Partial Energy Level Diagrams

Transcription

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2 Partial Energy Level Diagrams 460 nm 323 nm 610 nm 330 nm 819 nm 404 nm 694 nm 671 nm 589 / 590 nm 767 / 769 nm Lithium Sodium Potassium

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5 Gas Mixtures Maximum Temperatures, C Air-Coal Gas 1825 Air-Propane 1725 Air-Hydrogen 2045 Air-Acetylene 2250 Oxygen-Hydrogen 2677 Oxygen-Acetylene 3060 Nitrous Oxide- Acetylene Argon-Hydrogen- Entrained Air

6 surrounding air interconal zone secondary combustion zone primary combustion zone preheat zone

7 Maxwell-Boltzmann Equation: N 1 N 0 g 1 g 0 e (E 1 E 0)/kT (nm) Energy (ev) N 1 /N 0 g 1 /g K 3000 K 4000 K Cs X X X10-2 Na X X X10-3 Ca X X X10-4 Zn X X X10-6

8 The nm line of Cadmium corresponds to the 1 S 0-1 S 1 transition. N 1 Calculate the ratio of in air/ N 0 C 2 H 2 The temperature is 2250 C or 2523 K Degeneracy ratio of the two levels is: g 1 /g 0 = [2(1)+1]/[2(0)+1] =3/1

9 N 1 N 0 g 1 g 0 e (E 1 E 0 )/kt First find the frequency of light at 228 nm so that the energy difference can be calculated from E = h c cm sec cm sec 1

10 N 1 N 0 g 1 g 0 e (E 1 E 0 )/kt Find the energy difference between the levels: E 1 E 0 h ( erg - sec)( sec 1 ) erg

11 Find the ratio: N 1 N 0 g 1 g 0 e (E 1 E 0 )/kt erg 1 e[ ( erg K -1 )(2523 K) ] 3e

12 SI Units 1 Joule = 10 7 ergs

13 SOLUTION NEBULIZATION LARGE AND SMALL DROPLETS DRAIN FLAME COMPOUND FORMATION MO THERMAL EXCITATION M + X M* DISSOCIATION MX M + + e - IONIZATION Desolvation RADIATIONAL EXCITATION M + hv EMISSION OR FLUORESCENCE

14 Types of Interferences chemical ionization spectral background excitation

15 chemical - formation of stable compounds - hotter flame, releasing agent, separation ionization - ionization suppressant spectral - atomic and molecular - improve spectral resolution of spectrometer background - flame gas or matrix emission -matrix match, resolve spectrally, modulation excitation- temp. change by matrix or solvent - standard addition, matrix match

16 analyte, aluminum ionizes in flame Al Al e ionization suppressant sodium at g l 1 Na Na e forces equilibrium of Al to left

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18 C B A

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21 Photographic plate -UV spectrum 302 nm 310 nm Iron Aluminum Magnesium Lead Steel C e T i A g Z n Z r Nickel Beryllium ore N i C u C u Fe Al Be Na Be

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23 Emission ce f Q L h 0 A 21 (g 1 g 2 )e E 21 kt f, g c = concentration, L = path length h 0 = energy of photon A 21 = Einstein coefficient = rate of sample introduction = efficiency of sample introduction = efficiency of atomization

24 Emission ce f Q L h 0 A 21 ( g 1 g 2 )e Q = flow rate of flame gases E 21 kt f, g e f = increased volume on combustion = solid angle of light collection = wavelength g = efficiency of detector

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29 BURNER HEADS ATOMIC ABSORPTION EMISSION OR FLUORESCENCE

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34 Advantages of graphite furnace long residence time compared to flame micro samples electrically heated

35 Features of graphite furnace matrix modifiers L vov platform size: mm x 6-8 mm blackbody radiation rapid heating absolute analysis

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37 electrode light path electrode light path

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40 magnetic field OFF magnetic field ON absorption absorption profile absorption source emission profile - analytical wavelength

41 S-5 S-4 Absolute Sensitivity ma / W S-5 RCA IP28 S-1 RCA 7102 S-4 RCA IP21 S-1 Wavelength, nm

42 I 0 light source Absorption Cell b I detector Transmittance T= I I 0 %T= I I0 x 100

43 Fraction of light transmitted decays exponentially with both path length: T k is a constant I I 0 10 kb and concentration: T I I 0 10 k ' c

44 or: lgt lg I I 0 kb and: lgt lg I I 0 k' c combination of these two: lgt lg I I 0 abc

45 define: Absorbance, A = - lg T which results in Beer s law: A lg T lg I 0 I abc and: A 2.00 log%t

46 Instrumental Limitations of Beer s law Stray Light A lg I 0 I lg 1 10 A 0 - fraction of light that is not absorbable A 0 - true or ideal absorbance

47 2.0 Deviations due to 0% 0.2% 1% A 1.0 5% (%) 0 Concentration

48 Effect of Instrumental noise on precision of analyses 100 instrumental noise limit %T T T c 0 10 c concentration limit caused by exponent T 10 k'c

49 Effect of Instrumental noise on precision of analyses relative concentration uncertainty, % c C best precision: absorbance 0 absorbance 1.0 transmittance 100 0

50 Differentially pumped region from nebulizer argon in ICP ion lenses channel electron multiplier detector ICP RF supply quadrupole mass filter computer control mechanical pump cryogenic pump quad RF supply

51 Quadrupole Mass Spectromter ion with unstable trajectory to electron multiplier ions from ICP ion with stable trajectory dc and rf voltages

52 Atomic mass units (Daltons)

53 SPECTRAL INTERFERENCES in ICP-MS Polyatomic ions from mineral acids Diatomic ions from plasma and carrier gases Oxides of matrix elements

54 ICP-MS interferences Acid Ion m/z Overlap HNO3 N+ 14 ArN Fe+ 54 Cr+ HClO4 Cl ClO Y Cr+ H2SO4 S+ 32,33, 34 SO Ti Ti Cr+

55 ICP-MS interferences plasma ion m/z Overlap N Si+ NO Si+ O S S+ ArO Cr Cr Fe+ Ar Ge Se+

56 ICP-MS interferences Analyte ion m/z Interferant Ni Ca 16 O Ca 16 O Ca 16 OH Cu Ca 16 OH Co Ca 16 O Zn Ca 16 O Cd Zr 16 OH Sb Zr 16 O 2

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59 This is a new slide This is to test for conversion from ppt v3.0 to ppt v4.0