Características Generales y Proceso de Diseño
3.4 Proceso de desarrollo hipermedial en OO-H
Absorption The taking in (of radiation) which causes an effect (vibration, rotation, electron transition).
Absorption spectrum A pattern of black lines on the background of the continuous spectrum in which the black lines represent those energies of light absorbed by the electrons moving from the ground state to higher energy levels.
Adsorption The formation of weak bonds between the stationary phase and the components of a mixture during chromatography.
Atomic absorption (AA) spectroscopy Study of (usually the amount of) light absorbed by an element.
Atomic emission spectroscopy Study of the light emitted by an element.
Base peak The peak on a mass spectrum with the greatest height.
Bathochromic shift In UV–visible spectroscopy this is the movement towards absorbing longer wavelengths of light that occurs when more double bonds are
present in a sample.
Chemical shift (δ) The position of the peak along the horizontal axis of an NMR spectrum when compared to the position of the peak due to the standard, TMS.
Chromophore The double- or triple-bonded part of a molecule that causes it to absorb UV or visible radiation.
Conjugated Alternating multiple single and double (or triple) bonds in a molecule.
Desorption The breaking of weak bonds between the stationary phase and the components of a mixture during chromatography.
Elute To come out of the bottom of the chromatography column.
Emission (line) spectrum Spectrum of bright lines on dark background generated when an element is excited and then releases energy as light.
Excited state The state of an atom when electrons are in higher than usual energy levels.
Fragmentation pattern A pattern of peaks or lines
Frequency Number of waves passing a given point each second.
Functional group An atom or group of atoms bonded to a molecule that affects the chemical reactivity of the molecule.
Gas–liquid chromatography (GLC) A type of chromatography that uses a liquid stationary phase and a gaseous mobile phase or carrier gas.
Ground state The energy level to which unstable electrons return, releasing light as they do so.
High performance liquid chromatography (HPLC) A type of column chromatography that uses a solid stationary phase and a liquid mobile phase under pressure.
HOMO Highest occupied molecular orbital. It is the molecular orbital from which electrons are excited when they absorb UV radiation.
Infrared (IR) spectroscopy Study of the effects of infrared electromagnetic radiation that is absorbed by a substance in solution.
Interpolation The process of obtaining a value from a graph by reading from the line between points on the graph.
LUMO Lowest unoccupied molecular orbital. It is the molecular orbital to which electrons are excited when they absorb UV radiation.
Magnetic resonance imaging (MRI) Medical technique using the principles of NMR spectroscopy to obtain a three-dimensional image of organs and parts of the body.
Mass spectrometry Study of the movement of charged particles in the infl uence of a magnetic fi eld in order to determine the masses of those particles.
Mobile phase In chromatography, the solvent or gas that passes over the stationary phase, and carries the components of the mixture with it.
Molecular ion The positive ion formed in a mass spectrometer when the molecule has only lost one electron.
Monochromatic light source Source of light of only one wavelength.
Monochromator The part of a spectrophotometer that allows only one wavelength of light to be transmitted.
Chapter 1 Summary
CHAPTER 1 MODERN ANALYTICAL CHEMISTRY Nuclear magnetic resonance (NMR)
spectroscopy Study of the effects of radio wave electromagnetic radiation on certain nuclei placed in a magnetic fi eld.
Partition The distribution of a mixture between two phases.
Percentage transmission In IR spectroscopy, the proportion (percentage) of light that passes through a sample.
Qualitative analysis Analysis in which the type of compounds or functional groups present in a sample are identifi ed.
Quantitative analysis Analysis in which the amounts of components of a mixture or of specifi c compounds present in a sample are identifi ed.
Retention (retardation) factor (Rf) Rf= distance moved by component
distance moved byy solvent , a measure of how far a component of a mixture has travelled in comparison to the solvent during paper or thin-layer
chromatography.
Retention time (Rt) The time taken for a solute to move through a column in column chromatography (including GLC and HPLC).
Spectrometer An instrument that is used for
viewing the results of the interaction between a sample and the electromagnetic radiation being passed
through it.
Spectrometry The measurement of the amount of light absorbed or emitted.
Spectrophotometer A more elaborate instrument that measures amounts of radiation.
Spectroscopy The study of the radiation absorbed or emitted by matter.
Spin The behaviour of an electron as if it were spinning about an axis. The spinning charge generates a magnetic fi eld whose direction depends on the direction of spin.
Stationary phase The solid phase (or liquid coated on a solid) that does not move during chromatography.
UV–visible spectroscopy Study of electromagnetic radiation in the ultraviolet and visible regions when it is absorbed by a substance in solution.
Wavelength The distance between successive crests of waves.
Wavenumber The inverse of wavelength 1 λ , measured in cm–1.
Concepts
• Many forms of spectroscopy involve the absorption of electromagnetic radiation by matter to produce either line or band spectra. The position of lines or bands on the horizontal axis is used to determine the identity of the substance. The intensity of the line or band is used to determine the concentration of the substance.
intensity of the signal measures the amount of the substance
location of the peak on the horizontal identifies
• Atomic absorption (AA) spectroscopy involves the absorption of specifi c wavelengths of light by the vaporized atoms in a sample solution sprayed into a fl ame. It is used in the analysis of metals, and can be used because the wavelength of light required to excite an electron is specifi c to each element, thus identifying the element.
