PTP-MAL Guide

(Version 2008-04-25)
In the event of a discrepancy between this web version
of the Guide and the CANMET-MMSL ISO document, the latter will prevail.

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Proficiency Testing Program for Mineral Analysis Laboratories

Canadian Certified Reference Materials Project

The Canada Centre for Mineral and Energy Technology has offered reference materials and spectroscopic standards since 1962. The Canadian Certified Reference Materials Project (CCRMP) was created as a formal entity in 1973 to promote the production and distribution of certified reference materials for use in the analytical community associated with the mining industry in Canada and abroad. Currently, CCRMP provides over 100 certified reference materials and distributes to over 65 countries. It offers the largest selection of sulphide mineral and precious metal certified reference materials. CCRMP is also active in preparing and characterizing custom reference materials using the raw material provided by individual companies.

CCRMP was certified to ISO 9002 in March 1997 for the production and distribution of certified and custom reference materials. In March 1998, ISO 9002 certification of the CCRMP quality system was extended to include the operation of the Proficiency Testing Program for Mineral Analysis Laboratories (PTP-MAL). In March 2002, the quality system of CCRMP was upgraded to ISO 9001:2000.

In December 2001, PTP-MAL was accredited by the Standards Council of Canada to CAN-P-1593 (which comprises ISO/IEC Guide 43-1 and ILAC G13:2000). By this accreditation, PTP-MAL meets the recognized international standards for proficiency testing providers. PTP-MAL is listed on the Asia Pacific Laboratory Accreditation Cooperation website as a proficiency testing provider: http://www.aplac.org/documents/pt/aplac_pt_003_issue_10.pdf

Introduction

CCRMP operates the Proficiency Testing Program for Mineral Analysis Laboratories in cooperation with the Task Group Laboratories Mineral Analysis Laboratories Working Group (TG LABS MA-WG) of the Standards Council of Canada (SCC). TG LABS MA-WG is responsible for defining the metals of interest and the concentration range for each as well as establishing the criteria and target values for assessing laboratory proficiency. Participating in PTP-MAL is open to any laboratory for which its scope of testing is relevant. Participation is obligatory for laboratories seeking or holding accreditation under CAN-P-1579.

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Description of PTP-MAL

The operation of the proficiency testing program is in full accord with ISO/IEC Guide 43-1 "Proficiency Testing by Interlaboratory Comparison - Part 1: Development and Operation of Proficiency Testing Schemes”, ILAC G13:2000 “Guidelines for the Requirements for the Competence of Providers of Proficiency Testing Schemes”, and the proficiency testing components of CAN-P-1579 “Guidelines for the Accreditation of Mineral Analysis Testing Laboratories”, while at the same time striving to respond to the needs of Canadian mineral analysis laboratories.

The proficiency testing program has two objectives. First, it is a vehicle to allow a mineral analysis laboratory to assess its performance for one or more analytical methods independently of internal quality control. Second, participation in the program is obligatory if a laboratory is to be accredited or is to retain its accreditation for mineral analysis activities by SCC to CAN-P-1579 “Guidelines for the Accreditation of Mineral Analysis Testing Laboratories” (June 2006), which includes meeting the requirements of ISO/IEC 17025 "General requirements for the competence of calibration and testing laboratories".

Given the wide variety of analytical demands, this proficiency testing program cannot cover all aspects of mineral analysis testing but will instead be representative of this area of activity. The current focus, which was selected in response to current market demand, is:

Metal Target Concentration Range
Lower Upper
Au 0.1 ppm 15 g/ metric ton
Ag 1 ppm 1000 ppm
Cu 1 ppm 2%
Zn 1 ppm 3%
Pb 1 ppm 2%
Ni 1 ppm 2%
Co 1 ppm 0.1%
Pd 0.1 ppm 3 ppm
Pt 0.1 ppm 3 ppm

The scope of the proficiency testing program may be modified and/or extended in future depending on market acceptance and demand, and according to regulatory or other requirements, where relevant. Furthermore CCRMP may, as samples permit, provide an opportunity to laboratories to assess their proficiency in the analysis of other metals.

Basic Proficiency Testing Program

The proficiency testing program consists of two test cycles issued during a fiscal year. Each cycle includes four or more test samples to cover as best as possible the target concentration range of the metals specified above. A participating laboratory is requested to perform one analysis for the identified metals in each sample by a method of its choice in a manner identical, to the greatest extent possible, to that applied to client samples. A participant is expected to use the same method for the determination of a metal in all test samples, as much as possible, in order for PTP-MAL to assess the proficiency in the method.

Test samples that have been lost or destroyed in shipping are replaced at no cost by PTP-MAL at the request of the participant.

