Determination of cadmium in rice by atomic fluorescence spectrometry - Master's thesis - Dissertation

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1

Foreword

Cadmium is a soft white metal with a silvery white or a slightly blue luster at room temperature. from

20

Since the beginning of the century, the production and use of cadmium has been increasing, and the annual release of cadmium into the environment worldwide

3

Ten thousand tons, of which

82%~94%

Will enter the soil. The soil is related to the quality of rice, and the uniqueness of rice itself.

gene

", also affects the ability of rice grains to absorb specific substances in the soil, and the adsorption of rice on cadmium pollution is significantly stronger than that.

corn

,

Soy

Other crop varieties.

In recent years, there have been many reports on soil pollution caused by heavy metals such as cadmium in China. last century

80

In the mid-2000s, studies on contaminated areas caused by cadmium-contaminated water irrigation in a southern province showed that the cadmium content in rice exceeded the rate.

71.69%

The meat and poultry eggs are not exceeding the limit.

2005~2009

Year survey of food cadmium pollution in a southern province, the detection rate of cadmium

64.4%

Over-standard rate

7.3%;

Cadmium exceeding standard foods involve food, fruit, edible fungi, aquatic products, animal internal organs, etc., indicating that cadmium pollution is more common in some areas. Excessive cadmium pollution will cause harm to the bones and kidneys of the human body. "Bone pain" will occur, causing the kidneys to fail to work properly, and excessive intake of cadmium will also have a "sputum effect", hindering the absorption of the human body. Indispensable trace elements

——

Absorption of zinc.

2 Experimental part

2.1

Reagent

(1)

Hydrochloric acid: (excellent grade,

36%

,

ρ=1.19g/ml

).

(2)

Nitric acid: (excellent grade,

65%

,

ρ=1.42 g/ml

).

(3)

Perchloric acid: (excellent grade,

72%

,

ρ=1.67 g/ml

).

(4) 0.1%

Special reagent for cadmium analysis

2

No.: accurate weighing

0.1g

Special reagent for cadmium analysis

2

Number in the beaker, measure

100ml

Ultra-pure water, stir and dissolve to be used.

2.2

Using the instrument

(1)

Two-channel atomic fluorescence spectrometer

AFS200T

), cadmium hollow cathode lamp;

(2)

Heating plate

(SB-2.4)

;

(3)

Laboratory grade ultrapure water purifier;

2.3

Instrument working conditions

table

1

Instrument parameter setting

Serial number

parameter

Parameter value

1

Negative high pressure

V

)

260

2

Lamp current

mA

)

35/35

3

Argon flow rate (

Ml/M

)

300/800

4

Filament brightness

3

5

Reading time

s

)

13

6

delay(

s

)

3

7

Blank discriminant value

s

)

5

2.4

Analysis step

2.4.1

Sample digestion

Weighing rice samples

0.2g

Left and right in the beaker, join

8ml

Nitric acid and

2ml

Perchloric acid, placed on a hot plate to heat and dissolve, the sample is completely digested and evaporated to dryness

2ml HCl

Transfer the digested solution to ultrapure water to

100ml

In the volumetric flask, add to the volumetric flask

0.1%

Special reagent for cadmium analysis

2

number

5ml

, with ultrapure water to volume

100ml

Tick ​​the line and shake it. (At the same time, do the sample blank in the same way)

.

2.4.2

Sample determination

According to the performance of the respective instrument model, refer to the working conditions of the instrument, adjust the instrument to the best measurement state, and stabilize

10min-20min

Start measuring afterwards. Continuous injection with standard blanks. After the readings have stabilized, transfer to the standard series and draw a standard curve. Before transferring to the sample measurement, enter the blank value measurement state, and use the sample blank liquid to inject, let the instrument take the average value as the blank value of the bottom. The sample can then be determined according to law. After the measurement is completed, select “Print Report” to automatically print the measurement results.

3

Experimental result

3.1

Drawing of standard curve and correlation coefficient

3.1.1

Preparation of standard solution

Use cadmium (

Cd

Standard use solution

(0.1ug/ml)

, excellent grade pure hydrochloric acid (

HCl

)

,

0.1%

cadmium(

Cd

Special analysis

2

No. reagent, ionized water (resistivity ≥

10M

Ohm) and other reagents.

table

2

Preparation of cadmium standard solution

Serial number

Concentrated hydrochloric acid volume (

Ml

)

0.1%

cadmium(

Cd

) analysis dedicated

2

No. reagent volume (

Ml

)

cadmium(

Cd

Standard use solution

(0.1ug/ml)

volume(

Ml

)

Constant volume

Ml

)

Standard solution concentration

Ng/ml

)

1

2

5

1

100

1

2

5

5

3

10

10

3.1.2

Standard curve and correlation coefficient of cadmium

table

3

Cadmium concentration and fluorescence intensity value

Cadmium concentration

Ng/ml

)

0

1

5

10

Fluorescence intensity value

0

496.152

1873.085

3602.660

3.2

Measurement of cadmium content in rice samples

table

4

Sample measurement result

sample

Measurements

/

(

Ng/ml

)

average value

/

(

Ng/ml

)

Rice

88.92

85.95

82.98

3.3

Method recovery

table

5

Method for measuring the recovery rate of cadmium

sample

Theoretical value

The actual measured value

Recovery rate

/%

Rice

87.00

88.92

102.21

82.98

95.38

4

summary

95.38%

Moreover, the method has the advantages of high sensitivity, low detection limit, less basic interference, quick and simple, and the like.