sumber ion

Hard vs. Soft Ionization methods, ICP sourcesSpark SourcesGlow DischargeSecondary Ion/Neutral Mass Specfast atom bombardment (FAB) sourcesdesorption sources field ionization (FI)field desorption, laser desorption . . . (especially MALDI)plasma desoprtion sources electron impact (EI)chemical ionization (CI)electrospray ionization sources (ESI) Desorption electrospray ionization (DESI)

ICP sourcesgas, liquid or solid sample is introduced into hot plasmaan efficient sourceof positively charged analyte ionsAr plasma is generated and maintained at the end of the glass torch locatedinside the loops of a water cooled copper load coil. RF potential applied to the coil produces an electromagnetic field in the part of the torch located within its loops. electrons are accelerated and collide with Ar atoms in the Ar gas flowing through the torch producing Ar+ ions and free electrons - a plasma.

ICP sourcesthe ions have to be extracted from the high temperature (~ 6000K or more), atmospheric pressure (760 torr) environment of an often chemically corrosiveAr plasma into a mass spectrometer operating in a high vacuum (10-5 torr) at room temperature. interface regioncontains two successive cones (mm orifices)ions in the center of the plasma are sampled into the region between two cones held at a pressure of about 1-3 torr At this stage, most of the Ar atoms are removed by a vacuum pump. ion beam is further extracted through the skimmer cone orifice into the front section of the mass spectrometer (pressure of about 10-3 - 10-4 torr)

Spark Ionization Sourcessamples are physically incorporated into two conductive electrodes (usually either carbon or silver) a high-voltage arc is produced, ionizing the materialsemiquantitative trace element technique for solids and liquidssamples: conducting, semiconducting and insulating solids, powders, crystals, liquids, organometallics, ash from organics, unknowns and many other sample forms.detection capabilities encompass the periodic table (Li U)has the ability to determine impurity levels from the sub-ppm level to 0.1%. SSMS total simultaneous elemental coveragelow detection limitshigh res. capabilities - eliminates many spectral interferences.

Glow Discharge MSanalytical technique for the bulk elemental analysis of inorganic solid samples. capable of analyzing, conducting, semi-conducting and insulating samples. amenable to solids, powders, crystals, wafers, and many other sample forms. elemental coverage encompasses Li Udetermine impurity levels from the sub-ppb to percent leveladvantages include high precision and low detection limits, quantitative accuracy (+/- 25% on average), without the use of standardshigh resolution capabilities eliminate most spectral interferences.

Secondary Ion/Neutral Mass Speca primary, high-energy beam of ions (usually oxygen, argon, or cesium) is aimed at a small area of a sample, such as a mineral grain. the primary ions have energies of ~ 10 keVthe primary ions sputter away the sample by causing the ejection of atoms and ions (called secondary neutrals and ions) these secondary ions (approximately 1% of the sputtered material) are accelerated into a mass spectrometer to reveal the elemental and isotopic characteristics of the sample.

Fast Atom Bombardment (FAB)material to be analyzed is mixed with a non-volatile chemical protection environment called a matrix This is bombarded under vacuum with a high energy (4 10 keV) beam of atoms.atoms are typically an inert gas (Ar or Xe)common matricies include glycerol, thioglycerol, 3-nitrobenzyl alcohol (3-NBA), 18-Crown-6 ether,2-nitrophenyloctyl ether, sulfolane, diethanolamine, and triethanolamine.

Field DesorptionField desorption (FD) is a method for emitting ions into the gas phase. Sample spread on an emitter is heated while a high electric field is applied. Ions are then emitted by the tunneling, ion-molecule reactions, thermal fusion effects, and other phenomenon occurring on the emitter surface and around thewhisker ends. The ionization phase depends strongly on the sample material and the spread condition.

