What is the difference between infrared spectroscopy and mass spectrometry

IR Spectroscopy. Cleophas Rwema Follow. Crystal structure and xrd. Basics of xrd. Xrf and xrd application. Uv visible spectroscopy. Uv vis. Uv vis spectroscopy. Uv vis and raman spectroscopy. Uv spectroscopy. Application of uv spectroscopy. Metabolism basic concepts qa. Related Books Free with a 30 day trial from Scribd. Related Audiobooks Free with a 30 day trial from Scribd.

Empath Up! Abhishek Arang , Student at DR. Bharani Voleti. Views Total views. Actions Shares. No notes for slide. Infrared spectroscopy and mass spectrometry 1. Wade, Jr. Infrared Spectroscopy and Mass Spectrometry 2. MS can give the molecular weight of the compound and functional groups. This gives useful clues as to the alkyl and other functional groups present. Chapter 12 6 The Electromagnetic Spectrum 7.

Two of these are stretching modes, and one is a bending mode scissoring. Chapter 12 13 The Infrared Spectrometer Thus, for instance, a compound containing a highly electronegative atom would tend to leave the hydrogen nuclei protons more exposed to the magnetic field because the electronegative atom "hogs" the electrons.

Conversely, a compound without a highly electronegative atom would tend to allow greater shielding of protons by electrons. Less shielded protons which are more exposed to the applied field thus have a greater difference between high-energy and low-energy spin states, whereas more-shielded protons have a lesser difference between the spin states.

As with IR spectroscopy, NMR spectroscopy passes light through a sample and looks at the spectrum that is transmitted. In this case, however, absorption occurs at frequencies corresponding to the energy difference between two spin states of a proton in the compound. A slightly revised but still simple view of NMR spectroscopy is depicted below. NMR spectra are typically displayed as a series of peaks, such as the sketch shown below not necessarily representative of any existing compound.

Instead of displaying the peaks on a frequency or wave number scale, however, the horizontal axis is often displayed according to chemical shift, which is a number proportional to the difference in frequency between the sample peak and a reference peak typically tetramethylsilane, or CH 3 4 Si. Although we will not delve much further into the details of NMR spectra, we can note that we can interpret these spectra by way of the number of peaks indicating the number of different proton types in the compound , the peak heights indicating the relative numbers of proton types , and peak splitting indicating the number of protons near the one creating the peak.

Thus, NMR is useful for determining the structure of a sample. Although it is not truly a type of spectroscopy, mass spectrometry is nevertheless another instrumental method that chemists use to analyze compounds. Fundamentally, mass spectrometry involves ionization of a sample through bombarding it with high-energy electrons. When these electrons collide with a molecule in the sample, they can dislodge an electron, creating either a cation radical or a cation and a neutral radical.

The result is a number of charged particles that can be accelerated by an electric field and then deflected by a magnetic field as shown in the diagram sketched below. Lighter ions relative to their respective charges will be deflects more by the magnetic field than will heavier ions also relative to their respective charges. Thus, the detector can identify different ion masses actually, mass-to-charge ratios by the amount of deflection they undergo, and chemists can use this information to identify the type of compound in the sample.

An example mass spectrometry spectrum is shown below. Again, this spectrum is for illustration; it does not necessarily correspond to an actual compound. Mass-to-charge ratios are often calculated as the atomic weight essentially the number of protons and neutrons in the nucleus of an atom of the entire molecule divided by the charge in the number of missing electrons.

Open Main Menu. Browse Courses My Classes. Sign In Subscribe Course Catalog. Infrared Spectroscopy Infrared IR spectroscopy, as the name indicates, uses infrared radiation a band of frequencies below the visible portion of the spectrum to analyze a sample. Interested in learning more?

Why not take an online Organic Chemistry course? The hydrogen atoms could then vibrate by "bending" or "stretching" the bonds: Different compounds will absorb different wave numbers of infrared radiation to cause certain of these vibrational modes.

Nuclear Magnetic Resonance Spectroscopy Nuclear magnetic resonance NMR spectroscopy takes advantage of the spin states of protons and, to some extent, other nuclei to identify a compound.

Mass Spectrometry Although it is not truly a type of spectroscopy, mass spectrometry is nevertheless another instrumental method that chemists use to analyze compounds. A sample of white powder has been delivered to us and it's our job to identify it.

