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60 Cards in this Set
- Front
- Back
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How can you tell if there is a matrix effect?
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You can tell if there is a matrix effect by checking the percent yield. If there is a percent yield there is a matrix effect.
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The two natures of light are?
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Light can act like a particle and like a wavelength.
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What is absorption?
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Absorption is when electromagnetic radiation is transfered through a medium in the form on energy.
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What is emission?
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Emission is when excited state returns to ground state. The exact opposite of absorption and is a part of fluorescence.
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What are the five basic components for optical instruments?
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sample holder, light source, wavelength selector, detector, signal processor
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What processes is hollow cathode lamps used for and briefly describe them.
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AAS and AFS. Produces a small amount of light from an excited metal that produces narrow emission from atomic species.
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What is the abbreviation for laser and briefly describe the advantages for lasers.
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Light amplified by the stimulated emission of radiation. Lasers emit a narrow light that excites only the wanted species, which improves detection limits.
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What are the components for lasers?
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amplfication membrane, full reflecting mirror, partially transmitting mirror.
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Name the amplification membranes available?
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crystals, organic dyes, gases, ions
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What are the four laser actions?
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pumping, spontaneous and stimulated emission, and absorption
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What is pumping and what does it cause specifically?
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Pumping is when the active species of the laser becomes excited by electrical discharge. Carries out population inversion.
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What is spontaneous emission?
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releases incoherent monochromatic radiation and is random. laser can lose all or some of excess energy here.
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What is stimulated emission?
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The basis for lasers behavior. The emitted photon travels in the same direction and is precisly in phase with the photon that caused the emission. The stimulated emission is coherant with the incoming radiation.
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What is population inversion?
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more excited state molecules then ground state. and stimulated emission is greated than stimulated absorption
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What does population inversion depend on?
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Lasing medium.
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Name two solid-state lasers.
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Ruby laser and YAG laser (four level and easier to cause population inverstion).
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How can you get monochromatic light?
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Add a wavelength processor. Replace partially transmitting mirror with wavelength processor to only allow stimulated emission. Tunable lasers.
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What is a phototube detector?
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A phototube detector takes incoming photon and converts it to a current pulse. Photoelectric phase (least sensitive detector)
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What is a PMT?
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Takes in incoming photon through the cathode and changes it to a photoelectron. Photon electron becomes attracted by the (+) on the dynode and changes it into a cascade of electrons. Then the electrons are read by the anode.
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What are the advantages of the PMT?
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rapid response, good price, linear, sensitive, stable, long lifespan
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What are the properties of a photodiode?
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more sensitive then phototube but not PMT, cheap and small
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What are some limitations to Beer's Law?
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Stray light can skew read. reactions of analyte with solvent and instrumental deviation.
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What should the transittance be at to get a good measurement?
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At least 10 percent.
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What is the parts of a single beam instrument?
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Lamp, monochromator, sample, detector (PMT), amplifier, readout
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What are the parts of a double-beam instrument?
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lamp, monochromator, chopper mirror, mirror, sample, reference, 2 detectors, ratio
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Advantages of single beam to double beam?
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Single beam is simpler and easy to manage, good for one wavelength. (Double opposite)
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What are the 5 processes of deactivation?
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vibrational, external, internal, intersystem crossing, fluorescence, phosphorescence
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Describe each deactivation process.
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vibrational is molecule collision which leads to a quick change to groundstate. External is reaction to solvents to lose energy. Internal is radioactive decay. Intersystem crossing is changing from one energy level to another (spin). Fluorescence is the losing of a photon.
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What is the stokes shift?
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difference of the lowest peak of absorbance and the highest of energy emission. ideally 50 nm.
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How do you increase fluorescence?
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pi to pi* absorption transitions, lower intersystem crossing, lower temp, aromaticity, nonpolar solvents
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How do you decrease fluorescence?
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paramagnetic species, big atoms, charged ions
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What is fluorescence polarization?