Plasma DesorptionPlasma desorption ionization mass spectrometry (PDMS; also called fission fragment ionization) is a mass spectrometry technique in which ionization of material in a solid sample by bombarding it with ionic or neutral atoms formed as a result of the nuclear fission of a suitable nuclide, typically the Californium isotope 252Cf

Californium-252 plasma desorption mass spectroscopy RD Macfarlane and DF Torgerson We have shown that 252Cf-PDMS is capable of producing mass spectra of quasi-molecular ions for a wide variety of compounds, including amino acids, moderately large peptides, nucleotides, and natural products. Positive and negative ion mass spectra can be obtained, and in many cases quasi-molecular ions are observed in both. The method is nondestructive, as only a relatively few molecules are used and samples can be recovered after the measurement is made. Fragmentation patterns are obtained which can yield structure information. The present sensitivity of the method is at the nanogram level and there are possibilities for reducing this to picograms. The mass resolution is sufficient to give elemental identification up to mass 500. This may be extended to higher masses with improved time-of-flight techniques. There are indications that 252Cf-PDMS may extend the mass range of molecules that can be studied to as high as 3000 or more. Science, Vol 191, Issue 4230, 920-925Copyright 1976 by American Association for the Advancement of Science

Especially MALDIMatrix-assisted laser desorption ionization (MALDI) Ionization method using matrix-assisted laser desorption. a soft ionization technique analysis of biomolecules proteins, Peptidessugars)large organic molecules polymers, dendrimers other macromoleculestend to be fragile and fragment when ionized by other methods.

MALDI contdidentity of suitable matrix compounds is determined using specific molecular design considerationsfairly low molecular weight (to allow facile vaporization)large enough (with a high enough vapor pressure) not to evaporate during sample preparation or while standing in the spectrometerare acidic / act as a proton source to encourage ionization of the analytehave strong absorption in the UV so they rapidly and efficiently absorb the laser irradiationfunctionalized with polar groups - allowing use in aqueous solutionsmatrix solution is mixed with the analyte (e.g. protein-sample)organic solvent allows hydrophobic molecules to dissolvewater allows for hydrophilic molecules to do the samesolution is spotted onto a MALDI platesolvents vaporize, leaving only the recrystallized matrixanalyte molecules spread throughout the crystals in co-crystallized MALDI spot

laser desorption . . .

UV MALDI Matrix ListCompoundSolventl (nm)Applications2,5-dihydroxy benzoic acidacetonitrile, water, methanol, acetone, chloroform337, 355, 266peptides, nucleotides, oligonucleotides, oligosaccharides3,5-dimethoxy-4-hydroxycinnamic acidacetonitrile, water, acetone, chloroform337, 355, 266peptides, proteins, lipids4-hydroxy-3-methoxycinnamic acidacetonitrile, water, propanol337, 355, 266proteins-cyano-4-hydroxycinnamic acidacetonitrile, water, ethanol, acetone337, 355peptides, lipids, nucleotidesPicolinic acidEthanol266oligonucleotides3-hydroxy picolinic acidEthanol337, 355oligonucleotides

Field Ionization Field ionization (FI) is the generation of M+ ions by removal of electrons, primarily from gas sample molecules, using a high electric field.This generally occurs at a sharp edge or tip that is biased to a high electrical potential

Field ionization (FI) is a method that uses very strong electric fields to produce ions from gas-phase molecules. Its use as a soft ionization method in organic mass spectrometry is principally due to Beckey [8]. Like EI or CI, FI is only suitable for gas-phase ionization.Therefore, the sample is introduced into the FI source by the same techniques that are commonly used in EI and CI sources, for example using a direct probe that can be heated or the eluent from a gas chromatograph.The intense electric fields used in this ionization method are generally produced by a potential difference of 812 kV that is applied between a filament called the emitter and a counter-electrode that is a few millimetres distant. Sample molecules in the gas phase approach the surface of the emitter that is held at high positive potential. If the electric field at the surface is sufficiently intense, that is if its strength reaches about 107108 Vcm1, one of the electrons from the sample molecule is transferred to the emitter by quantum tunnelling, resulting in the formation of a radical cation M+. This ion is repelled by the emitter and flies towards the negative counter-electrode. A hole in the counter-electrode allows the ion to pass into the mass analyser compartment. In order to achieve the high electric field necessary for ionization, the emitter constituted of tungsten or rhenium filament is covered with thousands of carbon microneedles on its surface. It is at the tips of these microneedles that the electric field strength reaches its maximum. FI leads to the formation of M+ and/or MH+ ions depending on the analyte. The formation of protonated molecular species results from ionmolecule reactions that can occur between the initial ion and the sample molecules close to the surface of the emitter. It is not unusual to observe both M+ and MH+ in the FI spectrum.

