Measurement of calcium and magnesium in water
Measurement of calcium and magnesium in water
The specimens were drawn into an air-acetylene flame to atomize calcium and magnesium, and the absorption of the 422.7 nm resonance line was chosen to quantify calcium and the absorption of the 285.2 nm resonance line was used to quantify magnesium.
Operation method
Flame atomic absorption spectrophotometry
Principle
The specimens were drawn into an air-acetylene flame to atomize calcium and magnesium, and the absorption of the 422.7 nm resonance line was chosen to quantify calcium and the absorption of the 285.2 nm resonance line was used to quantify magnesium.
Materials and Instruments
Water samples Move I. Reagents Caveat 1. Atomic absorption method for the determination of calcium, magnesium, the main interference with aluminum, sulfate, phosphate, silicate, etc., they can inhibit the atomization of magnesium, resulting in interference, can be added to lanthanum, strontium, or other releasing agents to eliminate interference. 2. flame conditions directly affect the sensitivity of the determination, must choose the appropriate amount of acetylene and flame observation height. 3. The specimen needs to be checked whether there is background absorption, if so it should be corrected. For more product details, please visit Aladdin Scientific website.
Lanthanum or strontium oxide Calcium carbonate Magnesium oxide
Atomic absorption spectrophotometer Calcium and magnesium hollow cathode lamps Volumetric flasks Pipettes
1. Concentrated nitric acid
2. Perchloric acid
3. (1+1) Nitric acid solution
4. Lanthanum solution (0.1 g/mL): weigh lanthanum oxide ( La2O3 ) 23.5 g, dissolve with a small amount of nitric acid solution (reagent 3), evaporate until nearly dry, add 10 mL of nitric acid solution (reagent 3) and the appropriate amount of water, dissolve over a slight heat, cool down, and then dilute with water to 200 mL.
5. Calcium standard stock solution (1,000 mg/L): accurately weigh 105 ~ 110 ℃ dried calcium carbonate ( CaCO3, G.R) 2.4973 g in a 100 mL beaker, add 20 mL of water, carefully add drops of nitric acid solution (reagent 3) to the dissolution, and then add 10 mL of nitric acid solution (reagent 3), heating and boiling, cooling and then water to 1000 mL of water capacity.
6. Magnesium standard stock solution (100 mg/L): accurately weigh 0.3658 g of magnesium oxide (MgO, G.R) burned at 800°C to a constant weight in a 100 mL beaker, add 20 mL of water, add nitric acid solution (reagent 3) dropwise until completely dissolved, and then add an additional 10 mL of nitric acid solution (reagent 3), heat and boil, and then cool and then volume with water to 1000 mL.
II. Experimental steps
1. Preparation of specimens
(1) analysis of filterable calcium, magnesium, such as water samples have a large number of sediment, suspended solids, samples should be collected in a timely manner after clarification, the clarified solution through the 0.45 μm organic microporous filtration membrane filtration, filtrate with nitric acid (reagent 1) acidification to pH 1 ~ 2.
(2) When analyzing the total amount of calcium and magnesium, add nitric acid (Reagent 1) immediately after collection to acidify to a pH of 1 to 2. If the sample needs to be ablated, the calibration solution, and the blank solution should also be ablated.
(3) Elimination: Take 100 mL of the feint to be treated, put it in a 200 mL beaker, add 5 mL of nitric acid (reagent 1), and heat it on the hot plate to eliminate it, and evaporate it to about 10 mL, then add 5 mL of nitric acid (reagent 1) and 2 mL of perchloric acid (reagent 2), and continue to eliminate it. Steam to about 1 mL, remove and cool, add water to dissolve the residue, and filter through medium-rate filter paper washed with acid into a 50 mL volumetric flask and dilute with water to the mark (Note: the perchloric acid used in the digestion is explosive, and it is required to be carried out in a fume hood).
2. Calcium and magnesium mixed standard solution (calcium 50 mg/L, magnesium 5.0 mg/L): accurately suck the calcium standard stock solution (reagent 5) and magnesium standard stock solution (reagent 6) each 5.0 mL in a 100 mL volumetric flask, add 1 mL of nitric acid solution (reagent 3) diluted with water to the standard line.
3. Preparation of calcium and magnesium standard series: accurately suck the above calcium and magnesium mixed standard solution 0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 mL in 50 mL volumetric flasks, add 1 mL of nitric acid solution (reagent 1) and 1 mL of lanthanum solution (reagent 4) diluted with water to the standard line, shaking well, then 0, 0.50, 1.00, 2.0, 3.00, 4.00, 5.00, 5.00, 5.00, 5.00, 5.00, 5.00, 5.00, 5.00, 5.00, 5.00, 5.00, 3.00, 4.00, 5.00,6.00 mg/L calcium standard series and 0, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60 mg/L magnesium standard series solution. Prepare at least 5 calibration solutions (not including zero).
4. Measurement of sample solution: accurately draw 1.00~10.00 mL of pretreated sample (containing not more than 250 ug of calcium and 25 ug of magnesium) into a 50 mL volumetric flask, add 1 mL of nitric acid solution (reagent 1) and 1 mL of lanthanum solution (reagent 4) diluted with water to the standard line, and shake well.
5. Blank test: A blank test is conducted at the same time as the measurement. For the blank test, 50 mL of water is used in place of the specimen. The reagents used and their dosages are identical to those of the test material.
6. Determination: Adjust the flame of the instrument to the optimum state, determine the absorbance of the standard series and the specimen sequentially from dilute to concentrated, and find out (or calculate by regression equation) the concentration of calcium and magnesium in the specimen on the calibration curve, or read it directly from the instrument.
IV. Calculation of resultsX = f cEq:X--Calcium or magnesium content in Ca or Mg, mg/L;f - the ratio of the constant volume of the test material to the volume of the specimen;c - Calcium and magnesium concentration found from the calibration curve, mg/L.