Determination of Total Chromium in Wastewater by Flame Atomic Absorption Spectrophotometry

The total chromium in the environmental samples was determined by flame atomic absorption spectrophotometry. The optimal experimental conditions were determined by selecting different experimental conditions, and the accuracy and precision of the method were verified by analysis of standard samples and experimental samples. Experiments show that this method is fast, convenient, accurate and precise.
Total chromium waste is generally used potassium permanganate, Diphenylcarbazide dihydrazide spectrophotometry and ferrous sulfate titration. Since the current method for measuring total chromium is to convert trivalent chromium into hexavalent chromium with an oxidizing agent, the operation is cumbersome, and the measurement result is prone to error. Therefore, this study used flame atomic absorption spectrophotometry to determine total chromium in wastewater, and verified the feasibility of this method by analyzing standard samples and wastewater samples.
First, the experimental part
(1) Reagent chromium standard stock solution Weigh 0.2829g of potassium dichromate (excellent grade pure) dried at 120 °C for 2h, dissolved in fresh deionized water and transferred to a 100mL volumetric flask, and diluted to the mark. The solution contained chromium 1.00 mg/mL.
Chromium standard use solution: Dilute the standard stock solution with deionized water to 50 g of chromium per ml of solution. 10% ammonium chloride solution was weighed 10.0 g of ammonium chloride, dissolved in deionized water, and diluted to 100 mL. Nitric acid is pure grade.
(two) working parameters
Adopt TAS. Model 986 Atomic Absorption Spectrophotometer. Light source chrome hollow cathode lamp; wavelength 357.9 nm; slit width 0.4 nm; flame type richness; acetylene flow rate 1.8 L/min; burner height 8 Inm.
The sample is sprayed with air. In the acetylene rich flame, the chromium compound can be atomized and measured at a wavelength of 357.9 nm.
Adjust the instrument to the best working conditions, spray the sample directly into the flame, measure the absorbance, subtract the corresponding reagent blank absorbance, and find the chromium content from the calibration curve.
Second, the results and discussion
(I) Selection of instrument operating parameters Different instrument working conditions have great influence on the accuracy and precision of the analysis results. According to the actual situation, the absorbance results of the standard solution containing 2.00 mg/L of chromium were determined experimentally, and the optimal parameters of the experimental conditions were found: the flame type was rich; the burner height was 8 mm; the slit width was 0.4 nm.
(2) Interference and elimination
Interference with coexisting elements is greatly affected by the flame state, and chromium tends to form insoluble oxides in the flame. Therefore, the cosolvent NH4C1 is added to eliminate the experiment. At the same time, NH4C1 is also an inhibitor of coexisting elements, and can also inhibit the interference of CO, Fe, Ni, V, Pb, and Mg.
(3) The calibration curve is respectively removed from the chromium standard solution using 0.00, 0.50, 1.00, 2.00, 3.00, 5.00mL in a 50mL colorimetric tube, respectively, adding 10% NH, C1 solution 2mL, adding water to the marking line, shaking, in turn Spraying a flame,
The absorbance is measured to make a calibration curve.
(4) Precision and accuracy of the method
In order to test the effect of the method, the accuracy and precision of the standard sample with a concentration of 0.490±0.014 mg/L were tested and oxidized with potassium permanganate. The diphenylcarbazide was spectrophotometrically compared and the number of measurements was 20 times.
(5) Analysis of actual samples
In order to check the practicability of the method, the actual samples were tested in parallel and spiked, and compared with potassium permanganate oxidation and diphenylcarbazide spectrophotometry. From the measurement results, the precision of the flame atomic absorption spectrophotometry is better than the potassium permanganate oxidation-diphenylcarbazide spectrophotometry.
Third, the conclusion
The experimental results show that the determination of total chromium in wastewater by flame atomic absorption spectrophotometry is fast and simple, and the method has high accuracy and precision. It can meet the requirements of wastewater monitoring technology and can be used and promoted as emergency monitoring and analysis.

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