A participant may request one (1) replacement specimen of a test sample that has been lost, destroyed, etc. after satisfactory receipt by the participant, in order to report analytical results for that sample. There is no cost for such a replacement but is limited to once in a three (3) year period.

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Extended Proficiency Testing Program

A participant may choose to extend the scope of its participation in the proficiency testing program by submitting results for a metal to assess its proficiency in more than one analytical method, either on the same set of test samples or on more than one set of the same test samples. The latter option is not available for laboratories accredited by SCC to CAN-P-1579. There is a supplemental fee for extended participation.

Accreditation by SCC

Those laboratories accredited, or seeking accreditation, by SCC under the Program Specialty Area – Mineral Analysis Testing (CAN-P-1579) must follow Appendix A of CAN-P-1579 “Guidelines for the Accreditation of Mineral Analysis Testing Laboratories”. In particular, those laboratories must submit test results for each of their accredited test methods for each analyte where a relevant test sample is provided

Submission of Results

Analytical results must be submitted to PTP-MAL Coordinator no later than the identified due date, usually four (4) weeks after forwarding the set of samples to participants. Results must be reported to at least two (2) significant figures.

PTP-MAL sends a confirmation of receipt to each participant within three working days.

The results of the analysis of the proficiency testing program will be issued to participants by PTP-MAL Coordinator within 4 weeks after the due date for the submission of analytical results.

Report on Assessment of Proficiency

The results of the analysis of the proficiency testing program will be issued to participants by PTP-MAL Coordinator within 4 weeks after the due date for the submission of analytical results.

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Reports to Participants

Performance Report to Individual Participant

A report is issued to each individual participant that contains the assessment of proficiency for each metal.

Note: PTP-MAL reserves the right to limit this report to the assessment of proficiency of each individual participant or to include the assessment of proficiency for all participants. If the latter, participants are identified only by a code to maintain confidentiality.

For those laboratories accredited or seeking accreditation by SCC to CAN-P-1579, the performance report will also be sent to SCC at about the same time.

Comprehensive Report

Within eight weeks of the due date for submission of analytical results, a comprehensive report is issued to each participant that contains, for each metal in each sample:

  1. Scope of Program and description of samples
  2. value reported by each participant;
  3. method descriptor for each participant;
  4. consensus/assigned value;
  5. standard deviation of consensus/assigned value;
  6. calculated values of statistical parameters described in Section 10.0 for each participant; and
  7. assessment of proficiency for each statistical parameter for each participant.

To maintain confidentiality, participants are identified only by a code.

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Participation in PTP-MAL

Application to Participate

  • PTP-MAL assumes that current participants will continue to participate unless otherwise notified.
  • A laboratory wishing to participate in this proficiency testing program for the first time should return the attached "Intent to Participate" form by mail or facsimile to:

    PTP-MAL Coordinator
    CANMET-MMSL
    555 Booth Street
    Ottawa, Ontario
    Canada
    K1A 0G1

    Tel.: (613) 995-4738
    Fax: (613) 943-0573
    e-mail: ptp@NRCan.gc.ca
    web: www.ccrmp.ca

A laboratory wishing to extend the scope of its participation in PTP-MAL should contact PTP-MAL Coordinator.

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Fee

The fee structure and payment for participation in PTP-MAL are given on the website:

http://www.nrcan.gc.ca/mms/canmet-mtb/mmsl-lmsm/ccrmp/ptp/ptpfee-e.htm

Unsatisfactory Laboratory Performance

A laboratory that fails a set of samples in a test cycle may request another set of the same samples to assist in undertaking the required corrective action for the analytical method.

Laboratories accredited, or seeking accreditation, to CAN-P-1579 by SCC may require a remedial sample or samples. Refer to Appendix A of CAN-P-1579 for the SCC-required Corrective Actions.

Additional fees are payable in both cases (see:

http://www.nrcan.gc.ca/mms/canmet-mtb/mmsl-lmsm/ccrmp/ptp/ptpfee-e.htm

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Feedback and Participant Complaints

PTP-MAL welcomes feedback from participants at any time.

If a participant has a complaint with regard to PTP-MAL, he or she should contact PTP-MAL Coordinator directly by telephone, post, e-mail or fax.

Accreditation to CAN-P-1579: Note to Participants

SCC and CCRMP have a Cooperation Agreement to define mutual responsibilities in PTP-MAL wherein:

  1. SCC will provide PTP-MAL Coordinator with a list of the names of laboratories that are accredited or seeking to be accredited by SCC in the Program Specialty Area – Mineral Analysis Testing (CAN-P-1579); and
  2. PTP-MAL Coordinator will submit to SCC and the Convener, TG-Labs MA-WG, a copy of the performance report of these laboratories in each cycle of test samples, as stated in CAN-P-1579 Clause 6.1.11.

