Questions tagged [mass-spectrometry]

Mass spectrometry (MS) is an analytical technique which takes advantage of the mass-to-charge ratio of gas-phase ions in order to elucidate the composition of a sample.

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17 views

How can mass spectrometry be used to determine concentration?

Which forms of mass spec will determine accurate concentrations of metal ions in a sample? Preferable not using GC/MS but can MALDI ToF or quadrupole do this somehow. Also, not relative concentration ...
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How would you examine samples of rocks using a handheld spectrometer?

My friend has an old spectrometer set that his father used to own and we are trying to figure out how to use it. Asking his father about it is not an option unfortunately. The box contains a handheld ...
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Stubborn CuAAC reaction as derivatization for ESI-MS

Problem description I have a substance that is extremely non-polar and therefore does not ionize in the ESI source, which makes it impossible to quantify small amounts. The substance contains only two ...
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Do some particles get ionised to 2+ or higher in a mass spectrometer or do they only get ionised to 1+?

In a mass spectrometer the sample is vapourised, then ionised, then accelerated. My textbook says that the high energy electrons from the electron gun knock electrons off the sample molecules and ...
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How long does it take to run an MS/MS experiment

I am not planning to do these types of experiments but I would like to know the order of magnitude of the time it takes to run an LC-MS/MS experiment. Let's assume that I have the sample prep (protein)...
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What are the fragments that result from taking the Mass Spectrum of o-fluronitrobenzene?

I am doing my online lab, and we are on mass spec right now. I am having a very tough time figuring out the shape of the fragments of o-fluronitrobenzene, especially the large peaks. Especially the ...
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Explaining base peak for but-3-en-1-ol mass spectrum?

The mass spectrum for but-3-en-1-ol shows 42 as the base peak, but I don't know how this fragment ion is generated. I would expect the most favorable fragmentation to occur between C1 and C2, but ...
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32 views

1/8 instead of 1/12 of mass of carbon atom as relative atomic mass [closed]

If we consider that 1/8 in place of 1/12 mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will: (1) Decrease by 1.5 times (2) Increase by 1.5 times ...
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49 views

Confused on the peak intensities in this mass spectrometry problem

A problem from Introduction to Spectroscopy by Pavia et al. [1, p. 137]: *4. An unknown hydrocarbon has a molecular ion peak at $m/z = 84,$ with a relative intensity of $31.3.$ The $\ce{M + 1}$ peak ...
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92 views

Using the right equipment for successful detection of Novichok [closed]

Apparently, Navalny’s biomaterials were flown to Moscow's Nii Sklif lab which didn't find any traces of the poison. But they used an American Agilent Technologies GC-MS [1], while Bundeswehr ...
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128 views

Behavior of Natural Abundance and Mass Spec Ratios

The presence of sulfur in a mass spec is 96% and 4%. I believe this to be because the natural occurrence of sulfur isotopes are within these proportions. However, chlorine behaves in a 66%/33% ratio ...
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501 views

Cone voltage on mass spectrometers

Why is the cone voltage on mass spectrometers positive for positive ions? I would have thought that the positive ions would be attracted to the cone by a negative potential. Is the voltage, perhaps, ...
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107 views

Why does the heat of formation of organic radicals and positive ions decrease with their size and degree of branching at the radical or ionic site?

I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following: The heat of formation ...
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50 views

Meaning of “MS1 and MS2 resolution” and “MS1 and MS2: Unit” in a tandem mass-spectrometry parameter list

I'm translating a Certificate of Suitability that very briefly describes procedures used to measure several impurities in a drug substance. There is a short description of the parameters of a Gas ...
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547 views

Which unit should I use for m/z?

I've written m/z 300 - 1100 Thomson in my paper, but the reviewer said that the Th is already deprecated. So in this case, should I write m/z 300 - 1100 Da? or something else?
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117 views

How did Thomson calculate the momentum of electron when he didn't know the mass of electron?

