Atomic Absorption Spectrometer (AAS) PerkinElmer Aanalyst 100

Transcription

1 Atomic Absorption Spectrometer (AAS) PerkinElmer Aanalyst 100 January 5 th -6 th, 2015 Instrument Center Science and Technology Faculty Prince of Songkla University Pattani Campus

2 Contents Schedule Trainee List Part 1 Introduction and Application of AAS Part 2 Using and Maintenance of AAS (Perkins Elmer Aanalyst 100)

3 Schedule of Using Atomic Absorption Spectrometer (AAS) Perkins Elmer Aanalyst 100 Training January 5 th -6 th, 2015 At Instrument Center, 3 th floor, Building 25 Faculty of Science and Technology, Prince of Songkla University ******************************* January 5 th, am Registration am Inauguration am Introduction of AAS Assoc.Prof.Dr. Boonsong Krisornpornsan am Coffee Break am Application of AAS Assoc.Prof.Dr. Boonsong Krisornpornsan pm Launch pm Using and Maintenance of AAS (Perkins Elmer Aanalyst 100) Mr.Pisipong Meunprasertdee pm Coffee Break pm Workshop 2 groups pm Workshop #1 Preparation of standard and sample for using AAS (Perkins Elmer Aanalyst 100) January 6 th, am Workshop # 2 Using AAS (Perkins Elmer Aanalyst 100) am Coffee break am Workshop # 2 Using AAS (Perkins Elmer Aanalyst 100) am pm Launch pm Workshop # 3 Maintenance Perkins Elmer Aanalyst pm Coffee break pm Test AAS principle and using ***********************************

4 Training of Using Atomic Absorption Spectrometer (AAS) Perkins Elmer Aanalyst 100 Training January 5 th -6 th, 2015 At Instrument Center, 3 th floor, Building 25 Faculty of Science and Technology, Prince of Songkla University ******************************* No Name - Surname Year/Degree/Major Code Signature 1 Dr. Areefen Rassamesard Lecturer, Physics 1 2 Miss Nussaba Boonyasak 4 th year, Bachelor's degree, Food Science and Nutrition 3 Miss Pawwida Wongna 4 th year, Bachelor's degree, Food Science and Nutrition 4 Mr. Bashir Algaily 2 nd year, Master's degree, Applied Physics 2 5 Mr. Atthapon Saman 5 th year, Bachelor's degree, Agricultural Technology 6 Ms. Trinh Ngoc Thao Ngan 2 st year, Master's degree, Food Science and Nutrition 7 Dr.Sunaree Bordeepong Lecturer, Physics 1 8 Ms.Haleemoh Weasamaae 4 th year, Bachelor's degree, Fishery Technology Mr. Roslan Chemae 4 th year, Bachelor's degree, Fishery Technology 1 10 Mr.Viroj Pinprom Graduate, Bachelor's degree, Chemistry and Biology 11 Mrs.Saijai Maneerat Graduate, Master's degree, Soil Management 1 2

5 Part 1 Introduction and Application of AAS

6 Atomic Absorption Spectrophotometry (AAS) By Assist. Prof. Dr. Boonsong Krisornpornsan ผศ. ดร. บ ญส ง ไกรศรพรสรร 1 History of optics and light studies His experiment - lens, mirrors etc. His study - Ray of light Ibn Alhazen (Father of optics) 2 1

7 Historical background of spectroscopy The first to turn his telescope to the heavens. - Moon, sun spots etc. Galileo Galilei ( ) 3 A quantitative study of light The first people to study light scientifically. -Prism - Spectrum Sir Isaac Newton ( ) 4 2

8 Original studies of light 5 Newton s contribution to spectroscopy 6 3

9 Classification of electromagnetic radiation 7 Advancements in the study of light -Fraunhofer lines in the sun s s spectrum - Developed a spactroscope -Dratings Joseph von Fraunhofer ( ) German optician 8 4

10 Color of light -heat the element Gustav Robert Kirchhoff ( ) German physicist Robert Wilhelm Eberhard Bunsen ( ) German chemist 9 Emission spectra complement absorption spectra 10 5

