Comparative study of sample decomposition methods for the determination of total Hg in crude oil and related products

This paper presents a comparative study of three decomposition methods (A, B and C) for the determination of total Hg (THg) in crude oil and related products by cold vapor atomic absorption spectrometry (CV-AAS). Methods A and B employed closed-pressurized (HPA-S) and cold-finger systems, respectively. Method C employed a pyrolysis system. Some procedures were introduced to improve the weighing of samples in quartz boats, as well as for the cleaning of the boats, after sample pyrolysis. Also, the weighing of samples and their transfer into the cold-finger vessels, which were too long and heavy, were facilitated. Furthermore, the digestion time of the sample in the HPA-S was optimized. Spiked certified reference materials and one spiked crude oil sample were used for accuracy tests. Satisfactory recoveries (75–123%), repeatability and reproducibility (RSD ≤ 14%) for the THg results were obtained for all tested methods. Also, the THg concentrations in crude oil and oil sludge samples obtained by all tested methods were statistically similar. Although method B is commercially available in a low cost and can simultaneously pre-treat many samples, it showed the highest blank concentration, the highest LOQ, the longest digestion time and a high burst risk.

► Three sample decomposition systems were compared for determination of THg in oils.
► Improvements were introduced for weighing of samples.
► Cold-finger vessels presented high burst risk.
► High pressure asher system presented the lowest detection limit.
► Pyrolysis system showed the lowest blank measurement.