关 键 词：

AOAC Official 984.16 N-Nitrosodimethylamine in Nonfat Dry Milk Gas Chromatog

资源描述：

AOAC Official 984.16 N-Nitrosodimethylamine in Nonfat Dry Milk Gas Chromatographic First Action 1984 Final Action 1992_AOAC.rar,AOAC Official 984.16 N-Nitrosodimethylamine in Nonfat Dry Milk Gas Chromatog

内容简介：

33.5.11AOAC Of fi cial Method 984.16N-Nitrosodimethylaminein Non fat Dry MilkGas Chro mato graphic MethodFirst Ac tion 1984Fi nal Ac tion 1992Cau tion:NDMA is po tent car cin o gen; use ex treme cau tion inhan dling com pound. Pref er a bly, pur chase di lutedstan dard avail able from com mer cial sup plier and carry out all work in fume hood. Use mechanical pipettingaids for mea sur ing all so lu tions and wear protectivegloves while han dling NDMA stan dard. Be foredis posal, de stroy stan dards ac cord ing to method ofWil liams Food Cosmet. Toxicol. 13, 302(1975).A. Prin ci pleTest portion is mixed with Celite, am mo nium sulfamate, anddi lute H2SO4 and packed in chro mato graphic col umn con tain ingan hy drous Na2SO4. N-Nitrosodimethylamine (NDMA) is elutedwith CH2Cl2, con cen trated and an a lyzed by GC with ther mal en ergyan a lyzer (TEA).B. Re agents(a) Celite 545.Not acid-washed. Heat over night at 700C, cool,and store in tightly sealed jar.(b) Am mo nium sulfamatesul fu ric acid so lu tion.Dis solve 1 gam mo nium sulfamate in 100 mL 0.5M H2SO4.(c) Di chloro methane.Dis tilled in glass CH2Cl2. Test forNDMA con tam i na tion be fore use: Con cen trate 200 mL to 1 mL asde scribed un der con cen tra tion,E, and then an a lyze 10 mL aliquot byGCTEA. Test must show ab sence of NDMA.(d) Wa ter.Dou ble-distilled, or equiv a lent. Test for NDMAcon tam i na tion be fore use; use through out: Take 50 mL H2O, add2 mL 10M KOH (570 g/L), ex tract with two 50 mL por tions ofCH2Cl2, and test for NDMA con tam i na tion as in (c). If test in (c) isneg a tive (which in cludes 50 mL H2O), there is no need to test watersep a ra tion.(e) NDMA stan dard.Serially di lute pre vi ously pre pared stockso lu tion (100 mg/mL) to work ing stan dard (0.1 mg/mL) with CH2Cl2.C. Re agent BlankTo en sure ab sence of con tam i na tion, carry re agent blank,ex clud ing non fat dry milk, through all steps. If con tam i na tion isin di cated, test each re agent sep a rately. CH2Cl2 and H2O are mostlikely sources.D. Ap pa ra tus(a) Chro mato graphic tube.Glass, 32 id 400 mm long, withstop cock.(b) Tamping rod.19 mm di am e ter disk.(c) Pow der fun nel.Top di am e ter 140150 mm, stem2528 mm od.(d) Evap o ra tive-concentrator.Kuderna-Danish (K-D),250 mL with 4 mL con cen tra tor tube and 0.1 mL sub di vi sions from0 to 2.0 mL, and 3-chamber Snyder col umn (Kontes Glass Co.,570001, 570050, and 503000, re sp e c tive ly ;). Check ac cu racy of grad u a tions in tubebe fore use.(e) Gas chromatograph-thermal en ergy an a lyzer.Gaschromatograph in ter faced to TEA Model 502L (Thermo Elec tronCorp., 115 Sec ond Ave, Waltham, MA 02154, USA) and with2.7 m 4 mm id glass col umn packed with 10% Carbowax 1540 and 5% KOH on 100120 mesh Chromosorb WHP. Pro gram col umnfrom 100? to 180C at 4C/min for each anal y sis with car rier gas(Ar) flow rate set at 40 mL/min. In jec tion port, 200C.Op er ate TEA at ca 1.1 mm Hg vac uum, 450C fur nace, and 2 to4 at ten u a tion ranges, with liq uid N2 trap. Con nect out put of TEA to1 mV re corder (chart speed, 1.3 cm/min, or equiv a lent).E. DeterminationWeigh 25.0 0.1 g non fat dry milk into tared 600 mL beaker. Add40 g Celite, 25 mL am mo nium sulfamateH2SO4 so lu tion, and mixus ing stainless steel spat ula un til ho mo ge neous and fluffy incon sis tency. Place small glass wool plug at bot tom ofchro mato graphic tube with end of tamp ing rod ex tend ing throughfun nel open ing and cover with 20 g an hy drous Na2SO4. Slowly pournon fat dry milkCelite mix ture (through fun nel) into col umn, a lit tle at a time, and tamp down firmly (avoid pack ing too tightly) to depthof 1620 cm. Rinse beaker with 125 mL CH2Cl2 and pour rinse oncol umn through fun nel be fore re mov ing tamp ing rod. Re movetamp ing rod and col lect eluate in 250 mL K-Devap o ra tive-concentrator fit ted with 4 mL con cen tra tor tube. Ifnec es sary, ad just col umn flow to 12 mL/min. (Fail ure to ob tainad e quate sol vent flow in di cates that col umn is too tightly packed.)End col lec tion when col umn stops drip ping.Add 23 car bo run dum boil ing chips, fit Snyder col umn, andcon cen trate CH2Cl2 eluate to ca 4 mL in 55?60C water bath. Raisecon cen tra tor out of bath, let Snyder col umn drain com pletely, anddis con nect con cen tra tor tube. Fur ther con cen trate ex tract in tube to1.0 mL un der gen tle stream of N at am bi ent tem per a ture. Fi nalcon cen tra tion must be done slowly, over ca 30 min.In ject 8 mL NDMA stan dard (0.1 mg/mL) into GC-TEA ap pa ra tusun der con di tions stated above, D(e). Sim i larly, in ject 8 mL testex tract and re peat anal y sis. Mea sure peak heights (1 mm) of bothstan dard and test ex tract, and cal cu late NDMA con cen tra tion in testsam ple us ing fol low ing for mula:ppb (mg/kg) NDMA in NFDM =(PH/PH) C V (1000/W) Zwhere C = con cen tra tion of NDMA stan dard (mg/mL); V = fi nalvol ume of test ex tract (mL); PH = NDMA peak height from testextract (mm); PH =