Comparing apples and oranges: Handheld technology detects chemicals on store produce

Purdue University researchers recently took their miniature mass spectrometer grocery shopping to test for traces of chemicals on standard and organic produce.

In the technology's first venture out of the lab, it successfully identified specific chemical residues on apples and oranges in a matter of minutes right in the produce section without having to peel or otherwise prepare a sample of the fruit.

R. Graham Cooks, the Henry Bohn Hass Distinguished Professor of Chemistry, and Zheng Ouyang, an assistant professor of biomedical engineering, led the team that used the miniature mass spectrometer - that some have likened to Star Trek's "tricorder" - to test for a fungicide on oranges and a scald inhibitor on apples.

"We're trying to take powerful, sophisticated instruments out of the lab and into the real environment where they could help monitor fresh produce all along the supply chain from production and supply to the consumers," said Cooks, who is co-founder of Purdue's Center for Analytical Instrumentation Development. "This technology has the capability of testing for bacteria as well, like E. coli or salmonella, and it only takes a matter of minutes as opposed to hours or even days for a standard laboratory test."

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A miniature mass spectrometer invented by Purdue scientists can almost immediately detect contaminants in the field including E. coli, pesticides and other chemicals. Using the mobile device is faster than sending specimens to labs for testing.

Mass spectrometry is a commonly used analysis method known for its sensitivity and accuracy; however, most available mass spectrometers require that a sample be specially prepared and placed in a vacuum chamber for analysis. Cooks and his team developed a technique, called ambient ionization, that allows critical steps to be performed in the air or directly on surfaces outside of a mass spectrometer. Molecules from the sample's surface of the sample are then vacuumed into the equipment for analysis.

Conventional mass spectrometers also are cumbersome instruments that weigh more than 300 pounds. The miniature mass spectrometer Cooks' team developed, called the mini 10.5, is a handheld device roughly the size of shoebox that weighs 22 pounds.

"Accuracy is the price we pay for a much faster, cheaper and easier technology that can be taken out into the field almost anywhere," Cooks said. "The minis are not as precise as a standard mass spectrometer, but it would be a good first line defense to indicate when additional testing is necessary."

Fred Whitford, coordinator of the Purdue Pesticide Programs, said the ability to sample food quickly would be a great benefit to the regulation industry.

"Sometimes a test result comes too late and the food is already out, which can be a serious problem," Whitford said. "Currently only about 2 percent of the food is pulled and tested, and perhaps a faster and cheaper test would allow more samples to be taken."

The U.S. Department of Agriculture's most recent report stated that chemical residues exceeded the legal limits on 0.3 percent of the samples tested and 2.7 percent of the samples tested were found to have pesticides not approved for that crop, Whitford said.

"Chemicals can be misused in a variety of ways," he said. "Sometimes they are applied in the wrong amounts, sometimes the crop is harvested too soon after chemical application and sometimes a chemical is used that is not approved."

Graduate student Santosh Soparawalla and postdoctoral researcher Fatkhulla Tadjimukhamedov performed the grocery store field tests, which were limited to detecting the fungicide benzimidazole on oranges and the scald inhibitor diphenylamine on apples. Scald is a brown discoloration that appears on apples during storage.

"We could easily distinguish between treated produce, which had a strong signature for the chemicals, and organic produce, which showed no chemical residue on its surface," Soparawalla said. "This could be the first step toward a day when everyone will have the ability to make an informed decision of what they want to purchase and eat based on an analysis of the specific items."

In addition to the pilot test to validate the technology in the field, the team evaluated the quantities of diphenylamine, or DPA, present in a treated apple. The U.S. Environmental Protection Agency's limit for the concentration of DPA on an apple is 10 parts per million.

The team estimated a concentration of 15 parts per million of DPA was present on an apple, but the margin of error for the test is large enough that the concentration could easily be within the regulated limits, Soparawalla said.

"These tests of apples demonstrate how this technology could be a part of a larger regulatory system. The experiments were not a robust scientific examination of the levels of chemicals present on produce," Cooks said. "The test is what's called a factor of two test, meaning the actual concentration could be half or could be twice as much as the approximation. The results were not statistically above the legal limit, but it is food for thought."

The team also examined the distribution of the chemical in a cross section of the apple and found DPA throughout, with the greatest concentrations in the skin and near the core of the apple, Cooks said.

