DEET analysis in bug sprays

Tis the season for spraying DEET in our faces to make sure we don’t get eaten alive by bugs!

DEET, or N,N-diethyl-meta-toluamide, is one of the most widely used active ingredients in bug sprays.  It was developed by the US Army for this purpose in 1946 and made available to the public in 1957.  There have been concerns about negative side effects of DEET, but the purpose of this study is not to debate that, it’s simply to show the amount of DEET in bug sprays can be reliably determined via GC-FID.

In this study we analyze 3 different samples of bug spray in the Lucidity GC-FID and use a DEET standard obtained from a manufacturer to develop a calibration curve for DEET which can be used to quantitate the amount of DEET in the 3 samples.

We started with a 1000 mg/mL standard of DEET from a customer, which we then diluted to 10.0 mg/mL with IPA for our stock solution. We then created 3 standards of 1.00 mg/mL, 3.00 mg/mL, and 5.00 mg/mL of DEET in IPA.

We then ran these samples on the Lucidity GC-FID using the following method:

DEET method parameters for Lucidity GC-FID

DEET method parameters for Lucidity GC-FID

The 5.00 mg/mL standard produced the following cgram:

5.00 mg/mL DEET standard cgram

Overlaying the 3 standards (1.00 mg/mL, 3.00 mg/mL, and 5.00 mg/mL), you can see what the cgrams look like:

3 DEET standards overlaid

Using these three cgrams for the calibration curve, you get the following calibration curve:

Calibration curve for DEET on the Lucidity GC-FID

We then prepped the 3 samples by adding a volume of the sample to a sample vial and then diluting to volume with IPA using a micropipette.  The following spreadsheet shows the summary of our sample concentrations.  Each sample was diluted from an initial concentration shown on the label to a concentration within the range of our standards.  For example, Sample A was diluted from a label claim of 7% (70 mg/mL) to a concentration of 3.50 mg/mL by adding 50uL of sample to a sample vial and then diluting to 1.00 mL using IPA.

Sample preparation detail

Each sample was prepped and run twice against the calibration curve, which then allows the measured concentration of each sample to be shown in the chart on the right.  So, for example the first image shows the cgram of the first run of Sample A, and in the chart to the right you can see a measured concentration of 3.048 mg/mL, which is determined based on the calibration curve.

Sample A

Sample A prep 1 and prep 2

Sample B

Sample C

A summary of the 6 runs (2 runs of each sample) is shown in the chart below:

Summary of recoveries from the 3 samples

This shows the calculated amounts from each run against the labeled amount, and the %LC or percent of label claim of each run.  The recoveries are between 85-105% which is not too bad.  So, it looks like we have reasonable method for preparing and analyzing DEET in bug sprays, which is pretty important for manufacturers and consumers alike.