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

As a non-selective herbicide, the efficacy of glyphosate aqueous solutions is directly correlated with the content of its active ingredient and the corresponding counter-ions forming the salt. If the content of isopropylamine ions or dimethylamine ions in the product fails to meet the specified requirements (i.e., does not comply with the quality standards for pesticide products), the herbicidal efficacy will be significantly compromised. As a result, stubborn weeds such as reed and cogongrass may not be effectively controlled, potentially leading to reduced crop yields or even complete crop failure, thereby causing substantial economic losses to farmers.

In this study, a NovaChrom MS-5C-P2 cation chromatography column (4.6 × 250mm) with methanesulfonic acid eluent system was employed for the determination of a 30% glyphosate–dimethylamine aqueous solution and an 800g/L glyphosate aqueous solution (isopropylamine salt). The analytical procedure is straightforward, and the results are reproducible and reliable, fully meeting the testing requirements. This work provides a valuable reference for the determination of dimethylamine and isopropylamine in glyphosate aqueous formulations using 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 Main 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 reference standard into a 250mL volumetric flask, dilute to the mark with ultrapure water, and mix thoroughly. Transfer 10mL of the above solution into a 50mL volumetric flask, dilute to the mark with ultrapure water, and mix well to obtain an intermediate isopropylamine stock solution with a concentration of approximately 118.13 mg/L. Transfer 1 mL, 2 mL, 3 mL, 5 mL, 7 mL, and 10 mL of the intermediate isopropylamine stock solution into six separate 100 mL volumetric flasks, respectively, and dilute to the mark with ultrapure water to obtain isopropylamine calibration standards over a concentration range of approximately 1.1813mg/L to 11.813mg/L.

Weigh 0.1446g of dimethylamine reference standard (as dimethylamine hydrochloride) into a 100mL volumetric flask, dilute to the mark with ultrapure water, and mix thoroughly. Transfer 10mL of the above solution into a 50mL volumetric flask, dilute to the mark with ultrapure water, and mix well to obtain an intermediate dimethylamine stock solution with a concentration of approximately 158.30mg/L. Transfer 1mL, 2mL, 3mL, 5mL, 7mL, and 10mL of the intermediate dimethylamine stock solution into six separate 100 mL volumetric flasks, respectively, and dilute to the mark with ultrapure water to obtain dimethylamine calibration standards over a concentration range of approximately 1.583mg/L to 15.83mg/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 a factor of 50, then pass through a C18 solid-phase extraction cartridge, and finally filter 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 a factor of 50, then pass through a C18 solid-phase extraction cartridge, and finally filter through a 0.22μm aqueous syringe filter before use.

1.3 Instrument Working Conditions

Table 1

2. Result and Discussion

2.1 Linearity 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 Overlaid Chromatograms of Dimethylamine Linearity Test

Fig 2 Overlaid Chromatograms of Isopropylamine Linearity Test

Fig 3 Linearity Test Data

2.2 Sample Test

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

Fig 5 Chromatogram of 30% glyphosate–dimethylamine aqueous solution diluted 50-fold

Table 2 Test Results

2.3 Repeatability Test of Samples

Fig 6 Overlaid Chromatograms of 30% Glyphosate–dimethylamine Aqueous Solution Diluted 50-fold for 6 Consecutive Injections

Fig 7 Overlaid Chromatograms of 800g/L Glyphosate Aqueous Solution (isopropylamine salt) Diluted 50-fold for 6 Consecutive Injections

Table 3 Test Data

3. Conclusion

In this study, a NovaChrom MS-5C-P2 cation chromatography column (4.6 × 250mm) with methanesulfonic acid eluent system and a Wayeal ion chromatograph were used for the analysis of a 30% glyphosate–dimethylamine aqueous solution and an 800g/L glyphosate aqueous solution (isopropylamine salt). The method exhibited excellent linearity, good resolution, and high sensitivity, demonstrating its suitability for the intended analytical application.