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2021-02-02 17:42
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2021年2月2日发(作者:锁气器)



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.???????????? ?鱨????????????·¨



???????é± ¨????????????·¨??×???



2010-10-04 06:03



??·?×?±ê×??????鱨??????????



1.



abstract



2.



introduction



3.



method



4.



results



5.



discussion



6.



conclusion



7.



reference



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abstract



???????? ??????????????????????????



? ????¨?é???????????ê?ó??????????



°???????????·?????????×?????????????????????ab stract????



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1.


< p>
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???????°???????????í ???ò?????????à??????????



3 ???????°?è?????????é



4 ???????°???¨???????é?á??



5 ? ????°???????á???????????????????é???????ò?á??????? ???



×?????±?????example:



does a child??s focus correlate with barometric pressure? if so, does it


correlate positively or negatively? tucker (1999) hypothesized a negative


correlation, but this assertion has never been tested. our team used the misha cpt


to measure the focus of a group of 150 third-grade students. we divided the


students into three groups of 50 students. one group took the misha cpt when


barometric pressure was low, another group took it when barometric pressure was


neutral, and the final group took it when barometric pressure was high. the


results found that children focused significantly better when barometric pressure


was low than when



barometric pressure was neutral or high. the results suggest that when


diagnosing adhd, practitioners should give the cpt when barometric pressure is


neutral.



introduction



intr oduction?????é?????????·?????????????????é?è???¤?÷ ?????÷?????????é???


??????????鱨???¤??? ??¨????????????????????



???é???????ê?ó?é?????é?ù±??í???? ?é???? ???°???ò?????×?????à?ü?à???????é???


???? ??????????????°??????????·????¨well, ???????§??°????????ê????



×?? ????é???????à???à?????é??????°?????????·?×?????ref erence??


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