To integrate the IUPAC “International Harmonized Protocol for the Proficiency Testing of Analytical Laboratories” providing a guidance for intercomparison and proficiency testing on environmental sampling issue.
Guidance on evaluating measurement uncertainty is sometimes needed in particular areas of measurement where, for instance, measurement uncertainty can become rather large and where some key approximations of the GUM guide might break down (Pendrill, L.R., Accred Qual Assur (2008) 13:671-674). It’s well known that large uncertainties can arise preparing, treating and collecting samples, in many different fields (environment, food, clinical, industry, mining). Theories on sampling, and related influences on the measurement results were already and formally presented in the 50’s. (Gy, P., Rev Ind Minerale, St-Etienne (1954) 36, 311-345). Different approaches and an international guidance has been recently published to tackle this issue.
Basically two cases can be considered with reference to the role of sampling in the assessment of a property:
– analysis of the whole of a lot to be assessed (this is the most rare case and the only one in which the sampling should be not considered);
– analysis of a portion of the lot to be assessed.
If the measurement result is used to assess the properties and the characteristics of a wider batch of material, or a contaminated soil area (from which the samples analyzed are collected and prepared) the measurement process will include sampling, any sample preparation steps and the analysis.
When sampling is part of the measurement process, it should be also part of a general scheme of quality assurance (QA) within a laboratory. To this end, the external quality control activities, commonly pursued by carrying out PTs, should be aimed also to give an external and independent assessment of the samplers’ (operators) performances.
The IUPAC International Harmonized Protocol for the Proficiency Testing of Analytical Laboratories (M. Thompson et al., Pure Appl.Chem. Vol.78, NÂ°1, pp.145-196, 2006), updating a previous version of the Protocol, is strictly focused on the analytical part of a chemical measurement process. This Protocol, as well as other international references establishing a guidance on this issue for wider fields of application, does not consider anyway the sampling phase.
Quite recent experiences on inter-comparison exercise and collaborative trials on soil sampling suggest the need to a better definition of harmonized protocol for carrying out such activities.
Scopes, fields of application, terminology, scheme, structure, organization, logistic aspects and the fundamental tools for performing this kind of exercise should be discussed in the project and defined by the envisaged protocol.
Equivalence and/or analogies between reference materials (routinely distributed among the laboratories within chemical PTs schemes) and references used for sampling (soil reference sampling, reference sampling target, etc.) have been even debated in the past years. Moreover, these aspects involve also the requirements that such references must have to be properly used in sampling PTs.
Starting from the experience on soil sampling intercomparison exercise, the project will output:
- a general guidance for carrying out proficiency testing on sampling, integrating the protocols already published on proficiency testing for chemical analyses;
- include simple example of application (where possible).
The protocol should indicate and tackle, for example, the following items:
- the scope and field of application;
- the terminology to be used;
- the critical issues in the organization and design of PT on sampling;
- the requirements requested for the reference (assigned) values;
- the methods to be applied for performance assessment;
- consideration on the interpretation to be given to the results of the PT and the quality of the information obtained.
May 2011 – project announcement published in Chem. Int. May-June, p. 22