Determination of cadmium, lead, nickel, chromium and copper in soil by graphite furnace atomic absorption spectrometry - Master's thesis - Dissertation

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Determination of Cadmium, Lead, Nickel, Chromium and Copper in Soil by Graphite Furnace Atomic Absorption Spectrometry

Foreword

The soil is at the center of the inorganic and biological boundaries of terrestrial ecosystems, not only in the system, but also in the exchange of energy and matter, as well as in the exchange of water, atmosphere and organisms.

,

Once pollution occurs

,

There will be mutual transfer of pollutants between the three. China is a country with extremely scarce arable land resources. In recent years, its quantity has been decreasing, and it has become a major obstacle to the sustainable development of agriculture, and the problem of soil pollution in China is deteriorating.

The main pollutants in contaminated soil include: inorganic pollutants (such as heavy metals, acids, salt, etc.), organic pesticides (such as pesticides, herbicides, etc.), organic waste (such as biodegradable or refractory organic waste, etc.) ), fertilizers, sludge, slag and fly ash, radioactive materials, parasites, pathogens and diseases.

The contaminated soil changes its physical and chemical properties, such as soil compaction, reduced fertility, soil poisoning, etc. It can also be leached by rainwater. Contaminants are introduced into the groundwater or surface water from the soil, causing pollution and deterioration of water quality. . The organisms growing on the contaminated soil, after absorbing, accumulating and enriching the soil pollutants, enter the human body through the food chain, which can cause human impact and harm.

1

,Experimental part

1.1

Primary reagent

1.1.1

hydrochloric acid(

HCl

),

ρ=1.19g/mL

; excellent grade pure.

1.1.2

Nitric acid

HNO 3

),

ρ=1.42 g/mL

, excellent grade pure.

1.1.3

Nitric acid solution,

1+5

:use

1.1.2

Formulated.

1.1.4

Nitric acid solution, volume fraction is

0.2%

:use

1.1.2

Formulated.

1.1.5

Hydrofluoric acid

(HF)

:

ρ=1.49 g/mI

.

1.1.6

perchloric acid

(HCIO 4 )

:

ρ=1. 68 g/mL

, excellent grade pure.

1.1.7

Diammonium hydrogen phosphate

((NH 4 ) 2 HP0 4 ) (

Excellent grade

)

Aqueous solution, weight fraction is

5%

.

1.2

instrument

Graphite furnace atomic absorption spectrometer

AA7020

), electric heating plate, laboratory ultra-pure water meter.

1.3

Sample pretreatment

Soil sample to be collected

(

Generally not less than

500g )

After mixing, use the quartering method to reduce to about

100g

. The soil sample after shrinking is air dried

(

Naturally air dried or freeze dried

)

After removing the foreign matter such as stones and animal and plant residues in the soil samples, use wooden sticks.

(

Or agate stick

)

Squeeze, pass

2 mm

Nylon screen

(

Remove

2 mm

Above gravel

)

, mix. Will pass the agate mortar

2 mm

The soil sample of the nylon sieve is ground to the full diameter

0. 149 mm (100

Head

)

Nylon sieve, mix and use.

1.4

Sample digestion

Accurate weighing

0.1-0.2g (

Accurate to

0.00 01 g )

Sample

50m L

Teflon in PTFE, moistened with water and added

5m l

hydrochloric acid

(1.1.1)

, heating at a low temperature on a hot plate in a fume hood, causing the sample to decompose initially, when evaporating to about

2-3 mL

When, take a little cold, then add people

5mL-

Nitric acid

(1.1.2), 4m I

Hydrofluoric acid

(1.1.5), 2m l

perchloric acid

(1.1.6)

, after heating, heat on the hot plate at medium temperature

1h

Left and right, then open the cover, continue to heat the silicon removal, in order to achieve a good flying silicon effect, you should always shake the 坩埚. When heated to thick white perchloric acid, cover it to fully decompose the black organic carbide. After the black organic matter on the sputum disappeared, the lid was opened to drive the white smoke and steamed until the contents were viscous. Depending on the situation, then add people

5mL-

Nitric acid

(1.1.2), 4m I

Hydrofluoric acid

(1.1.5), 2m l

perchloric acid

(1.1.6)

, repeat the above digestion process. When the white smoke is almost completely exhausted and the contents are viscous, take a little cold and rinse the lid and inner wall with water. Warmly dissolve the residue. Then transfer the solution to

100 mL

In the volumetric flask, when measuring cadmium, add people

3 ml

Hydrogen phosphate divalent solution

(1.1.7)

After cooling, make up the volume, test the other elements to cool down and directly adjust the volume, shake and prepare for testing. Also make sample blanks.

