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Chemistry 254 Exam 2
| Term | Definition |
|---|---|
| White Noise | random noise, also called Gaussian noise, due to random movement of charge carriers in an electric circuit or from random arrival of photons or charge carriers to a detector =/=F(v) |
| 1/F Noise | biffer at low frequencies, associated with slow drift |
| Line Noise | specific to various frequencies |
| Signal | response given by instrument |
| Signal-to-Noise Ratio (S/N) | the height of the signal divided by the noise in the baseline around the signal. The higher the signal-to-noise ratio, the less uncertainty there is in the signal |
| Smoothing | use of mathematical procedure or electrical filtering to improve the quality of the signal |
| Polynomial Least Squares Fit | fits to moving groups of >=7 points and then pieces them together |
| Atomization | process in which a compound is decomposed into its atoms at high temperatures |
| Nebulizer | breaks the liquid sample into a mist of fine droplets |
| Premix Burner | a burner in which the sample is nebulized and simultaneously mixed with fuel and oxidant before being fed into the flame |
| Plasma | a gas that is hot enough to contain free ions and electrons, as well as neutral molecules |
| Graphite Furnace | a graphite tube that can be heated electronically to about 2500K to decompose and atomize a sample for atomic spectroscopy |
| Chemical Interference | any chemical reaction preventing free atoms like fermentation of stable oxides and formation of non volatile salts |
| Ionization Interference | when atoms you want to observe form ions that have different absorption/emission lambdas |
| Spectral Interference | the overlap of analyte signal with signals due to other elements or molecules in the sample |
| Releasing Agent | a chemical added to a sample to decrease chemical interference |
| Ionization Suppressor | decreases the extent of ionization of analyte |
| Heisenberg Uncertainty Principle | the shorter the lifetime of the excited state, the more uncertain is its energy (delta)E * (delta)t >= n/4(pi) OR ((delta)E)/E = ((delta)(lambda))/(lambda) |
| Linewidth | used interchangeably with bandwidth |
| Pressure Broadening | line broadening due to collisions between molecules |
| Hollow Cathode Lamp | a lamp that emits sharp atomic lines characteristic of the element from which the cathode is made |
| Continuum Source Background Correction | Hollow Cathode Lamp: A = Aana. + A(background) W Lamp: A ~= A(background) |
| Zeeman Effect | splitting degenerate E levels in B(vector) field, this exploits polarization of different transitions |
| Boltzmann Distribution | relative population of two states at thermal equilibrium |
| Inductively Coupled Plasma | a high temperature plasma that derives its energy from an oscillating radio-frequency field |
| Mass Spectrum | a graph showing the relative abundance of each ion as a function of its mass-to-charge ratio |
| Base Peak | most intense peak in a mass spectrum |
| Molecular Ion | an ion that has not lost or gained any atoms during ionization |
| Ion Focusing Lens | has a small potential that creates a focused beam |
| Acceleration Plate | has high voltage between plates that imparts a high velocity to ions as they are expelled from the bottom of the ion source |
| Resolving Power | m/(delta)m where "(delta)m" is the separation of two peaks when the overlap at the base is 10% of the peak height and m is the smaller of the two m/z values |
| Electron Impact Ionization | interaction of analyte molecules (M) with high energy electrons in the ion source of a mass spectrometer to give the cation radical, M^t0, and fragments derived from M^t0 |
| Chemical Ionization | a gentle method of producing ions for a mass spectrometer without extensive fragmentation of the analyte molecule (M). A reagent gas such as CH4 is bombarded with electrons to make CH5+, which transfers H+ to M, giving MH+ |
| Magnetic Sector Mass Spectrometer | a device that separates gaseous ions that have the same kinetic energy by passing them through a magnetic field perpendicular to their velocity. Trajectories of ions with a certain mass-to-charge ratio are bent exactly enough to reach the detector |
| Double Focusing Mass Spectrometer | a spectrometer that uses electric and magnetic sectors in series to obtain high resolution |
| Transmission Quadruple Mass Spectrometer | separates ions by passing them between four metallic cylinders to which are applied direct current and oscillating electric fields. Resonant ions with the right mass-to-charge ratio pass through the chamber to the detector while nonresonant ions are lost |
| Time of Flight Spectrometer | ions of different mass accelerated through the same electric field have different velocities. The lighter ions move faster. The time-of-flight spectrometer finds the mass-to-charge ratio by measuring the time that each group of ions requires to tavel |
| Reflection | converts apparent big O(Ek) into apparent small O(FK) |
Created by:
Marlene the Chemist
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