Quantification of Five Effective Components in Pesticides by Visible Near-Infrared Spectroscopy

Pesticides are chemical compounds that are used to kill pests that damage crops, including insects, rodents, fungi and unwanted plants (weeds). In addition, they are also used in public health to kill vectors of disease, such as mosquitoes. Due to the potential toxicity they pose to other organisms, including humans, pesticides need to be used safely and disposed of properly¹.

Quality Control of Pesticide Analysis

Exposure to pesticides could result from contact with them at work, at home or in gardens, such as through contaminated food. WHO reviews evidence and develops internationally-accepted maximum residue limits to protect people from potential health hazards caused by pesticides.²

Reversed-phase high performance liquid chromatography (HPLC) is generally used to estimate the concentration of effective components in pesticides. However, this type of chromatography requires the use of toxic solvents, and is time consuming and well-trained operators, resulting in relatively high costs for routine analysis. The use of visible near-infrared spectroscopy (Vis-NIRS) as an alternative to HPLC could save both time and money.

Table 1. Analyzed compounds and the effect as pesticide. ^[3]

Experimental Data

To test the validity of the use of Vis-NIRS as alternatives to HPLC, 24–37 pesticide samples with known concentrations of the effective compounds: Abamectin EC, Emamectin EC, Cyhalothrin EC, Cypermethrin and Glyphosate were prepared to evaluate the correlation between changes in spectral data and reference values.

NIRS RapidLiquid Analyzer was used to obtain the spectra over its full wavelength range (400– 2500 nm). The samples were filled into disposable glass vials with 4 mm diameter. Vision Air 2.0 Complete software was used for acquisition and management of data, as well as for the development of the quantification method. A Partial Least Squares (PLS) regression was carried out for each of the analyzed samples and Internal cross-validation (leave-one-out) was applied to confirm the performance of the derived quantitative models during the development of the method.

Table 2. Sample number and concentration range of the five effective compounds of interest.

Table 3. Used equipment and software.

Figure 1. The NIRS XDS RapidLiquid Analyzer was used for spectral data acquisition over the full range from 400 nm to 2500 nm.

Results

To build a robust prediction model, the wavelength regions used for each of these compounds were

1. Abamectin: 1360–1850 nm and 2050– 2500 nm,
2. Emamectin: 1300-1790 nm,
3. Cyhalothrin: 400–1080 nm and 1300– 2200 nm,
4. Cypermethrin: 1300–2200 nm
5. Glyphosate: 1300–2200 nm.

For the quantification of each of these compounds in pesticide, a model using 2 factors was developed with a Standard Error of Calibration (SEC) of 0.05% and a Standard Error of Cross Validation (SECV) of 0.06% was used. The R² values between the provided reference values and the calculated values for each of these effective compounds were found to be 0.9946, 0.9911, 0.9952, 0.0052 and 0.9952, respectively.

Figure 2. Raw data spectrum of 18 pesticide samples with Abamectin concentrations ranging from 1.8–3.8%.

Figure 3. Correlation plot of the predicted Abamectin content by Vis-NIRS versus the reference values evaluated by HPLC.

Figure 4. Raw data spectrum of 35 pesticide samples with Emamectin concentrations ranging from 1.5–3.5%.

Figure 5. Correlation plot of the predicted Emamectin content by Vis-NIRS versus the reference values evaluated by HPLC.

Figure 6. Raw data spectrum of 24 pesticide samples with Cyhalothrin concentrations ranging from 2.3–4.2%.

Figure 7. Correlation plot of the predicted Cyhalothrin content by Vis-NIRS versus the reference values evaluated by HPLC.

Figure 8. Raw data spectrum of 27 pesticide samples with Cypermethrin concentrations ranging from 4.0–5.8%.

Figure 9. Correlation plot of the predicted Cypermethrin content by Vis-NIRS versus the reference values evaluated by HPLC.

Figure 10. Raw data spectrum of 33 pesticide samples with Glyphosate concentrations ranging from 21.0–40.5%.

Figure 11. Correlation plot of the predicted Glyphosate content by Vis-NIRS versus the reference values evaluated by HPLC.

Table 4. Results of the quantitative method development for Abamectin content.

Table 5. Results of the quantitative method development for Emamectin content.

Table 6.  Results of the quantitative method development for Cyhalothrin content.

Table 7.  Results of the quantitative method development for Cypermethrin content.

Table 8.  Results of the quantitative method development for Glyphosate content.

Table 9.  Comparison of predicted Vis-NIR values with the HPLC reference values.

Conclusion

These high correlation values between the reference values and the calculated values using the Vis-NIRS indicate that it is a highly reliable and much faster quality control method for pesticide as compared to the traditionally used HPLC method. Therefore, Vis-NIRS can be used as excellent alternatives to HPLC for the routine analysis of pesticides, and it could save both time and money.

References

[1] http://www.who.int/topics/pesticides/en/

[2] http://www.who.int/

[3] https://en.wikipedia.org/

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.