Prohexadione

The residue definition is for the parent, prohexadione-calcium, only. 

Prohexadione-calcium in the samples is extracted with acidic acetone by shaking (extracted as the free acid, prohexadione). The extract is purified by a series of... 

Prohexadione-calcium, analytical grade (Ihara Chemical Industries Co., Ltd)... 

Prohexadione-calcium standard solutions Dissolve 10 mg of prohexadione-calcium in 100mL of water to prepare a lOOmgL" solution. Transfer 100 p.L of this solution into a 30-mL test-tube, evaporate water to dryness under reduced pressure and to methylate prohexadione-calcium according to Section 6.3. Dissolve the product in acetonitrile to prepare the 0.05,0.2,0.4,0.6 and 0.8 mgL acetonitrile solutions. 

Transfer crop and soil samples from Section 6.1 (strawberry and rice grain) and Section 6.2 with 5 mL of methanol to 30-mL test-tubes and add to each test-tube 0.05 mL of concentrated sulfuric acid. Attach a condenser and reflux the solution at 75 °C for 60 min to esterify prohexadione to its corresponding methyl ester. Cool the reaction mixture to room temperature, add 20 mL of water and extract the reaction solution twice with 20 mL of dichloromethane. Dry the dichloromethane layer with a small amount of anhydrous sodium sulfate and collect the dried solution in a 100-mL round-bottom flask. Evaporate the solvent under reduced pressure. 

The residue R, expressed in mg kg prohexadione-calcium, is calculated from the following equation ... 

Wa = amount of prohexadione calcium for Vi read from calibration curve (ng)... 

Since prohexadione-calcium degrades rapidly in soil, soil samples should be analyzed or frozen immediately after sampling. ... 

The extraction method for prohexadione-calcium in soil was developed using alluvial soil and volcanic ash soil. Extraction by shaking the soil with a mixture of 1N sulfuric acid-acetonitrile (1 3, v/v) and/or of 1N sulfuric acid-acetone (1 3, v/v) showed an acceptable extraction recovery efficiency. 

Prohexadione in aqueous solution is not partitioned in n-hexane. More than 85% of prohexadione in solutions of pH 4 or lower is partitioned in ethyl acetate. 

Methyl esterification When prohexadione was treated with methanolic HCl (3%, w/v) or sulfuric acid-methanol (1 %, v/v) under reflux at 75 °C for 60 min, or with BFs-methanol (14%, w/v) under reflux at 75 °C for 30 min, the yield of the methyl ester of prohexadione was 95,93 and 82%, respectively (prohexadione, 10 qg, volume 2 mL of methanolic HCl, 2 mL of sulfuric acid-methanol and 1 mL of BFs-methanol). A solution of 1% (v/v) sulfuric acid in methanol was chosen for ease of preparation. Even if prohexadione was treated with 1% sulfuric acid in methanol at room temperature for 12h, the yield of prohexadione methyl ester was not different from that under reflux conditions as described in Section 6.3. The conditions for methyl esteriflcation in Section 6.3 were chosen because of shortening of the analysis time and the reproducibility of the reaction yield in residue analysis samples which could contain large quantities of contaminants. 

Since the methyl ester of prohexadione had lower polarity compared with prohexadione, an ODS column was very useful for purifying the sample. 

Since the methyl ester of prohexadione degrades rapidly in 1 M NaOH, it should not be handled under alkaline conditions. 

Prohexadione-calcium degrades in aqueous sodium hypochlorite solution. 

Prohexadione-calcium at the level of 0.08 mg kg in tap water degrades and disappears rapidly. Degradation of prohexadione-calcium can be prevented by addition of ascorbic acid at about 1 mg kg in tap water. Degradation products of prohexadione-calcium by aqueous chlorination are identified by mass spectrometry. 

Sample storage stability Prohexadione-calcium in strawberry, rice grain, rice straw, wheat grain and barley grain is stable at -20 °C for 40, 140, 60, 80 and 100 days, respectively. Approximately 88% of the applied prohexadione-calcium remained in soil when stored at —20 °C after 80 days. 

M. Ikeda, Y. Asano, and Y. Yusa, Degradation of prohexadione-calcium by aqueous chlorination, in Abstracts of the 20th Annual Meeting of the Pesticide Science Society of Japan, p. 152 (1995). 

Roemmelt, S. et al., Formation of novel flavonoids in apple (Malus x domesticd) treated with the 2-oxoglutarate-dependent dioxygenase inhibitor prohexadione-Ca, Phytochemistry, 64, 709, 2003. 

Ruhmann S, Treutter D. 2003. Effect of N-nutrition in apple on the response of its secondary metabolism to prohexadione-Ca treatment. Eur J Hort Sci 68 152-159. 

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