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Bayer Corporation <strong>108139</strong>-1 Agriculture Division A Modified Analytical Method for the Determination of Cyfluthrin Residues in Various Plant Matrices by Chemical Ionization – GC/MS 1.0 Summary An existing analytical method 1 for the measurement of the total toxic residues (TTR) of cyfluthrin in various crop using gas chromatography/mass spectroscopy (GC/MS) with electron impact ionization(EI) was updated to GC/MS using chemical ionization (CI). The new method was developed for apple and pear matrices but was later modified to include all other matrices due to complications with some of the tougher crop matrices. This method works for all matrices analyzed except peanut nutmeat which required a modification due to its oily nature. The initial method used for apple and pear matrices consisted of homogenizing a 5.0 g sample in 45 mL of MeOH/aqueous 1.2 N HCl (4:1, v/v) for 2 min. After filtration into a 100-mL graduated mixing cylinder, the filter cake was returned to the extraction vessel and homogenized with 45 mL of MeOH for an additional 2 min followed by filtration and combination with the first extract. The sample was diluted to 100 mL with MeOH/aqueous 1.2 N HCl (4:1). A 50-mL aliquot of the sample was rotary evaporated to dryness. The dry residue was reconstituted in 25 mL of hexane in a boiling flask using sonication to dissolve as much of the solids as possible. A florisil column was prepared by adding 100 mL of hexane and a glass wool plug into a 250-mL glass bell column. Seven gram of florisil was added to the column followed by 6 g of sodium sulfate. The hexane was allowed to drain from the column until the level of hexane reached the top of the column packing. The 25-mL sample extract was added to the column and allowed to drain dropwise until the solvent level reached the top of the column packing. The boiling flask that contained the sample extract was washed with 40-mL of clean hexane. The wash was then added to the florisil column and allowed to drain until the solvent just reached the top of the column packing. A 125-mL boiling flask was placed under the florisil column, and the cyfluthrin was eluted from the column with 60-mL of hexane/acetone (9:1, v/v). The hexane/acetone mixture was rotary evaporated to dryness and reconstituted in 2.5 mL of toluene. The sample extracts were stored at < 10 ºC. The samples were analyzed using GC/MS equipped with a chemical ionization (CI) source and quantified using a known amount of deuterated internal standard. The internal standard was added to the samples after the extraction. The method used for the analysis of all other crop matrices except peanut nutmeat consisted of homogenizing a 5.0 g sample in 45 mL of MeOH/aqueous 1.2 N HCl (4:1) for 2 min. After filtration into a 100-mL graduated mixing cylinder, the filter cake was returned to the extraction vessel and homogenized with 45 mL of MeOH for an additional 2 min followed by filtration and combination with the first extract. The sample was diluted to 100 mL with MeOH. A 50-mL aliquot of the sample was added to a 60-mL vial and evaporated to approximately 4 to 5 mL using a Turbo Vap LV. Ten milliliters of water was added to the vial and mixed thoroughly. The sample extract was transferred to a 125-mL separatory funnel. The 60-mL vial was washed with two 15-mL aliquots of acetone/methylene chloride (1:2) with both aliquots being added to 22
Bayer Corporation <strong>108139</strong>-1 Agriculture Division the 125-mL separatory funnel. The separatory funnel was shaken for 30 s. The lower organic phase was drained through a funnel containing a glass wool plug, and 15 g of anhydrous sodium sulfate into a 60-mL vial. The sodium sulfate was washed with 10 mL of methylene chloride and collected in the same 60-mL vial. The sample was concentrated to dryness on a Turbo Vap LV and reconstituted in 25-mL of hexane. A florisil column was prepared by adding 50 mL of hexane and a glass wool plug into a 200-mL glass bell column. Seven gram of florisil was added to the column followed by 3 g of sodium sulfate. The hexane was allowed to drain from the column until the level of hexane just reached the top of the column packing. The 25 mL sample extract was added to the column and allowed to drain dropwise until the solvent level reached the top of the column packing. The 60-mL vial that contained the sample extract was washed with 40-mL of clean hexane. The wash was then added to the florisil column and allowed to drain until the solvent just reached the top of the column packing. A 60-mL vial was placed under the florisil column, and the cyfluthrin was eluted from the column with 40 mL of hexane/acetone (9:1, v/v). The hexane/acetone mixture was concentrated to dryness on a Turbo Vap LV and reconstituted in 2.5 mL of toluene. The sample extracts were stored at < 10 ºC. The samples were analyzed using GC/MS equipped with a CI source and quantified using a known amount of deuterated internal standard. The internal standard was added to the samples after the extraction. The peanut nutmeat samples required a significant change to the extraction scheme and clean-up due to the oily nature of the nutmeat matrix. In the normal extraction scheme, MeOH and water would not remove the cyfluthrin from the nutmeat once it was absorbed into the oil. The nutmeat method consisted of extracting a 5 g sample using 50 mL of hexane on a Soxtec extractor. The sample was boiled in 50 mL of hexane for 120 min and then rinsed for additional 30 min. The extract was transferred to a 50-mL graduated mixing cylinder. The Soxtec cup that contained the extract was washed with 5 mL of clean hexane and transferred to the 50-mL graduated cylinder. The sample was diluted to 50 mL with hexane and mixed thoroughly. A 25-mL aliquot of the sample was added to a 125-mL separatory funnel followed by 25 mL of ACN presaturated with hexane. The separatory funnel was shaken for 30 s. The lower ACN phase was transferred to another 125-mL separatory which contained 10 mL of hexane presaturated with ACN and shaken for 30 s. The lower ACN phase was collected in a 60-mL vial. Another 25 mL of ACN presaturated with hexane was added to the first separatory funnel and shaken for 30 s. The lower ACN phase was added to the second separatory funnel containing 10 mL of hexane presaturated with ACN and shaken for 30 s. The lower ACN phase was collected in the 60-mL vial with the first ACN phase. The extract was concentrated to dryness using a Turbo Vap LV. A florisil column was prepared by adding 50 mL of hexane and a glass wool plug into a 200-mL glass bell column. Seven grams of florisil was added to the column followed by 3 g of sodium sulfate. The hexane was allowed to drain from the column until the level of hexane just reached the top of the column packing. The 25-mL sample extract was added to the column and allowed to drain dropwise until the solvent level reached the top of the column packing. The 60-mL vial that contained the sample extract was washed with 40 mL of clean hexane. The wash was added to the florisil column and allowed to drain until the solvent reached the top of the column packing. A 60-mL vial was placed under the florisil column and the cyfluthrin was eluted from the column with 40 mL of hexane/acetone (9:1, v/v). The hexane/acetone (9:1, v/v) mixture was concentrated to dryness on a Turbo Vap LV and reconstituted in 2.5 mL of toluene. The sample extracts were stored at < 10 ºC. The samples 23
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