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Analytical Chemistry
Chapters 14,16-26 of Quantitative Chemical Analysis Daniel C. Harris.
| Question | Answer |
|---|---|
| Vaporization of a small volume of material by a laser pulse. | Ablation |
| A suspension of very small liquid or solid particles in air or gas. Examples include fog or smoke. | Aerosol |
| Absorption of light by free gaseous atoms. | Atomic absorption |
| Collisions in the very hot plasma promote some atoms to excited electronic states from which they can emit photons to return to lower energy states. | Atomic emission |
| Atoms in a flame are irradiated by a laser to promote them to an excited electronic state from which they can fluoresce to return to ground state. | Atomic fluorescence |
| A process in which a compound is decomposed into its atoms at high temperature. | Atomization |
| In atomic spectroscopy, a means of distinguishing signal due to analyte from signal due to absorption, emission, or scattering by the flame, furnace, plasma or sample matrix. | Background correction |
| Relative population of two states at thermal equilibrium: N2/N1 = g2/g1*e-(E2-E1)/kT Where Ni is the population of the state, gi is the degeneracy of the state, Ei is the energy of the state, k is the Boltzmann’s constant and T is temperature in K. | Boltzmann distribution |
| In atomic spectroscopy, any chemical reaction that decreases the efficiency of atomization. | Chemical interference |
| The number of states with the same energy. | Degeneracy |
| The smallest quantity of analyte that is significantly different from a blank. | Detection limit |
| A molecule moving toward a source of radiation experiences a higher frequency than one moving away from the source. | Doppler Effect |
| A hollow graphite rod that can be heated electrically to about 2,500 K to decompose and atomize a sample for atomic spectroscopy. | Graphite furnace |
| In instrumentation, linewidth is governed by this, which says that the shorter the lifetime of the excited state, the more uncertain is its energy. The linewidth of the source must be narrower than the linewidth of the atomic vapor for Beer’s law. | Heisenberg uncertainty principle |
| One that emits sharp atomic lines characteristic of the element from which the cathode is made. | Hollow cathode lamp |
| A high temperature plasma that derives its energy from an oscillating radio frequency field. It is used to atomize a sample for atomic emission spectroscopy. | Inductively coupled plasma |
| In atomic spectroscopy, a lowering of signal intensity as a result of ionization of analyte atoms. | Ionization interference |
| An element used in atomic spectroscopy to decrease the extent of ionization of the analyte. | Ionization suppressor |
| In mass spectrometry, overlap of two peaks with nearly the same mass. | Isobaric interference |
| The medium containing analyte. | Matrix |
| Substance added to sample for atomic spectroscopy to make the matrix more volatile or the analyte less volatile so the matrix evaporates before analyte does. | Matrix modifier |
| Process of breaking the liquid sample into a mist of fine droplets. | Nebulization |
| A crystal that deforms when an electric field is applied. | Piezoelectric crystal |
| A gas that is hot enough to contain free ions and electrons as well as neutral molecules. | Plasma |
| In atomic spectroscopy, one in which the sample is nebulized and simultaneously mixed with fuel and oxidant before being fed into the flame. | Premix burner |
| In spectroscopy, line broadening due to collisions between molecules. | Pressure broadening |
| In atomic spectroscopy, a substance that prevents chemical interference. | Releasing agent |
| Occurs when the concentration of analyte is so high that there is a decrease in the observed signal. | Self absorption |
| In atomic spectroscopy, any physical process that affects the light intensity at the analytical wavelength. Created by substances that absorb, scatter or emit light of the analytical wavelength. | Spectral interference |
| A way to join LC to MS. Liquid is nebulized into a fine aerosol by a coaxial gas flow & + q. e- from a high-voltage corona discharge create CAT+ & AN- from analyte exiting the c. column. Most common species observed is MH+, with little fragmentation. | Atmospheric pressure chemical ionization |
| Number of grams of an element containing Avogadro’s number of atoms. | Atomic mass |
| Most intense peak in a mass spectrum. | Base peak |
| 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+. | Chemical ionization |
| Fragmentation of ions in a Mass Spectrometer by high-energy collisions with gas molecules. | Collisionally activated dissociation |
| A spectrometer that uses electric and magnetic sectors in series to obtain high resolution. | Double focusing mass spectrometer |
| Interaction of analyte molecules (M) with high-energy electrons in the ion source of a mass spectrometer to give the cation radical, M+.., and fragments derived from M+.. | Electron ionization |
| A method for joining LC to MS. A high E applied to the liquid at the column exit, creates charged droplets in a fine aerosol. Gaseous ions are derived from ions that are already in the mobile phase on the column. | Electrospray |
