Determination of Dimethylamine and Isopropylamine in Glyphosate Aqueous Solutions Using Ion Chromatography Column

Glyphosate aqueous solutions, as non-selective herbicides, have their herbicidal efficacy directly correlated with the contents of active ingredients and salt-forming ions. If the contents of isopropylamine ions or dimethylamine ions in the product fail to meet the specified standards (i.e., do not comply with the quality specifications for pesticide products), the herbicidal efficacy would be significantly compromised, making it difficult to eradicate stubborn weeds such as reed and cogongrass. This may subsequently lead to reduced crop yields or even complete crop failure, thereby causing substantial economic losses to farmers.

In this test, the NovaChrom methanesulfonic acid-based cation chromatography column MS-5C-P2 (4.6 × 250mm) was used for the determination of a 30% glyphosate-dimethylamine aqueous solution and an 800g/L glyphosate aqueous solution (isopropylamine salt). The testing procedure is straightforward, and the results are stable, meeting the analytical requirements. This provides a reliable reference for the determination of dimethylamine and isopropylamine in glyphosate aqueous solutions by ion chromatography.

Keywords: Ion chromatography column; pesticide; 30% glyphosate-dimethylamine aqueous solution; 800g/L glyphosate aqueous solution (isopropylamine salt); cation chromatography column; isopropylamine; dimethylamine.

1. Experiment

1.1 Instruments and Reagents

Ion chromatograph: Wayeal ion chromatograph, equipped with a conductivity detector and a cation suppressor.

Cation chromatography column: MS-5C-P2, 4.6 × 250mm;

Cation guard column: MS-5CG, 4 × 30mm;

Isopropylamine;

Dimethylamine (dimethylamine hydrochloride);

Disposable syringes (5mL);

Aqueous syringe filters (0.22μm);

1.2 Sample Pretreatment

1.2.1 Preparation of Standard Stock Solutions

Weigh 0.1484g of isopropylamine standard and transfer it into a 250mL volumetric flask. Add ultrapure water to the mark, and mix thoroughly by shaking. Transfer 10mL of the above solution into a 50mL volumetric flask, add ultrapure water to the mark, and mix well to obtain an intermediate isopropylamine solution at a concentration of approximately 118.13mg/L. Transfer 1mL, 2mL, 3mL, 5mL, 7mL, and 10mL of the intermediate isopropylamine solution into six separate 100mL volumetric flasks, respectively, and fix to the volume with ultrapure water. This yields a calibration curve for isopropylamine over the concentration range of approximately 1.1813mg/L to 11.813mg/L.

Weigh 0.1446g of dimethylamine standard (as dimethylamine hydrochloride) and transfer it into a 100mL volumetric flask. Add ultrapure water to fix the volume, and mix thoroughly by shaking. Transfer 10mL of the above solution into a 50mL volumetric flask, add ultrapure water to the mark, and mix well to obtain an intermediate dimethylamine solution at a concentration of approximately 158.30mg/L.

1.2.2 Preparation of Sample Solutions

30% glyphosate-dimethylamine aqueous solution (0.3694g/100mL): Dilute the 30% glyphosate-dimethylamine aqueous solution (0.3694g/100mL) by 50-fold, then pass it through a C18 solid-phase extraction cartridge. Subsequently, filter the eluate through a 0.22μm aqueous syringe filter before use.

800g/L glyphosate aqueous solution (isopropylamine salt) (0.3753g/100mL): Dilute the 800g/L glyphosate aqueous solution (isopropylamine salt) (0.3753g/100mL) by 50-fold, then pass it through a C18 solid-phase extraction cartridge. Subsequently, filter the eluate through a 0.22μm aqueous syringe filter before use.

1.3 Instrument Working Conditions

Table 1

2.Result and Discussion

2.1 Linear Test

The standard curve concentration samples of dimethylamine and isopropylamine prepared in Section 1.2.1 were tested according to the instrumental method described in Section 1.3. The results obtained are as follows:

Fig 1. Linear Test Chromatogram for Dimethylamine

Fig 2. Linear Test Chromatogram for Isopropylamine

Fig 3 Linear Test Data

2.2 Sample Testing

Fig 4. Chromatogram of the 800g/L Glyphosate Aqueous Solution (isopropylamine salt) Diluted 50-fold

Fig 5. Chromatogram of the 30% Glyphosate-dimethylamine Aqueous Solution Diluted 50-fold

Table 2 Test Data

2.3 Repeatability Test of Samples

Fig 6. Overlaid Chromatograms of Six Consecutive Injections of the 30% Glyphosate-dimethylamine Aqueous Solution Diluted 50-fold

Fig 7. Overlaid Chromatograms of Six Consecutive Injections of the 800g/L Glyphosate Aqueous Solution (isopropylamine salt) Diluted 50-fold

Table 3 Test Data

3. Conclusion

In this study, the NovaChrom methanesulfonic acid-based MS-5C-P2 column (4.6×250mm) and the Wayeal ion chromatograph were employed for the determination of the 30% glyphosate-dimethylamine aqueous solution and the 800g/L glyphosate aqueous solution (isopropylamine salt). The results demonstrated good linearity, satisfactory resolution, and high detection sensitivity, fully meeting the analytical requirements.