11 Hydrogen line spectrum 11 Scanning spectrophotometer (side view) 12 6

12 Scanning spectrophotometer (top view) 13 Computer output from scanning spectrophotometer 14 7

13 Hydrogen spectrum The Balmer series Wavelength color (nm) red blue blue-violet violet Johann Jakob Balmer ( ) 15 Quantum properties of light ΔE = nhν ΔE the change in Energy n= 1, 2, 3, h (Planck s constant) h = Js ν - frequency Max Karl Ernst Ludwig Planck ( ) German physicist 16 8

14 Quantum model for the Hydrogen atom Neils Henrik David Bohr ( ) Danish physicist 17 Bohr s Model Nucleus Electron Orbit Energy Levels 18 9

15 Excitation Excited electron + energy +E Mo M* 19 Decay and Emission Back to ground state -E light +E -E M o M * M o 20 10

16 Origins of atomic spectra excited states light λ 3 λ 2 λ 1 E = hʋ 21 Atomic Spectra Every chemical element has own unit spectral fingerprint. i Emission spectrum of hydrogen Absorption spectrum of hydrogen 22 11

17 Emission spectroscopy Electrons jump from higher levels to lower ones. Energy is released or emitted in the form of light of specific energy (or color). Electrons must first be excited up to higher levels. This is done either with heat (eg. Flame tests) or light (atomic emission spectra). 23 Absorption spectroscopy Electrons jump from lower levels to higher ones. Energy is absorbed in the form of light of specific energy (or color). This is the method used in UV-Vis spectroscopy and atomic absorption spectroscopy (AAS) and many others

18 A spectrum Emission lines Absorption lines Continuum A spectrum = the amount of light given off by an object at a range of wavelengths. 25 The colors come from the different energies, frequencies and wavelengths of light. They are properties of light and all interconnected

19 Calculations for energy levels 2 18 Z E = J ( ) 2 n When Z = atomic number of element n = quantum number & the units are Joules 27 Calculations the Balmer & Lyman series Rydberg equation 1 1 ν = R( ) 2 n 2 1 n When Ʋ = frequency n = quantum number R = Rydberg constant t = 3.29 x Hz 1 Hz = 1 s

20 Frequency (ν) V.S Wavelength (λ) λ ν =c C = speed of light = X 10 8 m/s 29 Violet light has the shortest wavelength of visible light, and has the highest energy. Ab bsorbance Red light has the longest wavelength of visible light. This also means it has the lowest frequency and lowest energy Wavelengths (nm) The maximum absorption occurs 30 15

21 How are color and light absorption are related? 31 Just as light can be split into its various colors, so these colors can be recombined to form white light. Mixing all these colored lights would give us white, but we can also use combinations of fewer colors to get white

22 We can see that red, blue and green light add together to make white light. But where green overlaps magenta, white light is also formed. Same with red and cyan. And with yellow and blue. We call these colors complementary 33 Complementary colors are on the opposite sides of the color wheel. They help us understand the colors we see when light is absorbed

23 If we take blue light away from white light (absorb blue), what color remains? 35 The absorption spectra of individual atoms have very distinct lines showing which energies of light have been absorbed as the electrons jump to higher levels

24 The absorption spectra of compounds tends to have broad overlapping regions for all the possible electron jumps. 37 This is the type of absorption spectra which is obtained using a using a UV-Vis spectrophotometer. The position of the peak shows the wavelength of the light most strongly absorbed and what % is absorbed

25 This substance is absorbing the red/orange light (~600 nm) and transmitting the rest which our eye mixes and interprets as blue/green. 39 White light shining on a white object. All light is reflected

26 White light shining on a red object. Red light is reflected- other colors absorbed (particularly green and similar colors). 41 This is a more realistic view of this. The reflected colors combine and are mixed in the brain to give the overall red color

27 White light shining on a blue object

28 White light shining on a black object. All light is absorbed. Black is the absence of light. White light shining on a grey object. A small amount of each color is reflected. 45 Atomic Spectroscopy Emission Mo + heat M* Mo + light Absorption Mo + light M* 46 23

