【導(dǎo)讀】標(biāo)注），操作人員也可以自行定制10種測(cè)定方法。80%的三氧化硫）是極為普通的。出于對(duì)操作人員的安全和環(huán)保因素考慮，后來(lái)這些。如果僅需控制蒸餾過(guò)程，就使用銨鹽。取ml溶液和10ml濃度為1N不含硫酸的氨水，被稀釋為1000ml氨水.1ml最后配成的溶液中含有–NH3.例如把上文中的數(shù)量換為100ml最終將得到每毫升N-NH3.當(dāng)必需控制消化時(shí)，先使用含化學(xué)藥品的純氮干燥至常重。在這種情況下推薦空白的有序控制。有多種處方來(lái)準(zhǔn)備催化劑(銅和硒)用于硫酸。硒和100g無(wú)水硫酸鈉被500毫升氨水溶解，加入500毫升濃硫酸。將毫升濃硫酸加入1公升蒸餾水中并再次蒸餾。機(jī)物中氨和氮的有機(jī)含量.液體，半固體或固體樣品同樣能夠予以分析。如果液體是以體積為準(zhǔn)，密度不是1，則測(cè)量結(jié)果指示的是體積而非重量。當(dāng)結(jié)果為干重量時(shí),含水固體或半固體樣品必須使之成為干粉狀稱重。的是為了更容易被消化，但主要目的是為了使物質(zhì)均勻以得到重要結(jié)果。重量與氮含量有關(guān)，至少應(yīng)含氨氮10-15mg。

　　

【正文】 1000 = conversion from mg mole to g mole W = sample w eight as grams. 10002319/A1 115 6) Comments: The described method proved its validity in determining sulphur dioxide and sulphites in a variety of foods. It’s simple and rapid and showed a good reproducibility. The correlation w ith the method MonierWilliams is 0,991. Using know n additions of sulphite, mean recovery is 97,9 177。 6,4%. 7) References: A) MonierWilliams method. Official Methods of Analysis (1984) n. and n. . Association of Official Analytical Chemists. Arlington. VA. USA. B) De Vries J. W., H. Ge, F. J. Ebert, J. M. Magnuson, M. K. Ogaw a. Analysis for total sulfite in foods by using rapid distillation follow ed by redox titration. . 69: 827 830 (1986). 10002319/A1 116 Determination of sulphur dioxide content in foods for quality control Sulphites and sulphur dioxide are monly used as preservatives in fruit, vegetable and other food products, for bleaching gelatins and beet sugar or as a disinfectant in brew eries and other food factories. In general terms the sulphur dioxide content (SO2) on foods should not overe 100 ppm. The SO2 content can be reduced by adding hydrogen peroxide w hich oxidizes it to sulphate. The amount of hydrogen peroxide can be calculated by the formula included in this method. Procedure 1) Equipment A)UDK 152 steam distillator B) magic stirrer and bar C) 25 ml glass burette having 0,1 ml subdivisions 2) Chemicals A) Hydrochloric acid concentrated, d. 1,16?1,18, 32–36% analytical grade, or B) Phosphoric acid concentrated, d. 1,69, 85%, analytical grade C) Solubile starch indicator. Mix 20 g of analytical grade starch pow der w ith deionized w ater to obtain a fluid mixture. Put the mixture in 1 l about of boiling deionized w ater w hile stirring. The starch solution stored at +4 176。C has a shelf life of one month. D) Iodine stock solution N. 18,0 g of potassium iodide (KI) analytical grade and 6,35 g of iodine (I) analytical grade are dissolved in a 500ml volumetric flask containing about 400 ml of deionized w ater. Mix, bring to volume and store in the dark in a dark glass bottle. The shelf life of the solution is 6 months about. E) Iodine w ork solution 5 x 103 N (0,005 N). 50 ml of the stock solution 0,1 N are diluted to 1000 ml in a volumetric flask by deionised w ater. 3) Sample 10 ? 0,1 g of representative processed material are tested directly 4) Distillation and titration Take off the distillate collecting tube from the condenser and fit a new silicone tube in the same position. Introduce about 75 ml of deionized w ater into a 250 ml flask. Add 10 drops of soluble starch indicator and some drops of 0,005 N iodine until a pale blu colour is obtained. Place the flask in the distillator and introduce the silicone tube inside. Weigh the sample (10 ? 0,1 g) in a beaker, add a few deionized w ater and mix. Introduce the sample ,and the w ashings w ith deionized w ater of the beaker used to w eight, into a test tube, introduce 30 ml of phosforic acid or 30 ml of hydrochloric acid and place in position the test tube in the distillator. Select the mode “Analisys without titration” and program a “Customizable method” having 0 ml of boric acid. 10002319/A1 117 Initiate the distillation cycle by START and collect about 100 ml of distillate. Take off the flask from the distillator, introduce a magic bar and place it on a magic stirrer. Regulate the level of the diluted solution of iodine in the burette and run the titration until a pale blu persists for 15 seconds. 5) Calculations The iodine solution volume used for the titration gives the content in ppm of sulphur dioxide: ppm of SO2 = iodine volume x 16 6) Addition of hydrogen peroxide If the content of sulphur dioxide overes 100 ppm, the amount of hydrogen peroxide to be added to bring the concentration below 100 ppm can be calculated by: ml of H2O2 3,5% (w /w ) per kg of treated mixture = (ppm SO2 – 100) x 1,8 10002319/A1 118 Method to determine the alcohol content on wines, musts and spirits by steam distillation and densimetry Official analytical method EEC The official journal of the EEC N176。 L272 dated 03/10/1990 presents the EEC regulation n. 2676/90, w hich describes the analytical methods for w ines. The alcohol steam distillation for w ines and musts w ith subsequent densimetry is described. Densimetry Equipment 1) Steam distillation unit. The alcohol can be distilled by steam。 increasing the speed of this phase. The equipment and technique must fulfil the requirements described for reference method. 2) Alcoholmeter – The alcoholmeter must fulfil the requirements of the Council Directive 76/765/EEC, dated 27 July 1987, related to alcoholmeters and densimeters for alcohol. This equipment must be controlled by a State service. A thermometer w ith degrees and tenths of degree in the range 030176。C and controlled w ithin 1/20 of degree centigrade must be used. The test tube is cylindrical w ith a diameter of 36mm and a height of 320mm kept vertical by a stand w ith a screw regulation. The internal diameter of the test tube must overe by at least 6 mm the maximum diameter of alcoholmeter. Procedure 1) Distillation – young or sparkling w ines w ill be deprived of most carbon dioxide by shaking 260 ml of w ine into a 500 ml flask previously siliconed. Into the distillation flask, introduce 250 ml of w ine measured in a volumetric flask w hose neck should have an internal diameter 12 mm maximum. Rinse the flask w ith 5 ml of w ater 4 times。 add 10 ml of milk of lime prepared w ith 120 g of Ca0 per liter. The pigments of w ine w ill change the colour due to alkalinity. If the w ines are very acid add more milk of lime until the touch reaction to phenolphtalein is clearly basic. Add some fragments of porous inert material and, if neces