The question was a bit unusual for the typical course in quantitative chemical analysis, but Randolph Larsen, an assistant professor at St. Mary's College of Maryland, asked anyway:

Is our currency covered in cocaine?

That question led to others. Was it likely that there would be more cocaine on one-dollar bills, fives or twenties? Mandie Schabdach, a 19-year-old junior, had a theory.

"I think it would be more on the twenties. If you're doing, like, a big drug deal, then you'd have a lot of twenties," she said.

This month, Larsen's chemistry class set out to find answers. This was the second time he had brought this experiment into his lab. A year before, he had his class perform the tests, which are based on similar studies elsewhere, as a way to get the students engaged and to practice techniques they could use to analyze other chemicals in real-world situations.

"This isn't cutting-edge research, it's a training exercise for the students," he said. "But I think they get a kick out of it more than the normal experience of going to the lab."

In the first year, the class tested currency from around the world to see whether it was possible to identify a correlation between the amount of cocaine on the bills and a country's gross domestic product. While no such link was found, the class found that 70 percent of the bills tested had traces of cocaine on them, levels greater than 140 nanograms (1 billionth of a gram). The highest concentrations, above 20,000 nanograms, were found on bills from Canada, England and the United States.

This time, the class wanted to look at bills of various denominations that Larsen obtained from a Calvert County bank on the day of the tests.

"Make sure I get all my money back," Larsen told his students.

To begin, the students folded the bills and put them in small vials with a mixture of the volatile liquids hexane and acetone. Then they put the vials in a sonicator, a machine the size of a big toaster that bombarded the vials and their contents with high-frequency sound waves so the traces of cocaine would be dislodged from the money into the solvent. Then the mixture was poured into evaporating tubes to reduce the amount of solvent and filtered to remove currency gunk such as dirt and grime.

To determine the amount of cocaine on the bills, each sample was run through a machine called a gas chromatograph-mass spectrometer, which can separate compounds by molecular weight. The machine was purchased with financing from the National Science Foundation, Larsen said.

"It allows us to do these kinds of advanced-level experiments with undergraduates," he said.

The initial results of the experiment showed that 19 of 21 bills sampled yielded measurable amounts of cocaine, he said.

Larsen said the conventional wisdom on such cocaine and currency experiments is that the relatively small number of bills that are used by drug abusers to snort cocaine are able to contaminate a large percentage of currency when they are mixed with other bills in money-counting machines, cash registers or ATMs.

A much larger sample should be tested to arrive at more definitive results on the proportion of circulating bills contaminated by cocaine, Larsen said. The students won't determine the relative frequency of cocaine traces on the denominations for a few weeks, he said.

"This is pretty cool," said Aaron Crapster, 20, a senior who participated in the experiment. "It's just a neat chance to think about drug trafficking and how it has infiltrated the currency; that's kind of exciting."

The students said they do not believe that cocaine use is prevalent on their campus.

"There are only like 1,800 people here, and most of them are really, really, really smart," Schabdach said.

"We don't have time to do cocaine," another student added.

Randy Larsen, an assistant professor of chemistry at St. Mary's College of Maryland, discusses a lab project with students Thursday.A St. Mary's College student shows a bill that she tested for traces of cocaine in chemistry lab using gas chromatography-mass spectrometry.

St. Mary's College of Maryland students Melanie Barner and Chris Cooper conduct chemical analyses of currency.