GB/T 4325.7-2013Methods for chemical analysis of molybdenum - Part 7: Determination of iron content - 1,10-phenanthroline spectrophotometry and inductively coupled plasma atomic emission spectrometry (English PDF)

4.2.15 Hydroxylamine hydrochloride solution (200 g/L)

The purification steps are as follows: Weigh 50 g of hydroxylamine hydrochloride; place it in a 500 mL beaker; add 150 mL of water to dissolve it; use ammonia (4.2.4) to adjust to pH 7 (check with pH test paper); add 20 mL of phenanthroline solution (4.2.10); heat to boiling; cool it down; add 3 g of potassium iodide; after dissolving, use water to transfer to a separatory funnel and dilute to a volume of 250 mL; trichloromethane (4.2.5) to make extraction several times (20 mL each time, shaking for 2 min), until the organic phase is colorless; discard the organic phase; put the aqueous phase in the reagent bottle to prepare for use.

4.2.16 Disodium ethylenediaminetetraacetic acid (EDTA) solution (100 g/L)

Weigh 10 g of EDTA (excellent grade pure); put it in a 250 mL beaker; add 90 mL of water and heat (50 °C ~ 60 °C) to dissolve; use ammonia water (4.2.4) to adjust to pH 7 (check with pH test paper); use water to dilute it to 100 mL; mix it uniformly to prepare for use.

4.5.4.2 Specimen with nickel content greater than 0.01%

4.5.4.2.1 Place the sample (4.5.1) in a 150 mL beaker; use 5 mL of water to moisten it; add 5 mL of nitric acid (4.2.3), 4 mL of sulfuric acid (4.2.2); heat to dissolve and evaporate it, until white sulfuric acid smoke is produced; remove and cool it; use water to rinse the watch glass and the wall of beaker; repeat the generation of white smoke of sulfuric acid once again; remove and cool.

4.5.4.2.2 Use hydrochloric acid (4.2.7) to rinse the watch glass and beaker wall (about 20 mL); place the beaker at a low temperature and heat until the solution is clear; remove it; cool to room temperature; use hydrochloric acid (4.2.7) to transfer it in a 125 mL separatory funnel; control its volume to be about 40 mL.

4.5.4.2.3 Add 20 mL of ethyl acetate (4.2.6); shake for 2 min; stand for stratification; discard the aqueous phase; add 10 mL of hydrochloric acid (4.2.7); gently shake for 30 seconds; let it stand for stratification; discard the aqueous phase. Add 20 mL of citric acid-ammonia mixed solution (4.2.13) in the organic phase and shake for 1 min. After standing for stratification, put the aqueous phase into a 150 mL beaker; add 10 mL of citric acid-ammonia mixed solution (4.2.13) and repeat the back extraction once; combine the water phase in a 150 mL beaker; discard the organic phase. Place the beaker on the electric stove to heat and boil for 1 min ~ 2 min; take it off and cool; proceed the following according to 4.5.4.1.2 ~ 4.5.4.1.5.

4.6 Drawing of working curve

Pipette 0 mL, 0.50 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL, 5.00 mL, 6.00 mL of iron standard solution (4.2.19); put them into eight 150 mL beakers; add 30 mL of citric acid-ammonia mixed solution (4.2.13); use sulfuric acid (4.2.2) to adjust the pH to 7; proceed the following steps according to 4.5.4.1.2 ~ 4.5.4.1.4; measure the absorbance. Subtract the absorbance of the reagent blank. Draw a working curve with iron content as the abscissa and absorbance as the ordinate.

5.1 Method summary

The sample is dissolved with nitric acid and hydrogen peroxide; under selected conditions, the emission intensity is measured with an ICP-AES instrument at a wavelength of 238.2 nm to calculate the element content. The molybdenum matrix is added to offset the influence of molybdenum.

5.2 Reagents

5.2.1 Hydrogen peroxide (rho = 1.10 g/mL).

5.2.2 Nitric acid (rho = 1.42 g/mL), excellent grade pure.

5.2.3 Hydrochloric acid (1 + 1), excellent grade pure.

5.2.4 Molybdenum trioxide, spectrally pure.

5.2.5 Ammonium molybdate, spectrally pure.

5.2.6 Iron standard storage solution: Weigh 0.1429 g of iron trioxide (mass fraction >= 99.9%); place it in a 250 mL beaker; add 10 mL of hydrochloric acid (5.2.3); heat and dissolve at a low temperature; use water to transfer it to a 1000 mL volumetric flask and dilute to the mark; mix well. This solution 1 mL contains 100 µg of iron.

5.2.7 Iron standard solution: Pipette 10.00 mL of iron standard stock solution (5.2.6); place it in a 100 mL volumetric flask; use water to dilute it to the mark; mix well. 1 mL of this solution contains 10 µg of iron.

5.3 Apparatus

Plasma emission spectrometer: resolution < 0.006 nm (at 200 nm).

5.4 Analytical procedures

5.4.1 Sample

Weigh the sample according to Table 3, accurate to 0.0001 g. […]