Determination of heavy metals in drinking water by Flame Atomic Absorption Spectrophotometry

Scheme Introduction: We use directly flame atomic absorption spectrophotometry to determine copper, iron, manganese, zinc, cadmium and lead in drinking water and its source water. The scheme is applicable to the determination of high concentrations of copper, iron, manganese, zinc, cadmium and lead in drinking water and source water. The suitable determination range of this scheme: Copper 0.2 mg / L ~ 5 mg / L, iron 0.3 mg / L ~ 5 mg / L, manganese 0.1 mg / L ~ 3 mg / L, zinc 0.05 mg / ml ~ 1 mg / L and cadmium 0.5 mg / L 05 mg / L ~ 2 mg / L, lead 1.0 mg / I ~ 20 mg / L.

Principle: after the metal ions in the water sample are atomized, they absorb the resonance line from the hollow cathode lamp of the same metal element (copper, 324.7nm; lead, 283.3 nm; iron, 248.3 nm; manganese, 279.5 nm; zinc, 213.9 nm; cadmium, 228.8 nm), and the amount of absorption resonance line is directly proportional to the content of the element in the sample. When other conditions remain unchanged, quantitative comparison with standard series is made according to the measured spectral line intensity after absorption.

Instruments and reagents

Macy ＡＡ-1800ＤＬ atomic absorption spectrophotometer and copper, iron, manganese, zinc, cadmium and lead hollow cathode lamp.

Hot plate.

The pure water used is deionized distilled water.

Standard stock solutions of various metal ions:

A.     Iron standard stock solution [P (FE) = 1 mg / ml]: weigh 1 000G pure iron powder [w (FE) ≥ 99.9%] or 1.4300g iron oxide (Fe2O3, superior pure), add 10ml nitric acid solution (1 + 1), heat slowly and add hydrochloric acid (P2O = 1.19 g / ml) to facilitate dissolution. After complete dissolution, add pure water to constant volume to 1000 ml.

B.     Copper standard stock solution [P (Cu) = 1 mg / ml]: weigh 1 000G pure copper powder [w (Cu) ≥ 99.9%], dissolve in 15ml nitric acid solution (1 + 1), and fix the volume to 1000ml with pure water.

C.     Manganese standard stock solution [P (MN) = 1 mg / ml]: weigh 1.291 2 g manganese oxide (MnO, superior pure) or 1.000 g metal manganese [w (MN) ≥ 99.8%], add nitric acid solution (1 + 1) to dissolve, and then fix the volume to 1000 ml with pure water.

D.     Zinc standard stock solution [P (Zn) = 1 mg / ml]: weigh 1.000 g of pure zinc [w (Zn) ≥ 99.9%], dissolve it in 20 ml of nitric acid solution (1 + 1), and fix the volume to 1000 ml with pure water.

E.     Cadmium standard stock solution [P (CD) = 1 mg / ml]: weigh 1.000 g pure cadmium powder, dissolve it in 5 ml nitric acid solution (1 + 1), and fix the volume to 1000 ml with pure water

F.     Lead standard stock solution [P (PB) = 1 mg / ml]: weigh 1.5985 g of dried lead nitrate [Pb (NO3) 2], dissolve it in about 200 ml of pure water, add 1.5 ml of nitric acid (P2O = 1.42 g / ml), and fix the volume with pure water to 1000 ml. ml)．

Nitric acid（ ρ 2o=1. 42 g / ml), superior pure.

Hydrochloric acid (P2O = 1.19 g / ml), superior pure.

Sample pretreatment

The clarified water sample can be determined directly; For water samples with more suspended solids, acidification and digestion of organic matter are required before analysis. If it is necessary to determine the dissolved metal, the water sample shall be passed through 0.45 at the time of sampling μ M filter membrane, and then add 1.5ml nitric acid per liter of water sample for acidification to make the pH less than 2. The organic matter in water samples generally does not interfere with the determination. In order to make all metal ions enter the aqueous solution and promote the dissolution of particulate matter, so as to facilitate extraction and atomization, hydrochloric acid and nitric acid digestion method can be used. Add 5 ml nitric acid (4.2.1.3.2) to each liter of acidified water sample. After mixing, take quantitative water sample and add 5 ml hydrochloric acid (4.2.1.3.3) per 100 ml of water sample. Heat on the electric heating plate for 15 min. After cooling to room temperature, filter with glass sand core funnel, and finally dilute to a certain volume with pure water.

Water sample determination

Dilute various metal standard stock solutions with pure water containing 1.5ml nitric acid per liter and prepare the standard series with the following concentration (mg / L): copper, 0.5ml 20~5.0; Iron, 0.30 ~ 5.5 0 Manganese, 0.10 ~ 3.5 0 Zinc, 0.050 ~ 1.000 0 Cadmium, 0.050 ~ 2.0; Lead, 1.0 ~ 20.

Note: when the measurement range listed changes due to the sensitivity and operating conditions of different models of instruments, the above measurement range can be changed as appropriate.

Spray the standard solution, blank solution and sample solution into the flame in turn and measure the absorbance. Draw the standard curve and find out the mass concentration of each metal element to be measured. The mass concentration (mg / L) of the metal to be measured in the water sample can be directly found out from the standard curve

Attention：

All glassware must be soaked in nitric acid solution (1 + 9) before use and directly cleaned with pure water. Zinc in tap water should be strictly avoided.