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ouyangqian铁杆木虫 (小有名气)
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[求助]
如何去除EP重金属检查2.4.8 方法F中混合酸的疑问
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如题:我有一品种的的质量标准是EP7.0,其中重金属检查项要求按EP7.0 上2.4.8重金属检查法的方法F进行检查,具体要求是这样的:精密称取1.0g供试品置干净的100ml长颈凯氏烧瓶中，用夹子将烧瓶夹成45°角。加几ml的硫酸-硝酸（8：10）的混合液充分润湿样品。缓慢加热到反应开始后停止加热，待反应平息，再分几次加硫酸-硝酸（8：10）的混合液,每次加酸后都加热，直至将18ml的混合酸全部加完。提高加热的温度使反应液轻沸直至反应液变暗。放冷，加2ml硝酸，继续加热至溶液变暗。继续加热，直至接着加硝酸溶液，不再进一步的变暗。然后加强热使溶液变稠，产生白烟。停止加热，放冷，小心加入5ml水，轻沸至粘稠，产生白烟，继续加热至反应液减少到约为2-3ml为止。 现在遇到的问题是混合酸（硫酸：硝酸=8:10)很难蒸发掉，要想蒸到只剩2~3ml,蒸了16h还未能蒸掉，这样，检验要做四个样品（空白样，对照样 供试品样和监控样）就很难办了，不知是否有人做过类似的检验，用的是怎样的电炉？ 附英文原文： METHOD F Test solution. Place the prescribed quantity or volume of the substance to be examined in a clean, dry, 100 ml long-necked combustion flask (a 300 ml flask may be used if the reaction foams excessively). Clamp the flask at an angle of 45°. If the substance to be examined is a solid, add a sufficient volume of a mixture of 8 ml of sulphuric acid R and 10 ml of nitric acid R to moisten the substance thoroughly; if the substance to be examined is a liquid, add a few millilitres of a mixture of 8 ml of sulphuric acid R and 10 ml of nitric acid R. Warm gently until the reaction commences, allow the reaction to subside and add additional portions of the same acid mixture, heating after each addition, until a total of 18 ml of the acid mixture has been added. Increase the amount of heat and boil gently until the solution darkens. Cool, add 2 ml of nitric acid R and heat again until the solution darkens. Continue the heating, followed by the addition of nitric acid R until no further darkening occurs, then heat strongly until dense, white fumes are produced. Cool, cautiously add 5 ml of water R, boil gently until dense, white fumes are produced and continue heating to reduce to 2-3 ml. Cool, cautiously add 5 ml of water R and examine the colour of the solution. If the colour is yellow, cautiously add 1 ml of strong hydrogen peroxide solution R and again evaporate until dense, white fumes are produced and reduce to a volume of 2-3 ml. If the solution is still yellow in colour, repeat the addition of 5 ml of water R and 1 ml of strong hydrogen peroxide solution R until the solution is colourless. Cool, dilute cautiously with water R and rinse into a 50 ml colour comparison tube, ensuring that the total volume does not exceed 25 ml. Adjust the solution to pH 3.0-4.0, using short range pH indicator paper as external indicator, with concentrated ammonia R1 (dilute ammonia R1 may be used, if desired, as the specified range is approached), dilute with water R to 40 ml and mix. Add 2 ml of buffer solution pH 3.5 R. Mix and add to 1.2 ml of thioacetamide reagent R. Mix immediately. Dilute to 50 ml with water R and mix. |
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