This is modern esi ms problem that focuses on the concepts of mass, charge, and molecular formula. Gas chromatography separates the components of a mixture and. Ei mass spectra, in most of cases, contain intense fragment ion peaks and much less intense molecular ion peak. This is caused by a different ion than the corresponding peak in the pentane mass spectrum. Here are approximate results for an instrument with 0. Mass spectra is a plot of relative abundance against mass tocharge ratio. A compilation of mz values for selected peaks in the spec trum of ia and for the corresponding peaks in the spectrum of each of the derivatives is shown in table i. Identity heteroatoms by their characteristic isotope ratios. These high sensitivity mass spectrometers, called hrms. If the molecule is not too large or complex, the determination should be very accurate. Objects atoms or groups of atoms of different masses may be detected due.
It can be used to find relative isotopic abundance, atomic and molecular mass, and the structure of a compound the result of a mass spectrometry is a graph plotting mass per charge against relative abundance. Data system mass detector analyzer vacuum system source inlet region more precisely mass spectrometry determines the mass of a molecule. Mass spectrum and molecular ion peaks chemistry stack exchange. Prominent peaks in a mass spectrum are generally those resulting from primary fragmentations. The outcome has been widespread use of complex instrumentation, often as a walk up service, by staff with little education or training relevant to the task. Draw the ions corresponding to the other three peaks.
These low intensity peaks are the result of heavier isotopes of the common isotope replacing atoms in the molecule. The heaviest ion shown on the spectrum is likely to be the molecular ion though peaks can appear higher than the molecular ion peak, for reasons well discuss shortly. Peaks are spaced by a unit mass all peaks in a cluster can be of same mz molecular formula the nominal mass is mz of the lowest mass isotopomer, i. The main aim of the guide is to enable those unfamiliar with mass spectrometry to generate mass spectra that are fit for purpose. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. This peak if it appears will be the highest mass peak in the spectrum, except for isotope peaks. The molecular fragmentation peaks in the mass spectrum can give clues as to the substructure of the molecule. Mass spectroscopy mass spectroscopy is a technique causing the formation of the gaseous ions with or without fragmentation. Finding the molecular formula from a mass spectrum youtube.
Naturally occurring iodine is virtually 100 percent 129 i, so unlike the spectra of chlorine and brominecontaining molecules, iodinecontaining molecules dont show isotope peaks. Mass spectrometry is a gas phase technique the sample must be vaporized. Molecular ion peaks are also often preceded by an m1 or m2 peak resulting from loss of a hydrogen radical or dihydrogen. Mass peak or parent peak or molecular ion peak is one with highest me value on xaxis.
How a mass spectrometer identifies isotopes dummies. Mass spectrometry tutorial chemical instrumentation. Peaks clustered really close to one another depicts isotopes. Mass spectrometry principle,types, instrumentation. Ion fragmentation of small molecules in mass spectrometry. When the molecular ion peak is not observed in the mass spectrum, chemical ionization can be used in order to get molecular ion information. However, the mass spectra gives the mass and formula of. The positions of individual peaks within the spectra. As the name implies, it is actually two techniques that are combined to form a single method of analyzing mixtures of chemicals.
Peaks mz 194 and 210 represent the intact alkaloid side chain. In fact, chemists wont try to assign every single peak in this spectrum rather, theyll look for characteristic peaks. Ions 43 and 57 are among the most stable of the spectrum with the highest peaks, consistent. Mass spectrometry has made significant contributions to coordination and organometallic chemistry. The instruments used in such studies are called mass spectrometers and mass spectographs. The base peak is the tallest peak most abundant species.
The results are typically presented as a mass spectrum, a plot of intensity as a function of the mass tocharge ratio. The molecular ion fragments due to covalent bonds breaking. Interpreting esi spectra the y axis is labeled relative intensity. Secondary fragmentations may be used as aids for spectrum analysis. Base peak is the one with the highest intensity on yaxis. This is the first in a series of 3 lessons about the interpretation of electron impact mass spectra. Which of the following peaks does not appear in the mass spectrum of hexane. Mass spectrometry mass spectrometry is the most accurate method for determining the molecular mass of the compound and its elemental composition.
Mass spectra can be quite complicated and interpretation difficult. A mass spectrometer in the laboratory types of peaks in mass spectra. After completing this section, you should be able to. Mar 24, 2020 mass spectrometry, analytic technique by which chemical substances are identified by the sorting of gaseous ions in electric and magnetic fields according to their mass tocharge ratios. Gas chromatography mass spectroscopy gcms is one of the socalled hyphenated analytical techniques. Mass spectrometry ms is an analytical technique that measures the mass tocharge ratio of ions. The 5 peaks in the mass spectrum shows that there are 5 isotopes of zirconium with relative isotopic masses of 90, 91, 92, 94 and 96 on the 12 c scale.
Oil hydrocarbon fingerprinting by gcms is based on analysis of selected mz ions with high sensitivity e. Which of the following regions in the electromagnetic spectrum corresponds to the radiation with the highest energy. Following is some general information which will aid ei mass spectra interpretation. Hf20 loss molecular ion peak the highest mass ion in the spectrum. By convention, m is the numerical value for the mass of the ion and z is the numerical value for the charge of the ion. The two higher mass peaks are due to the presence of isotopes of the compounds atoms. These other peaks are attributed to the cleavage of bonds in the original sample molecule.
