Instrumental Methods of Analysis ❗️ Flashcards
What are the three instrumental methods of analysis?
- spectroscopy
- electrochemistry
- chromatography
What is analytical chemistry divided into?
1) Chemical methods
2) Physical methods
What are the different chemical methods?
1) gravimetric method
2) volumetric method
What are instrumental methods about?
determining chemical compositions of compounds
What is classical analysis?
signal depends on the chemical properties of the sample:
- a reagent reacts completely with the analyte
- the relationship is measured between the analyte and titrant
What is instrumental analysis?
a physical property of the sample is measured:
- electrical potential
- pH
- etc.
What are the types of instrumental (physical) methods?
1) optical methods
2) chromatographic methodds
3) electrochemical methods
Why are the advantages of instrumental methods?
1) speed
2) sensitivity
3) selectivity (accurate in presence of many different components)
4) reproducibility
5) small sample requirements
Why are the disadvantages of instrumental methods?
1) cost
2) complexity
3) maintenance (eg. breaking of lab equipment, clogging of equipment, etc.)
What is an analytical technique?
Scientific phenomenon giving information on the composition of substances.
What is an analytical method?
specific application of technique used to solve an analytical problem.
What is a procedure?
instructions formilated to carry out a method (lists out steps to be followed for analysis).
What is a protocol?
The most specific description of a method.
- detailed directions must be followed without exception
What is a basic block diagram for instrumental measurements?
stimulus (energy) –> system under study –> response (analytical information)
What is absorption?
Process by which the energy of light (in the form of photons) is transferred to the atom or molecule raising them from the ground state to the excited state.
When does emission/radiation happen?
When molecules/atoms fall back down to lower energy levels, emitting radiation.
What is fluorescence?
absorbed energy is rapidly lost to the surroundings by collisions within the system and relax back to the ground state.
What is Beer-Lambert-Bouguer law?
relates the attentuation of light to the properties of the material through which the light is passing.
What is the equation of Beer-Lambert-Bouguer law?
A=Elc
A- absorbance
E- energy
l- optical path length
c- concetration of chemical species in mol/L
absorbance = path length
absorbance = sample concentration
= direc. prop
What is electromagnetic radiation?
form of energy that is transmitted through space at enourmous velocities.
electric field, magentic field, and electromagnetic wave are all at 90 * angles
What is wavelength?
distance from crest units (maximum points/minimum points)
What is frequency?
number of waves per second (Hz, Hertz)
What is wave number?
the number of waves per unit length
What is power? What else is it called?
- energy per unit time,
- also known as intensity
What is paramagnetic spectroscopy?
microwave technique based on the splitting electronic fields in a magnetic field.
- used to determine structures of samples containing unpaired electrons
What is a different name for “infrared spectroscopy”?
“molecular fingerprint”
- used to identify materials,
- quantify the number of absorbing molecules
What is x-ray spectroscopy?
- excitation of inner electrons of atoms, which may be seen as x-ray absorption.
- an x-ray fluorescence emission spectrum may be used
What is electrochemistry?
- concered with the interelation of electrical and chemical effects
eg. measurement of electrical quantities, current, potential, their relationship and parameters.
What is an electric current?
flow of charge through a medium
- moving electrons in a conductor
- carrid by ions in electrolyte
- carried by electrons and ions in plasma
What is potential?
- quantitative description of the driving force behind an electrochemical reaction
What is an electrochemical cell?
A cell consisting of two electronic conductors (electrodes) dipped into a solution (containing ions and electrolytes).
How does a pH sensor work?
based on an electric potential difference (build up of h+ ions within the pH meter)
What is potentiomentry?
measurement of electric potential
What are the two types of indicator electrodes?
1) metal electrodes (develop an electric potential in response to a redox reaction at the metal surface).
2) ion selective electrode (bind one type of ion to a membrane to generate an electric potential).
How is electric potential generated?
by the build up of H+ ions on one side of the glass meter.
What are the advantages of pH meters?
1) potentail is not affected by its presence of oxidizing or reducing agents
2) wide pH range
3) responds fast and functions well in physiological systems
What is chromatography?
technique for seperating mixtures into their components by their distinctive mechanisms of interations (reactions) of the solute (mobile phase) with the stationary phase. Differences occur due to differences in:
- size
- charge
- shape
What type of gel is used?
silica gel
What are the two phases in chromatography?
1) stationary phase (solvent)
2) mobile phase (column packing material)
What is chromatography used for?
- analyzing
- identifing
- purifing
- quantifing
What are the two types of chromatography?
1) column
2) planar
What is column chromatography?
- glass tube filled with silica gel
- fresh solvent is set on top
solvents seperate due to their mobile phases.
What is planar chromatography?
- stationary phase is placed on a flat plate and the mobile phase travels across it by gravity or capillary.
- paper chromatography
What is dissociation?
a substance dividing into ions and cations
What are strong electrolytes