Electron Ionization (EI)EI (formerly known as electron impact) is an ionization technique widely used in mass spectrometry, particularly for organic molecules.The gas phase reaction producing electron ionization is: M + e- M+ + 2e- low energies (around 20 eV), the interactions between the electrons and the analyte molecules do not transfer enough energy to cause ionizationat around 70 eV, the de Broglie wavelength of the electrons matches the length of typical bonds in organic molecules (about 0.14 nm), and energy transfer to organic analyte molecules is maximized, leading to the strongest possible ionization and fragmentation

Electron Ionization (EI)

Chemical Ionization (CI)Chemical ionization (CI) is an ionization technique used in mass spectrometryionization is achieved by interaction of its molecules with reagent ionsthe analyte is ionized by chemical ion-molecule reactions during collisions in the sourcethe process may involve transfer of an electron, a proton or other charged species between the reactants. a less energetic procedure than electron ionization and the ions produced are, for example, protonated molecules: [M + H]+. These ions are often relatively stable, tending not to fragment as readily as ions produced by electron ionization.

Chemical Ionization (CI)typical reagent gases (ex. CH4, isobutane, or NH3) are present in a millionfold excess with respect to the analyte. analyte is ionized by ion-molecule chemical reactions:Primary Ion Formation:CH4 + e- CH4+ + 2e-Secondary Reagent Ions:CH4 + CH4+ CH5+ + CH3CH4 + CH3+ C2H5+ + H2Product Ion Formation:M + CH5+ CH4 + [M + H] + (protonation)AH + CH3+ CH4 + A+ (H abstraction)M + CH5+ [M+ CH5] + (adduct formation)A + CH4+ CH4 + A+ (charge exchange)

Electrospray Ionization Sources (ESI)Electrospray ionization (ESI) was first introduced by Dole and coworkers in 1968 and coupled to MS in 1984 by Yamashita and FennIn ESI the sample is dissolved in a polar, volatile solvent, and transported through a needle placed at high positive or negative potential (relative to a nozzle surface)The high electric potential (1 to 4 kV) between the needle and nozzle causes the fluid to form a Taylor cone, which is enriched with positive or negative ions at the tip. A spray of charged droplets is ejected from the Taylor cone by the electric field. The droplets shrink through evaporation, assisted by a warm flow of nitrogen gas passing across the front of the ionization source (Fig. 2.6).

Mass Spektrometry, Dominic M. Desiderio & Nico M. Nibbering., Series Eddition.

Mass Spektrometry, Dominic M. Desiderio & Nico M. Nibbering., Series Eddition.

Ions are formed at atmospheric pressure and pass through a coneshaped orifice, into an intermediate vacuum region, and from there through a small aperture into the high vacuum of the mass analyzer.

Sample preparation requires only dissolution of the sample to a suitable concentration in a mixture of water and organic solvent, commonly methanol, isopropanol, or acetonitrile. A trace of formic acid or acetic acid is often added to aid protonation of the analyte molecules in the positive ionization mode. In negative ionization mode ammonia solution or a volatile amine is added to aid deprotonation of the analyte molecules.The sensitivity of ESI-MS is good, with low femtomole or attomole detection levels for many peptides. However, the sensitivity of ESI is a function of the concentration of the injected sample. High flow rates, that is, 1 to 1000 mL/min in conventional ESI-MS, result in high sample consumption. It is therefore advantageous to use the lowest possible flow rate. Nano-ESI (or nanospray) is a low-flow-rate (20 to 200 nL/min) version of ESI, with lower sample consumption and considerably higher sensitivity.

ESI is an soft ionization method, accompanied by very little fragmentation of the formed molecular ions. Consequently, weak bonds are often preserved and analysis of intact post-translationally modified peptides/proteins and noncovalently bound complexes, such as proteinligand complexes, can be successfully performed with ESI-MS.

Desorption Electrospray Ionization

Desorption ESI (DESI) was introduced by Takatz et al. The method is sensitive and large species such as proteins can be detected. The ions observed are more or less the same as with regular ESI.A DESI source consists of a spray capillary and a coaxial capillary providing the nebulizer gas. High voltage is applied to the spray needle, which is directed towards the target surface (Fig. 2.7). Mass Spektrometry, Dominic M. Desiderio & Nico M. Nibbering., Series Eddition.

Sample species are then desorbed and will subsequently enter the orifice to the mass spectrometer. Normal distances between the spray needle, sample, and orifice range from some millimeters to several centimeters.The optimum geometry depends on the sample and on the size of the desired sampling area. The advantages with DESI are that the target can be in principle any type of surface and that the analysis time often can be very short, on the order of seconds. This means that rapid analyses can be performed without the need for sample preparation.