Key Topics

Principle 4

There should be a regular independent assessment of the technical performance of a laboratory.

Why Is It Important?

• An external benchmark gives you feedback on your laboratory's technical performance compared with other competent laboratories.
  
  There are a large number of pitfalls in the process of performing an analysis. However much care is taken, there may be some key unidentified factors which influence the results. The entire process from sample receipt to reporting results should be tested using samples and procedures which closely follow day-to-day work.
  
  If your laboratory is entering an unfamiliar area of work, new methods will have to be developed and validated (see VAM principle 2). Independent assessment of your performance in this area will provide further confidence in your ability to produce reliable results.
• Regular independent assessment can, if satisfactory, be used to demonstrate to customers your commitment to, and achievement of, quality.
  
  As a manager, you will be able to use data from external assessment for both internal management purposes, and as part of your strategy for winning new business. In some technical areas, participation in external assessment programmes is a legal requirement for carrying out some kinds of work.

What To Do

• Participate in an appropriate Proficiency Testing (PT) scheme.
  
  Although proficiency testing schemes exist for many of the more commonly executed types of analysis, there might not be any scheme with a sample which closely matches those routinely dealt with in your laboratory. You should aim for a scheme where you would apply the same analytical technique to a similar analyte/matrix combination at similar concentration levels.
  
  The PT samples should be treated in all respects as a routine sample, and the staff involved should not be specially selected. Find out if your customer can provide some suitable assessment materials. It might be satisfactory to arrange with the customer for assessment samples to be included in a batch of work. The assessment material must be stable, homogeneous and well characterised. This approach would be most valuable where no proficiency testing schemes exist.

Additional Information

In PT schemes, an independent and authoritative third party arranges for the distribution of appropriate test samples to laboratories. The organiser of the scheme collates the results which are returned by the laboratory on an agreed timetable, and analyses them statistically and prepares a report which enables laboratories to compare their performance with that of peer laboratories. All results are treated confidentially, and no individual laboratory's performance can be identified, except by itself.

Proficiency testing schemes exist for many of the more commonly executed types of chemical analysis. There cannot, however, be complete coverage of all types of analyses, and a laboratory might find that, for the type of analyses they were doing, no suitable PT scheme existed. In this case, it would be sensible for the laboratory to speak to the customer and discuss alternative arrangements, such as use of a reliable check sample. Proficiency testing schemes may differ in the way they are organised and administered. One of the major differences is whether or not it is left up to individual laboratories to choose the method of analysis, or whether the method is specified by the organisers. There may also be differences in the statistical treatment of the results from laboratories.

In some countries, laboratories have to demonstrate satisfactory performance in a PT scheme before they are allowed to carry out the particular analysis for 'official' or regulatory purposes. In the UK, this is not the way in which proficiency testing is used. However, it is open to accreditation or certification bodies, and customers, to ask to see the results of participation in appropriate PT schemes and to draw their own conclusions on the objective evidence provided.

Examples

Better analytical methodology through proficiency testing

If producers of margarine declare the amounts of fatty acids in their products, they must comply with the requirements of the EC Nutrition Labelling Directive. The analysis which is needed for this must separate the fatty acids according to chain length and degree of unsaturation, and separate the cis- and trans- geometric isomers. This is a difficult analysis to perform, and requires considerable analyst expertise and experience. When the Food Analysis Performance Assessment Scheme (FAPAS) organised their first test round for this analysis, about 40% of the participants produced satisfactory results. This reflected the challenging technical difficulties with this analysis. In subsequent rounds, the scheme organisers offered technical advice to participants, which resulted in an improvement to around 60% satisfactory results. Recognising that there was still scope for much further improvement, the scheme organisers have now commissioned the development and publication of a recommended validated method. The technical lessons learned from this will benefit laboratories carrying out this and similar analyses, and application of the method will enable them to meet the requirements of the Directive.

Supporting resources

• Proficiency Testing in Analytical Chemistry
• Using proficiency testing in the analytical laboratory - Training Course
• Proficiency Testing - Key Topic