The mass to charge ratio mz is used to describe ions observed in mass spectrometry. The highest mass ion in a spectrum is normally considered to be the molecular ion, and lower mass ions are fragments from the molecular ion, assuming the sample is a single pure compound. Characteristic losses point to characteristic moieties in the molecule e. It reports a list of likely identifications along with the statistical probability of the match. Peaks with mass less than the molecular ion are the result of fragmentation of the molecule. Step 1 understand that the peak value observed in the spectrum equals mass divided by charge and that the mass is the mass of the molecule plus any adducts protons 190. It is commonly used for the identification of organic compounds from electron ionization mass spectrometry. Peaks detection and alignment for mass spectrometry data. There are more bars on the graph than just the mass of the sample molecule. May 07, 2015 the heaviest ion shown on the spectrum is likely to be the molecular ion though peaks can appear higher than the molecular ion peak, for reasons well discuss shortly. I have an input file containing precursor mass and peak list mz and intensity of tandem mass spectrum.
Give possible structures of the fragments giving rise to the large peaks at mz 85, 57, and 43. This video was created for a university course in instrumental analysis in chemistry. The instruments used in such studies are called mass spectrometers and mass spectrographs, and they operate on the principle that moving ions may be deflected by electric and. Improved peak detection and quantification of mass. Mass spectroscopy for structural determination chemistry tutorial.
Protein sequencing and identification with mass spectrometry. Whatever is the technique used, one obtains from a biological sample a calibrated output which is a mass spectrum characterized by numerous peaks, which correspond to individual proteins or protein fragments polypeptides present in the sample. The mass spectrums of the known unambiguous gc peaks of the individual. Introduction mass spectrometry mass spec or ms uses high energy electrons to break a molecule into fragmentation. In many cases, each peak in the spectrum of ia can be correlated to a single peak in the spectrum of each derivative. M3 to m14 and m19 to m25 peaks are unlikely, exceptions exist. Electrospray ionization mass spectrometry by richard b. The library compares the mass spectrum from a sample component and compares it to mass spectra in the library. Electron ionization mass spectra of ia and of the seven dlabeled derivatives ibih are shown in figures 46. Chapter 2 fragmentation and interpretation of spectra 2. Mass spectral fragments of common hydrocarbons mass spectral peaks can be identified to have originated from the fragmentation of specific hydrocarbon sources including. The appearance of this type of peak arrangement at the high end of the mz scale on the mass spectrum is characteristic of the molecular ion.
Careful examination and comparison of these spectra reveal intensity patterns that are reasonably consistent from one spectrum to the next. Isotopic percentage and nominal mass calculation are also. Infrared spectroscopy identifying functional groups 4. Zagorevskii, in comprehensive coordination chemistry ii, 2003. The molecular fragmentation peaks in the mass spectrum can give clues as. Intensity of peaks depends on the stability of the ion. This tells us the mass of the molecule in question, which can be of great use in identifying it. Mass spectra produced by gcms are one of the most valuable tools for identification of unknown compounds. Mass spectroscopy determining molecular weight, structural elements, molecular formula the various spectroscopies are the primary method for determining the structure of compounds. Mass spectrometry, also called mass spectroscopy, analytic technique by which chemical substances are identified by the sorting of gaseous ions in electric and magnetic fields according to their mass tocharge ratios. Follow these links if you are interested or explore them later via the mass spectrometry menu. The chapter includes an introduction to the main ionisation techniques in mass spectrometry and the way the resulting fragments can be analysed. The end result is that in most mass spectrometers, more than 5 but many fewer than 35 peaks will be observed for our example molecule of difluorotetrachlorobenzene.
Mass spectrometry and interpreting mass spectra compound. Structure determination how to determine what compound. Mass spectral interpretation is the method employed to identify the chemical formula, characteristic fragment patterns and possible fragment ions from the mass spectra. Electronimpact ionization sample inlet 107 108 torr rh electron beam 70 ev 6700 kjmol. The heights of the peaks represent the intensities or abundance of ions in the sample for a speci. We have previously described practical methods for the lowlevel processing of mass spectra. It is also called as positive ion spectra or line spectra. The existence of isotopes generates a cluster of peaks isotope peaks. Mass spectrometry is a process by which the atomic mass of atoms or molecules is determined. This time, the relative abundances are given as percentages. Nominal mw will be an odd number if the compound also contains an odd.
Alkaloid side chain mz 210 diterpenoid scaffold loss of 60 or 42 j. Some functional groups have characteristic fragmentation it is difficult to assign an entire structure based only on the mass spectra. First, the fundamental notions of mass spectrometry are explained, so that the reader can easily cover this chapter graphs, main pick, molecular ion, illogical pick, nitrogen rule, etc. On analyzing any sample, few peaks are formed in the mass spectra. At high energies, the ionising electron beam can fragment the molecule by cleaving particular bonds. Thomson used a primitive form of ms to prove the existence of isotopes with neon20 and neon22. The ionized molecule often fragments into smaller ionsradicals. In the spectrum for toluene for example, the molecular ion peak is located at 92 mz corresponding to its molecular mass. Mass spectrum of methanol should show a molecular ion peak for methanol 5 at 32 you should note that there may be peaks of greater mz me than the molecular ion peak but these peaks are of much lower intensity. This simplified list will help you to interpret many spectra, however there are other mechanisms of fragmentation which cannot be covered in this brief tutorial.
Before we can calculate the mass of the compound we must determine the charge state of the two peaks. To analyze the mass spec, we look to the base peaks of each of the known compounds to narrow down on a base peak that would help us distinguish between cyclohexane and benzene. Can use this to distinguish compounds with a similar rough mass. The following diagram displays the mass spectra of three simple gaseous compounds, carbon dioxide, propane and cyclopropane.