Comparison of different pre-treatment procedures for the determination of chromium in crude oil samples by GF AAS

In the present study three pre-treatment procedures were developed and compared following Cr determination by GF AAS: sample dilution with toluene, emulsion formation and direct sampling of crude oil. The limits of detection for the developed procedures were 1.9 ng g-1 for sample dilution with toluene, 2.8 ng g-1 for emulsion formation and 0.73 ng g-1 for direct sampling. The accuracy of the three procedures was assessed by analysis of NIST1085b and recovery tests. High recoveries and good agreement between found and certified values were obtained in all cases. However, results indicate that sample dilution with toluene is not recommended for samples below 15ºAPI. The other two procedures showed the same performance for the samples with different API degrees (8 to 38), but the direct sampling showed better sensitivity besides minimizing the chances of analyte losses or contamination.