Industrial Dimethylformamide (3)

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The water in the sample reacts with iodine and sulfur dioxide in the electrolyte, and the reaction formula is:

I ₂ -SO ₂ +H ₂ O→2HI+SO ₃

2I ^- -2E ^- → the I ₂

The number of iodine molecules participating in the reaction is equal to the number of water molecules, and the boron produced by electrolysis is proportional to the amount of electricity consumed.

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Electrolyte: Karl Fischer reagent or the electrolytic liquid (commercially available reagent) used in conjunction with the Karl Fischer Moisture Analyzer

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Add electrolyte, adjust the instrument according to the instrument manual, when the instrument enters the working state, calibrate according to the requirements of the instrument manual

Take about 5ml laboratory sample with a syringe (or adjust it according to the water content in the sample), seal the needle hole of the syringe with a rubber gasket, and weigh to the nearest 0.

4.

The mass fraction of water w ₂ , the value is expressed in %, calculated according to formula (2):

Where:

m ₁ —The value of water quality read on the display screen of the moisture analyzer, in grams (g);

m ₂ —The value of the mass of the syringe and the sample before injection, in grams (g);

m ₃ —The value of the mass of the syringe and the sample after the injection, in grams (g)

Take the arithmetic average of the two parallel determination results as the report result, and the absolute difference between the two parallel determination results shall not exceed 0.
0020%
.

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6.
2 Karl Fischer Capacity Method

According to the provisions of GB/T62832008
.

Take the arithmetic mean of the two parallel determination results as the determination result
.
The absolute difference between the two parallel determination results is not more than 0.
0020%
.

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7 Determination of iron content

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7.
1 Principle of the method

The sample of the experiment case was directly added with excess hydroxylamine hydrochloride solution and 1,10-phenanthroline ethanol solution, diluted with ethanol , and the iron content in the sample was determined by spectrophotometry at 510nm
.

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7.
2 Reagents

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2.
1 Anhydrous ethanol
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2.
2 Hydroxylamine hydrochloride solution: 100 g/L
.

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7.
2.
3 1,10-phenanthroline ethanol solution: 3g/L
.

Weigh 0.
9 g of 1,10-phenanthroline (C ₁₂ H ₈ N ₂ ·H ₂ O), dissolve it in 300 mL of ethanol , and mix well
.

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7.
2.
4 Iron (Fe ²⁺ ) standard solution: 0.
005mg/mL (Fe ²⁺ )
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Take 25.
00mL iron (Fe ²⁺ ) standard solution with a concentration of 0.
1mg/mL in a 500mL volumetric flask, dilute to the mark with water, and shake well
.

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7.
3 Apparatus

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3.
1 Visible spectrophotometer
.

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3.
2 Cuvette: 5cm
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4 Analysis steps

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1 Drawing of standard curve

Add iron standard solution 0.
00mL, 1.
00mL, 2.
00mL, 3.
00mL, 4.
00mL, 5.
00mL, 6.
00mL to 7 100mL volumetric flasks respectively, add water to about 75mL, add 5mL hydroxylamine hydrochloride solution, shake well, and let stand 5min, then add 10mL 1,10-phenanthroline ethanol solution, mix well, dilute with ethanol to the mark, stopper the bottle, shake well, at this time the amount of iron in each volumetric flask is 0ug, 5ug, 10μg, 15μg, 20μg, 25ug, 30ug
.
Let it stand for 5 min, and use the solution without adding iron standard solution as a reference.
Use a spectrophotometer at 510nm and use a 5cm cuvette to measure the absorbance of the solution with different iron content after color development
.
Take the iron content as the abscissa (ug) and the corresponding absorbance as the ordinate to make a standard curve
.

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7.
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2 Determination of samples

Add 75.
00mL laboratory sample crystals into two 100mL volumetric flasks, and add hydroxylamine hydrochloride solution.
The following steps are the same as those for making standard curve
.
Using the sample solution without the developer as a reference, measure the absorbance of the sample with the developer after color development
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Check the iron content (ug) of the sample from the standard curve
.

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7.
5 Result calculation

The mass fraction w ₃ of iron in the sample , the value is expressed in mg/kg, calculated according to formula (3)

Where:

m ₄ -the value of the iron mass in the sample found on the standard curve, in micrograms (ug);

p — The density of the dimethylformamide sample (0.
9455), the unit is grams per cubic centimeter (g/cm ³ );

V—the value of the sample volume, in milliliters (mL)
.

Take the arithmetic mean of the two parallel determination results as the determination result, and the absolute difference between the two parallel determination results shall not exceed 0.
005 mg/kg
.