specific approach Homogeneity testing Stability testing long-term storage short term transport Evaluating uncertainty

14 Assigning property values: several independent reference methods Pure substance reference materials Organic purity gas chromatography flame ionisation detector liquid chromatograph quantitative NMR Confirmation of identify microanalysis mass spectrometry infrared spectroscopy NMR Inorganic impurities/solvents thermogravimetric analysis direct scanning calorimetry Karl Fischer (water)

15 Assigning property values: several independent reference methods Matrix reference materials isotope dilution mass spectrometry techniques extensive cleanup two dimensional HPLC LC/MS GC/MS high resolution GC/MS high resolution ICP MS ICP MS/MS look for different ions and transitions Method defined measurand total recoverable hydrocarbons in soil

16 Folic acid (mg/kg) Stability testing y = x Time (weeks) Long-term stability testing of folic acid in wheat flour CRM

17 Isochronous Stability testing Accelerated stability 1, 3, 5, 7 and 14 days at 40 o C Long-term stability at -20 o C +40 o C -20 o C Samples removed from oven after 1, 3, 5, 7 and 14 days -80 o C Reference Samples removed from freezer after 1, 2, 3, 4, 5 and 6 months Stored at -80 o C until analysis Stored at -80 o C until analysis Samples and reference sample analysed in a single batch using same calibration standard

18 Ethanol (g/kg) Homogeneity testing Bottle No Homogeneity testing ethanol in water solution for breathalyser calibration. ANOVA to separate within-bottle and between-bottle variance.

19 Uncertainty in the property value of the CRM The combined standard uncertainty in the property value to include uncertainty due to characterisation, inhomogeneity, long and short term stability: u CRM = u 2 char + u 2 bb + u 2 lts +u 2 sts Degrees of freedom calculated from the Welch-Satterthwaite equation (ISO GUM) where k 95 (coverage factor) = t 95 (v eff )

20 ISO Guide 31: Certificates of Reference Materials Title of document Name of material Reference material code and batch no. Description of the CRM Intended use Instruction for use and storage Safety information Property value, MU, certification method Date of certification Traceability and period of validity Other relevant information

21

22 97% pure 9% water

23

24 Certification of a Reference Material in Accordance with Regulation 48 of the National Measurement Regulations 1999 (Cth) in Accordance with the National Measurement Act 1960 (Cth) Name or description of reference material: Aqueous ethanol solution. Permanent distinguishing marks: Bottles labelled with batch number ETOH Date on which property values of reference material were established: 17 March Date of certification: 29 March Date of expiry of certificate: 17 March Certified property value of reference material: 4.87 g of ethanol per kg of solution. Uncertainty of property value: ± 0.07 g of ethanol per kg of solution (k=2.0). This uncertainty is calculated in accordance with the principles of the JCGM 100: Evaluation of measurement data - Guide to the expression of uncertainty in measurement, with an interval estimated to have a level of confidence of greater than 95 % at the time of certification. Storage of the reference material at 4-10 C is recommended. Signature: Date: 29 March 2016 Name of Signatory: Paul Armishaw Being a person with powers delegated by the Chief Metrologist acting under Section 18D of the National Measurement Acts 1960 (Cth) in respect of regulation 48 of the National Measurement Regulations 1999 (Cth), I hereby certify that the above reference material is certified in accordance with the regulations.

25 Acknowledgements Organisers for the kind invitation to speak. NMI Colleagues in the CRV team whose data I have plundered

26 Department of Industry, Innovation and Science National Measurement Institute National Measurement Institute 105 Delhi Rd, Riverside Corporate Park, NORTH RYDE NSW 2113 Telephone info@measurement.gov.au