Resumen de la Edicion 20th del manual AOACDescripción completa
44.1.16 AOAC Official Surplus Method 906.03 Invert Sugar in Sugars and Sirups
J. Am. Chem. Soc. 28, 663(1906); 26, 541(1907). J. Res. Natl. Bur. Standards 24, 589(1940).
Munson-Walker General Method
Determination of Reduced Copper
Final Action Surplus 1989
By Direct Weighing Weighing of Cuprous Oxide 31.039
Reagents 31.037 Digest asbestos, amphibole variety Asbestos.— Digest (Caution: See Appendix B: Asbestos), with HC1 (1 + 3) 2–3 days. Wash acid-free, digest similar period with 10% NaOH soln, NaOH soln, and then then treat few hr with hot alk. tartrate soln, 923.09(A)(b)(alk. tartrate solns that have stood for some time may be used for this purpose). Wash asbestos alkali-free; digest several hr with HNO 3 (1 + 3); and after washing acid-free, acid-free, shake with H 2O into fine pulp. In prepg gooch, make film of asbestos 6 mm thick and wash thoroly with with H2O to remove fine fine particles. If pptd Cu 2O is to be weighed as such, wash crucible with 10 mL alcohol and then with 10 mL ether; dry 30 min at 100 , cool in desiccator, and weigh. Other reagents reagents and solns used are described in 923.09(A). Solns may be clarified by neut. Pb(OAc) 2 soln, 925.46(B)(d)(never (never basic Pb(OAc) Pb(OAc)2). Remove excess Pb with dry Na oxalate. Precipitation Precipitation of Cuprous Oxide Oxide 31.038 Tran Transf sfer er 25 mL each each of CuSO CuSO4 and and alk alk.. tar tartr trat atee sol solns ns to 400 400 mL mL be beaker aker of alka alkalli-re i-resi sist staant gla glass and and add add 50 50 mL redu reduci cing ng suga sugarr sol soln; n; or if smal smalle lerr vol vol.. of of sug sugar ar soln soln is use used, d, add add H2O to to mak makee fin final al vol vol.. 100 100 mL. mL. Hea Heatt beaker on asbestos gauze over Bunsen burner, regulate flame so that boiling begins in 4 min, and continue boiling exactly 2 min. (It is important that these directions be strictly observed. To regulate burner for this purpose it is advisable to make preliminary tests, using 50 mL reagent and 50 50 mL H2O, before proceeding with actual detn. Elec. heater may be used instead of burner.) Keep beaker covered with watch glass during heating. Filter hot soln at once thru asbestos mat in porcelain gooch, using suction. suction. Wash ppt of of Cu2O thoroly with with H2O at at ca ca 60 and either weigh directly as CuO, det. amt of reduced reduced Cu by 929.09 (See 44.1.17), or det. one of methods described in 929.09 (See 44.1.17). Conduct blank detn, using 50 mL reagent and 50 mL H2O, and if wt Cu2O obtained obtained is >0.5 mg, correct correct result result of reducing sugar detn accordingly. Alk. tartrate soln deteriorates on standing, and wt Cu 2O obtained in blank blank increases.
