Question

Elaborate about the principle, advantages and where do we widely use of

1) MALDI-TOF/TOF   (not MALDI-TOF)

2) LC-MS/MS   (not LC-MS)

Answer 1

1) MALADI -TOF =

Matrix -assisted Laser desorption ionisation (MALADI) is desorption ionisation technique ,commonly used for low volatile samples. In this technique the sample to be analyzed is dissolved or dispersed in a matrix and placed in path of a high energy ( 1 -10 Kev) .

Most MALADI spectrometer use a nitrogen laser that emits at 337 nm, but some application use an infrared (IR) laser for direct analysis of samples contained in gel .The matrix selected on the basis of their ability to absorb the ultraviolet (uv) light from a laser pulse (337 nm for N₂ laser ) .Substituted nicotinic acid, picolinic and cinnamic acid derivative are often used in MALADI technique. The matrix absorbed most of energy from nitrogen laser. MALADI spectrometry commonly used for analytes spanning wide range of molecular weight, from small polymer to high molecular weight compound . Example of common matrix used -

Nicotinic acid , picolinic acid ,3-hydroxy picolinic acid, sinapinic acid, dithranol etc.

TOF-

Time and flight mass analyser is based on simple idea that the velocities of two ions, created at the same instant with same kinetic energy ,will vary depending on mass of the ions -the lighter ion will have a higher velocity. If these ions are traveling towards mass spectrometers detector , the lighter ion will strike the detector first. Examining this concept further, the kinetic energy of an accelerated through an electrical potential V will be

zV = (mv²/2) (1)

And the velocity of the ion is the length of the flight path L , divided by the time t ,it take the ion to travel over distance -

V= L/t

So, replacing this expression for V in equation (1)

zV = ( mL²/2t²)

Thus ,it follows that,

m/z = (2Vt²/L²)

The TOP mass analyzer required very fast electronics to accurately measure ion flight times that may be submicosecond.

MALADI /TOF mass spectrometer have found most effective and commonly suite each other. MALADI/TOP generally used for analysis of molecules .In theory , TOP mass mass analyzer have no upper limit to their effective mass range and the mass analyser have highest sensitivity .The mass spectrometers commonly used for analysis of air sample ,it can detect release of any poisonous gases. TOF mass spectrometers used for kinetic study , especially with application to very fast reaction. Very fast reaction such as combustion and explosions can be investigated with this technique .

2) LC-MS=

This is an combined technique of HPLC and MS ,commonly called as LCMS. The combination of these two analytical technique reduce error and improve the accuracy .This technique commonly used for effluent characterization .LCMS involves separation of mixture in accordance with their physical and chemical properties ,then identifying the components within each peak and detecting based on their mass spectrum.  

The flow rate used in LC-MS should be less than those used for HPLC.This is to ensure complete ionisation and to maintain detection sensitivity of the MS, which start to decrease beyond 200 micro liter /minute ,therefore the column in LC-MS is much smaller to accommodate the the smaller solvents flow rate and samples volume .