Time for molecular analysis. Before we get too deep into our mystery, we need to set something straight. Spectroscopy and spectrometry are not interchangeable words. Spectroscopy is the study of how matter interacts with visible light and other electromagnetic radiation, from gamma rays to microwaves and everything in between.

These techniques are usually non-destructive, so the sample of our compound won't be changed after the analysis.

Spectrometry is the generation of interpretable data, or spectra, from a lot of different techniques, including spectroscopy. Some of the techniques that generate spectra can be destructive, like mass spectrometry that we're going to talk about today. Basically, the main difference is that spectroscopy is just observing how electromagnetic radiation interacts with molecules, while spectrometry provides data that we can use to interpret the structure.

Both of them can be used for individual substances or mixtures, but mixtures are way more complicated, so we'll stick to one substance at a time for now.

Now that we've cleared that up, let's dive into the techniques. Using a very small amount of sample, mass spectrometry, or mass spec for short, gives us information about a molecule's molecular mass, which is the added-up weights of all of its atoms.

Inside a mass spectrometer, there aren't any air particles whizzing around, so it's a vacuum, like outer space. A sample molecule goes into a chamber and the ion source, which generates a stream of electrons with a high temperature electrical current. In the ion source, a metal gets zapped, electrons get liberated, and that electron stream hits the sample molecule.

This technique is called electron impact. It's a destructive approach, but also one of the most common in mass spec. When this stream of focused electrons strikes a molecule, an electron splits off from the molecule and it forms a radical cation. It leaves behind an unpaired electron -- a radical. And it's a cation, with a positive charge, because a neutral molecule loses an electron.

This radical cation is called the molecular ion. In an ideal situation, it flies down the tube of the mass spectrometer to the detector as-is.

Any molecular ions and ion fragments are sent down a tube where a variable magnetic field sorts them by mass. This way, only particles of a specific mass can hit the detector at one time. Then, a mass spectrum is produced, with mass on the x-axis, and the relative number of ions on the y-axis. Technically, the units of the x-axis are m over z, which is the mass to charge ratio. This is related to how each ion traveled down the tube. Since most ions created by a mass spectrometer have a positive one charge, that equation simplifies down to m over one, or just m: the mass of the particle.

Now, the molecular fragments hitting the detector form a fragmentation pattern that's unique to the molecule. For example, let's look at mass spectra for octane and iso-octane, or 2,2,4-trimethylpentane if you wanna be IUPAC-official. Both molecules have the same molecular formula and therefore the same molecular mass of mass units. But mass spec can tell the two apart! Knowing the molecular mass of octane, mass units, that peak is the molecular ion.

If we subtract the next highest peak, so minus 85, the difference is 29 mass units. This means that the octane molecule split into two chunks here -- one of 85 mass units and one of 29 mass units. It's often easier to identify the smaller fragment that split off than the big one that got left behind and made the peak. To figure out what the 29 mass unit piece is, we know that one carbon has a mass of 12 and each hydrogen has a mass of 1.

Then we can add more carbons and hydrogens until we get to In this case, 2 carbons is 24 mass units, plus 5 hydrogens is 29 mass units. This gets us to CH3CH2-, an ethyl group fragment! So it's a hexyl group. There's always a bit of trial and error, but that's what we chemists do best!

All of the peaks in the mass spectrum represent different chunks of octane, and we can calculate them. But here's one peak that's very important to organic chemists: the base peak. If we do the same math, we know that corresponds to a pentyl fragment splitting off and a propyl group left over, which is what's causing the peak. The propyl group having the tallest peak means that it has the highest relative intensity, and it's the most stable ion that forms in the fragmentation.

Sometimes the most stable fragment can tell us a lot about the structure of a compound. Switching over to the spectrum for iso-octane, we can see that the pattern is very different. We know its molecular mass is also mass units, so we can see that the molecular ion isn't there. And minus 99 is 15 mass units, which corresponds to the loss of a CH3, or methyl group.

And using the same math, we can figure out that this is a 4-carbon group with 9 hydrogens. The branching of iso-octane leads to a very different base peak from octane. Over the years, we've developed databases called spectral libraries, which contain known spectra of different molecules.

Most operating programs can search through thousands of libraries to give us the most likely matches. But even with the help of computer programs, we still need to use our human brains to think critically and check whether the fragments make sense for our experiment!

Now that we have one tool, let's go back to the mystery white powder from that exploding building.