Lucidity LC-UV and RI Together

Lucidity LC-UV and RI Together

Sugar Pouring into Cup


Like most people, when the new year comes around I always make a resolution to eat healthy and lose some weight. This year I decided to cut back on the amount of sugar I eat on a daily basis.

Sugar is a major additive in foods and beverages. The American Heart Association recommends that men consume no more than 36 g of added sugar per day and 25 g for women. With the typical diet that is a tough thing to do, as sugar is added to a wide variety of foodstuffs.

Finding added sugar in food used to be much harder as manufacturers were only required to list total sugars on the label and not disclose how much was added sugar versus how much is naturally occurring sugars. Now with the updated nutrition facts label, added sugar has to be disclosed to make seeing where the sugar is coming from easier on the consumer.

Added sugar goes by many different names, but are all a source of calories. Sugar is reserved for sucrose or table sugar, but other sugars are glucose, fructose, dextrose.

Sugars aren’t generally detected by UV light, so another technique needs to be used. In my case I’m using a Refractive Index Detector. This detector works by passing light through two prisms, one filled with just mobile phase and the other where the sample passes through. The detector then compares the signal and the software draws the chromatogram based on the change in refractive index between the sample and the blank mobile phase.

The sugars used in this experiment are Sucrose, Glucose, Fructose and Maltose. Each of the sugars was run individually and then combined to show the separation of each of the sugars in a single chromatogram

The method needs to be isocratic flow, as RIDs don’t perform well in gradient methods because it is impossible to match sample and mobile phase as the mobile phase is changing throughout the run.
Lucidity LC-UV on RID

Lucidity LC-UV sits atop the Knauer Azura RID



Lucidity LC-UV Method
  Flow Rate 2.0 mL/min
  Column Ultra Amino 150 x 4.6 mm, 3 μm
  Oven Temperature 35 ℃
  Wavelength N/A  RID USED
  Flow Isocratic – 20 minutes
  Mobile Phase Acetonitrile:Water (75:25)


Sucrose chromatogram Maltose Chromatogram Glucose chromatogram Fructose chromatogram

This work demonstrates that we are able to connect the Lucidity LC-UV to an external RI detector and see peaks for each of the sugars we are interesting in.  Next steps include adding the standards together to test the method to ensure it separates the 4 sugars of interest sufficiently, then testing different foods and juices to determine their sugar content and matching against labelled amounts.

Stay tuned…

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