asked in 科學化學 · 1 decade ago

克爾大法(Kjeldahl methed)

6月底考試,考了一題試說明克爾大法之原理與應用範圍,執行此方法時需用的試劑,此方法於何時由何人所開發完成,麻煩各位高手解惑一下

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  • 1 decade ago
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    The Kjeldahl method in analytical chemistry is a method for the quantitative determination of nitrogen in chemical substances developed by Johan Kjeldahl.

    The method consists of heating a substance with sulfuric acid which decomposes the organic nitrogen present to ammonium sulfate. In this step potassium sulfate is added in order to increase the boiling point of the medium (from 337 to 373 °C). Chemical decomposition of the sample is complete when the medium has become clear and colorless (initially very dark).

    The solution is then distilled with sodium hydroxide(added in small quantities) which converts the ammonium salt to ammonia. The amount of ammonia present (hence the amount of nitrogen present in the sample) is determined by back titration. The end of the condenser is dipped into a solution of boric acid. The ammonia reacts with the acid and the remainder of the acid is then titrated with a sodium carbonate solution with a methyl orange pH indicator.

    Protein+H2SO4 → CO2 + (NH4)2SO4 + SO2

    (NH4)2SO4 + 2NaOH → Na2SO4 + NH4OH

    2NH4OH + H2SO4 → (NH4)2SO4 + 2H2O

    Nowadays, the Kjeldahl method is largely automated and makes use of specific catalysts (mercury oxide or copper sulfate) to speed up the decomposition.

    2008-07-11 01:18:25 補充:

    在硫酸、硫酸鉀及以硫酸銅為催化劑的消化條件下,樣品中許

    多含氨基氮的有機物質會轉換為硫酸銨[(NH4)2SO4]。樣品在消

    化過程中,先形成銅銨錯合物,而後被硫代硫酸鈉Na2S2O3

    分解,分解產生的氨,在鹼性溶液中蒸餾出,被吸收於硫酸

    溶液,再依水中氨氮檢測方法測定氨氮的濃度即稱為凱氏氮。

    參考http://www.niea.gov.tw/niea/WATER/W45151A.htm

    Source(s): wikipedia
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