Category: Instrumental Method of Food Analysis

Jul 31

Working Principle of Infra-Red (IR) Spectroscopy

Infra-Red (IR) radiation does not have enough energy to induce electronic transitions as seen with UV. Absorption of IR is restricted to compounds with small energy differences in the possible vibrational and rotational states. For a molecule to absorb IR, the vibrations or rotations within a molecule must cause a net change in the dipole moment of the molecule. Electromagnetic radiation consists of an oscillating electrical field and an oscillating magnetic field perpendicular to each other. The alternating electrical field of the radiation interacts with fluctuations in the dipole moment of the molecule. If the frequency of IR radiation matches the vibrational frequency of the molecule, then radiation will be absorbed, causing the change in amplitude of molecular vibration. Read more

Jul 29

Working Principle of Atomic Absorption Spectroscopy (AAS)

Atomic absorption spectroscopy (AAS) determines the presence of metals in liquid samples. Metals include Fe, Cu, Al, Pb, Ca, Zn, Cd and many more. It also measures concentration of metals in the sample. Typical concentration range in the low mg/L. In their elemental form, metals will absorb ultraviolet light when they are excited by heat. Each metal has characteristic wavelength that will be absorbed. The AAS instrument looks for a particular metal by focusing a beam of ultraviolet (UV) light at a specific wavelength through a flame and eventually detected by a detector. Read more

Jul 28

Gas Chromatography

Gas chromatography (GC) is a method of chemical analysis for separating chemicals in a complex sample. This technique uses a flow through narrow tube known as column through which different chemical constituents of a sample in a gas stream (mobile phase; carrier gas) at different rates depending on their various chemical and physical properties and their interaction with a specific column filling called stationary phase. As the sample exit the end of column, they are detected and identified electronically. The function of stationary phase in column is to separate different components, causing each one to exit the column at different times (retention time). Other parameters that can be used to alter the order of time of retention are
1. Carrier flow rate
2. Temperature Read more