Determination of iron and manganese in water and wastewater by AA-1800C flame atomic absorption spectrometry - Master's thesis - Dissertation

Determination of iron and manganese in water and wastewater by flame atomic absorption spectrometry with AA-1800C

Key words: flame atomic absorption method; iron and manganese content in wastewater; aesthetic analyzer ; 1. scope of application This standard specifies the direct determination of iron and manganese in water and wastewater by flame atomic absorption method. Simple, fast and accurate. This standard applies to the determination of iron and manganese in surface water, groundwater and industrial wastewater. The detection limits of iron and manganese were 0.03 mg/L and 0.01 mg/L, respectively. The concentration range of the line is 0.1 to 5 mg/L and 0.05 to 3 mg/L, respectively. 2 Principle The sample or the digested sample is directly inhaled into the flame. The iron and manganese compounds are easily atomized, and the absorption of the characteristic radiation of the hollow cathode lamp by the iron and manganese ground atoms can be measured at 248.3 nm and 279.5 nm, respectively. Under certain conditions, the absorbance is proportional to the metal concentration in the sample to be tested. 3 Reagents The reagents used in this standard use analytical reagents and deionized water or water of equivalent purity in accordance with national or professional standards unless otherwise stated. 3.1 Nitric acid (HNO3), P = 1.42g / mL, excellent grade pure. 3.2 Nitric acid (HNO3), P = 1.42 g / mL, analytically pure. 3.3 Hydrochloric acid (HCl), P=1.19g/mL, excellent grade pure. 3.4 Nitric acid solution, 1+1: Prepared with nitric acid (3.2). 3.5 Nitric acid solution, 1+99: Prepared with nitric acid (3.1). 3.6 Hydrochloric acid solution, 1+99: Prepared with hydrochloric acid (3.3). 3.7 Hydrochloric acid solution, 1+1: Prepared with hydrochloric acid (3.3). 3.8 Calcium chloride solution, 10 g/L: 2.7750 g of anhydrous calcium chloride (CaCl 2 ) was dissolved in water and diluted to 100 mL. / p8 t3 l' X3 }3.9 Iron standard stock solution: Weigh 1.0000g of pure metal iron (accurate to 0.0001g), dissolve it with 60mL hydrochloric acid solution (3.7), and accurately dilute to 1000mL with deionized water. 3.10 Manganese standard stock solution: Weigh 1.0000g of spectral pure metal manganese, accurate to 0.0001g (weigh the surface oxide with dilute sulfuric acid before washing, then wash the acid with deionized water, dry, cool in the dryer, as soon as possible Weighed) and dissolved in 10 mL of nitric acid solution (3.4). When the manganese is completely dissolved, it is accurately diluted to 1000 mL with a hydrochloric acid solution (3.6). 3.11 Mixed operating solution of iron and manganese: separately remove 50.00 mL of iron stock solution (3.9), 25.00 mL of manganese stock solution (3.10) in a 1000 mL volumetric flask, dilute to the mark with hydrochloric acid solution (3.6), and shake well. The concentrations of iron and manganese in this solution were 50.0 mg/L and 25.0 mg/L, respectively. 4 Instruments: 4.1 AA-1800C atomic absorption spectrophotometer. 4.2 Iron and manganese hollow cathode lamps. 4.3 Acetylene cylinder or acetylene generator. 4.4 Air compressors should be equipped with water removal, degreasing and dust removal devices. 4.5 Instrument working conditions: The best test conditions of different types of instruments are different, you can choose according to the instrument manual. 4.6 General laboratory equipment: The glass and plastic utensils used should be immersed in nitric acid solution (3.4) for more than 24 hours before use, and then washed with water. 5 Sample 5.1 Before sampling, the polyethylene bottle used should be washed with detergent, then soaked with nitric acid (3.4) for more than 24 hours, then rinsed with water. 5.2 If only the filterable ferromanganese is measured, the sample is filtered through a 0.45 μm membrane as soon as possible after collection, and the filtrate is acidified with nitric acid (3.1) to make the pH 1-2. 5.3 When the total amount of iron and manganese is determined, samples are collected. Immediately afterwards, acidify according to the requirements of (5.2). 6 Step 6.1 Samples; when determining the total amount of iron and manganese, the sample usually needs to be digested. After mixing, take appropriate amount of laboratory samples in a beaker. Add 5 mL of nitric acid (3.1) per 100 mL of water sample, place it on a hot plate and dilute the sample to near dryness in a near-boiling state. After cooling, add nitric acid (3.1) and repeat the above steps once. If necessary, add nitric acid (3.1) or perchloric acid until the digestion is complete. It should be steamed to dryness. Add hydrochloric acid (3.6) to dissolve the residue. If there is sediment, filter it into a 50mL volumetric flask with a quantitative filter paper and add calcium chloride solution. 3.8) 1 mL, diluted to the mark with hydrochloric acid solution (3.6). 6.2 Blank experiment Water is used instead of the sample to make a blank experiment. The same procedure was used and used in the same amount as the reagents used in the sampling and determination. The blank was measured while the sample was being measured. `6.3 Interference; 6.3.1 The main interference affecting the accuracy of iron and manganese atomic absorption method is chemical interference. When the concentration of silicon is greater than 20mg/L, it will cause negative interference to the determination of iron; when the concentration of silicon is greater than 50mg/L Negative interference also occurs in the determination of manganese, and the degree of these interferences increases as the concentration of silicon increases. If 200 mg/L of calcium chloride is present in the sample, the above interference can be eliminated. In general, the matrix interference of the flame atomic absorption method of iron and manganese is not serious, and the background absorption caused by molecular absorption or light scattering is negligible, but when a high salinity water sample is encountered, when background absorption is used, the background should be adopted. Correct the measure or dilute the water sample before measuring. 6.3.2 The spectral lines of iron and manganese are complex. To overcome spectral interference, a small spectral passband should be selected. 6.4 Draw the calibration curve. Take the iron and manganese mixed standard operating solution (3.11) in a 50mL volumetric flask, dilute to the mark with hydrochloric acid (3.6), and shake well. At least 5 standard solutions should be prepared and the concentration of the element to be tested should be within the range of this standard series. According to the instrument manual, select the best parameters, adjust the absorption with the hydrochloric acid solution (3.6), measure the corresponding absorbance under the selected conditions, and draw a calibration curve. During the measurement process, the calibration curve should be checked regularly. 6.5 Measure the absorbance of the sample solution and the blank solution while measuring the standard series solution. The blank absorbance was subtracted from the absorbance of the sample, and the content of iron and manganese in the sample solution was determined from the calibration curve. When measuring the filterable iron and manganese, the sample prepared by (5.2) was directly sprayed for measurement. When measuring the total amount of iron and manganese, the sample in (6.1) is used. 7 The result indicates the concentration of iron and manganese C (mg/L) in the laboratory sample, calculated by the following formula: where C: the concentration of iron and manganese in the laboratory sample, mg/L; m - in the sample Iron and manganese content V - the volume of the water sample, mL. 8 Precision and Accuracy 13 laboratories determined a uniform sample containing 2.00 mg/L of iron and 1.00 mg/L of manganese. The relative standard deviations of repeatability were 1.00% and 0.62%, respectively; the relative standard deviations of reproducibility were 1.36. % and 1.63%. The recoveries of iron were 93.3%~102.5%, and the recoveries of manganese were 94.9%~105.9%.