gh IDENTIFICATION OF GASOLINE, OR CHEMISTS HELP CRIMINALISTS

Researchers from the Institute of Petroleum Chemisorption, Siberian Branch, Russian Academy of Sciences (Tomsk) have developed a simple but very efficient method of motor gasoline marking for subsequent identification. The method is based on introduction of negligibly small amounts of special markers into the gasoline composition. The zest of the method is that nothing “alien”, atypical should be added to gasoline. On the contrary, everything to be added is its own, native, but in “nonnative”, unusual quantities. A special method should be applied to discover “one’s own among natives” – the method that was developed by a researcher Sergey Nekhoroshev and his colleagues under the guidance of Professor Anatoly Golovko, Doctor of Science (Chemistry).

At first sight, the essence of the method is simple enough. The point is that any gasoline, including motor gasoline – is mainly a mixture of carbohydrates, the molecules of which have five to ten carbon atoms. This is the lightest of liquid fractions. However, there are longer carbohydrates in gasoline, the carbonic “skeleton” of which consists of twenty and more carbon atoms. They are not of course numerous, but they are always present. So, if a known quantity of such “long” carbohydrates (their chain length being known in advance) is added to the initial gasoline, these carbohydrates will become forever a unique marker of this gasoline batch, the marker enabling to identify the source of gasoline practically for sure – like an individual can be identified by fingerprints. However, this marker can not be “made out” in an ordinary way. But if the sample is properly prepared, it is no trouble at all.

Of course, the authors started with thorough analysis of ordinary motor gasoline. Thus, they identified how many relatively “long” n-alkanes (paraffin hydrocarbons, in the molecules of which carbon atoms are bound to each other in long non-ramified chains) are contained in it. It has turned out that the A-92 gasoline contains indeed very few n-alkanes with the chain length of 15 to 28 carbon atoms – from hundredths through ten-thousandths of a percent. At that, the “longer” carbon is, the less is its content in gasoline, which is clear in principle – should n-alkanes be numerous, this would have been not gasoline but kerosene or even black oil fuel.

Then the most interesting part begins. The authors added a little of n-tetracosane into gasoline (its molecule contains 24 carbon atoms). The researchers added a tiny bit of it - 20 mg per 1 kg of gasoline, and tried to evaporate gasoline in a warm air current, they evaporated gasoline thoroughly, so that the sample mass reduced by 15 and by 700 times! And them they analyzed the residuum. A similar experiment was made on the initial, “non-marked” gasoline.

It has turned out that the ordinary analysis allows in principle to see the difference in the C-24 content between the initial and marked samples, but it is not striking. Absolute content of this substance in gasoline is insignificant – the researchers have to look for the little against a background of the huge. On the other hand, it is practically impossible not to notice tetracosane in the smaller part of the sample after evaporation of its larger part! The chromatogram of the marked gasoline evaporated by 700 times shows the tetracosane peak raises above the others like the Eiffel Tower dominated Paris in its younger years.

As the authors have determined that it is possible to mark gasoline by different n-alkanes (from C-20 through C-30), it’s no trouble at all to add a track quantity of these substances to gasoline directly during the production (a mixture of individual content to be added to each batch), and it’s a sure thing! Such marking will be concealed, stable and simple enough for discovering in gasoline per se, and in its leavings after storage or even in combustion materials. And this, in its turn, will help criminalists to solve a whole series of problems. For example, to reveal distribution channels of counterfeited and stolen gasoline. And, if required, to determine what particular gasoline was used by criminals, for example, when committing arson.

***