This was proven in 1903 by J. J. Thomson who calculated that the momentum of the electrons hitting the paddle wheel would only be sufficient to turn the wheel one revolution per minute. source J. J. ...
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218 views

Differences in Novichok agent mass spectra

As we have all heard, in 2018, a series of poisonings with a nerve agent alleged to be of the Novichok series was carried out on British soil. It is claimed that the agent used was A-234. However, a ...
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167 views

Stronger ESI signal for deuterated substances

I observe a constant phenomenon in my ESI measurements, which indicates that deuterated substances give a stronger signal than the same substance in non-deuterated form. Unfortunately I can't make any ...
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38 views

On the detection of molecules in electrospray ionisation (ESI)

Of the ESI spectra that I have encountered, positive & negative mode, the detected species always have charge (positive or negative) corresponding to the charge mode that the machine is in. Is it ...
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69 views

How can I simulate chromatograms and spectra?

Is there a tool which allows to generate simulated chromatogramms and spectra and export it into a mzML file? There is e.g. psims which allows to write mzML on a ...
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1answer
618 views

Predicting isotope patterns in mass spectrometry

Imagine you have a mixture of $\ce{^1H}$, $\ce{^2H}$ and $\ce{^3H}$ (hydrogen, deuterium and tritium) present as diatomic molecules and that the numbers of the atoms of the three species are the same. ...
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Identifying unknown compound using mass spectrum

I am currently studying the textbook Mass Spectrometry - A Textbook, third edition, by Jürgen Gross. In chapter 1.4.5 Statistical Nature of Mass Spectra, there's a following example: It is important ...
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27 views

Relative intensities are basically independent from the absolute ion abundances registered by the detector?

I am currently studying the textbook Mass Spectrometry - A Textbook, third edition, by Jürgen Gross. Chapter 1.4.4 Mass Spectrum says the following: The most intense peak of a mass spectrum is called ...
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68 views

Peak broadness and artifact peaks in intact antibody MS?

I am having an issue where the MS for my antibody (intact/nonreduced, deglycosylated by PNGase) shows multiple clusters of what appear to be ghost peaks after deconvolution, and the main peak is ...
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59 views

Why do we subtract the mass of one proton in mass spectrometry (negative mode)?

This is probably very basic, but I have been given the understanding that we subtract the mass of only one proton when looking for our compound in a mass spectrometry (negative mode). I dont really ...
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34 views

Disadvantages of SIM vs TIC in GC-MS [closed]

In GC-MS what are the relative advantages/disadvantages of using Selected-Ion Monitoring (SIM) vs using Total Ion Chromatograms (TIC)? I know that SIM offers a better S/N ratio, however if the S/N is ...
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109 views

Software platforms with integration of multi vendor mass spectrometer device data?

I know about ACD/Spectrus Processor which is a software platform to integrate analytical chemistry data from multiple mass spectrometer device vendors (e.g. Agilent Technologies, Bruker, Waters) to ...
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How does the mass composition affect the empirical formula? [closed]

I have to do an assignment of empirical formula, and how different percentage mass compositions affect the formula obtained, from experimental data. We did three trials and 2 of which of the same ...
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1answer
31 views

Conversion factor for chemical to physical scale of atomic masses

Before the 1960s chemists and physicists used to have different atomic mass tables. The main difference was that the physicists assigned the $^{16}$O as the O=16 from mass spectrometry. Chemists on ...
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92 views

Why we need the average atomic mass? [closed]

I know , Average Atomic Mass of an element is - the sum of the Masses of its isotopes,each multiplied by its Relative Abundance percentage (in decimal notation). But what confusing me is, what is ...
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51 views

Cause of m/z = 56 peak in 4-methyl-1-pentanol

This is the mass spectrum for 4-methylpentan-1-ol: From its structural formula, what could be the fragmentation which results in a peak at $m/z = 56?$ I was considering a few possibilities; could it ...
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Why doesn't laser ablation decompose sample

I was reading up on LA-ICP-MS and MALDI. All the sources I read for LA-ICP-MS simply say that when the laser hits the sample immediately goes into the gas phase. Why doesn't the laser immediately ...
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106 views

What am I doing incorrectly with this IR/ Mass spec data? [closed]

Hello, I am trying to determine the chemical formula for the following compound. From the IR spec, I see there is a carbonyl present. Moving on to the mass spec, I see an M+ peak of 142, with what ...
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197 views

