This part of GB/T 4372 specifies the method for determining the content of iron oxide in zinc oxide by direct method. This section is applicable to the determination of iron oxide content in zinc oxide by direct method. Measurement range: 0.010%~0.10%. 2 Method summary: The test sample is dissolved in hydrochloric acid and nitric acid、 evaporated to dryness、 and in a dilute hydrochloric acid medium、 an air acetylene flame is used to measure the absorbance of iron at the wavelength of 248.3 nm in an atomic absorption spectrometer. The amount of iron oxide is calculated using the standard curve method. Unless otherwise specified、 reagents confirmed to be of superior purity and primary water or water of equivalent purity shall be used in the analysis. 3.1 Nitric acid (p-1.42 g/mL). 3.2 Hydrochloric acid (p-1.19 g/mL). 3.3 Nitric acid (1+1). 3.4 Nitric acid (1+3). 3.5 Hydrochloric acid (1+1). 3.6 Iron standard storage solution: Weigh 1.0000 0g of metal iron [cut metal iron wire (w ≥ 99.9%) into small sections and immerse in dilute nitric acid (3.4) for 1 minute to 2 minutes. Take out. Soak in anhydrous ethanol for 1 minute to 2 minutes. Take out. After repeatedly drying with filter paper、 weigh immediately] and place it in a 300 ml. beaker. Add 40 mL of hydrochloric acid (3.5)、 heat at low temperature to dissolve it completely、 add 10 mI of nitric acid (3.3)、 let it dry at low temperature、 and remove and cool. Add 20 ml of hydrochloric acid (3.5)、 heat at low temperature to dissolve the salt、 cool、 and transfer to a 1000 ml volumetric flask. Add 400 mL of hydrochloric acid (3.2)、 dilute with water to the mark、 and mix well. This solution contains 1 mL of iron. 3.7 Iron standard solution: Transfer 10.00 mL of iron standard storage solution (3.6) to a 100 mL volumetric flask、 add 36 mL of hydrochloric acid (3.2)、 dilute with water to the mark、 and mix well. This solution contains 100 pg of iron in 1 ml. 4 instrument atomic absorption spectrometer、 with iron hollow cathode lamp attached. Under the optimal working conditions of the instrument、 anyone who can meet the following indicators can use it. Sensitivity: In a solution consistent with the blank matrix of the measured sample solution、 the characteristic concentration of iron should not exceed 0.3ug/ml. Precision: Measure the absorbance 10 times with the highest concentration standard solution、 and the standard deviation should not exceed 0.5% of the average absorbance of the highest concentration standard solution; Measure the absorbance 10 times with the lowest concentration standard solution (not zero standard solution). The standard deviation should not exceed 0.5% of the average absorbance of the highest concentration standard solution. The working curve is linear; Divide the working curve into five equal sections based on concentration、 and determine the ratio of the absorbance difference between the highest section and the lowest section

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