"It appears that washing or peeling an apple may not reduce one's exposure to the chemical much," Cooks said. "If the approximate levels held true, eating one apple a day would bring a person to the daily limit of exposure to diphenylamine."

The team found that benzimidazole was limited only to the skin of the orange.

The team tested two ambient ionization methods. Both involve ionizing molecules on a sample's surface. This ionization step gives charge to the molecules and allows them to be identified by the mass spectrometer.

In the first method, called paper spray ionization, a sample is wiped with a common lens wipe wet with alcohol. A small triangle is then cut from the wipe and placed on a special attachment of the miniature mass spectrometer where a high voltage is applied. The mixture of alcohol and residues from the sample's surface become fine droplets containing ionized molecules that pop off of the wipe and are vacuumed into the mass spectrometer for analysis.

In the second method, called low temperature plasma ionization, a special probe sprays a collection of charged particles onto the sample's surface using a slow stream of helium gas. The charged particles ionize molecules on the sample's surface, which then bounce off the surface and are vacuumed into a mass spectrometer for analysis.

This work was presented on Tuesday (June 7) at the American Society for Mass Spectrometry annual meeting in Denver. Funding from the National Science Foundation and Thermo Fisher Scientific supported this work.

The paper spray ionization method is licensed to the Alfred Mann Institute for Biomedical Development at Purdue University, and the low temperature plasma ionization method is licensed to Thermo Fisher Scientific Inc.

Provided by Purdue University (news : web)

An analyzer to measure the quantity and size of pollutants and aerosols in smoke emission

Chiang Mai University researchers invented an analyzer capable of measuring the quantity and size of pollutants and aerosols in smoke emissions, providing an equally accurate, lower-priced, local Thai substitute for pollution monitoring equipment imported from abroad.

CMU researchers invented an analyzer capable of measuring the quantity and size of pollutants and aerosols in smoke emissions, providing an equally accurate, lower-priced, local Thai substitute for pollution monitoring equipment imported from abroad. Small particles resulting from combustion processes in a variety of sectors including the burning of industrial waste, transportation (exhaust), and agriculture create environmental and health problems. Monitoring and controlling pollution levels is crucial. Producing an accurate, locally available and lower-priced emissions analyzer will make it easier to monitor air pollution levels in Thailand.

One of the researchers, Assoc. Prof. Dr. Nakorn Tippayawong, Department of Mechanical Engineering, Faculty of Engineering, Chiang Mai University, informed that the underlying system developed to measure aerosols modeled on electrical principles can be used to measure soot particles from burning. The emissions analyzer is made from materials, equipment and production technology produced inside Thailand. The analyzer is accurate, provides multi-channel measurement that can be conducted simultaneously, and produces results rapidly. It also includes automation and process control measurement software. The system is safe and uses low voltage. Moreover, the analyzer is less expensive than the comparable tool imported from abroad.

The research team is composed of Assoc. Prof. Dr. Nakorn Tippayawong from the Faculty of Engineering, Chiang Mai University and Dr. Panich Intra from the College of Integrated Science and Technology, Rajamangala University of Technology Lanna. The project is supported by NECTEC : Thailand : National Electronics and Computer Technology Center. The project was awarded the “Invention Awards Honor for Year 2011 of National Research Council Award” in the field of Engineering and Industrial Research.

Provided by Chiang Mai University

Chemistry with sunlight: Combining electrochemistry and photovoltaics to clean up oxidation reactions

The idea is simple, says Kevin Moeller, PhD, and yet it has huge implications. All we are recommending is using photovoltaic cells (clean energy) to power electrochemical reactions (clean chemistry). Moeller is the first to admit this isn't new science.

"But we hope to change the way people do this kind of chemistry by making a connection for them between two existing technologies," he says.

To underscore the simplicity of the idea, Moeller and his co-authors used a $6 solar cell sold on the Internet and intended to power toy cars to run reactions described in an article published in Green Chemistry.

If their suggestion were widely adopted by the chemical industry, it would eliminate the toxic byproducts currently produced by a class of reactions commonly used in chemical synthesis — and with them the environmental and economic damage they cause.

The trouble with oxidation reactions

Moeller, a professor of chemistry in Arts & Sciences at Washington University in St. Louis, is an organic chemist, who makes and manipulates molecules made mainly of carbon, hydrogen, oxygen and nitrogen.
One important tool for synthesizing organic molecules — an enormous category that includes everything from anesthetics to yarn — is the oxidation reaction.

