The Value of a Pragmatic Approach

People typically expect (or assume) that products that come into contact with their bodies (food, cosmetics, and so on) are free from potential health risks. To that end, international organizations study potentially toxic compounds and set limits of acceptability that industries and control organizations have to monitor. However, many foods and cosmetics include complex mixtures of natural products – so toxic compounds are typically present at trace levels, hiding amongst hundreds of other molecules. To detect trace toxins, analytical chemists must pay careful attention to both recovery and separation. Moreover, when developing a method, we must remember that many companies producing food and natural products do not have access to complex and expensive instrumentation – and high throughput (to control production) tops the list of priorities.

Our research group, led by Carlo Bicchi, is used to dealing with complex natural matrices, but even with optimized sample preparation and/or separation, the determination of possible contaminants in these samples can be challenging. What are the solutions? One route is to adopt highly sophisticated separation techniques (multidimensional chromatography, for example) and/or high-resolution mass spectrometry. Certainly, such techniques gain in popularity every day, but their complexity and cost puts them out of reach of many companies. We propose a simpler approach: conventional instrumentation combined with one-step sample preparation methods that make use of new materials tailored to the task.

In this respect, ionic liquids have great potential because of their unique selectivity. Even better, their chemical structures can be custom-designed to enhance extraction efficiencies of specific classes of analytes (when used to recover compounds of concern) or to improve critical separations (when used as stationary phases for their separation). In 2016, I visited Jared Anderson’s laboratory at Iowa State University for 3 months and found that our experience of complex natural matrices, combined with his expansive knowledge of ionic liquids, was a winning combination when it came to dealing with challenging issues.

One result of this collaboration was a method for measuring acrylamide in coffee samples. Acrylamide is an unsaturated amide formed when carbohydrate-rich foods, such as potatoes, bread, biscuits and coffee, are subjected to high temperatures during cooking or thermal processing. Several studies have revealed that acrylamide is toxic, and a possible carcinogen, which is why regulatory agencies have indicated that regulation on acrylamide levels will be introduced. However, acrylamide analysis in food is a considerable challenge because of its chemical characteristics and trace concentration. Established ISO methods adopt SPE-HPLC-MS/MS, but this methodology is time consuming and cannot easily be automated. Instead, we applied direct immersion solid-phase microextraction (SPME) coupled to GC-MS with polymeric ionic liquid (PIL) sorbent fiber coatings to recover acrylamide with very high selectivity.

The method was immediately effective but there was one flaw – a neo-formation of acrylamide at the high temperatures of the GC inlet, formed by the asparagine and glucose co-extracted with PIL fibers. To address this issue, we added a very simple quenching reaction using ninhydrin to selectively degrade free asparagine and inhibit the formation of additional acrylamide during the desorption step. By tailoring the PIL structure, it was possible to reach a limit of quantitation for acrylamide in the ppt range, comparable to those of the ISO method. In contrast to the official method, our PIL-based SPME method is considerably quicker, does not require solvents, can be made fully automated, and requires only conventional and simple instrumentation.

Our research group has also studied ionic liquids in another interesting application: GC stationary phases for one-dimensional separations of complex samples in the essential oil, flavor and fragrance fields. But that’s a story for another time.

I believe that the ultimate challenge for analytical scientists is not just to develop and study new technologies, but to make them simple enough for routine use.