Problems Associated With the Analysis of Glyphosate in Food Crops

Yusof, Mohtar Bin (1988) Problems Associated With the Analysis of Glyphosate in Food Crops. PhD thesis, University of Glasgow.

Abstract

The principle of this thesis concentrates particularly on developing a simpler method of determination of glyphosate at residue level with the emphasis on clean-up procedures. The difficulties of obtaining a simple method of quantitation of this compound are mainly due to its properties; its relatively high solubility in water, its insolubility in organic solvents and its complexing behaviour. These characteristics are quite similar to compounds naturally existing in plants or crops and thus make it difficult to isolate from these matrices. Its properties were investigated in detail in order to predict its behaviour more accurately. The work can be sub-divided as follows : 1. A brief discussion was made of the chemistry of glyphosate and the difficulties involved when it is quantified by GC or HPLC mainly because of the derivatization problem involved. The current methods of determination of glyphosate residues in various matrices were also presented as a reference. The justification of the choice of food crops as a key study were mentioned. 2. Analysis of glyphosate residues in a tuber food crop (potato). The main aim of this work was to develop a simple clean-up procedure for the determination of glyphosate residues in food crop (potato) that could be used for detection both by GC and HPLC. It was found that determination by GC especially with an EC detector involved simultaneous esterification and acylation and was not suitable for this purpose mainly because the derivative retention time was relatively short and easily masked by the impurities. Due to the glyphosate solubility behaviour, HPLC was advantageous over GC and was chosen for all subsequent detection. Simple clean-up procedures were developed for the determination by HPLC and pre-column derivatization was preferred because it was less complicated than determination by post-column derivatization. All types of Bond-Elut small cartridges ranging from non-polar to anion exchange were not effective in retaining glyphosate from potato extracts, although anion exchange cartridges could strongly retain glyphosate standards. A mixture of semi coarse and powdered forms of activated carbon was found to be useful as a clean-up material to adsorb impurities from the potato extract. Recovery was found to be 53 % at 0.1 ppm sample and up to 92 % at 10 ppm sample with the limit of detection at 0.05 ppm. This could be considered a reasonably good recovery and a good alternative procedure to those currently employed. 3. The translocated effect of glyphosate to the tuber crops was simulated by spraying it onto the plant leaves of a tuber crop (potato). The physical effects on the tubers were observed under normal storage conditions. Results showed that sprout lengths were reduced, number of eyes open and rotting increased with increasing rate of glyphosate application. The residue content in the tubers also increased with increasing amount of glyphosate applied. For the assessment of the injuries caused by glyphosate, all the above parameters could be taken into consideration. However better accuracy could be obtained if the rotting effect and glyphosate residue were used as references. If the rotting effect was to be used for the assessment all the possible diseases should be determined first in order to avoid the difficulty of differentiating their symptoms. Field growth performance indicated that all the treated tubers were affected by glyphosate even at the lowest treatment level (0.09 kg/ha glyphosate). Tubers from the lowest treatment level did not show any significant difference compared with controls in terms of sprout length, number of eyes open, rotting and residue level during storage. From this work, residue levels of 0.1 ppm or above had a decided effect on subsequent growth. Treatment with > 0.36 kg/ha glyphosate which gave significant effects during storage did not produce any healthy plants or daughter tubers when planted out. 4. A small comprehensive exercise on the determination of glyphosate in barley grain was undertaken. Adaptations of the experiments in chapter 2 were applied. It was found that anion exchange Bond-Elut cartridges could retain glyphosate in barley extracts better than in potato extracts. However its recovery was still relatively low to enable its use as a clean-up material. A chelating resin was also tried to retain glyphosate from barley extract. Its recovery was 52 % at 1 ppm and 42 % at 0.1 ppm level. Formation of gel during the extraction could reduce recovery and attempts on how to eliminate it were also mentioned. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Organic chemistry, Agriculture
• Date of Award: 1988
• Depositing User: Enlighten Team
• Unique ID: glathesis:1988-77734
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77734