Exam 2 Flashcards
what factors affect the choice of sampling plan?
-purpose of inspection
-nature of the population being investigated
-nature of the product
-nature of the test method
what is attribute versus variable sampling
- attribute: check for presence or absence of a variable; decide acceptability
- variable: quantitatively estimate characteristic on continuous scale
what are problems in sampling and sample storage
-sampling bias
-inappropriate sampling plan
-sample degradation due to poor sample storage
-mislabeling of samples
-susceptibility to tampering
how can you prepare samples for testing & considerations
-size reduction (grinding)
-considerations: enzyme inactivation, lipid oxidation protection, microbial growth and contamination
wavelength
lambda- represents the distance between successive maxima on any given wave
frequency
in general; the number of occurences of a repeated event per time unit (Hz = 1/s)
interference
- term used to describe the observation that when 2 or more wave trains cross one another, they result in an instantaneous wave, at the point of intersection, whose amplitude is the algebraic sum of the amplitubes of the individual waves at the point of intersection
- maximum constructive interference (positive): doubles amplitude
- maximum destructive interference (negative): zeroes out amplitude
what does amplitude correspond with
corresponds with the intensity of light and the brightness of colour perceived by an observer
reflection
study of light as a function of wavelength that has been reflected from a solid, liquid, or gas
light (color) perception
- light (electromagnetic radiation) has wave like properties: interference, diffraction, refraction
- interference (on other slide)
- diffraction: incident beam will split into multiple diffracted beams when going through or around an object
- refraction: what happens when a sticj looks broken when put into the water
what is a photon
-photons are the discrete packets of energy in a wave
-energy of a photon is defined in terms of frequnecy of the wave (E = hv)
what are the discrete energy levels of electric, vibrational, and rotational energy levels
-electric energy levels: ground electric state, first excuted electronic state, second excited electronic state
-vibrational energy levels: within electronic state; the atoms that compromise a molecule are in constant motion, IR region
-rotational energy levels: potential energy of molecule also quantized in terms of energy associated with rotation of the molecule about its center of gravity; customary to consider several rotational energy levels superimposed on each of the permitted vibrational energy levels
what are the energy states of matter
ground state vs excited state
summary of light: wave-like and photons
-the distinction between considerations of continuous wave-like properties and distinct particles depends on which aspects of light one is studying:
* **wave-like properties: **essential to understanding movement of electromagnetic radiation; through space or through a medium
* consideration of electromagnetic radiation as photons (distinct particles of energy) is essential to understanding **interaction of light with matter **
what is monochromatic light
- monochromatic light is electromagnetic radiation composed of waves having a single frequency and wavelength (ex. having equivalent energy)
- monochromatic light is obtained by optical dispersion in a prism or by diffraction using a diffraction grating with slits or ridges
how does a molecule go from ground to excited state
- under certain conditions a molecule struck by a photon may absorb the photon’s energy
- molecules energy is increased by an amount equal to the photon energy hv
- internal energy content of molecule varies in a series of discrete steps (not in continuous manner)
energy transitions: absorption
- process in which energy from a photon of electromagnetic radiation is transferred to the absorbing species
- when atom or molecule absorbs a photon of light, its internal energy increases by an amount equivalent to the amoung of energy in that particular photon
- in absorption => species goes from a lower energy state to a more excited state
energy transition: emission
- reverse of absorption; occurs when atom/molecule is released in the form of a photon of radiation
- molecule raised to excited state will typically remain in the excited state for short time before relaxing back into the ground state
what is the loss of energy represented as
- heat: the relaxation process in which a molecule will dissapate energy where they will collide with other molecules which is converted to kinetic energy
- emission of radiation (emission of a photon with lower energy and longer wavelength than photons that were absorbed in the excitation process)
what is definition of UV/Vis
method that investigates how light interacts with matter in the ultraviolet and the visible range of light
what is beer’s law
- A = abc
- a/epsilon = absorptivity (cm-1 & conc-1)
- b = path length through solution (cm)
- c = concentration of absorbing species (M, mM, mg/ml, %)
deviations of beer’s law
- only dilute solutions work on beer’s law (up to 10 mM)
- reversible association-dissociation of analyte molecules
- ionization of a weak acid in an unbuffered solvent
common uses for UV-VIs
- ELISA (enzyme-linked immosorbent assay); uses solid-phase type of EIA to detect presence of a ligand in a liquid sample using antibodies directed against the ligand to be measured directly or indirectly
