1、determination of heavy metals in soil by atomic absorption spectrometry(aas)name: xufei group: the 3rd groupdate: sep. 20th part 1 the introduction1the 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 appl

2、ication of atomic absorption spectrometry.2the principlesatomic 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 pro

3、duced 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

4、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 cal

5、ibration 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 apparatuspart 3 the procedure3.1 operating procedure for aas(2

6、) 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 monochrom

7、ator 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.

8、 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 tur

9、n 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 i

10、s 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 samples2.50 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 mi

11、xture is shaken for 1h and then filtered. the filtrate is preserved for analysis.(3) preparation of cu standard stock solution0.10 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

12、. 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 (10g/ml) is obtained by diluting 10 ml of cu standard stock solution to 100 ml withre-distilled water.(4) plotting of the standard curv

13、e0 ml, 1 ml, 2 ml, 3 ml, 4 ml and 5 ml of cu standard solution (10g/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 0g/ml, 1.00g/ml,2.00g/ml, 3.00g/ml, 4.00g/ml, 5.00g/ml of cu, res

14、pectively. the absorbance is measured at wavelengths of 3247 ?. the standard curve is constructed by plotting absorbance vs. concentration.(5) determination of samplesthe sample solution is analyzed using the same procedure and conditions as for the standard curve. the concentration of cu is obtaine

15、d from the standard curve based on the absorbance.part 4 the results4.1 the raw data4.2 aas standard curve4.3 calculationthe absorbance of sample is 0.0511.according to the formula above :y=0.0446x+0.0024,r2=0.9997the concentration of cu in the sample is:1.091mg/l.part 5 discussionin this experiment

16、, 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

17、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 1.091g/ml. we have known

18、 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 s

19、uggestions for our experiments. firstly when well 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, ev

20、eryone should understand his own task in the experiment.-10-04 06:03abstractintroductionmethodresultsdiscussionconclusionreferenceabstractabstractabstract 2 3 4 5 example:does a childs focus correlate with barometric pressure? if so, does it correlate positively or negatively? tucker (1999) hypothes

21、ized 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

22、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 whenbarometric pressure was neutral or high. the results suggest that when diagnosing adhd, pract

23、itioners should give the cpt when barometric pressure is roductionintroduction well, reference introduction exampleintroductionin this lab, we explore the theory of optimal foraging and the theory of central place foraging using beavers as the model animal. foraging refers to the mammalia

24、n behavior associated with searching for food. the optimal foraging theory assumes that animals feed in a way that maximizes their net rate of energy intake per unit time (pyke et al. 1977). an animal may either maximize its daily energy intake (energy maximizer) or minimize the time spent feeding (

25、time minimizer) in order to meet minimumthe central place theory is used to describe animals that collect food and store it in a fixed location in their home range, the central place (jenkins 1980). the factors associated with the optimal foraging theory also apply to the central place theory. the c

26、entral place theory predicts that retrieval costs increase linearly with distance of the resource from the central place (rockwood and hubbell 1987). central place feeders are very selective when choosing food that is far from the central place since they have to spend time and energy hauling it bac

27、k to the storage site (schoener 1979).the main objective of this lab was to determine beaver (castor canadensis) food selection based on tree species, size, and distance. since beavers are energy maximizers (jenkins 1980, belovsky 1984) and central place feeders (mcginley and whitam 1985), they make

28、 an excellent test animal for the optimal foraging theory. beavers eat several kinds of herbaceous plants as well as the leaves, twigs, and bark of most species of woody plants that grow near water (jenkins and busher 1979). by examining the trees that are chewed or not-chewed in the beavers home ra

29、nge, an accurate assessment of food preferences among tree species may be gained (jenkins 1975). the purpose of this lab was to learn about the optimal foraging theory. we wanted to know if beavers put the optimal foraging theory into action when selecting food.we hypothesized that the beavers in th

30、is study will choose trees that are small in circumference and closest to the water. since the energy yield of tree species may vary significantly, we also hypothesized that beavers will show a preference for some species of trees over others regardless of circumference size or distance from the cen

31、tral area. the optimal foraging theory and central place theory lead us to predict that beavers,like most herbivores, will maximize their net rate of energy intake per unit time. in order to maximize energy, beavers will choose trees that are closest to their central place (the water) and require th

32、e least retrieval cost. since beavers are trying to maximize energy, wehypothesized that they will tend to select some species of trees over others on the basis of nutritional value.methodsmaterial procedurematerial chromatographylight bulbslc-10avp plus high-performance liquid chromatography24 inca

33、ndescent 60w light bulbs arranged in a 6*4 rectangular matrix (see figure 2)dell precision t7500 (xeon x5550 2.66ghz, 6gb ram, 64 bit windows 7 professional)subjects subjectswe tested 150 third-grade students chosen at random from a pool of 346 applicants from eight london public and private element

34、ary schools. the students represented a fairly wide range of economic backgrounds. all agreed to participate in our study in exchange for a 25 pounds gift certificate from a local toy cedure example:t = mr (g-a),where a is the acceleration of the mass. if the assumption holds that the only

35、friction affecting the potentiometer was constant coulomb friction, then each mass would undergo a constant acceleration.the potentiometer measured voltage versus time for the masses as they dropped, but the measurement of interest to us was position versus time. for that reason, a calibration was p

36、erformed before we measured any data. in the calibration, the potentiometers initial voltage was measured. then the string was pulled a set distance (2 inches), and the voltage was recorded. this process of pulling the string a set distance and recording the voltage continued another two times (see

37、appendix a for the results). to determine the relationship between voltage and position, the differences in the voltages were averaged and divided by the length. the resulting relationship was 0.9661 volts/inch.five different masses were used to test the assumption of constant acceleration. for each

38、 mass, the string was rolled up on the shaft, the oscilloscope was triggered, and the shaft was released. as each mass dropped, the oscilloscope collected the potentiometers voltage versus the time. after obtaining plots for each mass, we used thevoltage-position relationship, mentioned above, to co

39、nvert the data from the form voltage versus time to the form position versus time squared.the residuals of the data determined whether the assumption of constant acceleration was valid.results sample calculation.resultssectionexample:resultsoverall, beavers showed a preference for certain species of

40、 trees, and their preference was based on distance from the central place.measurements taken at the study site show that beavers avoided oaks and musclewood (fig. 1) and show a significant food preference (x2=447.26, d.f.=9, p.05). no avoidance or particular preference was observed for the other tree species. the mean distance of 8.42 m away from the water for not-chewed trees was significantly greater than the mean dist