Mass Spectrometry

Summary

This chemistry video delves into mass spectrometry, a technique for separating atoms and molecules by mass. It discusses John Dalton's atomic theory and its evolution, particularly the discovery of isotopes. The video explains how mass spectrometry identifies isotopes, calculates average atomic mass, and analyzes elements within molecules. It illustrates the process with a practical example using chlorine, showing how isotopes' abundance affects the spectrum's peaks.

Takeaways

• 🔬 Mass spectrometry is used to separate atoms, isotopes, and molecular fragments based on their mass.
• ⚛️ John Dalton's atomic theory proposed that elements consist of small particles called atoms, but some points have been modified over time.
• 🧮 Dalton's second point, that atoms of the same element have identical mass, was later disproven due to the existence of isotopes.
• 💥 Dalton also believed that atoms cannot be subdivided, but atomic fission and fusion later showed this was incorrect.
• 🧪 Mass spectrometry helps identify isotopes, and this began in the early 1900s with a focus on isotopes having the same element but different masses.
• 📊 The basic components of a mass spectroscope include an ionizer, mass analyzer, and detector.
• ⚡ Inside the ionizer, samples are ionized by stripping away electrons, creating positive ions in a vacuum environment.
• 🧲 In the mass analyzer, a magnetic field is used to bend the ion's path, with heavier ions bending less than lighter ones.
• 🖥️ The detector amplifies signals from the ions to create a spectrum, showing the mass and intensity of ions in the sample.
• 🧮 The average atomic mass of elements, like chlorine, is calculated using the masses and natural abundances of their isotopes.

Q & A

What is mass spectrometry?

Mass spectrometry is a technique used to separate atoms, isotopes, and fragments of molecules based on their mass.

Who was John Dalton and what is his contribution to chemistry?

John Dalton was one of the pioneers of modern chemistry. He is known for presenting Dalton's atomic theory in 1803, which proposed that elements are made of small particles called atoms.

What are the five key points of Dalton's atomic theory mentioned in the script?

The five key points are: 1) Elements are made of atoms, 2) Atoms of a given element are identical, 3) Atoms of different elements differ in properties, 4) Atoms cannot be subdivided, created, or destroyed, 5) Atoms combine in whole number ratios to form compounds.

What are the two errors in Dalton's atomic theory according to the script?

The two errors are: 1) Not all atoms of the same element have the same mass due to isotopes, 2) Atoms can be subdivided in processes like fusion or fission.

What is an isotope and how does it relate to mass spectrometry?

Isotopes are variants of a particular chemical element which differ in neutron number, and hence in nucleon number. Mass spectrometry is used to identify isotopes by separating ions based on their mass-to-charge ratio.

How does mass spectrometry calculate the average atomic mass?

Mass spectrometry calculates the average atomic mass by determining the mass and abundance of isotopes and then multiplying the mass of each isotope by its relative abundance, summing these products to get the average.

What are the three main components of a mass spectrometer?

The three main components are the ionizer, the mass analyzer, and the detector.

What happens in the ionizer of a mass spectrometer?

In the ionizer, a sample is ionized by having electrons removed, creating positive ions.

How does the mass analyzer in a mass spectrometer work?

The mass analyzer uses an electric field and a magnet to bend the path of ions. Ions of different masses are deflected differently, allowing them to be separated.

What is the purpose of the detector in a mass spectrometer?

The detector in a mass spectrometer detects the ions after they have been separated by the mass analyzer and generates a signal that can be amplified and analyzed.

How is the mass spectrum of chlorine described in the script?

The mass spectrum of chlorine shows two peaks corresponding to its two stable isotopes, chlorine-35 and chlorine-37, with the peak for chlorine-35 being higher due to its greater abundance.

What is the significance of the average atomic mass listed on the periodic table?

The average atomic mass on the periodic table represents the weighted average mass of an element's isotopes as they naturally occur, which is determined using mass spectrometry.

