Common Analytical Techniques

Question 1

Composition

Answer 1

proportion of different constituents or species that comprise a population or mixture, describing the general makeup of a stream

Question 2

Concentration

Answer 2

refers to the relative abundance of a specific constituent or species in a mixture (without any reference to other species present in the mixture).

Question 3

Qualitative techniques

Answer 3

to identify analytes

Question 4

Quantitative techniques

Answer 4

to quantify analyte concentration

Question 5

Titrimetry

Answer 5

-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.

Question 6

Acid–Base Titrations

Answer 6

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)

Question 7

Redox Titrations

Answer 7

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.

Question 8

Karl Fischer Titration

Answer 8

is a special method used commonly to measure trace amounts of water in organic liquids (such as crude oils)

Question 9

The precipitation method (gravimetric analytical methods)

Answer 9

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.

Question 10

Gravimetric Analytical Methods

Answer 10

These methods are for the quantitative determination of an analyte based on its mass.

Question 11

The Volatilization method (gravimetric analytical methods)

Answer 11

involves separation of the analyte by heating or chemically decomposing the sample at a suitable temperature.

Question 12

Do gravimetric analytical methods need calibration?

Answer 12

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.

Question 13

Chromatography

Answer 13

is a physical method of separation that distributes components between two phases, namely, a stationary phase and a mobile phase

Question 14

Retention time

Answer 14

time it takes for an analyte to pass through the system

Question 15

Column chromatography

Answer 15

packed column

Question 16

Planar chromatography

Answer 16

classified into 2D, Paper and Thin layer chromatography (high school experiment)

Question 17

Displacement chromatography

Answer 17

in which a molecule with higher affinity displaces all molecules with lesser affinities

Question 18

High Performance Liquid Chromatography (HPLC)

Answer 18

Liquid chromatography with small adsorbing particles and high pressure.
HPLC has two sub classes:
-Normal Phase Liquid Chromatography (NPLC)
-Reversed Phase Liquid Chromatography (RPLC).

Question 19

Supercritical Fluid Chromatography (SFC)

Answer 19

use of a supercritical fluid (at T>Tc, P >Pc) as the mobile phase.

Question 20

Separation techniques chromatography methods

Answer 20

• 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.

Question 21

Spectroscopy

Answer 21

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

Question 22

How is spectroscopy classified

Answer 22

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.

Question 23

Atomic absorption spectroscopy (AAS)

Answer 23

is a common technique, which involves visible light radiation, for mostly 1st & 2nd group of elements

Question 24

Fourier‐transform infrared spectroscopy (FTIR)

Answer 24

measures infrared light absorption by a sample to determine its
chemical composition

Question 25

X‐ray diffraction spectroscopy (XRD)

Answer 25

is a non‐destructive technique (for solids) that uses X‐rays

Question 26

Spectrophotometer

Answer 26

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)

Question 27

Sequence of activities in a Spectrophotometer

Answer 27

-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

Question 28

Electro‐analytical methods

Answer 28

several techniques to study an analyte by measuring the potential (in Volts) and/or current (in Amperes) in an electrochemical cell
containing the analyte.

Question 29

Potentiometry

Answer 29

in which the difference in electrode potentials is measured (Electro‐analytical)

Question 30

Coulometry

Answer 30

in which the cell’s current is measured over time (Electro‐analytical)

Question 31

Voltammetry

Answer 31

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

Question 32

Potentiometry - details

Answer 32

-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

Question 33

Coulometry - details

Answer 33

-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.