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作为食品膨松剂使用的发酵粉,其主要成份为碳酸氢钠(NaHCO-3)和硫酸钾铝(KAl(SO_4)_2)。在测定重金属过程中往往因形成Al(OH)_3沉淀而影响比色。为此,我们作了一些改进,现介绍如下。1 材料与方法1.1 仪器与试剂50ml 纳氏比色管。试剂:硝酸(AR);硫酸(AR);盐酸(AR);1N 盐酸;氨水(AR),1:1氨水;pH3.5的醋酸盐缓冲液(称25.0g醋酸铵溶于25ml 水中,加45ml 6N 盐酸,用稀盐酸或稀氨水调节pH 至3.5,用水稀释至100ml);1%酚酞指示液;硫化钠溶液(5g 硫化钠溶于10ml 水和30ml 甘油的混和液中);铅标准使用液:1ml=10μg 铅(按GB602-77配制后稀释10倍)。1.2 方法1.2.1 样品处理称取4.0g 样品,以少许水溶解,加硝酸15ml 和硝酸5ml 消化,冒白烟时取下进行脱硝,脱硝时产生白色沉淀影响定容,所以在第2次加水脱硝时加热至白色沉淀消失,溶液澄清时立即取
As a leavening agent, the main ingredients of baking powder are sodium bicarbonate (NaHCO-3) and potassium aluminum sulfate (KAl (SO 4) 2). In the determination of heavy metals often due to the formation of Al (OH) _3 precipitation and affect the colorimetric. For this reason, we made some improvements and are introduced below. 1 Materials and Methods 1.1 Instruments and reagents 50ml Nessler colorimetric tube. Reagents: Nitric acid (AR); Sulfuric acid (AR); Hydrochloric acid (AR); 1N Hydrochloric acid; Ammonia water (AR), 1: 1 ammonia water; Acetate buffer pH 3.5 (25.0 g ammonium acetate, Add 45ml of 6N hydrochloric acid, adjust the pH to 3.5 with dilute hydrochloric acid or dilute ammonia, dilute to 100ml with water); 1% phenolphthalein indicator solution; sodium sulfide solution (5g sodium sulfide dissolved in a mixture of 10ml water and 30ml glycerol) Use solution: 1ml = 10μg lead (according to GB602-77 diluted 10 times after preparation). 1.2 Methods 1.2.1 Sample Processing Weigh 4.0g sample, with a little water to dissolve, add nitric acid and nitric acid 15ml 15ml digestion, remove white smoke when the denitrification, denitrification produce white precipitate fixed volume, so the second water When denitrification heated to a white precipitate disappeared, the solution was taken immediately when clarified