The document discusses measurement uncertainty (mu) in testing laboratories, particularly in the context of gold fire assay, highlighting the definitions, sources, and types of errors involved. It emphasizes the importance of accuracy and precision, as well as the necessity of following ISO 17025:2017 standards for evaluating measurement uncertainty. The document also outlines seven basic steps for determining mu and includes a general formula for its calculation.

1. Measurement Uncertainty
for testing Laboratories (bias
on gold fire assay)
Author: Selwyn Dickson

2. What is Measurement Uncertainty(MU)?
Definition: The margin of doubt that exists for the result of any measurement, as well as how
significant the doubt is.
In simple terms: It is the error in measurement , that is unavoidable and should be
accounted for in testing.

3. Terms associated with MU
• Trueness- Theoretical scientific value that cannot be obtained
practically. E.g. theoretical density of water is 1 g/cmᶟ but rather the
experimental average is 0.9998 g/cmᶟ.
• Accuracy- the closeness of experimental results to the true value.
• Precise- the closeness of experimental results to each other.
Source: CNX Introduction to CHEM
QUESTION: Which one is more important between Precision & Accuracy?

4. Sources of Uncertainty

5. 2 Types of Errors in MU
• 1.Random Errors
These are caused by unknown and unpredictable changes in the
experiment. This may include:
• temperature changes
• air pressure changes
• other environmental changes etc

6. 2 Types of Errors in MU
• 2.Systematic Errors
These result mostly from measuring devices being worn out or are out of
calibration.
Systematic errors may include:
• Calibration changes
• Instrument errors
• Change of standards used in calibration
• Wrong experiment procedures
• Incorrectly prepared reagents

7. Example of MU inception in Gold Cupellation
Fire Assay Method
• Preparation of Nitric acid solution for partying (gold-silver separation)

8. Example of MU inception in Gold Cupellation
Fire Assay Method
• Weighing of sample, silver and copper.

9. Example of MU inception in Gold Cupellation
Fire Assay Method
• Folding of samples in lead cones

10. Example of MU inception in Gold Cupellation
Fire Assay Method
• Placing samples in the furnace.

11. Example of MU inception in Gold Cupellation
Fire Assay Method
• Hammering of beads

12. Example of MU inception in Gold Cupellation
Fire Assay Method
• Stripping of beads

13. Example of MU inception in Gold Cupellation
Fire Assay Method
• Partying timing (Au-Ag separation) using nitric acid

14. Example of MU inception in Gold Cupellation
Fire Assay Method
• LIMS software

15. Example of MU inception in Gold Cupellation
Fire Assay Method
• Lab ventilation and conditions
• (temp & humidity)
NB: The mentioned uncertainties
Are not the only ones, a lot more
remain!!

16. ISO17025:2017 standard comments on MU
Clause 7.2.1
The laboratory shall use appropriate methods and procedures for all laboratory activities and, where
appropriate, for evaluation of the measurement uncertainty as well as statistical techniques for analysis
of data.
Clause 7.2.2.1.f Method validation shall be as extensive as necessary including:
evaluation of measurement uncertainty of the results based on an understanding of the theoretical
principles of the method and practical experience of the performance of the sampling or test method.
NOTES: According to the ISO standard, It is mandatory to prioritize MU and its evaluation in a testing lab,
especially that is accredited.

17. 7 Basic steps to determine MU
1.Specify the Measurement Process.
2.Identify Sources of Uncertainty.
3.Quantify Sources of Uncertainty.
4.Characterize Sources of Uncertainty.
5.Convert Uncertainties to Standard Deviations.
6.Calculate the Combined Uncertainty.
7.Calculate the Expanded Uncertainty.

18. General formula for calculation of mu
• Measurement Uncertainty (MU) = √ [∑ (xi – μ)2 / (n * (n-1))]
• Where xi is reading(measured value)
μ is mean
n is number of tests

19. What is
Standard Expanded Uncertainty?
Combined Expanded Uncertainty?

20. ASK ME ANYTHING of course not about my
breakfast

21. THE END
• SAD TO SEE YOU GO
Presentation by Selwyn Dickson