AOAC Official Method 973
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508C3E4F94114932A6E3890BDE4337D9 |
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0.07 |
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1 |
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日期： |
2016-2-28 |
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文本摘录（文本识别可能有误，但文件阅览显示及打印正常，pdf文件可进行文字搜索定位）：
8.1.03,AOAC Of fi cial Method 973.10,Flu o rides in Haz ard ous Sub stances,Potentiometric Method,First Ac tion 1973,Fi nal Ac tion 1975,A. Apparatus,(a) pH me ter.—With ex panded mV scale (Model 250, Nova,Analytics Corp., 6E Gill St, Woburn, MA 01801, USA;,www.novaanalytic.com; or equiv a lent), flu o r ide ion-selective,elec trode (Model 940900, Orion Re search, Inc., available through,ThermoElectron Corp., Waltham, MA 02454, USA;,www.thermo.com, or equiv a lent), and sin gle junc tion ref er ence,elec trode, plas tic sleeve-type (Model 900100, Orion Re search Inc.,or equiv a lent; or Orion com bi na tion elec trode 960900).,(b) Mag netic stir rer.—With PTFE-coated stir ring bar. Use foam,mat to in su late sam ple from mo tor heat.,(c) Beakers.—150 mL poly propy lene, or equiv a lent.,(d) Graph pa per.—Lin ear or semi-antilog, vol ume cor rected,No. 90-00-90 Gran’s plot pa per (Orion Re search Inc., or equiv a lent).,B. Re agents,(a) Buffer so lu tion.—pH 6.0. Add 77.0 g ammonium acetate and,0.452 g am mo nium ci trate to 1 L H2O. Ad just to pH 6.0 with,ammonium acetate.,(b) So dium flu o ride stan dard so lu tion.—1 mg F-/mL (re agent,grade, dried 4 h at 105°C). Pre pare NaF, 2.2108 g/L, in buffer,so lu tion. Store in plas tic bot tles. Com pare with 1 mg F- /mL so lu tion,pre pared from USP Ref er ence Stan dard; equiv a lent read ing of,±1 mV is sat is fac tory.,C. De ter mi na tion,(Stir all so lu tions con stantly at same rate through out ti tra tions.,Let elec trodes equilibrate 32 min be fore ad di ng F- stan dard so lu tion,and 30 s af ter each ad di tion of F- stan dard so lu tion.),(a) Blank.—Re cord mV val ues (E￠) of 100 mL buffer so lu tion,af ter ad di tion of 4 mL stan dard F- so lu tion from 10 mL buret and,af ter each ad di tional mL up to 10 mL. (Pre lim i nary mV val ues will,not fall on lin ear range of re sponse curve.) Vol ume stan dard so lu tion,added = V￠.,(b) Test so lu tions.—Es ti mate molarity of test so lu tions from,di rect read ing. Di lute test so lu tions, if nec es sary, to ca 0.001M F- .,Trans fer 50 mL test so lu tion to beaker and add 50 mL buffer,so lu tion. Re cord ini tial mV read ing (E0). If ini tial read ing is,<–50 mV, so lu tion is too con cen trated. Di lute test so lu tion to avoid,as ymp totic slope. Re cord mV reading (E) af ter each mL F- stan dard,so lu tion added, up to 10 mL. Rinse elec trodes with H2O be tween test,so lu tions. Vol ume stan dard so lu tion added = V.,D. Cal cu la tions,(a) Lin ear graph pa per.—For each ad di tion of F- standard,so lu tion and cor re spond ing E value, cal cu late for blank:,Z￠ = antilog [log(V0 + V￠) – 0.017(E￠)],where V0 is orig i nal vol ume of so lu tion to which F- stan dard,so lu tion was added (100 mL). E￠ is treated al ge bra ically ( + or – as,read). Plot Z￠ against mL (or mg) F- stan dard so lu tion added and,ex trap o late plot to F- axis to ob tain mL F- in blank, Ve￠. On graph,assign x axis to mL F- , with 0 at cen ter of axis and mL F- , in creas ing,in both di rec tions to left and right. Plot ex per i men tal read ings of mL,F- on right por tion of hor i zon tal axis so that ex trap o la tion is,per formed on left por tion of axis.,Sim i larly, cal cu late for test solution:,Z = antilog [log(V0 + V) – 0.017(E)],where V0 is orig i nal vol ume so lu tion to which F- stan dard so lu tion,was added (100 mL). Plot Z against mL (or mg) F- stan dard so lu tion,on same graph as blank and ex trap o late to mL F- axis ob tain ing mL,F- in test solution, Ve.,(b) Semi-antilog pa per.—Plot E ver sus Ve di rectly for both blank,and test material (scale E at 5 mV for each ma jor grid line cross ing,Y axis). Be gin plot with most neg a tive E read ing that al lows,ex trap o la tion of Ve on left por tion of mL F- axis. Ob tain Ve and Ve￠,by ex trap o la tion to left side of 0 mL (mg) F- .,F, % = ( ) ( ),( ),V V B,W C,e e - ￠ ′ ′,′ ′,100,1000 mg / g,where B = vol ume of di lu tion, W = mL or g test so lu tion, and C =,aliquot (50 mL max i mum) buf fered to 100 mL.,Ref er ence: JAOAC 56, 798(1973).,CAS-7782-41-4 (flu o rine),2006 AOAC INTERNATIONAL……
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