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Updated Mar 22, 2026
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Introduction to Mass Spectrometry: Basics and Applications
Florence Thomas
@florencethomas_cxht
1 / 4
How Mass Spectrometry Works
Ever wondered how scientists identify mystery substances? Mass spectrometry is like a molecular fingerprinting system that reveals exactly what's in a sample. The process starts by turning particles into ions (charged particles), then accelerating and deflecting them through the instrument.
The key to understanding mass spectrometry lies in the mass-to-charge ratio . Heavier isotopes have larger m/z values, so they follow wider curved paths when deflected. Since most ions carry a 1+ charge, the separation mainly depends on their mass.
Here's something interesting: if an ion picks up a 2+ charge instead of 1+, it gets deflected more because its m/z ratio is halved. The abundance stays the same, but the signal appears at a different position on the spectrum.
Quick Tip: Remember that doubling the charge halves the m/z ratio - this often catches students out in exam questions!
Calculating Isotope Percentages
Sometimes you'll need to work backwards from the average relative atomic mass to find isotope percentages. This is easier than it looks once you know the method. Take bromine with isotopes of mass 79 and 81, and an average atomic mass of 79.908.
Set up the equation: if x% is ⁷⁹Br, then % must be ⁸¹Br. So: 79x + 81 = 7990.8. Expanding this gives: 79x + 8100 - 81x = 7990.8, which simplifies to -2x = -109.2.
Solving gives x = 54.6, meaning ⁷⁹Br is 54.6% and ⁸¹Br is 45.4%. The key is setting up the algebra correctly and remembering that percentages must add up to 100.
Exam Hack: Always check your percentages add to 100% - it's an instant way to spot calculation errors!
Understanding Relative Masses
Relative isotopic mass compares the mass of one specific isotope to 1/12th of a carbon-12 atom. Think of carbon-12 as the universal reference point - like using metres to measure length. Relative atomic mass is the weighted average of all isotopes of an element.
Relative formula mass (RFM) is simply the sum of all atomic masses in a compound. For NH₃, you add nitrogen (14) plus three hydrogens (1+1+1) to get 17. For more complex compounds like Al₂(SO₄)₃, count each atom carefully: 2 aluminium, 3 sulphur, and 12 oxygen atoms.
Hydrated compounds like CuSO₄·5H₂O include water molecules in the calculation. The dot means the water is loosely attached, but you still count all the atoms when calculating the RFM.
Memory Trick: Write out each atom individually when calculating RFM - it prevents you from missing atoms in brackets!
Time of Flight Mass Spectrometry
Time of flight spectroscopy is the most common type of mass spectrometry you'll encounter. The entire apparatus operates under vacuum to prevent ions colliding with air molecules, which would mess up the results.
The process has three main stages: ionisation, acceleration, and ion drift. During ionisation, the sample dissolves in a volatile solvent and gets forced through a needle connected to high voltage. This creates tiny charged droplets that eventually become single positive ions.
All ions receive the same kinetic energy during acceleration, but heavier particles move slower than lighter ones. As ions travel down the flight tube, they separate based on their speed. The detector measures their arrival time and converts this into electrical signals.
Finally, a computer processes these signals to generate a mass spectrum - essentially a graph showing which masses are present and in what amounts. The whole system works because lighter ions reach the detector first.
Real-World Connection: Mass spectrometry is used everywhere from drug testing in sports to identifying explosives at airports!
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Elisha
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This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Introduction to Mass Spectrometry: Basics and Applications
Florence Thomas
@florencethomas_cxht
Mass spectrometry is a powerful analytical technique that scientists use to identify unknown compounds and determine the composition of elements. It works by turning particles into ions, accelerating them, and measuring how they deflect based on their mass-to-charge ratio.
How Mass Spectrometry Works
Ever wondered how scientists identify mystery substances? Mass spectrometry is like a molecular fingerprinting system that reveals exactly what's in a sample. The process starts by turning particles into ions (charged particles), then accelerating and deflecting them through the instrument.
The key to understanding mass spectrometry lies in the mass-to-charge ratio . Heavier isotopes have larger m/z values, so they follow wider curved paths when deflected. Since most ions carry a 1+ charge, the separation mainly depends on their mass.
Here's something interesting: if an ion picks up a 2+ charge instead of 1+, it gets deflected more because its m/z ratio is halved. The abundance stays the same, but the signal appears at a different position on the spectrum.
Quick Tip: Remember that doubling the charge halves the m/z ratio - this often catches students out in exam questions!
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Calculating Isotope Percentages
Sometimes you'll need to work backwards from the average relative atomic mass to find isotope percentages. This is easier than it looks once you know the method. Take bromine with isotopes of mass 79 and 81, and an average atomic mass of 79.908.
Set up the equation: if x% is ⁷⁹Br, then % must be ⁸¹Br. So: 79x + 81 = 7990.8. Expanding this gives: 79x + 8100 - 81x = 7990.8, which simplifies to -2x = -109.2.
Solving gives x = 54.6, meaning ⁷⁹Br is 54.6% and ⁸¹Br is 45.4%. The key is setting up the algebra correctly and remembering that percentages must add up to 100.
Exam Hack: Always check your percentages add to 100% - it's an instant way to spot calculation errors!
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Understanding Relative Masses
Relative isotopic mass compares the mass of one specific isotope to 1/12th of a carbon-12 atom. Think of carbon-12 as the universal reference point - like using metres to measure length. Relative atomic mass is the weighted average of all isotopes of an element.
Relative formula mass (RFM) is simply the sum of all atomic masses in a compound. For NH₃, you add nitrogen (14) plus three hydrogens (1+1+1) to get 17. For more complex compounds like Al₂(SO₄)₃, count each atom carefully: 2 aluminium, 3 sulphur, and 12 oxygen atoms.
Hydrated compounds like CuSO₄·5H₂O include water molecules in the calculation. The dot means the water is loosely attached, but you still count all the atoms when calculating the RFM.
Memory Trick: Write out each atom individually when calculating RFM - it prevents you from missing atoms in brackets!
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Time of Flight Mass Spectrometry
Time of flight spectroscopy is the most common type of mass spectrometry you'll encounter. The entire apparatus operates under vacuum to prevent ions colliding with air molecules, which would mess up the results.
The process has three main stages: ionisation, acceleration, and ion drift. During ionisation, the sample dissolves in a volatile solvent and gets forced through a needle connected to high voltage. This creates tiny charged droplets that eventually become single positive ions.
All ions receive the same kinetic energy during acceleration, but heavier particles move slower than lighter ones. As ions travel down the flight tube, they separate based on their speed. The detector measures their arrival time and converts this into electrical signals.
Finally, a computer processes these signals to generate a mass spectrum - essentially a graph showing which masses are present and in what amounts. The whole system works because lighter ions reach the detector first.
Real-World Connection: Mass spectrometry is used everywhere from drug testing in sports to identifying explosives at airports!
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user