Outlines

00:00

🔬 Introduction to Mass Spectrometry and Dalton's Atomic Theory

This paragraph introduces the topic of mass spectrometry, a technique used to separate atoms, isotopes, and molecular fragments based on their mass. It also discusses the historical context by mentioning John Dalton, a key figure in modern chemistry, and his atomic theory presented in 1803. Dalton proposed that elements are made of atoms, which are identical within an element but differ between elements. He also believed atoms could not be subdivided or destroyed, and that they combine in simple ratios to form compounds. The paragraph highlights two errors in Dalton's theory: the existence of isotopes and the possibility of subdividing atoms through nuclear reactions. The focus then shifts to the identification of isotopes using mass spectrometry, which was a significant development in the early 1900s. Isotopes are atoms of the same element with different masses due to varying numbers of neutrons. Mass spectrometry can also be used to analyze individual atoms in a sample and to study fragments within macromolecules.

05:02

🧪 How Mass Spectrometry Works and Analyzing Chlorine Isotopes

The second paragraph delves into the workings of a mass spectrometer, which consists of an ionizer, a mass analyzer, and a detector. The ionizer is a vacuum chamber where samples are ionized by electrons, creating positive ions. The mass analyzer uses an electric field and a magnet to separate these ions based on their mass, with heavier ions being less deflected. The detector, which includes an electron multiplier, amplifies the signal from the ions, which is then analyzed by a computer to produce a spectrum. The paragraph uses the example of chlorine, which has two stable isotopes, chlorine-35 and chlorine-37, to illustrate how mass spectrometry can be used to determine the average atomic mass of an element. The process involves calculating the mass-abundance product for each isotope and summing these products to find the average atomic mass, which corresponds to the atomic weight listed on the periodic table. The paragraph also mentions the broader applications of mass spectrometry in analyzing atoms within molecules and fragments within macromolecules, such as proteins.

Keywords

💡Mass Spectrometry

Mass spectrometry is a technique used to separate ions based on their mass-to-charge ratio. It's a central theme of the video, as it allows for the identification of isotopes and analysis of molecules. The script describes how mass spectrometry works by ionizing a sample, then using a magnetic field to separate the ions according to their mass, which is detected and analyzed to produce a spectrum.

💡John Dalton

John Dalton was a pioneer of modern chemistry and is mentioned in the script for his atomic theory presented in 1803. His theory laid the groundwork for understanding the composition of elements and compounds, which is foundational to the discussion of isotopes and mass spectrometry in the video.

💡Isotopes

Isotopes are variants of a particular chemical element which differ in neutron number, and hence in nucleon number. They are the same element but have different masses. The video discusses how mass spectrometry can be used to identify isotopes, such as chlorine-35 and chlorine-37, by their mass.

💡Atomic Theory

Dalton's atomic theory is briefly discussed in the script, which includes the idea that elements are made of small particles called atoms. The script points out that Dalton's theory has mostly held up over time, with the exception of isotopes and the ability to subdivide atoms, which are beyond the scope of normal chemistry.

💡Ionizer

The ionizer is a component of the mass spectrometer that ionizes the sample by removing electrons, creating positive ions. The script describes the ionizer as having a vacuum and using electrons to ionize the sample, which is a crucial step in mass spectrometry.

💡Mass Analyzer

The mass analyzer is another key component of the mass spectrometer, which separates ions based on their mass using an electric field and a magnet. The script explains how heavier ions are harder to bend than lighter ions, which is how the mass analyzer differentiates between them.

💡Detector

The detector in a mass spectrometer is responsible for detecting the ions after they have been separated by the mass analyzer. The script describes how it uses an electron multiplier to amplify the signal from the ions, which is then analyzed to produce a spectrum.

💡Calibration

Calibration is the process of adjusting the mass spectrometer to ensure accurate measurements. The script mentions that calibration involves adjusting the strength of the magnet to ensure that ions reach the detector at the correct time, which is vital for accurate mass spectrometry analysis.

💡Spectrum

A spectrum, as discussed in the script, is the graphical representation of the data collected by the mass spectrometer. It shows the mass-to-charge ratio on the x-axis and the intensity (or abundance) on the y-axis. Peaks in the spectrum indicate the presence of ions with specific masses.

💡Average Atomic Mass

The average atomic mass is calculated by taking into account the mass of each isotope and its natural abundance. The script uses chlorine as an example to explain how the average atomic mass is calculated by multiplying the mass of each isotope by its abundance and then summing these products.

💡Myoglobin

Myoglobin is a large protein used in the script as an example of how mass spectrometry can be used to analyze complex molecules. The script suggests that mass spectrometry can be used to identify the amino acids that make up myoglobin, which is an advanced application of the technique.

