Analytical Exam 3 Review

Sandy's Analytical Class, UWF

Spectrophotometry

Any technique that uses light to measure chemical concentration.

Colorimetry

A procedure based on absorbance of visible light.

Wave-Particle Duality

An electron can behave as both a wave and a particle. (pchem students should know this)

Ground State

The lowest energy state of a molecule.

How does a spectrophotometer work?

Light → Wavelength selector (monochromator) →Sample→Light detector *Po is before sample, p is after

Monochromator

A prism, grating, or filter to select one wavelength

Sample Position

Where a sample or blank cuvette is placed

Transmittance, T

The fraction of the original light that passes through the sample. T=P/Po

What does Beer’s Law tell us about absorbance and concentration?

Absorbance is directly to concentration

Absorption Spectrum

A graph showing how A varies with wavelength

Chromophore

Part of molecule responsible for light absorption

Cuvette

A cell with transparent walls used in spectrophotometric measurements.

Internal Conversion

A nonradiative transition between states with the same spin

Intersystem Crossing

A nonradiative transition between states with different spin

Fluorescence

Process in which a molecule emits light due to transition between states of the same spin

Phosporescence

Emission of light during a transition between states of different spin

Luminescence

The emission of light by a molecule in an energetically excited state

Bioluminescence

Emission of light from a living system

Chemiluminescence

Emission of light from a chemical reaction

Quartz-Tungsten Halogen Lamp

Source of continuous visible and near IR light.

Arc Sources

Provide continuum emission from electrical discharge through a suitable ionized gas; predominantly UV radiation

Laser

“Light Amplification by Stimulates Emission of Radiation”; provide isolated lines of a single wavelength for many applications

Monochromator

Disperses light into its component wavelengths and selects a narrow band of wavelengths to pass on to the sample or detector

Grating

A reflective or transmissive optical component with a series of closely ruled lines

Diffraction

Bending of light by a grating

Refraction

Bending of light by a lens or prism

Resolution

The minimum wavelength difference between two peaks that can be distinguished from each other

Detector

Provides an electrical signal when struck by photons

Photomultiplier Tube (PMT)

A very sensitive detector for measuring the irradiance of light

Photodiode

A compact, inexpensive and low-power consumption photodetector in which light striking a semiconductor generates and electrical current

Photodiode Array

An array of semiconductor diodes used to detect light

Photodiode Array Spectrometer

Measures all wavelengths at once, giving faster acquisition times and higher signal to noise ratio.

Fourier Transform

A procedure in which a curve is decomposed into a sum of sine and cosine terms, called a fourier series.

Explain How FTIR Works

1. IR source strikes beamsplitter

2. Beamsplitter reflects some light to a stationary mirror a distance “OS”, and transmits some light toa movable mirror at distance “OM”.

3. Stationary and movable mirrors reflect light back at beamsplitter; half of each ray is transmitted and half is reflected.

4. A singular recombined beam travels in direction of detector, another heads back to source.

Raman Spectroscopy

Vibrational spectroscopy based on Raman scattering

Rayleigh Scatter

Scattered light has same energy (frequency) as incident light.

Raman Scattering

Inelastic scattering of light in which the wavelength of scattered light is changed from that of the incident light by an energy corresponding to vibrational energy of the molecule responsible for scattering

Signal Averaging

Improvement of a signal by averaging successive scans

Atomic Absorption Spectroscopy

A technique in which the absorption of UV light by free gaseous atoms in flame or furnace is sued to measure the concentration of atoms.

Atomic Fluorescence Spectroscopy

A technique in which electronic transitions of atoms in a flame, furnace, or plasma are excited by light, and the furnace is observed at a right angle to the incident beam.

Atomic Emission Spectroscopy

A technique in which the emission of light by thermally excited atoms in a plasma, flame or furnace is sued to measure the concentration of atoms.

Inductively Coupled Plasma

1. Sample is digested into liquid form.

2. Liquid Sample is pumped slowly into nebulizer.

3. Coaxial flow of air nebulizes sample into an aerosol that sprays into the cyclone chamber.

4. Fine mist exiting chamber at the top of the plasma torch; emission is observed by excited atoms and ions.

X-Ray Fluorescence

The emission of x-rays following the absorption of x-rays by a moderial.

Chromatography

Same principle as recrystallization; but one phase is held in place while the other moves past it.

Mobile Phase

Solvent flowing through column

Stationary Phase

The phase that stays in place inside the column

Elution

Process of passing liquid or gas through a chromatography column

Eluent

Fluid emerging from the end of the column

Packed Column

Filled with particles of stationary phase

Open Tubular Column

A narrow, hollow capillary with stationary phase coated on the inside of the walls.

