1. Atomic Absorption Spectroscopy Elemental analysis Dissolved metals Source –Hallow Cathode Lamp –Cathode of specific element Sample –Acetylene-air flame, nebulizer Detector –PMT

2. Atomic absorption Gas-phase elemental atoms Narrow absorption lines (±0.01 nm) Element specific source Flame conditions control sensitivity 1-100 ppm (mg/L) varies with element

3. Hollow cathode lamp PMT Flame sample nebulizer Air Acetylene Coating of element AA Spectrometer monochrometer

4. Experiment Aspirate blank, set 100 % T Aspirate sample Matrix effects are common –Standard addition analysis

5. Standard Addition Analysis

6. Removal of Atomic Emission Place a chopper before the flame The signal from the source is modulated by the chopper Thus, a AC signal is produced on top of a DC signal that originates from emission in the flame

7. Atomic Emission Spectroscopy Emission of light from exited species ICP source Multi-element analysis –Fancy optics Greater sensitivity for most elements

8. ICP source Ar tourch –Very hot, 10000 K –Abundance of e- inhibits ionization –Lack of O 2 inhibits oxide formation –Excited atomic species predominate –5-20 L/min

9. Sample Introduction Nebulizer Electrothermal vaporization Laser ablation In either case Ar gas in used to carry sample into the ICP

10. Scanning Instruments Grating monochromator Slew-scan mode –Slew-The detector and slit is quickly moved to a specific wavelength for a given element –Slowly scan across the wavelength window near a line in very small steps-0.001 nm –Not limited to a set of specific elements Echelle grating/prism –Higher orders, 2-D plane, better dispersion –Slew-scan mode

11. Diffraction Equation n = d(sin i + sin r) Dispersion D = dy/d = F (n/d cos r)

12. Multi-channel Instruments Polychromators –60 photomultipliers in fixed positions Array-based –Echelle and prism for 2-D dispersion plane –Charge injection detector with 94672 different detector elements (8.7x6.6mm) –A set of 39 elements makes up a read window for a given element –CCD detectors

13. CCD detectors Array of semiconductor detection elements 512x320 array =163840 individual detectors Charge of impinging photons are stored The charge accumulated on each detector element is registered one by one by sending the charge to a preamplifier and readout (emptying the registrar) Very sensitive

14. Fig 10-6 and Fig 10-7 10-6 is the slew can instrument 10-7 is the multi-channel instrument

15. Performance Sensitivity: Ranges from 1-300 ng/mL Number of useful lines; 1-24 Calibration curves; almost 3 orders of magnitude Internal standards Self-absorption at higher concentrations

16. Other components of visible spectroscopy Photon Counting –Each time a photon strikes the PMT, a pulse of electrons are produced –Normally, an average current over time is integrated to produce the signal –In photon counting each pulse is counted, and the total number of pulses in a time interval is summed –Filters out noise –Fluorescence and Raman Spec

18. Fiber Optics Total Internal Reflections n 1 >n 2 >n 3

19. Lasers Qualities –High intensities –Narrow band width –coherence Lasing medium –Solid state, gas, dye Lasing mechanism –Figure 7.5