(Use only for detns in solns of reducing sugars of comparatively high purity. In products contg large amts of mineral or org. impurities, including sucrose, det. Cu in the Cu2O by one of methods methods described described in 929.09, since the Cu2O is likely to be contaminated contaminated with foreign matter.) Prep. gooch as in 929.09. Collect Collect pptd pptd Cu2O on matt as in 929.09; wash thoroly thoroly with with hot H2O, then with 10 mL alcohol, and finally with 10 mL ether. Dry ppt 30 min in over at 100 , cool, and weigh. Obtain wt invert invert sugar equiv. equiv. to wt Cu2O from 940.39. Number of mg Cu2O reduced by given amt of reducing sugar varies, depending upon whether or not sucrose is present. In table, absence of sucrose is assumed except in entries under invert sugar and lactose, where, in addn to columns for these alone, columns are given for their mixts with sucrose in specified ratios in the case of lactose adn in specified amts amts of tot total al sug sugar ar in in 50 mL mL soln soln in in the the case case of of inve invert rt sug sugar. ar. (Lat (Later er Hamm Hammon on tabl tablee has has repl replac aced ed orig origin inal al Muns Munson on-Walk Wa lker er tabl table, e, wher wheree appl applic icab able le.) .) By Titration with with Sodium Thiosulfate Thiosulfate 31.040
Prep. soln contg 39 g Thiosulfate std soln.— Prep. Na2S2O3.5H2O/L. O/L. Accur Accurate ately ly weigh weigh 0.20.2-0.4 0.4 g pure pure electrolytic Cu and transfer to 250 mL erlenmeyer roughly marked at 20 mL intervals. Dissolve Cu in 5 mL HNO3 (1+1), dil. to 20 or 30 mL, boil to to expel red fumes, add slight slight excess ssatd ssatd Br-H 2O, and boil until Br is completely removed. Cool, and add 10 mL NaOAc soln (574 g trihydrate/L). Prep. 42 g/100 mL KI soln made very slightly alk. to avoid formation and oxidn of HI. Add 10 mL of of the KI KI soln soln and titr. titr. with with Na2S2O3 soln to light yellow. Add enough starch indicator, 922.03(f), to produce marked blue. As end point nears, add 2 g KSCN and stir until completely dissolved. Continue titrn until ppt is perfectly white. 1 mL Na2S2O2 soln soln - ca ca 10 10 mg mg Cu. Cu. It is essential essential for Na Na 2S 2O 2 titrn titrn that that concn concn of KI in soln be carefully regulated. If soln contains <320 mg
2 Cu, at completion of titrn 4.2-5 g KI should have been added for each 100 mL totl soln. If greater amts of Cu are present, add KI soln slowly from buret with const agitation in amts proportionately greater. 31.041
Wash pptd Cu2O, cover gooch with watch glass, and dissolve the Cu2O with 5 mL HNO (1+1) directed 3 under watch glass with pipet. Collect filtrate in 250 mL erlenmeyer roughly marked at 20 mL intervals, and wash watch glass and gooch Cu-free. Proceed as in 929.09, beginning, “...boil to expel red fumes, ...” Obtain wt reducing sugar equiv. to wt Cu from 940.39. Refs.: JAOAC 12, 38(1929); 18, 83(1935). J. Am. Chem. Soc. 57, 845(1935). Anal. Chem. 21, 975(1949). By Titration with Potassium Permanganate 31.042
(a) Potassium permanganate std soln.—Approx. 0.1573 N , and contg 4.98 g/L. Prep. and stdze as in 940.35, using 0.35 g Na oxalate. (b) Ferric sulfate soln. —Dissolve 135 g FeNH4(SO4)2.12H2O or 55 g anhyd. Fe2 (SO4 )3 in H2 O, and dil. to 1 L. Det. Fe2(SO4)3 in stock supply by strong ignition to Fe2O3. Titr. 50 mL Fe2(SO4)3 soln, acidified with 20 mL 4 N H2SO4, with MnnO4 soln, and use this titer as 0-point correction. (c) Ferrous phenanthroline indicator .—Dissolve 0.7425 g o-phenanthroline.H 2O in 25 mL 0.025 M FeSO4 soln (6.95 g FeSO4.7H2 O/L). Determination 31.043 Filter the Cu2O thru gooch, and wash beaker and ppt thoroly. Transfer asbestos pad to beaker with glass rod. Add 50 mL Fe2(SO4 )3 soln and stir vigorously until Cu2O is completely dissolved. Examine for complete soln, holding beaker above eye level. Cu2O must be quant. transferred; if necessary, immerse crucible in soln and make sure adhering Cu2O is dissolved. remove crucible with glass rod and wash with H2O. Add 20 mL 4 N H2SO4 and titr. with std KmnO4 soln. As end point approaches, add 1 drop ferrous phenanthroline indicator. At end point, brownish soln changes to green. Obtain wt reducing sugar equiv. to wt Cu from 940.39.