“…Therefore, complexed matrices like fuels require sample preparation to convert them to aqueous phase [ [16] , [17] , [18] ]. Moreover, some of the metals in fuel oils are in trace levels (ppb-ppt) and require preconcentration step [ 12 ]. The most popular extraction and preconcentration methods reported for determination of metal ions in fuel oils are solid phase extraction (SPE) and liquid-liquid extraction (LLE) [ [19] , [20] , [21] , [22] , [23] , [24] ].…”