Common Analytical Techniques Flashcards
Composition
proportion of different constituents or species that comprise a population or mixture, describing the general makeup of a stream
Concentration
refers to the relative abundance of a specific constituent or species in a mixture (without any reference to other species present in the mixture).
Qualitative techniques
to identify analytes
Quantitative techniques
to quantify analyte concentration
Titrimetry
-used to determine the concentration of an analyte
* Start with a certain volume of a chemical reagent, called
the titrant, typically a solution of known composition.
* Allow the titrant to react with a sample of the analyte,
called the titrand, of known concentration and volume.
* Add an indicator to detect end‐point of neutralization.
* The volume of titrant that reacted with the analyte, at the
point of neutralization, is called the titration volume.
Acid–Base Titrations
are used in the analysis of: biodiesel fuel, in the Kjeldahl method (to measure nitrogen in organic wastes), acid value (to determine free fatty acids), saponification value (to determine chain lengths of fatty acids), amine value (to determine amine content), hydroxyl value (to determine hydroxyl group content)
Redox Titrations
are used for the Winkler test for dissolved oxygen, to determine Vitamin C content, in Benedict’s reagent (for glucose concentration in urine), to determine Bromine and Iodine numbers, etc.
Karl Fischer Titration
is a special method used commonly to measure trace amounts of water in organic liquids (such as crude oils)
The precipitation method (gravimetric analytical methods)
is used for the amount of a solute, which is converted into an insoluble precipitant by adding an excess amount of a reagent, followed by collecting, drying and weighing the precipitant.
Gravimetric Analytical Methods
These methods are for the quantitative determination of an analyte based on its mass.
The Volatilization method (gravimetric analytical methods)
involves separation of the analyte by heating or chemically decomposing the sample at a suitable temperature.
Do gravimetric analytical methods need calibration?
A gravimetric analysis provides precise results and does not require any calibration with standards. These are based typically on direct
mass (and/or volume) measurements. Hence, such
methods are used for calibrating other techniques and
instruments.
Chromatography
is a physical method of separation that distributes components between two phases, namely, a stationary phase and a mobile phase
Retention time
time it takes for an analyte to pass through the system
Column chromatography
packed column
Planar chromatography
classified into 2D, Paper and Thin layer chromatography (high school experiment)
Displacement chromatography
in which a molecule with higher affinity displaces all molecules with lesser affinities
High Performance Liquid Chromatography (HPLC)
Liquid chromatography with small adsorbing particles and high pressure.
HPLC has two sub classes:
-Normal Phase Liquid Chromatography (NPLC)
-Reversed Phase Liquid Chromatography (RPLC).
Supercritical Fluid Chromatography (SFC)
use of a supercritical fluid (at T>Tc, P >Pc) as the mobile phase.
Separation techniques chromatography methods
- Many specialized techniques:
o Ion exchange chromatography (IEC)
o Size exclusion chromatography (SEC)
o Expanded bed adsorption chromatography
o Reversed phase chromatography
o Hydrophobic interaction chromatography
o Fast protein liquid chromatography, etc.
Spectroscopy
deals with the interaction between matter and electro‐magnetic radiation energy as a function of wavelength or frequency
-acquired data can be represented by an emission spectrum, which is a plot of the response as a function of wavelength or frequency
How is spectroscopy classified
Spectroscopy can be classified by the wavelength or frequency of radiative energy involved in the interaction, such as microwave, infrared, visible, ultraviolet, x‐ray, and gamma‐ray, etc.
Atomic absorption spectroscopy (AAS)
is a common technique, which involves visible light radiation, for mostly 1st & 2nd group of elements
Fourier‐transform infrared spectroscopy (FTIR)
measures infrared light absorption by a sample to determine its
chemical composition
X‐ray diffraction spectroscopy (XRD)
is a non‐destructive technique (for solids) that uses X‐rays
Spectrophotometer
measures the intensity of a beam as a function of its colour (i.e., frequency or wavelength)
-It deals with visible light, near‐ultraviolet, and near‐
infrared wavelengths.
-Spectrophotometers require calibration with a
reference substance(s)
Sequence of activities in a Spectrophotometer
-The light is shone on the sample and focused into a slit,
-The transmitted light is refracted with the reflection grating,
-The resulting light strikes the photodetector and compared
with the standard,
- %transmission reading is converted into concentration
Electro‐analytical methods
several techniques to study an analyte by measuring the potential (in Volts) and/or current (in Amperes) in an electrochemical cell
containing the analyte.
Potentiometry
in which the difference in electrode potentials is measured (Electro‐analytical)
Coulometry
in which the cell’s current is measured over time (Electro‐analytical)
Voltammetry
in which the cell’s current is measured while the cell’s potential is altered
-Chemically modified electrodes are employed for the analysis of organic and inorganic samples
Potentiometry - details
-One electrode is the reference electrode with a constant potential, while the other is an indicator electrode, whose potential changes with the sample composition
-The potential difference between the two electrodes provides information about the sample composition
-The time for establishing equilibrium with the solution
can affect the measurement sensitivity and accuracy.
-Platinum is often used, although electrodes made from other metals have also been used
Coulometry - details
-uses applied current or potential to completely convert an analyte from one oxidation state to another
-The electrical current is measured directly or indirectly
to determine the number of electrons.