| An instrument that measures the drift time of gaseous ions migrating in an electric field against the flow of a gas. The “spectrum” of detector current versus drift time is really an electropherogram of a gas. | Ion mobility spectrometer |
| A device that separates gaseous ions that have the same KE by passing -> magnetic field perpendicular to their speed. Trajectories of ions with a certain m/z ratio are bent exactly to reach the detector. Other ions are deflected too much or little. | Magnetic sector mass spectrometer |
| A technique in which gaseous molecules are ionized accelerated by an electric field and then separated according to their mass. | Mass spectrometry |
| In mass spectrometry, a graph showing the relative abundance of each ion as a function of its mass to charge ratio. | Mass spectrum |
| A gentle technique for introducing predominantly singly charged, intact macromolecular ions into the gas phase. | Matrix-assisted laser desorption/ionization (MALDI) |
| In mass spectrometry, an ion that has not lost or gained any atoms during ionization. | Molecular ion |
| Number of grams of a substance that contains Avogadro’s number of molecules. | Molecular mass |
| A compound with an odd number of nitrogen atoms –in addition to C,H, halogens, O,S, Si, and P--- will have an odd nominal mass and vice versa. | Nitrogen rule |
| Integer mass of the species with the most abundant isotope of each of the constituent atoms. | Nominal mass |
| In tandem mass spectrometry (selected reaction monitoring), the ion selected by the first mass separator for fragmentation in the collision cell. | Precursor ion |
| In tandem mass spectrometry (selected reaction monitoring), the fragment ion from the collision cell selected by the final mass separator for passage through to the detector. | Product ion |
| An instrument that separates gaseous ions by trapping them in stable trajectories inside a metallic chamber to which a radio frequency electric field is applied. | Quadrupole ion trap mass spectrometer |
| In chromatography, a graph of the sum of intensities of all ions detected at all mass (above a selected cutoff) versus time. | Reconstructed total ion chromatogram |
| CcHhNnOx is c-h/2 + n/2 + 1, where c includes all Group 14 atoms (all make four bonds), h includes H + halogens (make one bond), and n is the number of Group 15 atoms (makes 3 bonds). Group 16 atoms (make two bonds) dont affect the result. | Rings + double bonds formula |
| A graph of detector response versus time when a mass spectrometer monitors just one or a few species of selected mass-to-charge ratio, m/z, emerging from a chromatograph | Selected ion chromatogram |
| Use of a mass spectrometer to monitor species with just one or a few mass-to-charge ratios, m/z. | Selected ion monitoring |
| A technique in which the precursor ion selected by 1 mass separator passes through a collision cell in which the precursor breaks into several product ions. A 2 mass separator then selects one/few of these ions for detection. | Selected reaction monitoring |
| Ions of diff. masses accelerate thru the same electric field have different speeds: The lighter ions move faster than the heavier ions. This spectrometer finds the m/z by measuring the (s) that each grp of ions requires to travel a fixed (m) -> detector. | Time of flight mass spectrometer |
| MS that separates ions by passing them btwn 4 metallic cylinders to which are applied DC and oscillating electric fields. Resonant ions w/right m/z pass thru the chamber->detector while nonresonant ions are deflected into the cylinder and are lost. | Transmission quadrupole mass spectrometer |
| In chromatography, this parameter is tr’=tr-tm, where tr is the retention time of a solute and tm is the time needed for mobile phase to travel the length of the column. | Adjusted retention time |
| A technique in which solute equilibrates between the mobile phase and adsorption sites on the stationary phase. | Adsorption chromatography |
| A technique in which a particular solute is retained by a column by virtue of a specific interaction with a molecule covalently bound to the stationary phase. | Affinity chromatography |
| In chromatography, the adjusted retention time for a peak divided by the time for the mobile phase to travel through the column. | Capacity factor |
| A graph showing chromatography detector response as a function of elution of time or volume. | Chromatogram |
| Defined by Fick’s first law of diffusion: J=-D(dc/dx), where J is the rate at which molecules diffuse across a plane of unit area and dc/dx is the concentration gradient in the direction of diffusion. | Diffusion coefficient |
| For a solute partitioned between two phases, the distribution coefficient is the total concentration of all forms of solute in phase 2 divided by the total concentration in phase 1. | Distribution coefficient |
| What comes out of the chromatography column. AKA effluent. | Eluate |
| Solvent applied to the beginning of a chromatography column. | Eluent |
| Process of passing a liquid or a gas through a chromatography column. | Elution |
| Process in which a solute is transferred from one phase to another. Analyte is sometimes removed from a sample by extraction into a solvent that dissolves the analyte. | Extraction |
| AKA Molecular exclusion chromatography | Gel-filtration chromatography, Gel-permeation chromatography |
| A technique in which solute ions are retained by oppositely charged sites in the stationary phase. | Ion-exchange chromatography |
