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ouyangqian鐵桿木蟲 (小有名氣)
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[求助]
如何去除EP重金屬檢查2.4.8 方法F中混合酸的疑問
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如題:我有一品種的的質(zhì)量標(biāo)準(zhǔn)是EP7.0,其中重金屬檢查項(xiàng)要求按EP7.0 上2.4.8重金屬檢查法的方法F進(jìn)行檢查,具體要求是這樣的:精密稱取1.0g供試品置干凈的100ml長頸凱氏燒瓶中，用夾子將燒瓶夾成45°角。加幾ml的硫酸-硝酸（8：10）的混合液充分潤濕樣品。緩慢加熱到反應(yīng)開始后停止加熱，待反應(yīng)平息，再分幾次加硫酸-硝酸（8：10）的混合液,每次加酸后都加熱，直至將18ml的混合酸全部加完。提高加熱的溫度使反應(yīng)液輕沸直至反應(yīng)液變暗。放冷，加2ml硝酸，繼續(xù)加熱至溶液變暗。繼續(xù)加熱，直至接著加硝酸溶液，不再進(jìn)一步的變暗。然后加強(qiáng)熱使溶液變稠，產(chǎn)生白煙。停止加熱，放冷，小心加入5ml水，輕沸至粘稠，產(chǎn)生白煙，繼續(xù)加熱至反應(yīng)液減少到約為2-3ml為止。 現(xiàn)在遇到的問題是混合酸（硫酸：硝酸=8:10)很難蒸發(fā)掉，要想蒸到只剩2~3ml,蒸了16h還未能蒸掉，這樣，檢驗(yàn)要做四個(gè)樣品（空白樣，對照樣 供試品樣和監(jiān)控樣）就很難辦了，不知是否有人做過類似的檢驗(yàn)，用的是怎樣的電爐？ 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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