sensitivity
the magnitude of the change in signal resulting from an incremental change in analyte concentration
the higher the sensitivity, the lower the limit of detection
limit of detection (LOD)
the lowest concentration of a compound that may be statistically differentiated from the background noise
selectivity
the ability of the method to discriminate between two different atoms/ions/compounds
what is spectroscopy
it typically involves the measurement of the interaction of matter and radiation
radiation may be in the form of light, electrons, or magnetic fields
what does Beer’s Law quantitate
absorbance (in spectrophotometry)
advantages of absorbance spectroscopy
- spectral data possible (absorption spectra are characteristic)
- technology widely available
- may be used as detection scheme in chromatography (improving selectivity)
- multiple species may absorb at a given wavelength (useful if epsilon(lambda) is know for multiple lambda for each species in the particular matrix in question)
limitations of absorbance spectroscopy
- epsilon is environmentally sensitive (pH, solvent, etc.) so matrix effects may be problematic
- sensitivity typically limited (not great for trace analysis)
- linearity of Beer’s Law limited (often to < 0.01 M)
what does UV absorbance spectroscopy involve
promotion of electrons to higher energy levels
what does IR absorption spectroscopy involves
it excites vibrational energy levels of the absorbing molecule (bandes de Maude)
group frequency region
contains spectral features corresponding to particular functional groups
fingerprint region
contains features arising from the characteristic combination of functional units in the molecule
what is vapour-phase IR spectroscopy used for
measurement of breath ethanol concentration
advantages and limitations of IR spectroscopy
- compounds have characteristic IR spectra (ID easier)
- IR is a form of absorption so Beer’s law is possible to a certain extent
- acuracy and precision may be lower than that encountered with UV-Vis techniques
basics of atomic spectroscopy
- in some cases, knowledge of the relative elemental composition is required
- flame atomic absorption spectroscopy : solutions converted to aerosols and then introduced into a flame
fluorescence
occurs when an electron is excited through photon absorption, and the excited state energy is dissipated through re-emission of a photon
advantages and limitations of fluorescence spectroscopy
- significantly more sensitive than absorptive methods
- selectivity can be enhanced by judicious choice of both lambda exc and lambda em
- may require labeling when used as detection scheme in chromatography, electrophoresis
- environmentally sensitive
applications of fluorescence spectroscopy
detection of semen stains on fabric
chromatography
separation of constituents in a mixture through differential interaction between two phases - a mobile phase and a stationnary phase
resolution
ability of a method to separate two constituents (manifested as the extent of peak overlap)
what is electrophoresis used for
inorganic ions, amino acids, catecholamines, drugs, proteins and nucleic acids
mechanism of amphetamin / methamphetamine
increasing the concentration of norepinephrine and dopamine in the synapse, through inhibition of reuptake and neurotransmitter release
MDMA (ecstasy)
synthetic drug that promotes release and inhibits reuptake of serotonin in nerve synapses
stimulants presented in class
- amphetamine / methamphetamine
- MDMA
- cocaine
cocaine mechanism
inhibition of dopamine reuptake