29 Atomic Spectroscopy (AS) 1. Atomic Absorption Spectroscopy (AAS) 2. Flame Atomic Emission Spectroscopy (FAES) 3. Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP) 47 Basic principle AAS is an analytical technique that measures the concentrations of elements. It makes use of the absorption of light by these elements in order to measure their concentration. -จ านวนหร อปร มาณของ unexcited atoms ท จะ absorb แสง ซ ง emit มาจาก excited atoms ของ element ชน ดเด ยวก น 48 24

30 - AAS quantifies the absorption of ground state atoms in the gaseous state. - The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels. The analyte concentration is determined from the amount of absorption. - Concentration measurements are usually determined from a working curve after calibrating the instrument with standards of known concentration. - Atomic absorption is a very common technique for detecting metals and metalloids in a samples. 49 detectable 50 25

31 AAS AAS have 4 principal p components 1. A light source (Continuum and line source) (usually a Hallow Cathode Lamp (HCL)) 2. An atom cell (atomizer) 3. A monochromator 4. A detector, and read out device 51 Schematic Diagram of an AAS Light source Atomizer Monochromator Detector and readout device 52 26

32 53 Quartz window HCL Pyrex body HCL contains a tungsten anode and a hollow cylindrical cathode made of the element to be determined. These are sealed in a glass tube filled with an inert gas (Ne or Ar)

33 How HCL works? Applying a potential difference between the anode and the cathode leads to the ionzation of some gas atoms (Ne/Ar). These gaseous ions bombard the cathode and eject metal atoms from the cathode in a process called sputtering. Some sputtered atoms are in excited states and emit radiation characteristic of the metal as they fall back to the ground state. The shape of the cathode which is hollow cylindrical concentrates the emitted radiation into a beam which passes through a quartz window all the way to the vaporized sample. Since atoms of different elements absorb characteristic wavelengths of light. Analyzing a sample to see if contains a particular element means using light that element. 55 HCL emission process 1. Ionization 2. Sputtering Ne o Ne + Ne + M o 3. Excitation 4. Emission + M + - M - o M* M * Ne + M o light 56 28

34 For example with sodium, A lamp containing sodium emits light from excited sodium atoms that produce the light mix of wavelengths to be absorbed by any sodium atoms from the sample. A beam of the electromagnetic radiation emitted from excited sodium atoms is passed through the vaporized sample. Some of the radiation is absorbed by the sodium atoms in the sample. The greater the number of atoms there is in the vapor, the more radiation is absorbed. 57 Considerations 1. Type of HCL 2. Position of HCL 3. Current adjust of HCL 58 29

35 Atomizer Elements to be analyzed needs to be in atomic sate. Atomization is separation of particles into individual molecules and breaking molecules into atoms. This is done by exposing the analyze to high temperatures in a flame or graphite furnace. 59 The role of the atom cell is to primarily dissolved a liquid sample and then the solid particles are vaporized into their free gaseous ground state form. In this form atoms will be available to absorb radiation emitted from the light source and thus generate a measurable signal proportional to concentration. There are two types of atomization: Flame and Graphite furnace atomization

36 61 Flame Flame AA can only analyze solutions, Where it uses a slot type burner to increase the path length, and therefore to increase the total t absorbance Sample solutions are usually introduced into a nebulizer the sample is dispersed into tiny droplets, which can be readily broken down in the flame

37 Flame Atomizers 1. Used in all atomic spectroscopic p techniques 2. Converts analyze into free atoms in the form of vapor phase free atoms 3. Heat is required 4. Routes for sample introduction 63 Various flame atomization techniques 64 32

38 Types of flames used in Atomic spectroscopy Fuel and Oxidant Temperature, o C Gas/air Gas/O H 2 /air H 2 /O Acetylene/air Acetylene/O Acetylene/N 2 O Solution of analyze Nebulization Processes that take place in flame Spray Desolvation Solid/gas aerosol Volatilization Gaseous molecules Dissociation Atoms Ionization Atomic ions Excited molecules Excited atoms Excited ions hʋ molecular hʋ atomic hʋ ionic 66 33