Peak at m/z = 39 in mass spectrum of 3-chloropropene

I've noticed that in the mass spectrum of 3-chloropropene, there is a peak at m/z = 39, which to me, indicates the formation of the C3H3 ion. However, given that 3 bonds would have to be broken to ...
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47 views

Amide fragmentation of salicylamide

I want to ask a question about the fragmentation of the $\ce{M_17}$ peak of Salicyclamide to a phenolic fragment. I was reading the following paper giving a profile about salicyclamide. I want to ...
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111 views

Heats of formation of neutral molecules and homolytic vs heterolytic bond dissociation in mass spectrometry

I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following: Great efforts have been ...
2
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1answer
107 views

Conditions for choosing quantifying and qualifying ion in LC-MS/MS

In my PhD-work, we are trying to develop LC-MS/MS methods for targeted analysis. Usually, I determine my quantifying ion/fragment based on a few different criteria: If there is a 13C internal ...
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74 views

How do we weigh one C atom? [closed]

As far as I get it, we did weigh one carbon (12,6-isotope) atom. Then we said that electrons have nearly zero weight and protons weight nearly the same as neutrons. Hence we took the weight of that ...
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Calculate the mass of iron in the original mixture!

I seemingly can't solve the following problem, I've spend over 30 mins on it, no progress, can any of you geniusses give a step by step solution to me? Thank you so much Problem: A mixture of ...
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How can the formula of WD-40 remain a trade secret?

Wikipedia says WD-40's formula is a trade secret How can it remain a secret today? Can't mass spectrometers, NMR and other equipment be used to determine the structure of the compounds that go ...
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550 views

Mass Spectra: 1-pentanol vs 3-pentanol

In mass spectrometry, 1-pentanol can be observed to have no peak at $m/z = 59$, whilst 3-pentanol can be observed to have a peak at $m/z = 59$. Clearly the 3-pentanol peak at $m/z = 59$ is due to the ...
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1answer
47 views

How does a mass spectrometer treat ions? [closed]

I always thought that in a mass spectrometer all the ionized fragments were going in the quadrupole at the same time, and then this quadrupole was sorting them by ratio. But last week I learn that a ...
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How is the distance between m/z axis values in mass spectrums called?

The output data of mass spectrometers is relative intensity (y axis) over m/z (x axis). How is the distance between m/z values on the x-axis called (in case of centroided data and profile/raw data ...
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How do I figure out how many hydrogens my compound actually has using a mass and NMR spectrum?

Question 3: It said $m/z = 122,$ and $m/z = 124$ is in a $3:1$ ratio, so I figured that meant that chlorine is present. Then I thought $m/z$ was the actual compound's molecular mass. So I used ...
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71 views

Identifying Structure based off 1H-NMR & Mass Spectroscopy Data [closed]

I have almost the whole night trying to identify this structure with no avail as there is always one part that does not fit. The determined formula for this structure was $\ce{C13H17BrO}$ from the $m/...
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876 views

How Does Benzyl Alcohol Produce a Peak at m/z = 79?

I have understood the mechanism for converting ion 1 (benzyl alcohol) to ion 2 (m/z = 107) but not the mechanism for the conversion of ion 2 to ion 3 (m/z = 79). Please elaborate the mechanism for ...
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1answer
141 views

Choosing LC-MS modifier - why only acids?

During method selection our chromatographists have options like NH4, TFA, Formic Acid. What's the point of choosing only between acid? Why not use the strongest that guarantees ionization? The sample ...
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52 views

Increasing concentration of acetylcholine via SPE

I am trying to increase the final yield of acetylcholine (ACh) in my biofluid samples. I need to get the yield high enough for high confidence annotation of ACh (currently all I can really say is that ...
5
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1answer
2k views

Difference between HCD and CID collision induced dissociations?

With the Thermo-Fisher Fusion Orbitrap mass spectrometer I can do both CID (collision-induced dissociation) and HCD (higher energy C trap dissociation) collision-induced dissociation studies. When I ...
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1answer
2k views

In a mass spectrum, how can the sum of relative abundances be greater than 100?

I apologise if this seems a very simple question, and also if I am overlooking something that is very simple. For part of my A Level course, we have to be able to interpret mass spectrometer readings ...