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jackchen129

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[交流] 铵根离子测定中出现的奇怪问题

我用以下方法测定铵根离子浓度,为什么吸光值随着铵根离子浓度的增加而减小(也就是反应之后随着铵根离子浓度的增加,蓝色逐渐变浅)?不是正比关系而是反比关系。

Chemical needed
Phenol
Sodium nitroprusside (sodium pentacyanonitrosylferrate III)
Sodium hydroxide
Sodium hypochlorite (5% available chlorine)
Ammonium sulfate
2M KCl

Reagent A: 5 g phenol and 25 mg sodium nitroprusside in 500 ml water
Reagent B: 2.5 g sodium hydroxide and 0.2 ml 5% chlorine in 500 ml water
Ammonia standards: Using ammonium sulfate, prepare a stock standard containing 6.0 g ammonia/100 ml (will be more than 0.3 g as need to adjust for sulfate).  

Analytical Procedure
Take 4, 8, 12, 16 or 20 氀 of stock standard ammonia standard and add to 5.0 ml of reagent A in screw cap test tube.
Close tube and votex for 10 sec.
Immediately add 5.0 ml of reagent B and close tube
Place test tubes at 37C for 20 min
Read absorbance immediately at 625 nm

Prepare a reagent blank containing 5.0 ml reagent A and 5.0 ml of reagent B.  Hold for 20 min at 37C before zeroing instrument

谢谢!!!
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