This report presents the results of the fourth inter-laboratory comparison for BTEX automatic analysers performed at the JRC Ispra from the 19th to the 22nd of September 2016. Twelve national reference laboratories with fourteen instruments participated in this exercise. Six concentration levels were tested during the inter-laboratory comparison. Benzene concentrations ranged from 1 to 50 µg/m3. The exercise was evaluated according to ISO 13528 methodologies for the evaluation of inter-laboratory proficiency assessment and the recommendation of the protocol N37 of the AQUILA network. Participating laboratories are identified as requested by the AQUILA protocol.
The report, compares reference and robust average values for the concentrations tested during the exercise, gives information on the technique and instrumentation used by each participant and shows the results of linearity tests, identification of outliers, repeatability, reproducibility and robustness of the methodology, and also parameters to evaluate laboratory results: repeatability score, bias and En values.
In general, the results showed a relative improvement with respect to the previous inter-laboratory exercises from 2013. This was mainly reflected in the inter-laboratory exercise reproducibility values of the C8 compounds (ethyl-benzene and xylenes). Repeatability and reproducibility values for benzene and toluene were approximately 4 % and 9 %, providing consistent robust values. Ethyl-benzene, m,p-xylene and o-xylene showed higher variability with repeatability values ranging from 6 to circa 7.5 % and reproducibility values between 12 and 14 %.