Allergy Season is Upon Us!

Now that spring is here and all things pollen are happening it’s time to get the allergy medicine ready.  In honor of this wondrous time of year, we thought we would test some allergy meds!

While not the usual way to test these medications, I decided to see if I could test using the Lucidity GC-FID.  I first looked into the most common active ingredients in allergy and cold medicines, purchased those in pure form to use as standards, then purchased two different OTC medications that contained these compounds.  The three common active ingredients we decided to test were Dextromethorphan HBr, a cough suppressant,  Chlorpheniramine Malate, an allergy medication, and Guaifenesin, a mucus expectorant.  Each of these were purchased from Sigma Aldrich in a 99%+ pure form.

The two samples we purchased for testing were from the pharmacy section of a local store.  The first sample was an allergy pill that contained Chlorpheniramine Malate and the second a cold and flu liquid that contained Dextromethorphan HBr and Guaifenesin.

The first thing that needed to be done was to identify each of the compounds using the GC-FID.  I first tried to dissolve each of the compounds in water, then do a liquid-liquid extraction using ethyl acetate.  Unfortunately, that extraction didn’t produce any results. Next, I tried to dissolve each in methanol, and that worked great. Once the standards and samples were in solution, I had to inject them all on the Lucidity GC-FID.

The standards were combined into three concentrations 1.00 mg/mL, 0.500 mg/mL and 0.100 mg/mL.  These three standards were used to make calibration curves.  The R squared value on each curve was excellent and the lowest R squared was 0.9996, showing great linearity for this concentration range.

Chlorpheniramine Malate calibration curve

Dextromethorphan HBr calibration curve

Guaifenesin Calibration Curve

After the calibration curves were run the samples were diluted to be within the calibration curve.  Each sample was diluted in methanol to a concentration of 0.400 mg/mL and run on the GC-FID.  The liquid sample contained something that caused a precipitate and the fillers in the pill didn’t dissolve either.  Both samples were filtered using a 0.45 μm filter before injection into the GC-FID.

Samples diluted in Methanol

Chromatogram of Dextromethorphan HBr from the liquid cold medicine

Chromatogram of liquid cold medicine diluted to show Guaifenesin

Chromatogram of allergy pill to show Chlorpheniramine Malate

The software calculated the concentration of the samples based on the calibration curves.  The Dextromethorphan HBr came out to 0.397 mg/mL, the Chlorpheniramine Malate come out to 0.416 mg/mL and the Guaifenesin came out to 0.399 mg/mL.

Taking into account the dilution factor and serving size for the samples, the recoveries for the 3 compounds of interest (the active ingredients) were 99.3% recovery for Dextromethorphan HBr from the liquid sample, 99.8% recovery for Guaifenesin from the liquid sample, and 104% recovery for Chlorpheniramine Malate in the pill sample.  

The calibration curve for the Guaifenesin could have been adjusted to allow for me to run both the active ingredients in the liquid cold medicine in one sample, but I was running short on the Guaifenesin standard and had to make a more dilute standard, but overall the method was successful in detecting the three active ingredients in OTC allergy and cold medicines.