AOAC Official Method 995
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444BE547C95842B4B604AEFDA688F606 |
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2024-7-30 |
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7.3.08A,AOAC Official Method 995.01,Dithianon in Technical Products,and Formulations,Liquid Chromatographic Method,First Action 1995,Final Action 1998,CIPAC–AOAC Method,(Applicable to technical, suspension concentrate, and wettable powder,formulations.),See Table 995.01 for the results of the interlaboratory study supporting,the acceptance of the method.,Caution: See Appendix B, safety notes for the safe handling of,special chemical hazards—pesticides. Dithianon is a,broad spectrum fungicide, a mild mammalian eye and,skin irritant.,A. Principle,Test portion is dissolved in dioxane and acetonitrile and separated,on reversed-phase C18 column using acetonitrile–water mobile,phase. Dithianon is measured by the peak area of UV absorbance at,254 nm, using an external standard.,B. Apparatus,(a) Liquid chromatograph (LC).—With 10 mL loop injector. Operating,conditions: mobile phase flow rate, 1 mL/min; temperature,22 ± 2°C.,(b) LC column.—250 ′ 4.0 mm id, stainless steel, packed with,reversed-phase C18 on 5 mm silica. Number of theoretical,plates/25 cm must be 310 000, calculated on dithianon peak with retention,time 4–5 min (ca 4.5 min). Theoretical plates may be calculated,as 16 ′ (tR/W)2 where tR is the peak retention time andWis the,width at the baseline, both in the same units.,(c) UV detector.—Set at 254 nm to give 80–90% full scale deflection,for the highest concentration of dithianon standard solution,used in calibration.,(d) Electronic integrator.—Preferred for peak area measurements.,(e) Ultrasonic bath.,C. Reagents,(a) Dithianon standard solutions.—Accurately weigh 20, 40, 60,and 80 mg dithianon reference standard (analytical grade of defined,purity, available from Shell Forschung GmbH, PO Box 100, D-6501,Schwabenhein, Germany; or Chem Service, Inc., PO Box 599, West,Chester, PA 19381-0599, USA, www.chemservice.com) to the nearest,0.01 mg into separate 25 mL volumetric flasks, and dissolve in ca,20mLdioxane using sonication. Let solution adjust to room temperature.,Dilute to volume with dioxane. From each flask, transfer 5 mL,solution into separate 100mLflasks, add small volume of acetonitrile,and mix. Dilute to volume with acetonitrile. Label solutions, in order,of increasing concentrations, as standards A, B, C, and D.,(b) Solvents.—H2O, acetonitrile, and dioxane; LC grade.,(c) LC mobile phase.—Acetonitrile–water (70 + 30, v/v).,D. Preparation of Test Solution,Technical and formulated products.—Into 25 mL volumetric,flask, accurately weigh to the nearest 0.1 mg test portion, equivalent,to ca 50 mg dithianon. Dissolve in ca 20 mL dioxane by shaking or,sonicating 2–3 min. Let solution equilibrate to room temperature,and dilute to volume with dioxane. Transfer 5 mL solution into,100mLvolumetric flask. Dilute to volume with acetonitrile and mix,well.,E. Determination,[Note: Before analysis, it is necessary to equilibrate LC system by,pumping LC mobile phase 310 h with flow rate 1 mL/min. Metallic,parts (fritted metal filter) may be activated under acid conditions and,cause reduction of analyte to a hydroquinone.],Inject dithianon standard solution D and adjust instrument controls,to give 80–90% full scale deflection for dithianon peak. Continue,to make injections until system is stable, i.e., peaks are,symmetrical and retention time variations are ￡2%.,Make duplicate injections of dithianon standard solutions A–D,and record peak areas. Plot of mean peak areas vs concentrations,should pass through zero and should produce straight line. Alternatively,calculate response factors (area vs. concentration) for,dithianon standard solutions A–D. Individual response factors divided,by the calculated mean response factor should differ by ￡0.02.,Make duplicate injections of dithianon standard solutions and test,solution so every 2 tests (4 injections) are bracketed by 2 dithianon,standard solutions closest to analyte concentration, e.g.,SB, SB, T1A, T1A, T2A, T2A, SC, SC,where SB = dithianon standard solution B; SC = dithianon standard,solution C; T1A = solution 1 from test solution A; T2A = solution 2,from test solution A.,Response factors of sequential standard solutions should agree,within 2%.,F. Calculations,Calculate response factor (f; general) as follows:,. 2000 AOAC INTERNATIONAL,Table 995.01 Interlaboratory study results for determination of dithianon in technical products and formulations,by liquid chromatography,Product Dithianon, % Mean, % sr sR ra Rb RSDr, % RSDR, %,Technical 94–92 94.0–92.1 0.45–0.66 0.79–1.40 1.26–1.85 2.21–3.92 0.48–0.72 0.84–1.5,Suspension concentration 57c 57.3 0.46 0.82 1.29 2.30 0.80 1.4,Wettable powder 25c 25.3 0.20 0.26 0.56 0.73 0.97 1.0,a r = 2……
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