A laboratory that is accredited or seeking accreditation by SCC should consult CAN-P-1579 "Guidelines for the Accreditation of Mineral Analysis Testing Laboratories" for a description of requirements regarding method validation, frequency of participation, and unsatisfactory performance in PTP-MAL, as well as non-compliance with the conditions of participation in PTP-MAL.

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Assessment of Proficiency

Estimation of Statistical Parameters

Note: When a participant reports an analytical result for an element as “less than [value]”, the reported result is not used in the statistical assessment of results but may be considered by SCC MA-WG for overall proficiency

1. Consensus Value

1.1) After the removal of outliers as determined by an appropriate test such as Grubbs or standard T test (ASTM E- 178), the mean value of the results from all accepted laboratories for a metal in a sample is used as the consensus value as:

Consensus/Assigned Value and Standard Deviation

where:
XM = the consensus value;
Xi = the result reported by laboratory i; and
k = the number of accepted results (laboratories).

1.2) The standard deviation of the consensus value, SM, is estimated by:

standeviationequation

1.3) Calculation of z-score for an analysis

A z-score is calculated for each analysis by:

XM = the consensus

Analytical results reported as "less than a limit value."

When a participant reports an analytical result for an element as "less than value," a z-score is not calculated. The reported result is not used in the statistical assessment of proficiency, but may be considered by SCC MALWG for overall proficiency.

2. Scope of Assessment of Proficiency

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The two test cycles in the year are treated as independent assessments of proficiency by PTP-MAL.

Where an analytical method is not applied at least three times in a cycle, the assessment of proficiency is restricted to the assessment of individual z-scores. .

3. Tests for Assessment of Proficiency

TASC-WG-MAL sets targets for four statistical tests to assess proficiency:
  1. the individual z-score to assess a single analysis;
  2. the behaviour of the absolute values of a set of z-scores to assess a series of analyses for the same metal;
  3. the Re-scaled Sum of z-Scores (RSZ) to detect consistent bias in an analytical system; and
  4. the Squared Sum of z-Scores (SSZ) to detect abnormally high deviation in the overall performance of a laboratory.

3.1 Assessment of proficiency: z-score

z-Score Range Rating
l zi l ≤ 2 Satisfactory
2 < l zi l < 3 Questionable
l zi l ≥ 3 Unsatisfactory

3.2 Combining z-scores: distribution of absolute values

The distribution of the absolute value of z-scores when there are three or more analytical results for a metal is assessed as:

Absolute z-Scores Rating
All z-scores < 2 Good
All z-scores < 3 Satisfactory
Only one z-score ≥ 3 Questionable
Two or more z-scores ≥ 3 Unsatisfactory

The combined z-scores are used to assign an assessment of performance based on the analyses for a given analyte in a series of test samples.

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3.3 Combining z-scores: Re-scaled Sum of z-Scores

The Re-scaled Sum of z-Scores (RSZ) is calculated by Σ zi / √ n when there are three or more analytical results for a metal. RSZ uses the signs of the z-scores to detect consistent bias in an analytical system.

In order to avoid undue emphasis on an isolated poor result, z-scores greater than +3 or less than -3 are assigned the value of 3 and -3, respectively.

l RSZ l Range Rating
l RSZ l ≤ 2 Good
2 < l RSZ l ≤ 3 Satisfactory
3 < l RSZ l < 4 Questionable
l RSZ l ≥ 4 Unsatisfactory

3.4 Combining z-scores: squared sum of z-scores

The Squared Sum of z-Scores (SSZ) is calculated by ∑ zi2 when there are three or more analytical results for a metal. SSZ does not take into account the signs of the z-scores and is used to detect abnormally high deviations between values from the same population.

SSZ is compared with the value in the Χ2 ( chi-squared) distribution table at the agreed confidence levels with n degrees of freedom, where n = the number of analyses for a metal.

Confidence Limit Rating
95% Satisfactory
99% Questionable
> 99% Unsatisfactory

Table of Χ2 versus confidence interval

  Χ2
Conf. Int. n = 2 n = 3 n = 4 n = 5 n = 6
95% ≤5.99 ≤ 7.82 ≤ 9.49 ≤ 11.07 ≤ 12.59
99% > 5.99
≤ 9.21		 > 7.82
≤ 11.34		 > 9.49
≤ 13.28		 > 11.07
≤ 15.09		 > 12.59
≤ 16.81
> 99% > 9.21 > 11.34 > 13.28 > 15.09 > 16.81

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4. Overall Assessment of Proficiency

PTP-MAL applies a fifth assessment test that is not formally part of the ISO Guide 43-1 or the SSC MALWG assessment. The "Overall Assessment of Proficiency" is given by the lowest rating achieved by a laboratory for distribution of absolute values of z-scores, Re-scaled Sum of z-Scores, or Squared Sum of z-Score.

