Carfentrazone-ethyl

Stable at pH 5, moderately stable at pH 7 and 9 Undergoes hydrolysis rapidly. The half-life ti/2) of carfentrazone-ethyl in aqueous photolysis at pH 5 is... 

The metabolism of carfentrazone-ethyl in animals and plants is similar. The major plant metabolites are carfentrazone-chloropropionic acid (C-CI-PAc), 3-desmethylcarfentrazone-chloropropionic acid (DM-C-CI-PAc), and 3-hydroxymethylcarfentrazone-chloropropionic acid (HM-C-CI-PAc). The major animal metabolites are carfentrazone-chloropropionic acid (C-CI-PAc) and carfentrazone-propionic acid (C-PAc). The tolerance expression for livestock and plant commodities is carfentrazone-ethyl plus the ester hydrolysis product, C-CI-PAc. 

The analytical method for carfentrazone-ethyl and its major metabolites in/on corn grain, grits, meal, flour, and starch (nonoil matrices) consists of extractions with acetone and deionized water, followed by a partition with hexane, which allowed the separation of the parent carfentrazone-ethyl from the acid metabolites. The hexane... 

Figure 1 Method flow chart for carfentrazone-ethyl determination...

Vigorously mix the aqueous and hexane fraction to partition carfentrazone-ethyl into the hexane fraction. Centrifugation may be necessary to break any emulsion that occurs. Remove and collect the hexane fraction for analysis of carfentrazone-ethyl. Partition the aqueous fraction with an additional 10 mL of hexane and add the hexane to the hexane from the first partition step. The aqueous fraction will be used for the analysis of the acid metabolites (see below). 

Concentrate the sample to 0.1 mL in a TurboVap at ca 50 °C and adjust the sample to a final volume of 1.0 mL with acetonitrile. Note there is the potential for loss of analyte if the samples go to dryness at this step. Analyze the sample for parent carfentrazone-ethyl by GC/ECD. 

Crop refined oils should be dissolved in hexane and partitioned with deionized water in a separatory funnel. The hexane fraction containing the carfentrazone-ethyl should be further partitioned with acetonitrile, and the rest of the analytical procedures for the parent compound should be followed. Concentrated HCl is added to the aqueous fraction to make the solution 1N and the samples are boiled under reflux for 1 h the rest of the analytical procedures for the acid metabolites should be followed. 

The analytical method to determine carfentrazone-ethyl and the major animal metabolites (C-Cl-PAc and C-Pac) in bovine matrices is similar to the method for crop matrices. The hexane-aqueous partition to separate carfentrazone-ethyl from the acid metabolites can be replaced by a Cig SPE cartridge. After the SPE, use 12 mL of water-acetonitrile (7 3, v/v) to elute the metabolites and then use 12 mL of hexane-ethyl acetate (4 1, v/v) to elute carfentrazone-ethyl after drying the cartridge. Follow the rest of the respective analytical procedures for carfentrazone-ethyl and the acid metabolites described in Sections 6.3 and 6.4. However, no reflux under boiling is necessary for the analysis of acid metabolites based on a goat metabolism study, because no conjugated acid metabolites were detected. Also, since HM-C-Cl-Pac is not analyzed for in the bovine matrices, no acylation is needed in the method. Analyze the metabolites by GC/MS, and monitor the ions at m/z 362 for C-Cl-Pac and 303 for C-PAc. 

A calibration curve was generated for each analyte at the initiation of the analytical phase of the smdy. Standard solutions for injection contained carfentrazone-ethyl or derivatized acid metabolites. Standard solutions were injected at the beginning of each set of assays and after every two or three samples to gage the instrument response. 

Carfentrazone-ethyl, C-Cl-PAc, C-PAc, DM-C-Cl-PAc and HM-C-Cl-PAc stock solutions of 1000 xg mL were prepared by dissolving the appropriate amounts of the analytical standards in acetonitrile. Working solutions were prepared in volumetric flasks by appropriate dilutions of the stock solutions for each analyte or combination of analytes. Working solutions containing the parent were prepared only in acetonitrile and working solutions containing acid metabolites were prepared in acetonitrile (underivatized) or hexane (derivatized). Underivatized solutions (containing the parent and/or metabolites in acetonitrile) were used for fortification. Solutions of derivatized esters were prepared simultaneously with the samples. Standard solutions... 

The amounts of carfentrazone-ethyl, C-Cl-PAc, C-PAc, DM-C-Cl-PAc and HM-C-Cl-PAc were quantitated by the external standard calibration method. 

The extraction efficiencies using a blender and a shaker were compared and both methods gave similar results. A corn sample treated with radiolabeled carfentrazone-ethyl and collected from a metabolism study was used for comparison. Multiple samples can be extracted simultaneously if extraction is performed by shaking. In addition, since the extraction procedures in the residue study closely followed the extraction scheme in the metabolism study, the resulting extraction efficiencies from both studies were almost identical. 

During the initial partition with hexane and water, the aqueous pH must not exceed 8. Carfentrazone-ethyl is extremely unstable under alkaline conditions and will rapidly degrade to C-Cl-PAc. At times, the workup of the crop samples, including the fortification step, should be completely separated for carfentrazone-ethyl and the acid metabolites, to avoid any possible interference from the parent compound. 

The injection standards of carfentrazone-ethyl must be in acetonitrile. Other solvents (e.g., ethyl acetate) lead to poor chromatography following injection of matrix samples. This can lead to apparent enhanced recoveries of analyte in the fortified samples. 

Matrix level (mgkg ) analyses Carfentrazone-ethyl C-Cl-PAc C-PAc... 

More recently, liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) have been evaluated as possible alternative methods for carfentrazone-ethyl compounds in crop matrices. The LC/MS methods allow the chemical derivatization step for the acid metabolites to be avoided, reducing the analysis time. These new methods provide excellent sensitivity and method recovery for carfentrazone-ethyl. However, the final sample extracts, after being cleaned up extensively using three SPE cartridges, still exhibited ionization suppression due to the matrix background for the acid metabolites. Acceptable method recoveries (70-120%) of carfentrazone-ethyl metabolites have not yet been obtained. 

Storage stability studies for carfentrazone-ethyl compounds on crop matrices have shown a pattern of stability for at least 7-24 months, depending on the study program or the maximum sample storage interval for the study. Carfentrazone-ethyl was not stable in field corn starch, potato tuber and bovine kidney. The residue results indicated that a significant portion of carfentrazone-ethyl was converted to C-Cl-PAc in these matrices however, the total amount of carfentrazone-ethyl and C-Cl-PAc accounted for the original spiking level. Since both carfentrazone-ethyl and C-Cl-PAc were determined in these stability studies, the instability of carfentrazone-ethyl was not of any concern. 

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