Page 50: of Maritime Reporter Magazine (October 1973)

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Chemical Fingerprints Identify

Vessels Responsible For Spills

Scientists at the famed Woods Hole Oceano- graphic Institution, Woods Hole, Mass., are developing a precise method for identifying which ship has polluted the ocean with oil.

Using a gas chromatograph, they are learn- ing to take chemical "fingerprints" of individu- al batches of crude petroleum and petroleum products. By comparing the fingerprint of spilled oil to the fingerprints of oil from sus- pected sources, they can trace the spill to the particular ship, storage tank, underwater pipe- line or offshore oil well that is responsible for the spill.

Dr. Oliver Zafiriou, a research scientist at the Oceanographic Institution in Woods Hole, has worked extensively on the development of oil-fingerprinting, using a gas chromatograph manufactured by Varian Associates. He re- cently described his techniques in a paper in "Analytical Chemistry."

Petroleum and its products—such as gaso- line, fuel oil and jet fuel—are mixtures that may contain dozens of different hydrocarbons.

The complexity of these mixtures makes them hard to analyze; but it also provides the basis for precise identification of particular sour- ces— or even particular batches—-of oil.

Because so many different hydrocarbons are involved, it is virtually impossible for the oil from two different sources to be precisely iden- tical in composition. Crude petroleum from one well will contain more of certain hydro- carbons and less of others than petroleum from a neighboring well. Fuel oil from one re- finery will not be exactly like oil from another refinery. Even successive batches of oil from the same refinery will be slightly different from each other in their hydrocarbon compo- sition.

Detecting such subtle differences requires a very sensitive analytical method. The Varian gas chromatograph that Dr. Zafiriou uses at

Woods Hole is one of the most precise analy- tical instruments ever developed for this kind of work.

An oil sample is vaporized as it enters the chromatograph, and the vapor then passes into a tube of absorptive material. As they move through this material, different hydrocarbon substances in the sample are retained for dif- ferent periods of time before they emerge from the other end of the tube.

This is the key to identifying each substance —measuring its "retention time" in the tube.

As each substance emerges from the chrom- atograph tube, it is sensed by a detector, which sends a signal, to a recorder. The recorder im- mediately draws a peak on a paper chart, thus registering the retention time of that substance.

By comparing each observed retention time to a list of known retention times for known hydrocarbons, each hydrocarbon in the origi- nal sample can be identified.

More importantly, the gas chromatograph also shows how much of each hydrocarbon was contained in the sample. The size of the peak drawn by the recorder precisely indicates the quantity of the hydrocarbon corresponding to that peak.

The completed fingerprint of the sample, then, is a series of peaks that tell which sub- stances, and how much of each, were in the original sample. An oil spill can be traced by comparing its fingerprint to the fingerprints of oil from suspected sources, until a match is found.

Using this technique, Dr. Zafiriou was able to distinguish many different types of crude petroleum and fuel oils gathered in the hart>ors at Portland, Maine, and New York City.

Dr. Zafiriou also tackled the fingerprinting and tracing of oil spills that have lain exposed to the sea, the sun and the air for a consider- able period of time.

This is an important practical problem : An oil spill may not be discovered or sampled un- til several days after it occurs. During that time, the composition of the oil may change significantly, as certain hydrocarbons evapor- ate and others undergo chemical change. For this reason, scientists and Government officials who are interested in tracing spills are seeking methods that will be valid for "weathered" spills as well as for fresh ones.

Dr. Zafiriou took 35 samples of oil from 17 different sources and subjected them to artificial weathering-conditions that would simulate the effect of sun and air on a spill at sea. Even .after this weathering, gas-chromatographic fingerprints of these samples permitted them to be matched to their original sources with a high degree of accuracy.

Concluding his article in "Analytical Chem- istry," Dr. Zafiriou points out that his tech- niques can be further refined through more re- search. But, he observes, gas chromatography even now offers a practical method for pinpoint- ing the source of an oil spill. He believes that it is feasible for scientists to begin building up libraries of the gas-chromatographic finger- prints of crude petroleum and its products, to be used in tracing actual oil spills and leaks.

Varian Associates, headquartered at 611

Hansen Way, Palo Alto, Calif. 94303, is a lead- ing manufacturer of analytical instruments and computing equipment used in science, medi- cine, engineering and industry.

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