"They are the one tool we have that allows us to increase the functionality of a molecule, to add more "handles" to it by which it can be manipulated," says Moeller.

"Molecules interact with each other through combinations of atoms known as functional groups," he explains. "Ketones, alcohols or amines are all functional groups. The more functional groups you have on a molecule, the more you can control how the molecule interacts with others."

"Oxidation reactions attach functional groups to a molecule," he continues. "If I have a hydrocarbon that consists of nothing but carbon and hydrogen atoms bonded together, and I want to convert it to an alcohol, a ketone or an amine, I have to oxidize it."

In an oxidation reaction, an electron is removed from a molecule. But that electron has to go somewhere, so every oxidation reaction is paired with a reduction reaction, where an electron is added to a second molecule.

The problem, says Moeller, is that "that second molecule is a waste product; it's not something you want."

One example, he says, is an industrial alcohol oxidation that uses the oxidant chromium to convert an alcohol into a ketone. In the process the chromium, originally chromium VI, picks up electrons and becomes chromium IV. Chromium IV is the waste product of the oxidation reaction.

In this case, there is a partial solution. Sodium periodate is used to recycle the highly toxic chromium IV. A salt, the sodium periodate dissociates in solution and the periodate ion (an iodine atom with attached oxygens) interacts with the chromium, restoring it to its original oxidation state.

The catch is that restoring the chromium destroys the periodate. In addition, the process is inefficient; three equivalents of periodate is consumed for every equivalent of desired product produced.

Seeking cleaner byproducts

"All chemical oxidations have a byproduct, says Moeller, so the question is not whether there will be a byproduct but what that byproduct will be. People have starting thinking about how they might run oxidations where the reduced byproduct is something benign."

"If you use oxygen to do the oxidation, the byproduct is water, and that is a gentle process," he says.

But there is a catch. Like all other molecules, oxygen has a set oxidation potential, or willingness to accept electrons. "So whatever I want to oxidize in solution has to have an oxidation potential that matches oxygen's. If it doesn't, I might have to change my whole reaction around to make sure I can use oxygen. And when I change the whole reaction around, maybe it doesn't run as well as it used to. So I'm limited in what I can do," Moeller says.

Enlarge

?Electrochemistry can oxidize molecules with any oxidation potential, because the electrode voltage can be tuned or adjusted, or I can run the reaction in such a way that it adjusts itself. So I have tremendous versatility for doing things,? says Kevin Moeller, professor of chemistry at Washington University in St. Louis. Moreover, the byproduct of electrochemical oxidation is hydrogen gas, so this too is a clean process.Bit electrochemistry can be only as green as the source of the electricity. The answer is to use the cleanest possible energy, solar energy captured by photovoltaic cells, to run electrochemical reactions. Credit: David Kilper/WUSTL

There's another way to do it. "Electrochemistry can oxidize molecules with any oxidation potential, because the electrode voltage can be tuned or adjusted, or I can run the reaction in such a way that it adjusts itself. So I have tremendous versatility for doing things," says Moeller.

Moreover, the byproduct of electrochemical oxidation is hydrogen gas, so this too is a clean process.

But again there is a catch. Electrochemistry can be only as green as the source of the electricity. If the oxidation reaction is running clean, but the electricity comes from a coal-fired plant, the problem has not been avoided, just displaced.

The answer is to use the cleanest possible energy, solar energy captured by photovoltaic cells, to run electrochemical reactions.

"That's what the Green Chemistry article is about," says Moeller. "It's a proof-of-principle paper that says it's easy to make this work, and it works just like reactions that don't use photovoltaics, so the chemical reaction doesn't have to be changed around."

The next step

The Green Chemistry article demonstrated the method by directly oxidizing molecules at the electrode. No chemical reagent was used. Since writing the article, Moeller's group has been studying how solar-powered electrochemistry might be used to recycle chemical oxidants in a clean way.

Why would manufacturers choose to use a chemical oxidant, if the voltage of the electrode can be matched to the oxidation potential of the molecule that must be oxidized?

"An electrode selects purely on oxidation potential," Moeller explains. "A chemical reagent does not. The binding properties of the chemical reagent might differ from one part of the molecule to another. And there's also something called steric hindrance, which means that one part of the molecule might physically block access to an oxidation site, forcing substrates to other sites on the reagent."

