Recently, we partnered with FoodProductionDaily.com to present a webinar on the use of universal Charged Aerosol Detection and selective pulsed amperometric detection for the direct determination of carbohydrates in complex food and beverage matrices. The advantages of two novel approaches, HPAE-PAD and HILIC-CAD was also discussed. The attendees asked several interesting questions on the types of detection and I thought they would make for good reading along with a couple of other resources.
The webinar, titled, Novel HPLC Approaches for Carbohydrate Analysis in Beverages and Food, (link to view the webinar on-demand after filling out a short registration form) featured Qi Zhang, Senior Scientist, Thermo Fisher Scientific, and Jeffrey S. Rohrer, Ph. D., Director of Applications Development, Dionex Products, Thermo Fisher Scientific; the moderator was Jenni Spinner, US Editor, FoodProductionDaily.com.
The transcript has been edited for clarity and readability.
ELSD is also a nebulization-based HPLC detector. How does Charged Aerosol Detection (CAD) compare with ELSD?
You can say that they are similar in that they are both nebulizer-based detectors, but the detection mechanisms are very different. Evaporative light scattering detection (ELSD) measures light scattered by the particles, but CAD measures charges associated with the particles. The difference in the detection mechanism also has a major impact on their performance overall. Our studies have shown that the CAD has a lower detection limit and a wider dynamic range, less inter-analysis variability, better precision, and much better linearity compared to an ELSD detector. We have a poster on this topic. If anyone is interested, I can send a copy of the poster.
Editor’s Note: The poster is titled, Charged Aerosol Detection and Evaporative Light Scattering Detection – Fundamental Differences Affecting Analytical Performance, (downloadable PDF).
I saw on your website that you have a number of carbohydrate analysis columns. Which one should I use to separate maltodextrins in a beer sample?
That’s a good question. You could use a number of different columns for that. Today, if I was going to start a separation, I’d use our high-resolution carbohydrate column (Thermo Scientific DionexCarboPacPA200 column). But even though the DionexCarboPacPA100 column and the DionexCarboPac1 column will work, they just won’t deliver as many peaks and the peaks will not be as sharp.
Do you think you could separate mannitol and sorbitol on the Thermo Scientific DionexCarboPac SA10 column?
That’s another good question. Yes, I certainly believe we could do that. We showed mannitol in the presentation. I’m sure sorbitol would elute just before mannitol, if I had to take a guess. Although I have not done that separation, I believe it could be done.
Like what you are learning?
Editor’s Note: Thermo Scientific DionexCarboPac SA10 column is intended for the analysis of simple sugars.
Do you have a column capable of separating cellobiose and maltose?
Yes, a number of our columns can do that separation, all the way back to the Dionex CarboPac PA1 column. Today, I’d probably use a Dionex CarboPac PA20 column to do that separation, but even the Dionex CarboPac SA10 that I showed earlier can do that separation.
How do organic acids such as gluconic acid, tartaric acid, glucaric acid, glycolic acid, interact with the carbohydrate columns? Do they introduce interference for this type of analysis?
It depends. Basically, anything that is a sugar-based acid, like glucuronic acid and galacturonic acid, they will be detected by the PAD detector. Now, all the acids will take up a certain amount of column capacity; what I mean is, if they are anionic, they are going to bind to the column. If they are in large excess to the sugars that you want to determine, then they might cause interference just in taking capacity, but generally those compounds are in a similar concentration to the sugars that you are interested in analyzing, although perhaps you are interested in analyzing the sugar acids too. Some of the organic acids, like tartaric acid, will not be detected by the PAD detector under these conditions and the only concern is how much column capacity they are going to take but they are not going to interfere otherwise. In general, we analyze a lot of different samples for sugars that contain organic acids and they are not problematic.
What did HILIC stand for in the slide that discussed the three HPLC detectors?
HILIC is hydrophilic interaction chromatography. They use a hydrophilic stationary phase, and usually a reverse-phase type of mobile phase to separate the polar and ionic samples. This is another form of separation for carbohydrate analysis other than the anion exchange that we use with the CAD detector.
Editor’s Note: You might be interested in checking out this Poster Note, Simple Separation and Detection Techniques for the Analysis of Carbohydrates, (downloadable PDF).
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