原子吸收光谱

Lab 2 determination of heavy metals in soil by atomic absorption spectrometry DATE 2012 9 19 Name xxx Group number x Partners xxx Objectives 1 To further understand the principles of atomic absorption spectrometry 2 learn how to operate the atomic absorption spectrometry 3 Get familiar with the application of atomic absorption spectrometry 4 Learn how to use a standard curve for quantitative analysis 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 Theory 1 Atomic Absorption Spectrometry is a technique for measuring quantities of chemical elements present in environmental samples by measuring the absorbed radiation by the chemical element of interest The atoms absorb ultraviolet or visible light and make transitions to higher energy levels A detector measures the wavelengths of light transmitted by the sample and compares them to the wavelengths which originally passed through the sample 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 2 The concentration is calculated based on the Beer Lambert law The absorbance within a certain range is proportional to the concentration of the element under test in vapor phase ground state atoms The concentration is usually determined from a calibration curve obtained using standards of known concentration 3 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 Procedures 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 lamp 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 laboratory 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 100 g 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 V Data and results 1 data of the standard solution samples is shown as the Table 2 324 8nmSample no Concentration mg l ABS1ABS2ABS3 AverageSTDEVRSD 10 000 0 0006 0 0003 0 0011 0 0003 0 0009 318 9338 21 000 0 1082 0 1083 0 1103 0 1089 0 0012 1 0875 32 000 0 2140 0 2152 0 2164 0 2152 0 0012 0 5576 43 000 0 3271 0 3279 0 3280 0 3277 0 0005 0 1505 54 000 0 4155 0 4133 0 4111 0 4133 0 0022 0 5323 65 000 0 5054 0 5021 0 5079 0 5051 0 0029 0 5759 Table 2 the data of standard solution samples 2 standard curve plotted as follows y 0 1015x 0 0079 R2 0 9977 0 1 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 01 02 03 04 05 06 0 Concentration mg l ABS Figure1 the calibration curve Experiment measured the absorbance of Cu is 0 5012 we read from the AAS that the concentration of Cu is 4 860 mg l We can Calculate the concentration of Cu by the following equation y 0 1015x 0 0079 x concentration of Cu mg l y absorbance Bring the experiment measured value of ABS into the equation we can get the value of x x 4 860 mg l The concentration of heavy metals in soil is 4 860 0 1 1000194 4 25 cmg kg VI Conclusion and discussion 1 Summarize This experiment first we use the given Cu standard stock solution 10 mg l to get different concentration of standard solution Our estimated concentration of standard solution respectively 0 mg l 1 00 mg l 2 00 mg l 3 00 mg l 4 00 mg l 5 00 mg l of Cu then we measure the absorbance of this group of Cu standard solution by AAS thus we can get the Standard curve At last 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