-
determination of heavy metals
in soil by atomic absorption
spectrometry(aas)
name:
xufei group: the 3rd group
date: sep. 20th 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 .
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
part 3 the procedure
3.1 operating procedure for
aas
(2) instal
l
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.
(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.
(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 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
re-distilled water.
(4) plotting of the standard
curve
0 ml, 1 ml, 2 ml, 3
ml, 4 ml and 5 ml of cu standard solution
(10??g/ml) are
added respectively to 6
volumetric flask (10 ml) with 1 ml of 5 mol/l
hydrochloric
acid. the mixture is
diluted with re-distilled water and mixed well to
give
0??g/ml, 1.00??g/ml,2.00??g/ml,
3.00??g/ml, 4.00??g/ml, 5.00??g/ml of cu,
respectively. the absorbance is
measured at wavelengths of 3247 ?. the standard
curve is constructed by plotting
absorbance vs. concentration.
(5) determination of samples
the sample solution is analyzed using
the same procedure and conditions as
for the standard curve. the
concentration of cu is obtained from the standard
curve based on the
absorbance.
part 4 the
results
4.1 the raw
data
4.2 aas standard
curve
4.3
calculation
the absorbance
of sample is 0.0511.
according to the formula above
:y=0.0446x+0.0024,r2=0.9997
the concentration of cu in the sample
is:1.091mg/l.
part 5
discussion
in this
experiment, we use the aas to determine cu in
soil. i learn how to
operate the aas
and the limitation. in the experimental process,
standard solution
was prepared in
strict accordance with the experimental
requirements and i learn
how to deal
with the data. finally we get the standard curve,
then, the sample
concentration is
calculated according to the absorbance of the
sample.
ultimately, we get
the linear formula is y = 0.0446x + 0.0024 and
r2=0.9997.
from according to the
formula and the absorbance of cu in the sample is
0.0511, we
draw the concentration of cu
in the sample is 1.091??g/ml. we have known that
the
concentration of test sample
measured by instrument is 1.091mg/l.
we can say our result of experiment is
so very accurate from the standard
curve of cu and the value of
r(r2=0.09997). the accurate data is due to the
efforts of we everyone. thanks for
every members of our group.
i have some suggestions for our
experiments. firstly when we??ll do an
experiment, we must prepare our pre-lab
by ourselves and translate it into
chinese .only do like this, we can
understand the experiment well. secondly we
should prefer to solute the problems in
the experiment rather than ask for ta.
finally, everyone should understand his
own task in the
experiment.????????????
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2010-10-04 06:03
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1.
abstract
2.
introduction
3.
method
4.
results
5.
discussion
6.
conclusion
7.
reference
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