scinco Mega-800 - Application Example

51 Mega-800 SCINCO
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5.11 Application example
Determination of nitrite in food is an important item in food safety and inspection.
The quantitation mode of MEGA-800 series spectrophotometers can be used to determine the nitrite
content, the procedures are shown as follows:
A. Reagent preparation
Distilled water should be used for preparing solution. The reagents, if not explained,
should be a.r..
 Ammonium chloride buffer: Pipet 500ml distilled water, 20.0ml hydrochloric acid into
a 1L volumetric flask. Shake up. Then pipet 50ml ammonium chloride into the
volumetric flask. Dilute to the mark with distilled water. If necessary, adjust the buffer
PH to 9.6-9.7 with dilute hydrochloric acid and dilute ammonium hydroxide.
 Zinc sulfate solution (0.42ｍｏｌ／Ｌ): dilute 120g zinc sulfate (ＺｎＳＯ4·７Ｈ2Ｏ)
to 1000ml with distilled water.
 Sodium dydroxide solution (20g/L): Dilute 20g sodium dydroxide to 1L with distilled
water.
 Sulfanilic acid solution: Dilute 10g sulfanilic acid into the mixed solution of 700ml
water and 300 ml glacial acetic acid. Put the solution into a brown bottle, and then
shake up. Preserve it room temperature.
 Ｎ－１－Naphthyethylenediamine (1g/L): Dilute
0.1gＮ－１－Naphthyethylenediamine to 100ml with 6% acetic acid solution. Put it
into a brown bottle, and shake up. And then put it into a refrigeratory for a week.
 Chromogenic agent: Mix Ｎ－１－Naphthyethylenediamine sloution (1g/L) with
sulfanilic acid solution equally.
 Sodium nitrite standard solution: Put 250.0mg sodium nitrite, dried in a silica gel dryer
for over 24 hours, into a 500ml volumetric flask. Dissolve it with water (about 200ml).
Add 200ml ammonium chloride buffer to it, and then diute it to the mark with water.
Swirl to mix. Preserve the solution at 4℃, avoiding light. Each milliliter of the solution
equals 500μｇ sodium nitrite.
 Sodium nitrite standard: Before measurement, pipet 1.0ml standard solution into a
100ml volumetric flask, and then dilute it to the mark with water. Each milliliter of the
solution is equal to 5.0μｇ sodium nitrite.
B. Sample Processing
Put measuring sample 10.00g (foodstuff 5g) into the breaker to break. Mix it with 70ml
water and 12ml sodium hydroxide. Adjust the sample PH to 8 with sodium hydroxide
(20g/L). And then put the sample solution into a 200ml volumetric flask. Mix it with 10ml