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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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1answer
72 views

Impact of flow rate on peak areas in Mass Spectrometry

As a follow up to the discussion in comments: it's now clear that UV peaks will have larger area if flow rate is decreased, because the same portion of molecules are measured again and again. With ...
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1answer
69 views

What is the mass of a proton?

My textbook explains that the deviation from integer atomic mass is caused by mass difference between proton and neutron, which are $1.67262·10^{-27}$ kg and $1.67493 ·10^{-27}$ kg, respectively. If ...
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Mass spectrometer Ions with same mass/charge ratio but different charges [closed]

The mass spectrometer identifies ions based on mass/charge ratio. What happens when two ions have the same mass/charge ratio but different charges or masses?
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2answers
137 views

What is the difference of spectra of EI-MS and ESI-MS/MS?

I want to ask not difference about the principle or applicability to GC and LC, but the peak behavior of spectra. EI is hard ionization method, so there occurs many fragments, sometimes losing ...
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104 views

Why is the base peak of my MS spectra of 2,3,5-tribromothiophene at m/z=382?

I recently requested a tandem MS analysis of 2,3,5-tribromothiophene and got this spectrum: These are the analysis conditions: Detector: ESI(+) Source Tem: 150 Capillary voltage: 1.5 kV Cone Voltage:...
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1answer
131 views

Relative abundance of mixture in mass spectra

In MS, as far as I know, the $y$-axis, relative abundance means the number of ions detected. Then does ratio of heights of two peaks stand for molar ratio, not mass ratio For example, given that I ...
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44 views

Does the Atomic Mass listed for each element on the periodic table reflect the relative abundances of their isotopes on Earth? Or in the Universe? [duplicate]

Somehow, I cannot find a site or book or paper explaining exactly how the average atomic masses for the elements on the periodic table are weighted.... I posted a question either here or on Physics S....
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1answer
48 views

Can ions of a pure substance be obtained in only gaseous form? [closed]

I was studying mass spectrometry where I learned that the sample is first vaporized before ionization. And ions are formed in gaseous from in an ionization chamber. Why is there need of vapourizing ...
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30 views

Can acetone be used as a GC–MS solvent for a sample containing ammonia?

Сan acetone be used as a GC–MS solvent/diluent for a sample containing ammonia? Will there be a reaction between these two species?
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1answer
41 views

What exactly is causing analyte protonation in electrospray ionization MS?

I commonly see explanations that the presence of acid in the mobile phase is a source of protons for the analyte, and that you should be multiple pH units below the pKa of the analyte, but in practice ...
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1answer
50 views

How is electron-impact mass spectrometry data formally reported?

NMR data has the following format when reported in a paper: How would I go about reporting my EIMS data formally? I tried looking for documents online but couldn't find anything.
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3answers
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Why do I see two peaks for methyl salicylate in my GC–MS spectrum?

I ran a neat sample of methyl salicylate (CAS: 119-36-8) on the GC–MS and used $m/z~120$ as the quantifier and $m/z~92$ and $152$ as qualifiers. Below is the SIM spectrum for these ions, with two ...
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46 views

Why is atomic mass unit/unified atomic mass defined against Carbon 12?

I have searched the web all over this question and I have not really found an answer to my satisfaction. From my understanding of the topic so far, I understand that reason why concept of unified ...
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1answer
642 views

What are quantifier and qualifier ions in mass spectrometry data for GC-MS or LC-MS?

I've read that one should pick an ion peak that is unique to an analyte for quantification purposes and then pick at least 2 qualifier peaks and use their ratios to identify the analyte (or avoid ...
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1answer
56 views

Prediction/computation of mass spectral ionisation intensity

There are quite a few approaches (ranging from empirical additive rules based on presence of functional groups to full blown in silico QM calculations) to predicting molecular properties such as UVmax ...
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1answer
136 views

Why do dihaloalkanes lose both halogen atoms during mass spectrometry?

I was looking through mass spectrums of haloalkanes and found the one for 1,2-dibromobutane confusing: The base peak is at 55 m/z, and the only fragment I can think of with that ration will be $\ce{...
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1answer
54 views

What are the benefits of using zero capillary voltage for discarding fractions in LC–ESI–MS/MS?

In the second episode of The Association for Mass Spectrometry & Advances in the Clinical Lab (MSACL) podcast, namely Getting going with mass spectrometry : Josh learns chromatography (aired 2021-...
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58 views

Finding the structure based on spectra

I had to identify the structure of a drug based off the spectra I had. I suck at this. I gave it my best go and got some ugly structure, only to check it using a database and find out I was wrong. I ...
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1answer
66 views

Does using same calibration curve for chemical analysis introduce correlation in sample error/uncertainty values?

I am using a hypothetical case to explain my question Let us consider a chemical analysis method A (using a certain instrument), which is used to quantify the value of a particular species b. ...
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0answers
43 views

1,5-Pentanediol MS

I'm having troubles assigning the signals m/z = 41 and 56 of the compound 1,5 pentanediol. I tried the basic fragmentations (McLafferty, loss of OH radical, etc.) but I can't figure the structure of ...
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1answer
83 views

Detecting impurities in polyethylene glycol 3350

I would like to test samples of polyethylene glycol 3350 ($\ce{H−(O−CH2−CH2)_n−OH}$ with an average molecular weight of 3350, so n is around 75) to determine if there are any impurities and if so the ...
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1answer
156 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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34 views

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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1answer
97 views

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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137 views

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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54 views

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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1answer
216 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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1answer
135 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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1answer
146 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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1answer
83 views

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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1answer
87 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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312 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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1answer
173 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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1answer
47 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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80 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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0answers
195 views

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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0answers
111 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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1answer
115 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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0answers
166 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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0answers
33 views

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
35 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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2answers
473 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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1answer
91 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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0answers
28 views

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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1answer
135 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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1answer
236 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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1answer
59 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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1answer
203 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 ...
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2answers
97 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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1answer
90 views

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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