GB/T 223.23-2008Iron, steel and alloy - Determination of nickel content - The dimethylglyoxime spectrophotometric method (English PDF)

3.1 Principles

Dissolve sample by acid, perchloric acid smokes and oxidize chromium to hexavalence, screen iron with sodium tartrate; in the strongly alkaline medium, take ammonium persulfate as the oxidizer; nickel and dimethylglyoxime generate red complex compound, and measure the absorbance.

The manganese content larger than 1.5 mg, copper content larger than 0.2mg and cobalt content larger than 0.1 mg in the color reagent may interfere with the determination.

3.2 Reagents and materials

Unless otherwise specified, during the analysis, only confirmed analytical reagent and distilled water or purity-equivalent water may be used.

3.2.1 Ethanol, more than 95% (volume fraction).

3.2.2 Perchloric acid with rho 1.67 g/mL.

3.2.3 Nitric acid with rho 1.42 g/mL, and dilute to 2+3.

3.2.4 Mixed acid of hydrochloric acid-nitric acid; mix one hydrochloric acid (rho is about 1.19g/mL), one nitric acid (rho is about 1.42g/mL) and two waters.

3.2.5 Sodium tartrate solution, 300 g/L.

3.2.6 Sodium hydroxide solution, 100 g/L.

3.2.7 Dimethylglyoxime solution, 10 g/L, prepare with ethanol (3.2.1).

3.2.8 Ammonium persulfate solution, 40 g/L.

3.2.9 Nickel standard solution

3.2.9.1 Nickel stock solution, 100 µg/mL. Weigh 0.1000 g of pure nickel (mass fraction above 99.99%) into 150-mL conical flask, add 20 mL of nitric acid (3.2.3), cool to room temperature after heating and dissolution, transfer into 1000-mL volumetric flask, dilute with water to the scale, and mix well.

3.2.9.2 Nickel standard solution, 10.0 µg/mL. Shift 25.00 mL of nickel stock solution (3.2.9.1) into 250-mL volumetric flask, add 5 mL of nitric acid (3.2.3), dilute with water to the scale, and mix well.

3.3 Instruments and equipment

In the analysis, only the general laboratory instruments and equipment as well as the spectrophotometer are used.

3.4 Sampling and sample preparation

The sampling and sample preparation shall be carried out according to GB/T 20066 or proper national standards.

3.5 Analysis procedures

Warning. when generally existing ammonia, nitrous acid smog or organic substance, the emission of perchloric acid smoke may cause explosion.

3.5.1 Specimen quantity

Weigh the sample by Table 1 according to the nickel content (mass fraction) to the accuracy of 0.0001 g.

3.5.2 Blank test

Carry out the blank test together with the specimen.

3.5.3 Determination

3.5.3.1 Place the specimen (3.5.1) into 150-mL conical flask, add

5mL~10mL of nitric acid (3.2.3) or hydrochloric acid-nitric acid mixed acid (3.2.4), add 3mL~5mL of perchloric acid (3.2.2) after heating and dissolution, evaporate to emit perchloric acid smoke and oxidize chromium to hexavalence, slightly cool.

3.5.3.2 Add a small amount of water to dissolve salt, transfer into 100-mL volumetric flask after cooling (transfer into 50-mL volumetric flask when the mass fraction of nickel is 0.03%~0.10%), dilute with water to the scale, and mix well. The sediment shall be filtered.

Take two parts of 10.00 mL of (take 5.00 mL when the mass fraction of nickel is 1.00%~2.00%) test solutions and place them into 50-mL volumetric flask respectively according to 3.5.3.2.1 and 3.5.3.2.2.

3.5.3.2.1 Color reagent. add 10 mL of sodium tartrate solution (3.2.5), 10 mL of sodium hydroxide solution (3.2.6), 2 mL of dimethylglyoxime solution (3.2.7) and 5 mL of ammonium persulfate solution (3.2.8), mix well after adding one reagent, dilute with water to the scale, and mix well.

3.5.3.2.2 Reference solution. add 10 mL of sodium tartrate solution (3.2.5), 10 mL of sodium hydroxide solution (3.2.6), 2 mL of ethanol (3.2.1) and 5 mL of ammonium persulfate solution (3.2.8), dilute with water to the scale, and mix well.

3.5.3.3 Shift partial solution into 2cm or 3cm absorption vessel after placing for 10min~20min, and measure the absorbance at wave length 530nm on the spectrophotometer taking the reference solution as the reference. Subduct the absorbance of blank test, and search out the corresponding nickel mass (µg) from the calibration curve.

3.5.4 Drawing of calibration curve

Respectively transfer 0, 2.00 mL, 4.00 mL, 6.00 mL, 8.00 mL and 10.00 mL of nickel standard solution (3.2.9.2) into 50-mL volumetric flask, render color according to 3.5.3.2.1, and measure the absorbance taking the reagent blank as the reference. Draw the calibration curve taking the nickel mass as the lateral coordinate and the absorbance as the longitudinal coordinate.

3.6 Result calculation

The nickel content shall be calculated by mass fraction wNi; […]