Meeting the ISO/IEC 17025 Requirements for Traceability and Measurement Uncertainty APLAC Approaches...
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Transcript of Meeting the ISO/IEC 17025 Requirements for Traceability and Measurement Uncertainty APLAC Approaches...
Meeting the ISO/IEC 17025 Requirements for Traceability and Measurement Uncertainty
APLAC Approaches
Dr Bernard King NARL, Australia
Interpretation of ISO/IEC 17025 Requirements
Extensive consultation leading to common
interpretation and new Guides
APLAC held 3 day Workshop in May 01 to develop a
common interpretation, across five fields. Draft guide produced
Final guide expected by end of 2002
Will supplement an ILAC guide
Some of the Difficulties
Anxiety in labs and accreditation bodies Need for training of lab staff and assessors Time / cost of additional work Lack of customer demand Some countries / fields are moving faster than others
Need to interpret requirements in a pragmatic, progressive and common sense way
ILAC MRA will help ensure level playing field
Interrelated Requirements in ISO/IEC 17025
Specification of measurement requirement
Method validation
Traceability
Measurement Uncertainty
ISO/IEC 17025 Method Validation Requirements
Specifically required for in-house methods Implicitely required for all methods Long standing requirement, but often inadequately addressed Needs to be subject to closer scrutinyIf method validation data is available, then evaluating
MU is not difficult
ISO/IEC 17025 Traceability Requirements
Measurements must be traceable to SI, where
feasible
Where above is not feasible, traceability to
other measurement standards must be
established
This can be achieved by use of transfer
standards, that are themselves traceable to
higher level standards
Example 1- Cd in soil Measurand &Units - Total Cd in soil, measured
in mg/kg Equation C = I . dC . V mg/kg dI m . R I . dC is traceable to SI through PSRM
dI R is traceable to SI through matrix RM or ... m and V are traceable to SI through calibrated
standards
If the model is valid then C is also traceable to SI
Traceability of RMs Reference Comments / Traceability
CRM Can be accepted
RM Can be accepted after assessment
CommercialChemicals
Lab are responsible, however: Often ‘best available’ Often entirely adequate
For physical measurements there are accreditationrequirements for calibration, but for chemical measurements
there is little yet in place!
ISO/IEC 17025 MU Requirements
An uncertainty evaluation is required for all measurements
Labs shall at least attempt to: identify all significant components make a reasonable estimation of U ensure that reported results do not give a false
impression of U.
Reproducibility Based MUCombine other significant effects with
reproducibility
Reproducibility
MU
Bias Effects
Sampling Effects
Summary of International MU Policy Target implementation date - Dec 2002 ISO GUM and Eurachem / CITAC strategies
are recommended but not compulsory Strategies based on reproducibility need to also
consider other significant effects MU estimates can be based on available or
readily obtainable data, including professional judgement
The degree of rigour required in evaluating uncertainty depends on the end use of the measurement
cont... The evaluation of uncertainties associated with
qualitative tests is not required, but the probability of false identification does need to be considered.
Any limitations associated with traceability and MU claims need to be reported with results
It is expected that reporting MU, where relevant and necessary, will become the norm with time
Conclusions Measurements need to facilitate sound
decisions
Effort required depends on the level of
acceptable MUA matter for professional judgment Not as difficult as it first seems Eg- If validation data available MU takes 0.5 to 2
days
Reasonable progress is being made in implementing the new requirements in a pragmatic and harmonized way.
Sources of Help Literature - policy papers, guides, journals,
web Training courses, seminars, workshops,
eg. On RMs, MU and validation Web- based training on MU at
www.mutraining.com