Researcher Robert Schwartz says it is just as reliable as a fingerprint. Using kitchen chemistry, sophisticated analytic machinery and off-the-shelf computer software, the U.S. Customs Service can determine the source country of virtually any agricultural product on Earth.

In the past 15 years, Schwartz, the senior research chemist at the Customs Research Laboratory in Springfield, has used his technique to track down smuggled pistachio nuts, underpriced garlic and fancy coffee spiked with cheap foreign beans. Going to court "would be interesting," he said, but it hasn't happened. The bad guys have always settled.

Schwartz's method detects "trace elements"--elements that have been ingested by a suspect plant from the soil where it was grown--and matches them with the trace element profiles of known samples. If Iranian pistachio nuts are masquerading as Turkish to elude the U.S. embargo against Iranian agricultural products, Schwartz will know it.

This month Schwartz is helping Customs analysts in San Francisco get started on the first field lab use of the technology. Their job is to find out whether shippers are illegally spiking bags of top-quality American walnuts with cheap Chinese imports, or bagging the Chinese nuts and calling them American.

With this technology transfer, also to be accomplished this year at two other field labs, Customs will have transformed one of its most exotic techniques into an everyday law enforcement tool: "We've been hardening the technology at the same time we've been doing sampling," said Paul Nicholas, the lab's acting director. "But the field labs get the samples, and they should be doing the testing."

As is the case for many federal law enforcement agencies, much of Customs' high-profile work involves illegal drugs, and the lab still does "aroma testing" to profile drug samples used to train sniffer dogs. It also provides smells for a burgeoning Customs program to enable dogs to detect money when criminal couriers are trying to smuggle it out of the country.

But Customs also must defend a host of trade agreements, sanctions and protocols involving almost every known product. The Springfield lab does everything from testing the polyester content of textiles (to see if countries are violating the Multi-Fiber Agreement) to determining whether a video game called "Cook Race" is a brilliant original creation or the illegal knockoff of a patented American game called "Burger Time" (it was a knockoff).

Customs has done country-of-origin analysis for years, using a variety of techniques. Agents have proved that smugglers have been in Mexico by testing their aviation gasoline for the signature dye used by Pemex, Mexico's state oil company.

Thermal analysis has produced a profile for the behavior of heated Iranian pistachio oil. Legendary Customs research chemist Bruce Pettitt could spot a Cuban cigar just by looking at the wrapper. And Pettitt once hired a coffee tester to see if he could tell the difference between arabica and robusta beans (no one remembers the result).

Schwartz began using trace elements analysis in 1984, when Customs charged him with defending U.S. markets from Brazilian orange juice trying to sneak into the United States duty-free under the Caribbean Basin Initiative, a popular Reagan administration program designed to give trade breaks to commodities produced in Caribbean island nations.

The Florida Citrus Commission had already pioneered the analysis, and Schwartz adopted it. By dissolving the substance in nitric acid and cooking it at high temperature and pressure, all the organic material boiled away as carbon dioxide, leaving only a liquid suspension containing nitric acid and "traces" of the inorganic elements--especially metals--unique to the soil of the country where the product was grown.

Schwartz diluted the solution, then fed it into a spectrometer, which determined the elements in the solution as it was converted into a fine mist by a nebulizer--a sophisticated atomizer. Schwartz started with an optical emission spectrometer, which records the elements by the light frequencies they emit. Nowadays he relies more on a mass spectrometer, which records the elements by weight.

What emerges from the spectrometer is a series of readings of various trace elements in the sample. Particularly useful are metals, anything from rubidium to molybdenum or zinc. Schwartz once found uranium in Chinese garlic and finds iron in practically everything, but he has never struck gold or silver.

By comparing the signature produced by his mix of readings to a "reference sample" from a known source country, Schwartz can tell whether a suspect specimen comes from the source country or somewhere else.

Schwartz said he never had many orange juice samples to test and cannot remember finding any Brazilian interlopers. But the method was in place, and a few years later a prolonged pistachio nuts investigation succeeded in uncovering extensive efforts to circumvent the Iranian embargo.

By this time, Schwartz had found a software package that could conduct simultaneous "multivariant analysis" of his entire menu of readings, enabling him to produce a sample's signature in a single, easy-to-read table without having to pore over the results element by element. Schwartz said multivariant analysis is "my contribution" to the process.

Getting reference samples can be difficult, because some of the suspect commodities come from countries or areas where U.S. representatives do not go. A Customs attache found Iranian pistachios in a Roman market. Another attache visited a Chinese farm to get raw peanuts prohibited from entry into the United States because of suspicions they harbored a dangerous virus.

And over the years, Schwartz's work has closely tracked U.S. trade policy. In the 1980s, he tested for South African macadamia nuts restricted by anti-apartheid legislation. In the early 1990s, he busted Vietnamese coffee beans trying to sneak into the United States in violation of the long-standing postwar trade embargo.

He has found Panamanian and Costa Rican coffee beans masquerading as Kona coffee from Hawaii. He has found Chinese garlic coming into the United States illegally under the North American Free Trade Agreement after the United States had imposed draconian anti-dumping duties.

In 1998, he tested 71 garlic samples from Mexico: 16 were Chinese, but only 28 were Mexican. Apparently China was cheating, but China wasn't the only one.

CAPTION: Customs researcher Robert Schwartz examines a sample before testing it for country of origin.

CAPTION: Plants contain distinctive quantities of elements from the soil where they were grown. Customs researchers pinpoint the host country by examining the profile of aluminum from a sample.