This method is for determining trace concentrations of non-volatile, hydrocarbon soluble forms of copper present in gasoline, naphtha, kerosene and similar distillates by either Flame-Atomic Absorption Spectrometry (Flame-AAS) or Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). It is particularly useful on products that have been copper sweetened. The lower limit of quantitation is 5mg/kg (mass-ppb) copper. The method can be extended to other organic materials and concentration ranges. This method can be used in place of UOP Method 144.