Choosing Your Citral Column

Image credit: Wikipedia

The name ‘citral’ or 3,7-dimethyl-2,6-octadienal, suggests the scent of lemons so it’s not surprising that another name for this compound is lemonal. There are two isomers of this compound with the same chemical formula (C10H16O); geranial (citral A) and neral (citral B). As seen in the image to the right, the difference between these compounds is subtle1.

Geranial and neral both have a lemon scent, however, neral has a milder, and sweeter lemon odor. These compounds are used individually or together depending upon the desired scent or flavor since they are used in perfumes, candy and even soft drinks. They can also be added to enhance other flavors for artificial grapefruit, orange and lime. The most common uses are cleaning products, laundry and dishwashing detergents. Chances are good you will use citral today. Interestingly lemongrass has significantly higher amounts of citral compared to lemons1.

As you will see from the chromatograms below column choice is important. Two different columns were evaluated; the Stabilwax and the Rtx-Wax, for peak shape, resolution and bleed. The obvious column of choice is the Rtx-Wax as shown in the following chromatograms.

Shown below are chromatograms of a custom citral mix on both columns with the Rtx-Wax column showing excellent peak shapes and separation. The Stabilwax column shows a fronting effect leading up to the citrals, which can cause problems with integration/quantitation.

 

Figure 1: Image of Custom Citral Mix on an Rtx-Wax

 

Figure 2: Image of Custom Citral Mix on a Stabilwax, notice the fronting peak shape indicating interaction with the analyte and stationary phase.

 

Figure 3: Zoomed image of the Custom Citral Mix on the Rtx-Wax and the Stabilwax. The red trace represents Rtx-Wax whereas the blue trace represents the Stabilwax.

 

Figure 4: Chromatogram of lemon Oil using the Rtx-Wax column. Lemon oil contains percent levels of citrals.

Reference/link: https://www.chemistryworld.com/podcasts/citral/3008193.article

 

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