Simultaneous Determination of Residual Glyphosate, Glufosinate and Their Major Metabolites in Rice and Soybean Products, and The Effect of Ozonation on Their Residues

Autor: Su-Hsiang Tseng, 曾素香
Rok vydání: 2004
Druh dokumentu: 學位論文 ; thesis
Popis: 92
Procedures were developed for simultaneous quantification of glyphosate [N-(phosphonomethyl)glycine] and glufosinate [DL-homoalanine-4-yl-(methyl) phosphinic acid], and their major metabolites, AMPA (aminomethylphosphonic acid) and 3-MPPA [3-(methylphosphinico)propionic acid], in rice and soybean products by gas chromatograph (GC) equipped with a pulsed flame photometric detector (PFPD). Sample pretreatments, including anion-exchange chromatography, TMOA (trimethyl orthoacetate) derivatization and Florisil cleanup, were favorable for the GC-PFPD analysis. Four types of derivatives spiked in rice and soybean products matrices were eluted, reaching a base-line separation, in a sequence of 3-MPPA, AMPA, glyphosate, and glufosinate within 14 min using a DB-608 capillary column. Recoveries of 3-MPPA, AMPA, glyphosate and glufosinate (0.5, 2.5 ppm) spiked in sample matrices were determined to be 83 to 96, 67 to 88, 72 to 103, and 95 to 119 %, respectively, while the coefficient of variation (CV) was determined to be less than 10 % in three repeated determinations. The limit of detection (LOD) for 3-MPPA, AMPA, glyphosate, and glufosinate in sample matrices was 0.01, 0.03, 0.02, and 0.02 ppm, respectively. Comparison of EI-MS (electron ionization-mass spectrometry) and CI-MS (chemical ionization-mass spectrometry) results for TMOA derivatized 3-MPPA, AMPA, glyphosate, and glufosinate revealed that better responce and less matrix interference were obtained by CI-MS method. Analytical conditions for CI-MS/MS detection were optimized, and m/z 181, m/z 182, m/z 254, and m/z 252 were chosen as parent ions and 0.5, 0.3, 0.3, and 0.5 volt were chosen as the CID (collision-induced dissociation) excitation amplitudes for 3- MPPA, AMPA, glyphoste, and glufosinate derivative, respectively. The optimized CI-MS/MS method was highly sensitive for the confirmation of these herbicides and their major metabolites in foods. LOD for 3-MPPA, AMPA, glyphosate and glufosinate in sample matrices was 0.01, 0.02, 0.005, and 0.02 ppm, respectively. Soybeans incubated in 152 ppm glyphosate solution for 6 hr before cultivation grew up to sprouts with normal size in 5-day cultivation (20~23℃). Quantification of herbicides revealed that glyphosate was transported fast from seeds (cotyledons) to sprouts (hypocotyls) and then concentrated in sprout tips with a low amount of AMPA formation during sprouting. Twenty-seven commercial samples, including 22 soybean, 3 soybean sprout, and 2 soybean milk samples, from local markets were analyzed for 3-MPPA, AMPA, glyphosate, and glufosinate residues. None of the above four analytes was detected in soybean sprout, soybean milk, and Non-GM (genetically modified) soybean samples. However, all 14 GM soybean samples were found to contain glyphosate, ranging from 0.23 to 0.94 ppm (mean value of 0.59 ppm), and AMPA residues, ranging from 0.10 to 0.34 ppm (mean value of 0.24 ppm). Kinetics of ozone-induced degradation of glyphosate, glufosinate, ethion, and permethrin in respective aqueous solution were determined for both reagent grade and commercial products. It was found that pesticides degraded faster in the absence than in the presence of formulating agents. At an initial concentration of 50 mg/mL, permethrin, ethion, and glyphosate reduced 98, 61, and 32 %, respectively, while glufosinate remained almost intact, after 60-min ozonation at a dosage of 18 mg/min. Two intermediates were found in GC chromatograms for both ethion and permethrin, whereas AMPA and 3-MPPA were detected from their parent glyphosate and glufosinate, respectively, during ozonation at a dosage of 32 mg/min.
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