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Chemistry 254 Exam 2

TermDefinition
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)