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Local Round Robin Test for Determination of Aromatics in Diesel Fuels by HPLC

Determination of aromatics in diesel fuels by HPLC is covered by EN 12916 European Standard based on the former IP 391/90 and IP 391/95 standards. The method used for measurements is the normal phase HPLC and separation is performed on polar columns (silica or –NH2/-CN modified silica), and in the non-polar mobile phase (n-heptan) using RI detector. The columns have a little afinity to non-aromatic hydrocarbon (NHC), but a pronounced selectivity for aromatic (HC). As a result of selectivity, aromatic HC is separated from NHC and into distinct peaks according to their ring structure i.e. mono, di and tri+ aromatics. The last one with some heterocompounds elute as a single sharp peak due to a backflush valve. Precision of the method has been established for samples containing 4%-40%(m/m) mono, 0%-20%(m/m) di, 0%-6%(m/m) tri+, 0%-26%(m/m) poly and 4%-66%(m/m) total aromatics. Due to the increasing environmental requirements, the content of aromatics, specially polyaromatics in diesel fuel has a tendency to decrease. It is very important to check the method capability to follow the mentioned requirements with expected range of precision. We are using the opportunity to work on three different pieces of equipement on different locations to evaluate the method statistic, precision, ruggedness and robustness. Samples used in RRT were real ones known in Croatia as diesel or eurodiesel, collected from different sources at different time. The analyses have been performed on Waters (Lab I), Shimadzu (LabII) and Varian (Lab III) instruments with slightly different instrumental and working condition and a different way of measurment data evaluation. Repeatibility was measured by ten or more injections of the same sample under the same conditions and by the same operator in the particular lab. The reprducibility was evaluated by measuring the content of aromatics in twenty samples in all three labs. The results for repetibility showed that RSD for polyaromatics were from ą2.1%-10.3% and for total aromatics from 1.3%-3.0% . The awerage RSD for determined reproducibilities were ą19.7%, for polyaromatics and ą10.2% for total aromatics content. The inter-laboratory agreements were close to the proposed precision from the EN standard.

HPLC repeatibility; HPLC reproducibility; HPLC determination of PAH

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