Absorption Chromatography

Stationary Phase: Solid

Mobile Phase: Liquid or Gas

Solute is absorbed onto surface of solid particles

More strongly a solute is absorbed; slower it elutes

Partition Chromatography

Stationary Phase: Liquid bonded to a solid support

Mobile Phase: Liquid or Gas

Solute partitions between the stationary liquid and mobile phase

Ion Exchange Chromatography

Stationary Phase: Anions or Cations covalently attached to the stationary phase, usually resin

Mobile Phase: Liquid containing eluent ions

Solute ions of the opposite charge are attracted to the stationary phase

Size Exclusion Chromatography

Stationary Phase: Porous Gel

Mobile Phase: Liquid or gas

Separates molecules by size; larger solutes pass though most quickly

Affinity Chromatography

Stationary Phase: A covalently bound molecule that uses molecular recognition to bind with incredibly high specifity to the analyte

Mobile Phase: Liquid

Analyte is eluted by washing solutes from column and is dislodged by changing pH or ionic strength

Isolates a single compound or a class of compounds from a complex mixture

Flow Rate, F

The volume of mobile phase per unit time eluted from the column

Linear Velocity, Ux

The distance per unit time traveled by the mobile phase

Retention Time, t_R

Time between injection of mixture onto column and when that component reaches detector.

Baseline Resolution

Occurs in chromatography when two adjacent peaks are sufficiently resolved that the signal between the peaks returns to the baseline

Gas Chromatography

A form of chromatography in which the mobile phase is a gas.

1. Volatile liquid or gaseous sample is injected through a septum into a heated port.

2. Sample evaporates

3. Vapor gets swept through column by carrier gas and separated analytes move through detector.

Guard Column

3-10 cm length of empty capillary placed in front of capillary chromatography column to trap nonvolatile contaminants.

Injection Port

1. Needle is inserted into rubber septum in the glass liner within the heated injector port.

2. Liquid sample is vaporized

3. Carrier gas sweeps vaporized sample from port into column

Split Injection

Used in capillary gas chromatography to inject a small fraction of a sample onto the column.

1. Sample gets injected

2. High injector temperature evaporates the sample

3. Carrier gas sweeps sample through heated zone

4. At split point; small fraction of vapor enters column, other fraction is injected from the column

Splitless Injection

Used in capillary GC for trace analysis and quantitative analysis

On-Column Injection

Used in GC to place a thermally unstable sample directly on column without excessive heating in an injection port

Thermal Conductivity Detector

A device that detects substances eluted from a gas chromatography column by measuring changes in the thermal conductivity of the gas stream

Flame Ionization Detector

A GC detector in which solute is burned in H_{2 ^-} air flame to produce CHO⁺ ions

Electron Capture Detector

GC detector that is particularly sensitive to compounds with halogen atoms, nitro groups, and other groups with high electron affinity

Reconstructed Total Ion Current

Sum of intensities of all ions in selected range of mass-to-charge ratio (m/z) vs time

Extracted Ion Chromatogram

Collected consecutive full-range mass spectra, but graphs just one or a few m/z vs time

Selected Ion Monitoring

Graph of detector vs time when a mass spectrometer monitors just a few selected m/z

Mass Spectrometry

Measures m/z of atomic or molecular ions

Mass Spectrum

Displays the number of ions detected at each value of m/z

Electron Ionization

Method used to create ions of gaseous molecules in the inlet of a mass spectrometer by bombardment of the gas with high-energy electrons

Chemical Ionization

A gentle method of producing ions for a mass spectrometer without extensive fragmentation of the analyte molecule.

HPLC

Uses higher pressure to force solvent through closed columns containing fine particles that give high-resolution separations.

Efficiency

Columns ability to produce narrow peaks

Normal Phase Chromatography, NPLC

Stationary Phase: Polar

Mobile Phase: Less polar solvent

Reverse Phase Chromatography

Stationary Phase: Nonpolar / Weakly Polar

Mobile Phase: More Polar

Isocratic Elution

Constant solvent mixture for the mobile phase

Gradient Elution

The composition of the mobile phase is progressively changed to increase the eluent strength of the solvent

Eluent Strength

The ability for the mobile phase to move components through the stationary phase

UV Detector

Liquid chromatography detector that measures UV absorbance of solute emerging from the column

Evaporative Light-Scanning Detectors

Responds to any analyte significantly less volatile than the mobile phase

1. Eluate enters detector from the top and is neutralized

2. Solvent evaporates in heated drift tube

3. Fine mist of solid particles containing concentrated analyte enters detection zone at the bottom

Refractive Index Detector

Liquid chromatography detector that measures the change in refractive index of eluate as solutes emerge from the column

Anion Exchangers

An ion exchanger with positively charged groups covalently attached tot eh support

Cation Exchangers

An ion exchanger with negatively charged groups covalently attached tot eh support

Resins

Amorphous particles of organic material

Equivalent

The amount of monovalent ion that will exchange with one mole of cation

Ion-Exchange Capacity

The number of ionic sites on a resin that can participate in the exchange process

Suppressed-Ion Chromatography

Separation of ions by using an ion-exchange column followed by a suppressor to remove ionic eluent

Ion-Pair Chromatography

Separates polar and ionic compounds using a reversed-phase HPLC column

Gel Filtration

Usually refers to hydrophilic stationary phase and aqueous solvent

Desalting

Removal of low molar mass salts from solutions of large molecules by size exclusion chromatography

Electrophoresis

Migration of ions in solution under the influence of an electric field

Capillary Electrophoresis

The separation of a mixture into its components by a strong electric field imposed between the 2 ends of a narrow capillary tube filled with electrolyte solution

Titration

Procedure in which 1 substance is carefully added to another until complete reaction is occurred

Titrant

Substance added to the analyte in a titration