39 Effect of flame temperature on excited state population E *, g * = 3 Excited state E E o, g o = 2 ground state Atoms in excited state Atoms in ground state Emission N * = g * e - E/kT N o g o Statistical factor Absorption Energy difference Temperature (K) Boltzmann constant (1.381x10-23 ) 67 The lowest excited state of a sodium atom lies 3.371X10-19 J/atom above the ground state. The degeneracy of the excited state is 2, while that of the ground state is 1. Let s calculatethe the fraction of sodium atoms in the excited state in an acetylene-air flame at 600 K. N * = g * e - E/kT N o g o N * = 2e x10-19/(1.381x10-23*2600) N o 1 = 1.67x10-4 That is, less than 0.02 % of the atoms are in the excited state

40 Thus % of Na atoms are in the ground state. Atomic emission uses excited atoms. Atomic absorption uses ground state atoms. 69 How would the fraction of atoms in the excited state change if the temperature were K instead? N * = 2e x10-19/(1.381x10-23*2610) N o 1 = 1.74x10-4 The fraction of atoms in the excited state is still less than 0.02 %, but that fraction has changed by 100*( )/1.67 = 4 % 70 35

41 Ratio of excited- to ground-state atoms for lines with varying excitation energies at increasing temperature element Line g * /g o E (J) Ratio of excited- to ground-state atoms (nm) 2000 K 4000 K 6000 K 8000 K Cs x x x x x10-1 Na x x x x x10-2 Ca x x x x x10-2 Zn x x x x x Atomization devices Atomization: 1. A process of forming free atoms by heat 2. Atomizers are devices that t carry out atomization: ti 2.1 Continuous (constant temperature with time) -Flame -Plasma 2.2 Non-continuous (temperature varies with time) -Electrothermal -Spark discharge 72 36

42 Sample introduction systems In continuous atomizers sample is constantly introduced in form of droplets, dry aerosol, vapor. Nebulizer: A device for converting the solution into fine spray or droplets Continuous sample introduction is used with continuous nebulizers in which a steady state atomic population is produced. Sample is introduced in fixed or discrete amounts. 73 Discontinuous samplers are used with continuous atomizers 1. Discrete samples are introduced into atomizers in many ways: Electrothermal atomizers A syringe is used. A transient signal is produced as temperature changes with time and sample is consumed. 2. Indirect insertion (probe) Sample is introduced into a probe (carbon rod) and mechanically moved into the atomization region vapor cloud is transient because sample introduced is limited

43 3. Flow injection The analyte is introduced into the carrier stream into a nebulizer as mist 4. Hydride generation The volatile sample is stripped from the analyte solution and carried out by a gas into the atomizer. This strip is followed by chemically converting the analyte to hydride vapor form. 5. With Arc spark Solids are employed. 6. Laser microbe technique A beam of laser is directed onto a small solid sample, gets vaporized, atomized by relative heating, Either sample is probed by encoding system or vapor produced is swept into 75 a second absorption or fluorescence. Nebulization gas is always compressed, usually acts as the oxidant, it is oxygen in flame and argon in plasma Nebulization chambers produce smaller droplets and remove or drain larger droplets called aerosol modifiers. Aspiration rate is proportional to compressed gas pressure. The pressure drops through capillary, here ¼ capillary diameters are recommended. d This is inversely proportional to viscosity of the solution. Peristaltic and/or syringe pumps could be used

44 Oxidant and fuel are usually brought into nebulization chamber through a separate port. They mix and pass the burner head called premixed burner system. Add organic solvents to reduce the size of the drop. 77 The atomic absorption spectrometer Sample Introduction System Nubulizer Capillary Solution 78 39

45 The fine mist of droplets is mixed with fuel (acetylene), and oxidant (air or nitrous oxide) and burned. The flame temperature is important because it influences the distribution of atoms. It can be manipulated by oxidant and fuel ratio. 79 Monochromators This is a very important part in an AAS. It is used to separate out all of the thousands of lines. Without a good monochromator, detection limits are severely compromised. A monochomator is used to select the specific wavelength of light which is absorbed by the sample, and to exclude other wavelengths. The selection of the specific light allows the determination of the selected element in the presence of others

