For measurement uncertainty for routine measurements we recommend the Nordtest TR537, www.nordtest.info together with the MUkit software. An example of a summary report using MU is shown below. The software also provides a full detailed report of your uncertainty calculations.

  FAQ for Nordtest 537 (2017)    Here are questions and answers on this handbook     Printing error?  Example A:  BOD with Internal quality control+ a CRM  in part 4 it shows a term sbias2/√n, should read (sbias/√n)2 ? Reply: This is missing a parenthesis THANKS. The parenthesis is shown in next part of the formula.     GENERAL   Is this approach ISO GUM compatible?d Reply: This handbook follows the GUM principles of uncertainty and is widely used by accredited laboratories in many different sectors.   BIAS    1.      Calculation of u(bias) from a bias limit  If a method has an acceptable bias limit of say ± 10%, and the data is within these limits this can lead to very high expanded uncertainties in some cases- can this be corrected or is it just the ‘natural’ consequence of high bias levels? Reply: If instead of applying  the measured bias you use the acceptable bias limit in the formula you can regard this as a rectangular distribution (i.e. the bias is anywhere within these limits for all samples within the scope of the method) and then  divide by sqrt3 to get a standard uncertainty. If we take data from the EU drinking water directive where max bias is 10 % and max precision is 5 % (2 sRw  max 10 %) at the relevant level for many parameters, the expanded uncertainty can then be calculated to be about 15 % relative.  See further details on page 158 in a chapter on  measurement quality  in a book  2.  How to calculate bias using recovery data  In section 6.3 Recovery is an example of a validation of 6  different matrices . For  each  matrix we have a mean recovery and the overall mean recovery is 96,8 %. We use the same formula as for several CRM. The RMS of these values are 3,44 %. NOTE The guidance given in this section is applicable for test methods that do not include a recovery correction in the procedure for each analytical run. If however you have a fixed recovery in your method then you can validate the method with new experiments and use the same formula. The  MUkit software  handles recovery where at least 6 matrices are tested.    3. Sampling uncertainty  In order to estimate  measurement  uncertainty for a sampling target also the sampling uncertainty should be estimated. Here you can use duplicate sampling according to Nordtest 604. The  measurement  uncertainty can then be calculated by combining the  u (sampling) with the  u (analysis) where the  u (analysis) is estimated from Nordtest 537.       

FAQ for Nordtest 537 (2017)

Here are questions and answers on this handbook

Printing error?
Example A: BOD with Internal quality control+ a CRM in part 4 it shows a term sbias2/√n, should read (sbias/√n)2 ?
Reply: This is missing a parenthesis THANKS. The parenthesis is shown in next part of the formula.
 

GENERAL

Is this approach ISO GUM compatible?d
Reply: This handbook follows the GUM principles of uncertainty and is widely used by accredited laboratories in many different sectors.

BIAS

1.    Calculation of u(bias) from a bias limit
If a method has an acceptable bias limit of say ± 10%, and the data is within these limits this can lead to very high expanded uncertainties in some cases- can this be corrected or is it just the ‘natural’ consequence of high bias levels?
Reply: If instead of applying  the measured bias you use the acceptable bias limit in the formula you can regard this as a rectangular distribution (i.e. the bias is anywhere within these limits for all samples within the scope of the method) and then  divide by sqrt3 to get a standard uncertainty. If we take data from the EU drinking water directive where max bias is 10 % and max precision is 5 % (2 sRw  max 10 %) at the relevant level for many parameters, the expanded uncertainty can then be calculated to be about 15 % relative.

See further details on page 158 in a chapter on measurement quality in a book

2. How to calculate bias using recovery data
In section 6.3 Recovery is an example of a validation of 6 different matrices. For each matrix we have a mean recovery and the overall mean recovery is 96,8 %. We use the same formula as for several CRM. The RMS of these values are 3,44 %. NOTE The guidance given in this section is applicable for test methods that do not include a recovery correction in the procedure for each analytical run. If however you have a fixed recovery in your method then you can validate the method with new experiments and use the same formula. The MUkit software handles recovery where at least 6 matrices are tested. 

3. Sampling uncertainty
In order to estimate measurement uncertainty for a sampling target also the sampling uncertainty should be estimated. Here you can use duplicate sampling according to Nordtest 604. The measurement uncertainty can then be calculated by combining the u(sampling) with the u(analysis) where the u(analysis) is estimated from Nordtest 537.