1.5

Standard solution preparation

Use cadmium standard solution (

1000

μ

g/mL

Diluted to cadmium

0

,

1.0

,

2.0

,

4.0

,

6.0

,

10.0

μ

g/mL

,in

25mL

In the volumetric flask, add people

3.0 mL

Diammonium hydrogen phosphate solution

(1.1.7)

With nitric acid solution

(1.1.4)

Volume. To be tested.

1.6

Instrument test conditions

Serial number

parameter

cadmium

copper

lead

chromium

nickel

1

wavelength(

Nm

)

228.8

324.7

283.3

357.9

232.0

2

Lamp current

mA

)

2

2

2

2

2

3

Injection volume (μ

L

)

20

20

20

20

20

4

Slit

Nm

)

0.2

0.2

0.2

0.2

0.2

5

Protective gas

Ar

Ar

Ar

Ar

Ar

1.7

Rise

Temperature curve setting

1.7.1

Cadmium heating curve

name

Starting temperature

(

°C

)

Termination temperature

(

°C

)

Time (seconds)

1

dry

40

120

20

2

dry

120

120

15

3

Ashing

120

250

15

4

Ashing

250

250

8

5

Ashing

250

250

6

6

Atomization

1800

1800

3

7

Clear

2000

2000

3

8

cool down

0

0

30

1.7.2

Copper element heating curve

name

Starting temperature

(

°C

)

Termination temperature

(

°C

)

Time (seconds)

1

dry

40

120

20

2

dry

120

120

15

3

Ashing

120

500

15

4

Ashing

500

500

8

5

Ashing

500

500

6

6

Atomization

2500

2500

4

7

Clear

2600

2600

3

8

cool down

0

0

30

1.7.3

Lead element heating curve

name

Starting temperature

(

°C

)

Termination temperature

(

°C

)

Time (seconds)

1

dry

40

120

40

2

dry

120

120

15

3

Ashing

120

400

15

4

Ashing

400

400

10

5

Ashing

400

400

6

6

Atomization

2000

2000

4

7

Clear

2200

2200

3

8

cool down

0

0

30

1.7.4

Chromium heating curve

name

Starting temperature

(

°C

)

Termination temperature

(

°C

)

Time (seconds)

1

dry

40

120

40

2

dry

120

120

15

3

Ashing

120

500

15

4

Ashing

500

500

8

5

Ashing

500

500

6

6

Atomization

2700

2700

4

7

Clear

2800

2800

3

8

cool down

0

0

30

1.7.5

Nickel heating curve

name

Starting temperature

(

°C

)

Termination temperature

(

°C

)

Time (seconds)

1

dry

40

100

40

2

dry

100

100

10

3

Ashing

100

130

15

4

Ashing

130

1300

10

5

Ashing

1300

1300

15

6

Atomization

2600

2600

5

7

Clear

2800

2800

2

8

cool down

0

0

30

2

,Results and discussion

2.1

Method detection limit

Determination of sample blank solution under optimal working conditions

11

Then, the sample blank standard deviation σ value is obtained. Take

3

σ× volumetric volume

/k

×Sample quality

(

k

The method detection limit is obtained for the slope of the linear equation of the working curve. See the table below

element

cadmium

copper

lead

chromium

nickel

Detection limit (μ

g/Kg

)

0.1 1.4 0.1 1.1 1.3

Remarks: The following table is for outgoing data

element

cadmium

copper

lead

chromium

nickel

Detection limit (μ

g/Kg

)

2.0

2.5

3.5

3.0

2.3

2.2

Recovery and precision

The content of each element in the soil standard sample was determined experimentally, and the precision and recovery rate were measured. See the table

3

table

3

Determination of lead and copper in tea standard samples

sample

standard value(

Mg/kg

)

measured value(

Mg/kg

)

RSD

(

%

,

n=6

)

Recovery rate(

%

)

cadmium

0.45

0.45

2.2

100.0

copper

11.4

11.7

1.0

102.6

lead

26

25.5

3.0

98.1

chromium

32

30.9

4.2

96.6

nickel

12.5

12.6

3.3

100.8

2.3

discuss

Methods The soil standard materials were analyzed. The cadmium, copper, lead, chromium and nickel contents were close to the actual values. The method has the advantages of high sensitivity, low detection limit, less matrix interference, good recovery rate, good relative standard deviation, fast and simple.

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