Outcome of a proficiency test with individual laboratory results, assigned value and tolerance limits (blue and red lines)

Source: BAM, Organic Trace and Food Analysis division

Mineral oil based fuels and lubricants belong to the most important contaminants in soils and sediments. Their quantification as total petrol hydrocarbons (TPH) has been done for about 20 years using gas chromatography flame ionization detection (GC-FID) which replaced the formerly employed infrared spectroscopic procedure after extraction with a meanwhile banned fluorochlorohydrocarbon solvent. Routine analysis of environmental samples is done in accredited testing laboratories (small and medium enterprises). BAM offers certified reference materials for the internal quality assurance in testing laboratories. These include the standard TPH mix for the calibration of the gas chromatographs as well as matrix reference materials – soil samples with known TPH content - for the checking of the complete analytical procedure in the laboratories. In addition BAM operates the proficiency testing scheme „Contaminated sites“ for routine laboratories. Herein, the participating laboratories need to quantify the TPH content in soil samples with TPH contents unknown to them. The image depicts the result of a proficiency test with 37 laboratories. The individual laboratory in interested in a result within the tolerance limits of a given test round. The relative reproducibility standard deviation SR rel. is a measure for the scatter of individual laboratory results, in the depicted case 14.7%. This article elaborates on the development of SR (rel) which amounted to 30 – 50% directly after introduction of the GC-FID procedure and decreased to currently 10 – 20% and discusses the improvement of the comparability of results from different laboratories.

Fifteen years of proficiency testing of total petrol hydrocarbon determination in soil: a story of success
Roland Becker, Andreas Sauer, Wolfram Bremser
Accreditation and Quality Assurance, Volume 24, Issue 4, pp 289-296, 2019
BAM Department Analytical Chemistry; Reference Materials and Division Organic Trace and Food Analysis