46 Detector and read out device The light selected by the monochromator is directed onto a detector that is typically a photomultiplier tube, whose function is to convert the light signal into an electrical signal proportional to the light intensity. The processing of electrical signal is fulfilled by a signal amplifier. The signal could be displayed for readout, or further fed into a data station for printout by the requested format. 81 Calibration curve A calibration curve is used to determine the unknown concentration of an element in a solution. The instrument is calibrated using several solutions of known concentrations. The absorbance of each known solution is measured and then a calibration curve of concentration vs absorbance is plotted. The sample solution is fed into the instrument, and the absorbance of the element in this solution is measured. The unknown concentration of the element is then calculated from the calibration curve

47 Absorbance V.S Concentration 83 Interferences The concentration of the analyte element is considered to be proportional to the ground state atom population in the flame, any factor that t affects the ground state atom population can be classified as an interference. Factors that may affect the ability of the instrument to read this parameter can also be classified as an interference

48 The different interferences that are encountered in atomic absorption spectroscopy are: 1. Absorption of source radiation: Element other than the one of interest may absorb the wavelength being used. 2. Ionization interference: the formation of ions rather than atoms causes lower absorption of radiation. This problem is overcome by adding ionization suppressors. 3. Self absorption: the atoms of the same kind that are absorbing radiation will absorb more at the center of the line than at the wings, and thus resulting in the change of shape of the line as well as its intensity. 4. Background absorption of source radiation: This is caused by the presence of a particle from incomplete atomization. This problem is overcome by increasing the flame temperature. 5. Transport interference: rate of aspiration, nebulization, or transport of the sample (e.g viscosity, surface tension, vapor pressure, and density)85 Atomic emission spectroscopy Atomic emission spectroscopy is also an analytical technique that is used to measure the concentrations of elements in samples. It uses quantitative measurement of the emission from excited atoms to determine analyte concentration. The analyte atoms are promoted to a higher energy level by the sufficient energy that is provided by the high temperature of the atomization sources. The excited atoms decay back to lower levels by emitting light. Emission are passed through monochromators or filters prior to detection by photomultiplier tube

49 The instrumentation of atomic emission spectroscopy is the same as that of atomic absorption but without the presence of a radiation source. In atomic emission the sample is atomized and the analyte atoms are excited to higher energy levels all in the atomizer. 87 Schematic diagram of an atomic emission spectrometer 88 44

50 The source of energy in atomic emission could be a flame like the one used in atomic absorption, or an ICP. 1. The flame ( o C) is most useful for elements with relatively low excitation energies like sodium, potassium and calcium. 2. The flame ( o C) has a very high temperature and is useful for elements of high excitation energies. 89 Comparison between atomic absorption and emission spectroscopy absorption emission 1. Measure trace metal 1. Measure trace metal concentrations in complex matrices. concentrations in complex matrices. 2. Atomic absorption depends upon 2. Atomic emission depends upon the number of ground state atoms. the number of excited state atoms. 3. It measures the radiation 3. It measures the radiation emitted absorbed by the ground state by the excited state atoms. atoms. 4. Presence of a light source (HCL). 4. Absence of the light source. 5. The temperature in the atomizer is adjusted to atomize the analyte atoms in the ground state only. 5. The temperature in the atomizer is big enough to atomize the analyte atoms and excite them to a higher energy level

51 AAS applications They are many applications for atomic absorption: 1. Clinical analysis: Analyzing metals in biological fluids such as blood and urine. 2. Environmental analysis: Monitoring our environment: e.g finding out the levels of various elements in rivers, seawater, drinking water, air, soil and petrol. 3. Pharmaceuticals 4. Industry 5. Mining 6. Food, Cosmetics, Hair, Plant, Animal etc. 91 The use of AAS 1. The type and current of HCL 2. The wavelength for analysis 3. The flame 4. Chemical treatment 5. Interferences 92 46

52 Detection limit (DL) noise 3X -Standardization by IUPAC -DL = Conc. Producing signal that is 3 times noise level -DL = 3x std dev of blank -Defines signal to noise ratio -Provides information on: 1. Total instrument performance 2. Lower limit of concentration measurement 93 47