Chapter 13Terms & SymbolsBeer’s LawSlide 4The Effects of Instrumental Noise on Spectrophotometric AnalysesThe Effects of Instrumental Noise on Spectrophotometric AnalysesSlide 7InstrumentationSlide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18ReferencesChapter 13An Introduction to Ultraviolet/Visible Molecular Absorption SpectrometryTerms & SymbolsBeer’s Lawlog Po/P = ebc = A The derivation of this law assumes a) That the incident radiation is monochromatic. b) The absorption occurs in a volume of uniform cross-section.c) The absorbing substances behave independently of each other in the absorbing process.Beer’s LawLimitations to Beer’s LawReal Limitations to Beer’s Law Apparent Chemical Deviations Apparent Instrumental Deviations with Polychromatic Radiation Instrumental Deviations in the Presence of Stray RadiationThe Effects of Instrumental Noise on Spectrophotometric Analyses Types of NoiseShot noise – This noise is generated by current flowing across a P-N junction and is a function of the bias current and the electron charge. The impulse of charge q depicted as a single shot event in the time domain can be Fourier transformed into the frequency domain as a wideband noise.Thermal noise – In any object with electrical resistance the thermal fluctuations of the electrons in the object will generate noise.White noise- The spectral density of thermal noise is flat with frequency.Burst noise – Occurs in semiconductor devices, especially monolithic amplifiers and manifests as a noise crackle.The Effects of Instrumental Noise on Spectrophotometric AnalysesTypes of NoiseAvalanche noise – Occurs in Zener diodes are reversed biased P-N junctions at breakdown. This noise is considerably larger than shot noise, so if zeners have to be used as part of a bias circuit then they need to be RF decoupled.Flicker noise – This noise occurs in almost all electronic devices at low frequencies. Flicker noise is usually defined by the corner frequency FL. Sources of NoiseCase I: sT = k1Case II: sT = k2(T2 + T) ½Case III: sT = k3TThe Effects of Instrumental Noise on Spectrophotometric AnalysesEffect of Slit Width on Absorbance MeasurementsInstrumentationInstrument ComponentsSourcesWavelengths selectorsSample containersRadiation detectorsSignal processors and readout devicesInstrumentationSources- Light sourcesDeuterium and Hydrogen Lamps Tungsten Filament Lamps Tungsten Filament LampsInstrumentationTypes of InstrumentsSingle-beamDouble-beam in spaceDouble-beam in timeMultichannelInstrumentation Single-Beam InstrumentsInstrumentationDouble-Beam InstrumentsInstrumentationTypical InstrumentsPhotometersVisible PhotometersProbe-type PhotometersUltraviolet Absorption PhotometersSpectrophotometersInstrumentationMost common spectrophotometer: Spectronic 20.1. On/Off switch and zero transmission adjustment knob 2. Wavelength selector/Readout 3. Sample chamber 4. Blank adjustment knob 5. Absorbance/Transmittance scaleInstrumentationVisible RegionInstrumentationSingle-Beam Instruments for the Ultraviolet/Visible RegionInstrumentationSingle-Beam Computerized Spectrophotometers Inside of a single-beam spectrophotometer connected to a computer.InstrumentationDouble-Beam Instrumetents Double-Dispersing Instruments Diode Array InstrumentsReferences