In the lab

Two analytical techniques were used to detect and quantify pesticides in the samples. Both operate on the same principle — a chromatographic column separated all the pesticides from a prepared injection of a sample. As different pesticide compounds have a specific affinity for the column lining versus the solvent or gas that pushes them through the column, different compounds are retained in the column for different times before they exit and are detected. You can see that in the peak shown below, the pesticide compound Diuron was retained in the column for 5.980 minutes.

Above that peak, you can see that the peak has an area count of about 58,200 in this particular sample. This area count, which represents the integrated area under the peak, is proportional to the concentration of that compound in the sample. So if, along with the sample, we dilute and inject some purchased Diuron at known concentrations ranging from 10-0.001 μg/L, we can construct calibration curve that looks like the one below. By comparing the area count of the sample peak for Diuron against the area counts for the calibration curve, we can then calculate its concentration.

The sheer scale of the dataset is enormous, with hundreds of samples being screened for 792 pesticide targets, 340 of which could be quantified across both instruments. From the raw instrument data alone, we have been able to generate hundreds of thousands of datapoints, which can be used for many future investigations.