Comparison of three different analytical protocols for 2019 updated D2425 method for renewable jet fuel product certification analysis.

ASTM standard specification D7566 covers the manufacture of synthetic aviation turbine fuel components and their blends with conventional Jet fuel (Jet A or Jet A-1). One of the components is renewable jet fuel (RJF) which is synthetic paraffinic kerosene (SPK) made from hydroprocessed esters and fatty acids (HEFA). The specification D7566 dictates property requirements for the SPK-HEFA, including concentration limits for selected hydrocarbon types (paraffins, cycloparaffins, and aromatics), which are analyzed by using the mass spectrometry (MS) based standard method D2425. The most recent update for D2425 released in 2019 includes the synthetic hydrocarbon sample type (e.g., SPK-HEFA) and defines various analytical procedures for the analysis. Notably, the procedures differ considerably from each other, and the experimental conditions are not defined in details. This leads to laboratories setting up analytical schemes for D2425 that are likely to differ from each other, which may result in variation in the quality of the results obtained in different laboratories. In the present study, the performances of D2425 analytical protocols set up by three laboratories were tested in certification analysis (D7566) of SPK-HEFA type RJF. The tested analytical protocols were proven to comply with the requirements of the 2019 version of the D2425 standard. Furthermore, the precisions of the protocols did not differ significantly from each other. However, a significant bias was found for the results obtained for cycloparaffins and aromatics. Further, considerable differences were found in the bias values between the laboratories. Based on the results of this study, the guidelines of the 2019 updated D2425 standard may result in setting up an analytical protocol for D2425 which may not be optimal for RJF certification.

Bias, limit of detection, and limit of quantitation for the ASTM D2425 method updated in 2019.

An update for ASTM D2425, "Standard Test Method for Hydrocarbon Types in Middle Distillates by Mass Spectrometry," was recently released to expand its scope by adding modern mass spectrometric instrumentation and a new sample type, synthesized hydrocarbons. While the method update is a proper step towards modernization, it still lacks validation parameters. The description of the updated standard method contains precision estimations but no consideration for a possible bias, meaning that the method accuracy was not evaluated. The 2019 update does not either provide the lowest concentration of an analyte that can be detected and quantitatively determined, 'limit of detection' (LOD) and 'limit of quantification' (LOQ). In the present study, the LOD, LOQ, and bias were evaluated as an intra-laboratory study. The LOD and LOQ determination was based on the adjusted standard deviation of the least abundant hydrocarbon type in a sample, and were 0.004 and 0.01 w/w% in renewable jet fuel (RJF) and 0.01 and 0.02 w/w% in gas oil (GO), respectively. The bias was determined by measuring relative hydrocarbon recovery percentages for spiked samples. The renewable jet fuel was spiked with cycloparaffins and alkylbenzenes and the recovery percentages were 140% and 63%, respectively. The gas oil was spiked with paraffins and alkylbenzenes and the recovery percentages were 117% and 90%, respectively. Both sample sets were positively biased for paraffin content (recovery percentage over 100%) and negatively biased for alkylbenzene content (recovery percentage less than 100%). Based on above results, this method may not work well for RJF samples.