Glyphosate, the active ingredient in the herbicide Roundup®, is vital for successful crop cultivation. However, although glyphosate is an effective herbicide, it must be carefully monitored to protect human health. Glyphosate itself is a potential carcinogen[i], and it also breaks down in soil to form another potentially toxic compound – aminomethylphosphonic acid (AMPA)[ii]. It is therefore crucial to accurately quantify pesticides that may remain in food products.
Glyphosates: A residual problem
The widespread use of glyphosate means trace amounts of residues can be found in grown produce such as oats. To ensure food safety, the United States Environmental Protection Agency (EPA) has set a maximum acceptable amount of glyphosate in oats[iii]. While this is currently 30 mg/kg of product, nonprofit organizations such as the Environmental Working Group (EWG) are petitioning for lower acceptable amounts.
However, determining glyphosate and AMPA is tricky – the compounds are highly polar and have low volatility. Methods such as high-performance liquid chromatography (HPLC) or gas chromatography (GC) can be used, but as glyphosate has no chromophore it requires a derivatization step, complicating the workflow. Seeking a derivative-free determination method is worthwhile to save costs and time.
As glyphosate pesticides and their metabolites are ionic, ion chromatography with mass spectrometry (IC-MS) is an excellent solution for their direct determination.
Determination: Quantifying pesticides
We investigated three oat flour extracts using the Thermo Scientific™ ISQ™ EC single quadrupole mass spectrometer, integrating IC with MS. Anion exchange chromatography with eluent generation and suppressed conductivity detection enabled chromatographic selectivity, ionic analytes, and MS compatibility. This provided selectivity based on the analyte mass-to-charge ratio.
The oat flour sample extracts were directly injected for analysis and operating the MS in selected ion monitoring (SIM) mode gave sensitive and selective quantification with minimal sample cleanup. We ensured quantitation accuracy using isotope-labeled analogs of the target compounds, and collected recovery, precision, sensitivity, and calibration range data for the method.
For the chromatography, we used a Thermo Scientific™ Dionex™ IonPac™ AS19-4 μm analytical column, (2 × 250 mm). The column is high capacity and high resolution – essential to determine pesticides at low μg/L concentrations, when samples also contain common anions such as chloride, nitrate and sulfate[iv]. AMPA could be easily resolved from these inorganic anions, as seen below in Figure 1.
Figure 1: Separation of common anions, glyphosate, and AMPA.
IC-MS: A robust method
Our experiments showed that IC-MS effectively and simultaneously determined both glyphosate and AMPA in oat flour, achieving separation in 30 minutes. The limits of detection (LOD) and limits of quantification (LOQ) for both glyphosate and AMPA were excellent, as seen in Table 1 below. The method is sensitive, accurate and reproducible, offering a reliable technique for pesticide quantification in oat flour with trustworthy results.
| LOD (μg/L)
in solution |
LOQ (μg/L)
in solution |
LOD (ng/L)
in oat flour |
LOQ (ng/L)
in oat flour |
| Glyphosate | 0.0725 | 0.242 | 2.90 | 9.66 |
| AMPA | 0.284 | 0.947 | 11.4 | 37.9 |
Table 1: Limits of detection (LOD) and limits of quantification (LOQ).
Read more about using IC-MS to determine glyphosate and AMPA in oat flour in our application note, and keep an eye out for our upcoming blog on using HPAE-PAD to determine carbohydrates and glycols in pharmaceutical formulations.
[i]Internal Agency for Research on Cancer, Q&A about Glyphosate. https://www.iarc.fr/en/media-centre/iarcnews/pdf/Q&A_Glyphosate.pdf
[ii]Grandcoin, A.; Piel, S.; Baurès, E. AminoMethylPhosphonic acid (AMPA) in natural waters: Its sources, behavior and environmental fate. Water Research 2017, 117,187–197. https://doi.org/10.1016/j.watres.2017.03.055
[iii]Electronic Code of Federal Regulations. (2019). eCFR — Code of Federal Regulations. https://www.ecfr.gov/cgi-bin/text-idx?SID=652f6661f1c740545053c400dfe56616&node=pt40.24.180&rgn=div5…
[iv]Thermo Scientific Dionex IonPac AS19-4μm Column Product Manual. P/N 065532-03 http://tools.thermofisher.com/content/sfs/manuals/Man-065532-IC-IonPac-AS19-4um-Man065532-EN.pdf