"The chemistry community has learned how to use chemical reagents to make reactions selective," he says. "The reagents are usually expensive and toxic, so they are recycled," he says. "We are working on cleaning up reagent recycling."

In the chromium oxidation described above, for example, chromium IV could be recycled electrochemically instead of through a reaction with periodate. Instead of periodate waste[consistent with description above where periodate consumed?], the reaction would produce hydrogen gas as the byproduct.

"Another example is an industrial process for carrying out alcohol oxidations that convert the alcohol group to a carbonyl group," says Moeller. This process uses TEMPO, a complex chemical reagent discovered in 1960. TEMPO is expensive so it is recycled by the addition of bleach. This regenerates the TEMPO but produces sodium chloride as a byproduct."

In small quantities sodium chloride is table salt, but in industrial quantities it is a waste product whose disposal is costly. Once again, the TEMPO can be recycled using electrochemistry, a process that produces hydrogen as the only byproduct.

"We can't make all of chemical synthesis cleaner by hitching solar power to electrochemistry," Moeller says, "but we can fix the oxidation reactions that people use. And maybe that will inspire someone else to come up with simple and innovative solutions to other types of reactions they're interested in."

Provided by Washington University in St. Louis (news : web)

Cleaning up masterpieces with ... bacteria?

For most people the word bacteria will conjure up either images of nasty microorganisms that we fight against daily by cleaning the spaces around us, or the type of 'good' bacteria doctors advise us to consume to keep our digestive system's ticking over.

But who would have guessed that bacteria could be of use in the world of art restoration?

Well now, a team of art restoration experts from Spain and Italy have successfully shown that it is possible to clean up masterpieces with bacteria in a fast, targeted and careful manner. To boot, they have also shown that as well as being respectful to the paintings, these handy microorganisms are also kind to the restorers themselves and the surrounding environment. Until now the options were either restoration by aggressive, non-selective and toxic chemicals or erosion of the crust by often damaging mechanical means.

Through collaboration between the Institute of Heritage Restoration (IRP) at the University of Valencia, Spain, and experts working on the restoration of wall paintings at the Campo Santo di Pisa, Italy, these new methods have been tried and tested.

The collaboration came about while restorers from the IRP were working on the murals in the Church of Santos Juanes, Valencia, Spain. These murals were nearly completely destroyed after a fire in 1936 before becoming victim to a bad 1960s restoration job. The team from the IRP began experimenting with new techniques for 'filling' with transferred printed digital images in spaces without painting. However, salt efflorescence, the white scabs present on the paintings caused by a build-up of crystallized salts and gelatin glue, proved to be a major stumbling block.

"By the action of gravity and evaporation, the salts of organic matter in decomposition migrate to the paintings and produce a white crust hiding the work of art and sometimes can also cause the loosening of the painting layer," comments Dr. Pilar Bosch, one of the restorers from the IRP.

To investigate other options, the researchers from the IRP then travelled to Italy to learn about the pioneering work being carried out there in the Campo Santo di Pisa.

Under the guidance of microbiologist Gainluiggi Colalucci, restorers there were using bacteria to remove the hardened glue that conventional methods found so difficult to shift.

The bacteria used are a strain of Pseudomanas bacteria which literally eat the saline efflorescence that gathers in the arches where the paintings sit, normally where Pigeons like to reside.

Thanks to the collaboration between the two countries, the restorers were able to share best practices and find out what works best on different types of painting.

"In Italy they use cotton wool to apply the micro-organisms," comments Dr. Bosch. "We, however, have developed a gel that acts on the surface, which prevents moisture from penetrating deep into the material and causing new problems."

As bacteria only thrive in wet environments, Dr. Bosch explains how important the drying process is: "After an hour and a half, we remove the gel with the bacteria. The surface is then cleaned and dried."

Europe's greatest masterpieces have always been fragile; the ropes and museum cabinets separating us from our favourite pieces are evidence of this delicate nature. But now thanks to this research, ancient masterpieces could be kept 'young' for many years to come.

"After the good results of the tests we will continue the studies and improve the technique with the aim of transferring it to other surfaces," comments Dr. Bosch. "As in nature we find different species of bacteria that feed on almost anything, we are convinced that we can eliminate other substances from different types of materials."

Provided by CORDIS