Question

A detailed schematic of a quadrupole mass spectro thorough explanation for each part, as with al is required. One of the members of the group must draw tnis, u can not be copied from the web. meter along witha .A detailed comparison of 4 different types of MS ionization methods-- and how they each effect the spectra obtained-is required.

Answer 1

The choice of ionisation methods in MS depends upon the type of information required and the nature of the samples.

1) Electron ionization or electron impact ionisation(EI)

Electron ionisation is one of the oldest and best-characterized ionization methods. in this method, a beam of electrons is allowed to pass through the sample which s in the gaseous phase. An electron is then expelled from the gaseous sample resulting a positive ion. The electron bombardment results molecular ions and fragment ions. In this method electron beam of energy 70eV is used. A decrease in energy of the electron beam causes a decrease in the rate of fragmentation also reduces the number of ions formed. One limitation of this method is that the sample should be stable and volatile. this method is known for reproducible mass spectra. The fragmentation of the molecule will be useful in the determination of molecular structure. the mass spectra can be compared to other EI based mass spectra for the identification

2)Fast Atom Bombardment(FAB)

In FAB method, the analyte must be dissolved in a liquid matrix such as glycerol, diethanolamine etc. and placed on the target. The target is then bombarded with a fast atomic beam of energy 6 KeV that produces molecular ion and fragment ions from the analyte. This method also produces background signals from the matrix used. FAB is a simple method fo for high-resolution measurements on a wide variety of compounds. The major limitation of this method is background signal due to the matrix, the analyte should be soluble in the matrix, difficult to detect low molecular weight ions from the background signal.

3) Electrospray ionization(ESI)

In elecrtospray ionization, the sample is sprayed across a high potential difference, resulting in multiple charged ions.Here, the number of charge increases as the molecular weight increases and can be determined by looking for similar species having the same charge and different adduct mass or by examining the mass to charge ratio for the resolved isotopic clusters. this is a suitable method for polar and multiple charged compounds. The ESI results in excellent sensitivity with low background signal and low detection limit. Very low molecular mass compound s can be detected using this method.

4) Matrix-assisted Laser desorption ionization(MALDI)

In MALDI, the analyte is dissolved in an excess matrix, having a chromophore that absorbs the wavelength of the laser. A very small amount of this is the placed on the target. Here, the matrix absorbs energy from the laser and ionizes the sample. MALDI is a rapid method for molecular weight determination. Here, the laser is always pulsed and is in vacuum