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
),
Ï=1.19g/mL
; excellent grade pure.
1.1.2
Nitric acid
HNO 3
),
Ï=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)
:
Ï=1.49 g/mI
.
1.1.6
perchloric acid
(HCIO 4 )
:
Ï=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 å©åŸš. 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 1.3Remarks: 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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