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蟲號: 1638859
注冊: 2012-02-24
專業(yè): 藥物分析

[求助] 蔗糖按EP檢驗亞硫酸鹽檢查問題

蔗糖按EP7.0檢驗，其中亞硫酸鹽一項不太明白，特請教各位：
見粗體部分，添加多少試劑？如何判斷反應終點？
方法原文如下：
Sulfites: maximum 10 ppm, calculated as SO2.
Determine the sulfites content by a suitable enzymatic method
based on the following reactions. Sulfite is oxidised by sulfite
oxidase to sulfate and hydrogen peroxide which in turn is
reduced by nicotinamide-adenine dinucleotide-peroxidase in
the presence of reduced nicotinamide-adenine dinucleotide
(NADH). The amount of NADH oxidised is proportional to the
amount of sulfite.
Test solution. Dissolve 4.0 g of the substance to be examined
in freshly prepared distilled water R and dilute to 10.0 mL with
the same solvent.
Reference solution. Dissolve 4.0 g of the substance to be
examined in freshly prepared distilled water R, add 0.5 mL of
sulfite standard solution (80 ppm SO2) R and dilute to 10.0 mL
with freshly prepared distilled water R.
Blank solution. Freshly prepared distilled water R.
Separately introduce 2.0 mL each of the test solution, the
reference solution and the blank in 10 mm cuvettes and add
the reagents as described in the instructions in the kit for
sulfite determination. Measure the absorbance (2.2.25) at the
absorption maximum at about 340 nm before and at the end
of the reaction time and subtract the value obtained with the
blank.
The absorbance difference of the test solution is not greater
than half the absorbance difference of the reference solution.

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