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says that if a polar light is spin fast it will become depolarized and if polar light attached to receptor molecule spins slowly the light is still polarized
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fluorescence quenching
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is when a collision with a non-fluorescent molecule occursand a formation of a non-fluorescent complex occurs.
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What is FRET?
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Is when two fluorescent molecules overlap and there is a donor and acceptor between the two. They depend on the spectral overlap of the two, the distance between the two, and the dipole moment orientation
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What is phosphorescence?
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Is when molecules in their first excited triplet state can loose their energy by loss of a photon.
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Pros and cons of Luminescent spectroscopy.
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More sensitvie then absorption methods because of 90 degree geometry. Can use intense sources such as lasers but sample decompostion occurs easier.
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What are the spectral interferences in AAS?
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spectral, chemical, physical, and ionization
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Parts of a graphite furnace AAS.
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Light, rotating polarizer, graphite furnace, monochromator, PMT, electronics, atomic absorption
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Why use AFS?
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any atoms that fluoresce can be measured, not as used as AAs. Quantative technique for determination of a large amount of elements
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Parts of AFS?
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Light source, atomizer, chopper, monochromator, detector, singal processor.
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What is nebulization (AFS)?
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converts the sample solution into a mist made up of tiny liquid droplets
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What is atomization (AFS)?
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flow of gas carries sample into heated region where sample molecules are broken into free atoms.
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disadvantages of AFS?
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expensive equipment, quenching problems, precision and accuracy dependent on atomization step, light soruce
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What is AES?
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The heat from a flame or an electrical discharge promotes electron to a higher energy level. As the electron falls back to ground state it emits a wavelength characteristic of the excited atom or ion. Measures emission light from the atoms.
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Components of AES?
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Source to emission, wavelength selector, detector, signal processor
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Problems with AES?
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self-absorption, ionization
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With AES what 3 factors are associated with plasma?
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ICP, DCP, MIP
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What is ICP?
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Plasma created is argon and collision between argon and free atoms generate more argon thus forming plasma. With flow of argon until reaching insulating shield and optical path.
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What is DCP?
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Like ICP put has Yshape to directly insert argon from contact of cathode and anode. Less expensive, but graphite electrode has to be replaced.
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Advantages of Plasma:
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Lower inter-element interference, good emission spectra are obtained for a single set of excitation conditions, determines low concentrations of elements, allows determination of non-metallic elements, uniform
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What does atomic spectroscopy deal with?
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identification and quantification of elements
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Characteristics of atomic spectroscopy?
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involves electomagnetic radiation in the UV and visible regions of the spectrum, based on excitation of electron to excited state, atoms in gaseous state, involves atomization
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What is atomization?
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process by which analyte are simultaneously decomposed and converted to atoms in the gaseous state
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What is the atomization process?
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solution undergoes nebulization and becomes mist, mist undergoes desolvation and becomes solid then undergoes vaportization (gas), then atomization (gas), excitation or absorption, then emission back to ground state
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AAS basic components:
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line source, atomizer, monochromator, PMT, signal processor, then computer system
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What is a hollow cathode lamp?
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Used for AAS. A hollow cathode lamp causes ionized gas the generates a current flow in the lamp, since metal cations depend on them. A cation cloud forms around the cathode some that are in excited states go into inner glass surface making light
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What is a Electodeless discharge lamp (radiation source) used for?
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Used for AAS. An intense RF field is applied to the sealed quartz tube and Ar gas within the tube ionizes and gains kinetic energy from RF field. E is transferred to metal upon collision. Excited metal return to ground state emitting light
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FAAS components?
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hollow cathode lamp, chopper (reference beam creator other half goes to burner), half-silvered mirror, monochromator, detector
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Advantages of GFAAS?
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can do microsize samples, excellent detection limits, can be used for solid samples.
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Disadvantages of GFAAS?
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Poor precision, use standard addition method, sample does not have long lifespan
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