Highlights

Introduction to mass spectrometry as a method for separating atoms, isotopes, and molecular fragments based on mass.

Historical context: John Dalton's atomic theory and its significance in modern chemistry.

Dalton's five postulates of atomic theory and their evolution over the past 200 years.

Identification of isotopes as a correction to Dalton's theory.

The concept of average atomic mass and its representation on the periodic table.

Components of a basic mass spectrometer: ionizer, mass analyzer, and detector.

Process of ionization within the mass spectrometer's ionizer.

Role of the mass analyzer in separating ions based on their mass.

Functioning of the detector and electron multiplier in mass spectrometry.

Calibration process of a mass spectrometer to ensure accurate measurements.

Visual representation of a mass spectrum with peaks indicating ion abundance.

Use of mass spectrometry to analyze chlorine isotopes,氯35 and氯37.

Explanation of how mass spectrometry can determine the heavier isotope based on the bending of ions' path.

Calculation of average atomic mass using the masses and abundances of isotopes.

Practical application of mass spectrometry in identifying elements and isotopes.

Mass spectrometry's capability to analyze atoms within molecules and fragments within macromolecules.

Example of analyzing a massive protein, myoglobin, using mass spectrometry.

Measurement of mass to charge ratio (m/z) in mass spectrometry.

Summary of learning objectives: using mass spectrometry data to identify elements and individual atoms.

Transcripts

Hi. It's Mr. Andersen and this is chemistry essentials video 9. It's on mass

spectrometry which is a way that we can separate atoms, isotopes and even fragments of molecules

based on their mass. And so it's an incredibly effective machine. But before we get to the

specifics of that I want to talk a little bit about John Dalton. John Dalton was one

of the pioneers of modern chemistry. And he was presenting at a conference in 1803 when

he put forward his Dalton's atomic theory. And so let me go through that. And what I

want you to think about is which of these have we changed over the last 200 plus years?

He believed number 1 that elements are made of extremely small particles called atoms.

He believed that atoms of a given element are identical in size, mass and other properties.

Atoms of different elements differ in size, mass and other properties. He believed that

atoms cannot be subdivided, created or destroyed. He believed that atoms of different elements

combine in simple whole number ratios to form chemical compounds. Then number 5, in chemical

reactions, atoms are combined, separated or rearranged. And so over the last 200 plus

years, if we were to look at those five things he put forward, there's really only two errors

that I can find. Number 1, are all elements or all atoms of the same element going to

have the same exact mass? No. Remember there are going to be isotopes. Those are going

to be the same atom, excuse me, the same element, but they're going to vary in the number of

neutrons that they have. And then the other one is that we can subdivide atoms, so when

we're looking at fusion or fission. But those really lay outside of normal chemistry. And

so he did an incredible job. And what we're really going to focus on in this video is

number two. Identification of isotopes. And so mass spectrometry is a way that we can

modify Dalton's atomic theory. And we did that through the identification of isotopes.

And that's around the early part of the 1900s. Isotopes remember are going to be the same

element but they're going to have a different mass. And that's based on the number of neutrons

that they have. And what we can do from that is we can eventually calculate the average

atomic mass. And that's going to be on the periodic table. Sometimes referred to as the

atomic weight. Now also mass spectrometry can be used to look at individual atoms. Elements

in a sample. And we can even break apart big macromolecules and look at the fragments that

are found within that. Or molecules within it. And so if we look at a basic mass spectroscope,

what we're going to see are three parts. We're going to have a ionizer. A mass analyzer.

And then a detector. And so let's look inside the ionizer. What are we going to find? Well

the first thing we're going to find is it's a total vacuum. In other words this doesn't

work unless we remove all of the gas particles that are found inside the mass spec. The next

thing we're going to do is we're going to insert our sample in. That could be a solid.

It could be a liquid. It could be a gas. But we're going to inject it into this ionizing

tube. And then we're going to hit it with electrons. And so we're going to move electrons

through the sample. And so there's a little cathode ray tube. It produces all of these

electrons. What it's going to do is it's going to pull electrons away from the sample. And

then as it does that it's going to create a number of positive ions. And so we're going

to ionize that sample inside here. Remember it's still the sample, it's just ionized.