| In chromatography, the distance per unit time traveled by the mobile phase. | Linear flow rate |
| Diffusion of solute molecules parallel to the direction of travel through a chromatography column. | Longitudinal diffusion |
| Two liquids are miscible if they form a single phase when they are mixed in any ratio. | Miscible |
| In chromatography, the phase that travels through the column. | Mobile phase |
| A technique in which the stationary phase has a porous structure into which small molecules can enter but large molecules cannot. Molecules are separated by size, with larger molecules moving faster than smaller ones. | Molecular exclusion Chromotography |
| In chromatography, a capillary column whose walls are coated with stationary phase. | Open tubular column |
| A chromatography column filled with stationery phase particles. | Packed column |
| A technique in which separation is achieved by equilibration of solute between two phases. | Partition chromatography |
| The equilibrium constant for the reaction in which a solute is partitioned between two phases: solute (in phase1) =solute (phase 2). | Partition coefficient |
| H, Length of a chromatography column divided by the number of theoretical plates in the column. | Plate height |
| In chromatography, the ratio of adjusted retention times for two components. If component 1 has and adjusted retention time of t’r1 and component 2 has an adjusted retention time of t’r2>t’r1, the this would be is α=t’r2/t’r1. | Relative retention |
| How close two bands in a spectrum or a chromatogram can be to each other and still be seen as two peaks. In chromatography, it si defined as the difference in retention times of adjacent peaks divided by their width. | Resolution |
| The time, measured form injection, needed for a solute to be eluted form a chromatography column. | Retention time |
| The volume of the solvent needed to elute a solute form a phase is less polar than the mobile phase. | Retention volume |
| For components A and B separated by chromatography or electrophoresis, the separation factor γ is the quotient of linear velocities γ=uA/uB = tB/tA, where u is the linear velocity and t is retention time. | Separation factor |
| Treatment of a chromatographic solid support or glass column with hydrophobic silicon compounds that bind to the most reactive Si-OH groups. It reduces irreversible adsorption and tailing of polar solutes. | Silanization |
| In chromatography, the phase that does not move through the column. | Stationary phase |
| Describes the dependence of chromatographic plate height, H, on linear flow rate, ux: H=A + B/ux + Cux. | Van Deemter equation |
| In chromatography, the volume of mobile phase per unit time eluted form the column. | Volume flow rate |
| Explain how an immunoassay works. | Assay that utilizes antibodies to determine the concentration of analyte in a sample.Utilizing fluorescence emission spectroscopy and a series of tight biding reactions the concentration is determined. |
| Explain how a photodiode array detector works and what type of application it is used in. | It is a series of p.n junctions (semiconductor diodes) that respond to photon when holes migrate and discharge capacitor. An increase in radiation sking leads to less charge remaining. One wavelengths falls on each detector. Used in UV/Vis applications. |
| Define the role of a grating in a spectrometer. | Used to disperse light into its component wavelengths. |
| Briefly explain how a laser works, in chemical terms. | Lasers require an inverse population to work. Therefore molecules are excited to E3 relax to E2 where they have a long lifetime before relaxing to E1 where they have a short lifetime. Therefore lasers are based on excited state lifetimes and population. |
| Expalin three ways you can use spectroscopy to analyze art. | Xray= "picture" beneath picture. IR= determine color leads to time period authentication about artist. UV/Vis= color beneath varnish changes to original painting. |
| Describe a Scathcard plot and its use. | A graph used to find the equilibrium constant for a rxn such as X + P = PX. Graph [Px]/[x] vs [Px]. the Magnitude of the slope is the equilibrium constant. |
| Explain atomic absorption spectroscopy. | A liquid sample is aspirated into an atomization source. The remaining solid is atomized. The atoms are excited by light source from the left. Light passed through the flame is detected. Each element has a characterisitc absorption frequency. |
| Explain the inductively coupled plasma atomization process. | ICP uses a nebulizer 2 create aerosol & introd. sample 2 instru.,solvent is evap.& removed. Analyte reaches plasma flame as aerosol of dry, solid particles, more energy is avail.4 atomization. Cooling gas is req. n plasma flame is created uzn a tesla coil |
| Describe the path of a molecular ion (or fragment) in a time of flight mass spectrometer. | Reflectron is designed 4 ions of same mass but diff. speeds & therefore diff. Kinetic energies to catch up w/each other. Sample is ionized at backpllate & accel. to drift region where there is no further accel. Reflectron ensures that this occurs |
| What are four ionization sources? | Electron ionization-flame Chemical ionization-reagent gas Electrospray ionization MALDI. |
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