Oxalic acid for industrial use (3)

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According to the provisions of GB/T7531

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According to the provisions of GB/T7532

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Weigh an appropriate amount of laboratory samples to make the content of heavy metals in the sample within (0.

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Heat and decompose the oxalic acid sample to make the gas exhaust.

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3 Hydrochloric acid: spectrally pure;

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4 Iron (Fe) standard solution: 0.
1mg/mL
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3 Apparatus

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1 Flame atomic absorption spectrometer: equipped with iron hollow cathode lamp and flame atomizer, complying with GB/T9723 regulations;

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2 Electric furnace: adjustable temperature
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4 Instrument operating conditions

The operating conditions of the instrument recommended by this standard: wavelength 248.
3nm, slit width 0.
2nm, lamp current 2mA
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5 Analysis steps

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1 Drawing of working curve

Take iron standard solution (0, 1.
0, 2.
0, 3.
0, 4.
0, 5.
0) mL, add 5 mL hydrochloric acid to 6 100 mL volumetric flasks, dilute to the mark with water, and shake well
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As an iron standard working solution
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The solution contains (0, 1, 2.
3, 4, 5) ug of iron per milliliter
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Adjust to the best state according to the performance of the instrument, and under the given instrument operating conditions, measure the absorbance of the iron standard working solution, taking the absorbance as the ordinate, and the corresponding iron content (ug/mL) in the iron standard working solution as the abscissa , Draw a working curve.
The linear range of the working curve reaches 5ug/mL
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2 Determination of samples

Weigh 25g of the sample, accurate to 0.
01g, place it in a 100mL quartz beaker, cover it with the surface, and place it on an electric furnace to heat at low temperature until the oxalic acid is completely decomposed and the gas escapes.
Take it off and cool to room temperature.
Add 1.
25mL of hydrochloric acid and water.
Rinse and transfer to a 25mL volumetric flask, dilute to the mark, and shake well
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As a sample solution
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Measure the absorbance of the sample solution according to the operating conditions for drawing the working curve, and find out the iron content in the sample on the working curve
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6 Result calculation

The mass fraction w _{3 of} iron (calculated as Fe) , the value is expressed in %, calculated according to formula (3):

Where:

c ₁ —The iron content found from the working curve, in micrograms per milliliter (ug/mL);

V ₃ —The value of the volume of the sample solution, in milliliters (mL);

m—The value of the mass of the sample, in grams (g)
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Take the arithmetic average of the two parallel determination results as the determination result
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The absolute difference between the two parallel determination results is not more than 10% of the arithmetic mean of the two determination values
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