It's lost its electrons. And so now we move to the mass analyzer. That's really only going

to have two parts in it. It's going to have an electrical field. You can see that's negative

because we want to move the ions into the mass analyzer. And then we're going to have

a magnet. And what that magnet is going to do is it's going to bend the path of the ions.

And so as we're bending the path of the ions, it's just like driving around a corner. If

you're really heavy it's harder for you to make a corner, let's say if you're in a big

semi truck. But if you're in a little motorcycle, it's easier to make it. And so this is where

we're going to figure out the difference between the mass of those ions. And then finally we

have a detector. That detector is going to be made up of two things. We're going to have

an electron multiplier which is essentially a plate. As an electron hits it, it spawns

more electrons which hit the next plate, which spawns more electrons. And so we can really

have a small amount of ions or anything hitting that plate and we're going to get a signal.

Now that signal has to be amplified, but eventually we can send that into a computer. And we can

look at the spectrum coming from those different masses. And so the first thing you have to

do is you have to calibrate the machine. What does that mean? You're going to start sending

ions through. Okay. So that ion didn't hit the detector. Why is that? It's because the

magnet is turned up too high. And so we're going to have to lower the strength of that

electromagnet. We run another ion. Okay. Now the magnet's not quite strong enough. And

so now we run another ion. Another ion. Another ion. Okay. So we've calibrated it. And so

it seems like it's working well. Which of these would be heavier? Well the ones that

are heavier are going to be the ones that can't quite make the corner. And so they're

going to end up out here. And then the light ions are going to end up right here. Now let's

actually get to some sampling. And so this is what it's going to look like when we create

a spectrum. We're going to have the different weights across the bottom. And then we're

going to have the intensity. And so wherever the intensity is high, we're going to have

peaks. That means we have a lot of ions that are with that specific atomic weight. And

let's try chlorine. So we're going to put chlorine through here. Chlorine really only

has two stable isotopes. It's going to have chlorine 35 and 37. And so let's watch and

see what happens as we send this chlorine through the mass spec. Okay. So what did we

find? Well there's really only two types of ions. And so we're having two peaks. Which

one is going to be the chlorine 37, which one is going to be the heavier ion? Well that's

going to be this one right here, because it wasn't bent as much using that magnet. And

if we look back at that, let's look at those ions flow again. So you can see that chlorine

37 doesn't quite make it around the corner. And which do we have more of? Well we're going

to have more of that atomic, those with an atomic mass of 35. Okay. So once we've got

that we can really figure out this average atomic mass. And so how do we figure that

out? Well I'm using values right here that I grabbed from wikipedia. So here are going

to be the two stable isotopes that we have of chlorine. Here's going to be their mass.

Their actual mass. So that's based on the number of protons, neutrons and electrons

inside it. And then this is going to be their abundance. In other words it's around 75 percent

of chlorine 35. And around 25 percent of chlorine 37. And that's why this peak is going to be

three times the height of this peak, if you're looking at a spectrum. So how do we figure

that out? Well that average atomic mass, sometimes referred to as the atomic weight, is simply

going to be the mass times the abundance. Plus the mass times the abundance. And so

in this case since we only have two isotopes, we're just going to only have two values here.

But if we had a lot of isotopes we're just going to have more mass times abundance, mass

times abundance. We just add on like that. So let's throw in the values here. So we've

got mass A which is going to be 34.97. And we're going to take that times it's abundance

which is around 75%. We then take the other isotope which is chlorine 37. And times its

abundance. And what we get is 35.45. And that's what's going to be on the periodic table.

And so when you're looking at those values on the periodic table, what you're looking

at is the average atomic mass. And they've figured that out by looking at the natural

abundance. Okay. Now what's important is a mass spec that can be used for other things.

Not only for atoms and isotopes within individual or isotopes within an individual element,

but we could look at atoms within a molecule. And we can even look at fragments within macromolecules.

And this right here is myoglobin, which is a massive protein. And what we can do is we

can send it through a mass spec. And what we can figure out is all the amino acids that

are found within it. And so remember wherever the peaks are going to be little bit higher,

then we're going to have more of that amino acid. And so usually what they measure this

in is m to z, which is a mass to charge ratio. And so did you learn this? How to use data

from a mass spectrometry to identify elements? And mass of individuals atoms in an element?

Remember it all ends up on that curve. And if you can make the curve or not is going

to be based on your mass. We can look at a spectrum from that to figure out their abundance.

And I hope that was helpful.