One of my favorite lunches is a grilled cheese sandwich. In preparing this meal I pull out the butter from the fridge (where I keep it for freshness), but it is usually rock solid and I end up chipping away chunks that I then try to spread, ending up with patchy globs on torn bread. When I then put it in the frying pan, the results are spotty, to say the least. What I have discovered is, if I first put the butter in the heated pan, a pool of liquid is created that can then evenly coat the bread placed there, with the result being a uniform, golden hue indicative of pleasantly crunchy lunchtime goodness.
Applying heat is also transformative when you need to determine the ionic content of solids, which would otherwise be inaccessible to analysis. Ion chromatography (IC) is the gold standard for the determination of ions and polar molecules, such as chloride and bromide, but for analysis, samples need to be in a liquid form that can be injected into an IC system. This would typically exclude solid, semi-solid, or gaseous samples.
The solution for this is combustion ion chromatography (CIC). CIC combusts samples by heating them to ~1000 ℃ in the presence of humidified O2 (pyrohydrolytic oxidization) and then captures the gasses liberated into an absorption solution that can then be injected into an IC system. A recent workshop on CIC (view it on-demand here) outlines the principles of this technique, describing how you can overcome challenging matrices to determine the presence of potentially corrosive compounds, and presents a new integrated CIC workflow. This technique has been applied to a wide range of samples, including printed circuit boards, liquid petroleum gas (LPG), carbonated beverages, iron ore, and even green tea. A great place to find details about these applications is AppsLab, a vast repository of analytical methods containing detailed method information, chromatograms and application notes. There are even eWorkflows that can be imported directly into Thermo Scientific™ Chromeleon™ Chromatography Data System (CDS) software to give you a jump-start on your sample run setup.
One of the most exciting applications of CIC has been in the analysis of a family of chemicals that has made headlines due to their toxicity and ubiquity: PFAS (per- and polyfluoroalkyl substances). In the U.S., both the ASTM and the Environmental Protection Agency (EPA) are working on standard methods that use CIC to determine total adsorbable organofluorine (AOF) as a complement to more targeted analyses (see infographic). To get a taste for some of the work that has gone into developing a method, you can read the paper titled “Development of a standardized adsorbable organofluorine screening method for wastewaters with detection by combustion ion chromatography,” published in the September 2022 issue of the journal Analytical Methods. In it, researchers from the U.S. EPA describe a CIC method that combusts PFAS from surface and wastewaters following their adsorption onto activated carbon. While more than just PFAS can account for elevated levels of fluorine in environmental waters, AOF concentrations can provide an indication that more detailed analyses using targeted or even untargeted methods with high-resolution accurate mass (HRAM) spectrometry are justified.
By applying heat, CIC can transform your samples, unlocking their contents so that you can deliver the results you’ve been craving.
Here are a few CIC application notes to whet your appetite: