GC-FID App Note – Alcohols in hand sanitizer
Study Performed by Dan Iversen, R&D Chemist, Lucidity (daniel.iversen@luciditysystems.com)
Introduction
Ethanol and isopropyl alcohol (IPA) are the main ingredients in hand sanitizers. According to the World Health Organization, to be effective the labeled amount should be between 60% – 80%. Above 80% alcohol proteins aren’t denatured easily in the absence of water.
Other alcohols may be present either as impurities or as the main ingredient in order to make counterfeit products, which makes identification and measurement of the concentration important.
Gas chromatography is an easy and effective way to both identify both the alcohol and concentration used. A mid-polar to polar column should be used in the analysis of alcohols, either a 624 or Wax column work well for this purpose.
This study used an MXT-Wax column from Restek (cat #: 70623-273) and the Lucidity miniGC with FID for alcohol analysis.
Experimental
The Lucidity miniGC is equipped with a split/splitless inlet and an FID. Liquid sample injection was done using manual injection with a 10 μL syringe. The method used is outlined in Table 1.
| Lucidity miniGC parameters | |
| S/SL inlet | 140 ℃ |
| Injection volume | 1 μL |
| Carrier Gas | H2 |
| Column Flow Rate | 2.00 mL/min |
| FID | 200 ℃ |
| Oven | 40 ℃ for 1 minute, 25 ℃/min to 165 |
| Column | MXT-WAX 30 m, 0.25 mmID, 0.25 μm |
Chemicals and standards
The alcohol solvents and Acetonitrile were purchased from Reagents Specialty Chemicals and Solutions. The alcohol standard was prepared by adding aliquots of pure alcohol to pure HPLC grade water to a volume of 10 mL. Methanol and Ethanol are one standard, and Isopropanol was a standard by itself. The concentration of the alcohol standard is 4%, the concentration of the internal standard, acetonitrile, is 1%.
The hand sanitizer samples were too thick for direct injection and had to be diluted for analysis. Approximately 100 mg of sample and 20 mg of acetonitrile was added to water for a total mass of about 2000 mg.
Samples
Different hand sanitizers were purchased or received from various locations. No two sanitizers were purchased at the same location or time. The samples range from generic sanitizer provided by a company, to high end boutique sanitizer. Names of the sanitizers will be withheld.
Samples were made up in approximately the same manner as the standards but had to be done by weight due to the viscous nature of the sanitizer gels. The fully liquid sanitizers were made up by volume. Each sanitizer was made to a 4% solution in water with a 1% IS of acetonitrile and shaken for approximately two minutes to ensure a homogenous mixture.
Results and discussion
This application note focused on the analysis of the main alcohols used in the production of hand sanitizer, along with possible contamination from other alcohols. Three alcohols were used in the calibration standard. They are methanol, ethanol, and isopropanol. Ethanol and isopropanol concentrations are usually called out on the labels. The three alcohols of interest were analyzed and quantified using the relative retention time from the internal standard. The tailing factor for each of the alcohols and acetonitrile was 1.0 or less.
The quantitation of the alcohols was performed by area comparison. First the methanol and ethanol mixture was analyzed and then the isopropanol was analyzed by itself due to the inability to resolve the ethanol and isopropanol to the baseline.
The five samples were compared to the standard area and the results are outlined in Table 2. Chromatograms of the standards and samples are shown in Figures 1 through 3. As shown in Figure 3, the difference between the peaks of ethanol and isopropanol are easily seen, although the peaks would overlap if on the same chromatogram.
| Results | |||
| Sample No. | Alcohol Used | Result | Labeled Amount |
| Sample 1 | Ethanol | 67.9% | 70% |
| Sample 2 | Ethanol | 65.5% | 62% |
| Sample 3 | Ethanol | 69.3% | 75% |
| Sample 4 | Isopropanol | 68.9% | Unknown |
| Sample 5 | Ethanol | 65.6% | 70% |
Conclusion
The work outlined in this application note shows that the Lucidity miniGC is more than capable of producing easily quantifiable results. With its easy to use interface, programming, small form factor, and the toolless quick change column, the Lucidity miniGC will feel at home in any lab.
