Question

answer all te parts _the question is . What are the different techniques used by Mass-spectroscopes for ionization and detection of the required signal. What is ICP-MS ? What are its advantages over traditional MS.

Answer 1

Mass spectrometry is a technique for separating and identifying molecules based on mass. It has become an important tool for proteomics, the analysis of the whole range of proteins expressed in a cell. Mass spectrometry is used to identify proteins and to determine their amino acid sequence. It can also be used to determine if a protein has been modified by the addition of phosphate groups or sugars, for example. The technique also allows other molecules, including DNA, RNA, and sugars, to be identified or sequenced.

The use of mass spectrometry has greatly aided proteomics. Whereas DNA sequencing is simple and straightforward, protein sequencing is not. The ability to quickly and accurately identify proteins being expressed in a cell allows a range of hypotheses to be tested that cannot be approached by simply looking at DNA. For instance, it is possible with mass spectrometry to determine what proteins are expressed in cancer cells that are not expressed in healthy cells, possibly leading to further understanding of the disease and to development of drugs that target these proteins.

Data derived from mass spectrometry is usually analyzed by computer programs that search databases to help identify the analyzed protein. Such tools are the province of bioinformatics. The databases are usually located at a centralized institution and are searched via the Internet

Inductively Coupled Plasma Mass Spectrometry or ICP-MS is an analytical technique used for elemental determinations. The technique was commercially introduced in 1983 and has gained general acceptance in many types of laboratories. Geochemical analysis labs were early adopters of ICP-MS technology because of its superior detection capabilities, particularly for the rare-earth elements (REEs). ICP-MS has many advantages over other elemental analysis techniques such as atomic absorption and optical emission spectrometry, including ICP Atomic Emission Spectroscopy (ICP-AES), including:

• Detection limits for most elements equal to or better than those obtained by Graphite Furnace Atomic Absorption Spectroscopy (GFAAS)
• Higher throughput than GFAAS
• The ability to handle both simple and complex matrices with a minimum of matrix interferences due to the high-temperature of the ICP source
• Superior detection capability to ICP-AES with the same sample throughput
• The ability to obtain isotopic information.

Figure 1. The ICP Torch showing the fate of the sample.
(Figure reproduced with permission from PerkinElmer, Inc.)An ICP-MS combines a high-temperature ICP (Inductively Coupled Plasma) source with a mass spectrometer. The ICP source converts the atoms of the elements in the sample to ions. These ions are then separated and detected by the mass spectrometer.

Figure 1 shows a schematic representation of an ICP source in an ICP-MS. Argon gas flows inside the concentric channels of the ICP torch. The RF load coil is connected to a radio-frequency (RF) generator. As power is supplied to the load coil from the generator, oscillating electric and magnetic fields are established at the end of the torch. When a spark is applied to the argon flowing through the ICP torch, electrons are stripped off of the argon atoms, forming argon ions. These ions are caught in the oscillating fields and collide with other argon atoms, forming an argon discharge or plasma.