GeoPT – a proficiency test for laboratories engaged in the analysis of geological materials

To celebrate the 25th anniversary of GeoPT we intend to publish a special thematic issue of Geostandards and Geoanalytical Research during 2021. Please see the announcement on our Home page.

Our Purpose – The GeoPT proficiency testing programme is designed to be part of the quality control system employed routinely by an analytical geochemistry laboratory engaged in the measurement of elemental compositions in geological materials. Through proficiency testing, a laboratory can monitor its analytical procedures on a regular basis to confirm reliable performance, detect unsuspected bias, and take appropriate remedial action if necessary. Accreditation agencies are increasingly requiring laboratories to participate in such programmes.

Our Record – GeoPT is the IAG’s longest established PT scheme. It has been helping laboratories around the world monitor the quality of their analytical data for twenty-five years. Over 55 test materials have been distributed, and currently more than 110 laboratories from every corner of the world participate. These include a wide spectrum of commercial, governmental and academic institutions undertaking a huge variety of analytical measurements.

Our Procedures – Test materials of established homogeneity, normally silicate rocks or comparable materials of geological origin, are distributed to participants at six-monthly intervals. The usual test material may occasionally be accompanied by a supplementary material of a different matrix type intended to be analytically more challenging. Laboratories should analyse the test material following their normal analytical procedures. A period of at least six weeks is allowed for laboratories to submit their results online through our web-based system.

Our Feedback – A report is made available online for participants to download normally within six weeks of the submission deadline. It contains: tabulations of all contributed results, identified by only by a code number to maintain complete anonymity; a listing of the assigned and provisional consensus values that represent best estimates of the true values of measurands in the test material; and tabulations of z-scores for all laboratories that provide a means of performance assessment for around 50 to 60 analytes. In addition, every laboratory may download a Certificate of Performance for each round.

Over the years, in addition to the individual reports for each round, GeoPT has stimulated the publication of various research papers. These have provided insights into the characterisation of new reference materials and their stability, the general performance of laboratories over many years, the merits and limitations of specific analytical procedures, and the development of statistics and protocols related to proficiency testing. A list of papers relevant to the GeoPT programme is available.

Our Steering Committee for the GeoPT programme comprises:

  • Prof Phil Potts, Chair (The Open University, Milton Keynes)
  • Dr Peter Webb, Administrator (formerly of The Open University, Milton Keynes)
  • Prof Michael Thompson, Statistician (Birkbeck College, University of London)
  • Dr Charles Gowing (British Geological Survey, Keyworth, Nottingham)

Full details about the operation and organisation of the scheme are available in the GeoPT protocol

For further information see:

To register an interest in future participation, visit our login page at