5. An example of the assessment of the proficiency of a participating laboratory is given in Appendix B.

6. In the case where only two results have been submitted for a given metal, for purposes of the Certificate (11.0), a “satisfactory” overall assessment is given if both z-scores are satisfactory.

Certificate of Successful Participation in Proficiency Tests

PTP-MAL issues an annual Certificate of Successful Participation in Proficiency Tests to each participating laboratory for the metals for which the laboratory achieved a “satisfactory” rating overall in both cycles for that year. [Note that this is independent of SCC accreditation.]

References

  • ISO/IEC Guide 43-1 Proficiency Testing by Interlaboratory Comparison - Part 1: Development and Operation of Proficiency Testing Schemes
  • ILAC G 13:2000 "Guidelines for the Requirements for the Competence of Providers of Proficiency Testing Schemes
  • CAN-P-1579 Guidelines for the Accreditation of Mineral Analysis Testing Laboratories, June 2006
  • ISO/IEC Guide 25 Guidelines for the Recognition of Proficiency Testing Schemes
  • CAN-P-1593 Guidelines for the Recognition of Proficiency Testing Schemes
  • ASTM E 178 Standard Practice for Dealing with Outlying Observations

Fees for PTP-MAL

http://www.nrcan.gc.ca/mms/canmet-mtb/mmsl-lmsm/ccrmp/ptp/ptpfee-e.htm

PTP-Guide

http://www.nrcan.gc.ca/mms/canmet-mtb/mmsl-lmsm/ccrmp/ptp/ptpguide-e.htm

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APPENDIX A: Acronym for Analytical Methods

Method Descriptor = Code 1 "-" Code 2

For example, the method descriptor for analyzing a sample for copper (1) by sodium peroxide fusion followed by measurement by graphite furnace atomic absorption is FSP-GAA and (2) by X-ray fluorescence with pressed powder pellets is PPP-XRF.

Code1 Procedure for Decomposition/Preparation of Solid Samples
ADn Acid Decomposition, where n = the number of different acids used
FLM Fusion with Lithium Metaborate
FSP Fusion with Sodium Peroxide
FSC Fusion with Sodium Carbonate
FPP Fusion with Potassium Pyrosulphate
FAL Fire Assay with Lead Button Collection
FAN Fire Assay with Nickel Sulphide Collection
FAT Fire Assay with Tin Button Collection
PPP Pressed Powder Pellet
FP Fused Pellet
Code2 Procedure for Measurement
VOL Volumetry or Titrimetry
GRV Gravimetry
COU Couloumetry
OPT Visible and UV Spectrometry
FAA Flame Atomic Absorption Spectrometry
GAA Graphite Furnace Atomic Absorption Spectrometry
HAA Hydride Generation Atomic Absorption Spectrometry
ICPE Inductively Coupled Plasma - Atomic Emission Spectrometry
ICPM Inductively Coupled Plasma - Mass Emission Spectrometry
XRF X-Ray Fluorescence Spectrometry
IC Ion Chromatogaphy
INAA Instrumental Neutron Activation Analysis (sample analyzed without decomposition)
NAA Neutron Activation Analysis (measurement of a decomposed sample)

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APPENDIX B:
Example of Assessment of Proficiency

Analysis for Gold in a Cycle of Four Test Samples for the Assessment of Proficiency

Results for all laboratories
  Analytical Results for Gold (m g/g)
Sample 1 Sample 2 Sample 3 Sample 4
Number Labs. 35 35 35 34
Mean Value 26.20 3.10 8.67 0.28
Stand. Dev. 1.11 0.98 1.11 0.074
Results for Laboratory 5
  Analytical Results for Gold (m g/g)
Sample 1 Sample 2 Sample 3 Sample 4
Result 27.71 3.55 8.50 0.47

Assessment of Proficiency of Laboratory 5

(1) z-Score

  Sample 1 Sample 2 Sample 3 Sample 4
z-score 1.36 0.46 -0.15 2.56
Rating Satisfactory Satisfactory Satisfactory Questionable

(2) Distribution of Absolute Values

Absolute z-Scores Rating
All z-scores < 3 Satisfactory

(3) Re-scaled Sum of z-Scores

l RSZ l Rating
l RSZ l = 2.37 Satisfactory

(4) Squared Sum of z-Scores

SSZ = 8.68

Χ 2 Table at n = 4

Χ2  
n = 4 Conf. Int. Rating
≤ 9.49 95% Satisfactory
> 9.49 ≤ 13.28 99%  
> 13.28 > 99%  

(5) Overall assessment is "Satisfactory."