Analytical method for the determination of highly concentrated cobalt by atomic absorption spectrometry

Under acidic conditions[1], in the presence of selenium dichloride, ammonium thiocyanate is used to react with cobalt in drinking water to form a complex, acetone extraction and separation, the organic phase is heated and evaporated acetone, nitric acid and hydrogen peroxide are added to eliminate the organic phase, and then use the matrix improver technology[2], automatic sampling, graphite furnace atomic absorption spectrometry, the results of the measurement are satisfactory, and the limit of detection can be up to 0.47 g-L one.

1.1 Main instruments and reagents

Varian AA-64O atomic absorption spectrophotometer

Pyrolysis graphite tube (Varian)

Cobalt standard solution: 1.00mg-L (provided by National Standard Substance Center)

Magnesium and palladium mixture of matrix improvers: with excellent purity of magnesium nitrate and palladium nitrate formulated into 600~g-L magnesium and 400~g-L palladium nitrate. 600~g-L magnesium and 400~g-L palladium. The water is high-purity water, and the rest of the reagents are excellent pure.

1.2 Instrument working conditions

Wavelength 240.7 nm, spectral bandwidth 0.2 nm, lamp current 7 mA, deuterium lamp button background, injection volume 3O l, atomization stage of the gas.

1.3 test method

Transfer 250ml of drinking water, add 5.OOml of concentrated hydrochloric acid, 300g-L selenium dichloride solution 1.OOml, mixing with solid ammonium thiocyanate 0.020g, acetone 30.OOml, shaking for 5min, resting stratification, the organic phase is transferred to a 50ml beaker, heating and evaporation of acetone, to be evaporated by the acetone, and then add Nitric acid (1 + 3) 10.OOOml, plus hydrogen peroxide solution 1.OOOml, heating wet digestion, water samples clarified, cooled, plus a mixture of matrix improver 1.OOOml, and nitric acid (O.1 + 99.9) to 25 ml, on the machine automatic sample determination.

2.2 Selection of graphite furnace measurement conditions

2.2.1 Role and dosage of matrix improver

Tests have proved that the addition of magnesium and palladium mixed matrix improver, the maximum permissible ashing temperature of cobalt is significantly increased in the change of the amount of mixed matrix improver, the choice of mixed matrix improver 1.OOOml, the cobalt absorbance reaches a constant.

2. 2.2.2 Selection of ashing and atomization temperature

In the selected conditions, using 30.O0/lg-L cobalt solution, the injection volume of 3O l, after the test, the ashing temperature, atomization temperature can be selected 1450 ℃ and 2500 ℃, respectively.

2.3 Interference test and the role of selenium dichloride

Tests have proved that the water samples of Fe. + and SCN an easy reaction to generate Fe (SCN); a water sample of Cu2 + concentration is high, but also generates copper thiocyanate, which affects the determination of cobalt. And add selenium dichloride solution in the water samples can be Fe, Cu. + reduction for the low value of the ion, in order to eliminate the impact of the choice to add 300g -L selenium dichloride solution 1.00ml.

According to the test method for the determination of cobalt 3.00/lg-I, the following ions do not interfere with the determination of the 500-fold Fe jitter, Cu jitter, Zn jitter, 700 times the K +, Na +, Ca. +, Mg +, 50 times Mg +, Mg +, Mg +, Mg +, Mg +, Mg +, Mg +, Mg +, Mg +, Mg +, Mg +, Mg +, 50 times the Mn.+, Cd.+, Pb.+, Ni shake.

2.4 Calibration curve and detection limit

Take the cobalt standard solution, dilute with high purity water into a standard series of cobalt-containing 0.00~5.00/lg-L solution, according to the test method of processing and determination, cobalt concentration in the range of 0.o0~5.00/lg-L was linear, the correlation coefficient of 0.9985, and at the same time according to the test method of the l1 blank determination, the cobalt concentration of the cobalt concentration of the cobalt concentration in 0.o0~5.00/lg-L range is linear, the correlation coefficient of 0.9985. The limit of detection was 0.47 g-L -1 calculated by CL (is a 3)-3SA/S (injection volume of 30/A).