• Spectra may be used quantitatively. This involves measuring the absorbance (at a set wavelength) of solutions of known concentration and the
preparation of a calibration curve. The absorbance of the unknown solution (at the set wavelength) is measured, and its concentration determined by interpolation of the calibration curve.
absorbance (arbitrary units)
• Infrared spectroscopy involves the absorption of specifi c wavelengths of infrared radiation by a sample in solution. It is used to identify particular functional groups in organic compounds and can be used because the wavelength of radiation required to stretch and vibrate the covalent bonds in molecules is characteristic of the functional group.
• Mass spectroscopy is widely used to identify the structure of organic molecules. It requires the sample to be vaporized and subjected to a stream of high-energy electrons. The resulting positive ions are accelerated and passed through a
magnetic fi eld, which causes their path to alter, depending on the charge–mass ratio of the ions.
The fragmentation patterns when the molecules are broken are used to help determine the molecular structure.
• Nuclear magnetic resonance (NMR) spectroscopy is used to determine the precise structure of organic compounds. In NMR spectroscopy, the sample is placed in an extremely strong magnetic fi eld and
1H nuclei in different chemical environments absorb radio waves of different frequencies.
Infrared spectroscopy Mass spectrometry Type of radiation
used
Infrared: wavenumbers of 800–4000 cm–1 No radiation; a magnetic field deflects fragments of different sizes
Effect of radiation Causes molecular vibrations Appearance of
spectrum
absorbance
wavenumber (cm–1) increasing energy
3200 2400 2000 1600 1200 800
4000
Used to identify Functional groups Molecular mass and fragment masses
NMR spectroscopy UV–visible spectroscopy HL
Type of radiation used
Radio waves 100–800 MHz in addition to magnetic field
UV (200–400 nm) and visible (400–800 nm)
Effect of radiation 1H nuclei excited to opposite spin state Molecular electron excited to higher energy orbital (HOMO to LUMO)
Appearance of spectrum
increasing signal intensity
integrated 1H spectrum of ethanol CH3CH2OH
300 500 600 700 800 200
Used to identify 1H environments and hence the structure of organic compounds
• Conjugation of double bonds
• Quantity of sample
CHAPTER 1 MODERN ANALYTICAL CHEMISTRY
• In all forms of chromatography, components of a mixture are separated when a mobile phase moves over a stationary phase. Separation occurs because the components adsorb and desorb to different degrees. The weaker the bonds between a sample component and the stationary phase, the faster the component moves.
more soluble in the mobile phase, less strongly adsorbed, hence moves faster
• The results of paper and thin-layer chromatography are presented as a chromatogram. The retention factor (Rf) of each component is then found.
Rf= distance moved by component distance moved byy solvent
• Identifi cation of components in paper and thin-layer chromatography is made by comparing component Rf values to the Rf values of pure, known samples obtained under identical conditions.
Features Paper and thin-layer chromatography Equipment start
Plastic or glass plate coated with fine powder Mobile
phase
Liquid solvent or mixture of solvents
Collection of data
origin solvent front
component 1
component 2 5.5 cm 4.3 cm
Uses Coloured compounds, amino acids
• UV–visible spectroscopy involves the HL absorption of specifi c wavelengths of
visible light and ultraviolet radiation by a sample in solution. UV–visible spectroscopy is used in the analysis of coloured substances and many organic compounds and can be used because the wavelength of light required to excite an electron in a molecule is characteristic of that compound.
• Splitting patterns and chemical shifts of 1H nuclei in NMR spectra enable the complete determination of the structure of an organic compound, given the molecular formula.
• The results of gas–liquid chromatography and high performance liquid chromatography are presented as a chromatogram, showing a series of peaks at the various times taken for the components to elute from the column.
• Identifi cation of components in column chromatography including gas–liquid chromatography and HPLC is made by comparison of retention times (Rt), where Rt is the time taken for a component to move through the chromatography column.
• Gas chromatography may be used in combination with mass spectrometry or infrared spectroscopy to detect the presence of banned substances in the urine samples of athletes and is also used in a variety of forensic tests.
See the table on the next page.
Features High performance liquid HL chromatography (HPLC)
Gas–Liquid chromatography (GLC) HL
Equipment liquid
(mobile phase)
solid-filled column (stationary phase)
detector recorder
pump
syringe for injecting sample
waste
column filled with high boiling point liquid (stationary phase)
detector oven
carrier gas, usually nitrogen (mobile phase)
sample injection
port waste
recorder
Stationary phase
Solid packed in a column Inert granules coated with high boiling point liquid and packed in a column
Mobile phase Liquid solvent or mixture of solvents
Carrier gas: N2, Ar or He
Collection of data
retention time [A] : [B] = 1 : 2
A
B
peak area
concentration of unknown found by interpolation
concentration
Uses Non-volatile organic compounds Volatile organic compounds