Method of tagging hydrocarbon fuels

A method for determining that a first liquid hydrocarbon bulk material has been blended with a second liquid hydrocarbon bulk material to form a third liquid hydrocarbon bulk material,

• each such liquid hydrocarbon bulk material comprising a mixture of components, wherein each liquid hydrocarbon bulk material elutes from a chromatograph as a chromatograph stream composed of elution time windows containing components of the mixture and elution time windows consisting essentially of carrier fluid flow;
• each such elution time window having a characteristic mass spectrum composed of a plurality of mass spectrum peaks;
• said method comprising
• adding to the first liquid hydrocarbon bulk material a known quantity of a first chemical component which is soluble in said first liquid hydrocarbon bulk material and elutes from a chromatograph in a predetermined elution time window of a chromatograph stream formed from a sample of the first liquid hydrocarbon bulk material containing the first chemical component, said first chemical component having at least one mass spectrum peak which is different from any mass spectrum peak in the predetermined elution time window which is due to any component of the first liquid hydrocarbon bulk material,
• performing a chromatographic/mass spec analysis of the first liquid hydrocarbon material containing the first chemical component and obtaining a first mass spec signal representative of the concentration of the first chemical component added to the first liquid hydrocarbon material;
• and
• performing a chromatographic/mass spec analysis of the third liquid hydrocarbon material and obtaining a second mass spec signal representative of a lower concentration of the first chemical component in the third liquid hydrocarbon material.