英文实验报告模板

Lab 1

Determination of heavy metals in soil by

atomic absorption spectrometry(AAS)

Name: XuFei

Group: The 3rd group

Date:

Sep. 20

th

2012

Part 1

The introduction

1.1The purposes

(1)Learn how to operate the atomic absorption spectrometry;

(2)Learn how to do the pretreatment of soil samples;

(3)Get familiar with the application of atomic absorption spectrometry.

1.2The principles

Atomic Absorption Spectrometry (AAS) is a technique for measuring quantities

of

chemical

elements

present

in

environmental

samples

by

measuring

the

absorbed

radiation

by

the

chemical

element

of

interest.

This

is

done

by

reading

the

spectra

produced

when

the

sample

is

excited

by

radiation.

The

atoms

absorb

ultraviolet

or

visible light and make transitions to higher energy levels .

Atomic

absorption

methods

measure

the

amount

of

energy

in

the

form

of

photons of light that are absorbed by the sample. A detector measures the wavelengths

of

light

transmitted

by

the

sample,

and

compares

them

to

the

wavelengths

which

originally passed through the sample. A signal processor then integrates the changes

in wavelength absorbed, which appear in the readout as peaks of energy absorption at

discrete wavelengths. The energy required for an electron to leave an atom is known

as

ionization

energy

and

is

specific

to

each

chemical

element.

When

an

electron

moves

from

one

energy

level

to

another

within

the

atom,

a

photon

is

emitted

with

energy E. Atoms of an element emit a characteristic spectral line. Every atom has its

own distinct pattern of wavelengths at which it will absorb energy, due to the unique

configuration of electrons in its outer shell. This enables the qualitative analysis of a

sample.

The concentration is

calculated based on the

Beer-Lambert law.

Absorbance is

directly proportional to the concentration of the analyte absorbed for the existing set

of

conditions.

The

concentration

is

usually

determined

from

a

calibration

curve,

obtained

using

standards

of

known

concentration.

Calibration

Curve

Method:

Prepare

standard

solutions

of

at

least

three

different

concentrations,

measure

the

absorbance

of

these

standard

solutions,

and

prepare

a

calibration

curve

from

the

values

obtained.

Then

measure

the

absorbance

of

the

test

solution

adjusted

in

concentration to a measurable range, and determine the concentration of the element

from the calibration curve.

1

Lab 1

Part 2

The materials and apparatus

Atomic absorption spectrometry; Cu hollow cathode lamp; AC voltage stabilizer;

oil-free gas compressor; acetylene cylinder; oscillator; sample boat; Erlenmeyer flask

with stopper (100 ml); beaker; graduate cylinder; pipette.

Part 3

The procedure

3.1 operating procedure for AAS

(1) inspect major components to ensure operating normal.

(2) Install required hollow cathode lamp. Sele

ct “T” before

turning to the power and

hollow cathode lamp. Then select appropriate la mp current and preheat for 30min.

(3) Make sure electrical meter to point to zero and then turn on high-voltage power.

(4) Select appropriate slit width.

(5) Rotate monochromator and select required wavelength. If the power meter is too

high or low, adjust negative high voltage until the meter reads full scale.

(6) Adjust light point and wavelength so that the meter represents the maximum value.

(7) Turn on air compressor and acetylene gas and ignite flame. Adjust the flame

appropriately and preheat the burner.

(8) Inject distilled water into the flame and continue to preheat the burner. Inject

distilled water into the flame after each sample.

(9) Select “E”, inject blank solution into the flame and adjust

the meter to zero.

(10) Optimize analysis conditions and measure standard solution and samples.

(11) After completion of measurement, turn off acetylene gas valve and then air

compressor, cut off gas supply a moment later.

(12) Select

“T” before turning o

ff high voltage power, decrease lamp current and then

turn off the lamp. At the same time, all buttons should be on original positions.

(13) Check the equipment before leaving the laboratory.

3.2 Determination of soil samples

(1) Preparation of extracting solution (0.05 mol/l EDTA solution)

18.6 g of EDTA is dissolved with water in a beaker (500 ml). The PH is adjusted

to

7.0

using

dilute

ammonia.

The

mixture

is

transferred

into

a

volumetric

flask

(1000ml), dilute to the mark and mixed well.

(2) Treatment of soil samples

2.50

g

of

air-dried

soil

(60-

100

mesh)

is

put

into

an

Erlenmeyer

flask

with

stopper (100 ml). 12.5 ml of EDTA solution is added. The mixture is shaken for 1h

and then filtered. The filtrate is preserved for analysis.

(3) Preparation of Cu standard stock solution

0.10 g of Cu is dissolved in 15 ml of (1:1) nitric acid solution. The mixture is

transferred into a volumetric flask (1000 ml) and diluted to the mark with re-distilled

water. The concentration of the stock standard solution is 100g/ml. (The concentration

should be calculated according to the mass of Cu).The working Cu standard solution

(10?

g/ml) is obtained by diluting 10 ml of Cu standard stock solution to 100 ml with

2