Michael Fry, analytical instruments product manager, said it is seeing more people request the method.
“The advantage NMR has is the sample preparation is low, you can take whatever food fluid, typically olive oil or other juices, and add a solvent to dilute them down a bit and start quantitating right there or add a reference compound that allows you to quantitate,” he told FoodQualityNews at Pittcon.
“The response factor is one so you don’t have to have a calibration curve. If you add a known amount of a known compound you immediately know how much of the unknown compounds are in your sample.
“You don’t have to do chromatography, extractions or a lot of sample prep so that is a time saver even though the instrument is pricier than your average mass spec it cuts down time. Man power is the big expense these days not instrumentation.”
No hiding behind the test
Such a screening technique works because adulteration is usually not at trace levels, said Fry.
“It is easy to see what is added as NMR sees everything, there is no masking and you can’t hide behind the test anymore. They want a quick screening technique and they do not want something sitting there for two hours while they are waiting for a response,” he said.
“In some places they ship enough stuff they would like to screen more, so if you can shorten the time they can screen more samples and the more samples they can screen the more likely they are to pick up a fraud on the food that is coming through.
“With melamine the test they used was looking only for nitrogen in the milk, if you put a nitrogen source in, no matter how toxic it is, the nitrogen test will pass but now you’ve made the milk toxic. You can see those sorts of things happen in other food areas where they put something in there that is toxic as the test you are running is not diagnostic enough for adulteration.”
Fry said there has been fraud out of different parts of the world and it is going to be a bigger problem.
“You have an authentic sample of virgin olive oil, so you are looking if they have added other oils to it because high end olive oils are expensive and people want to maximise yield. So they will add a lower quality oil which if it has unsaturations or other contaminants you will pick those up,” he said.
“You want to get what you are paying for but also people can add oils that can be dangerous. That people have allergies to, if they add a nut oil and you are allergic to nuts you could kill people. That is why it is important to do these screenings rapidly on bulk shipments.”
Getting authentic samples in the first place is crucial.
“You have to go out and work with people you trust and know and go right to the orchard or the person making the first batch of oil and get authentic oils there," said Fry.
"You have to worry about seasonal and regional varieties so it does take a large database to get all the outliers because some of those may be expensive oils. The adulterants are typically common, you are looking for stuff added to the oil and not missing from it, so if you see a peak that is added in that particular oil it makes it easier.”
The science
Paper spray ionization mass spectrometry was used to detect and quantify levels of anthocyanin in elderberry fruit extracts and nutraceutical formulations.
A paper on matrix-assisted ionization in vacuum (MAIV) mass spectrometry to analyze polyphenol content of tea was accepted for publication in the American Society for Mass Spectrometry journal.
Applications notes for AccuTOF-DART include analysis of deoxynivalenol in beer, detection of lycopene in tomato skin, distribution of capsaicin in chilli peppers and direct analysis of caffeine in soft drinks and coffee and tea infusions.
Ambient ionization toolbox
Jeol USA also said while the main market of the AccuTOF-DART is forensics it is being used to screen for pesticides in food.
The atmospheric pressure ionization, high-resolution time-of-flight mass spectrometer (API-HRTOFMS) allows the user to determine chemical composition and produce high-resolution mass spectra by placing a sample between the DART ion source and AccuTOF mass spectrometer inlet.
The Direct Analysis in Real Time (DART) ion source was developed on the AccuTOF mass spectrometer.
Fry said it can screen for pesticides on the surfaces of fruit such as an orange peel.
“It is speed of analysis, you don’t have to do chromatography or clean-up, you take a scrape of an orange peel and pick up the fact there are pesticides on it,” he said.
“So a truck rolls up, you can pick out half a dozen oranges and by chromatography that is an all-day run but we can do half a dozen oranges in 10 minutes. We are trying to push speed of analysis, how quickly can we get an answer? Then if you want to quantitate you go back and find out exactly how much is in there.
“Most people when they do analysis look at when they receive the sample to when they get an answer. That includes all the sample prep, for example extractions, reduce the solvent down and add something to derivatize the compounds so they can go through chromatography and that is another step.
“Whereas if I can take a scraping and wave it in front of a mass spectrometer and get an answer I have saved hours of not just machine time but technician time and the most expensive thing in any lab these days is not the instruments, it is the people.”