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关于英语实验报告
关于英语实验报告
Determination of heavy
metals
in
soil byatomic
absorption spectrometry(AAS)
Name: XuFei
Group: The 3rd group
Date: Sep. 20th 20xx
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
thesample
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.
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. Select
“
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 off 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