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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5
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2answers
104 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
84 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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31 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 ...
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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." This is a ...
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1answer
453 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
36 views

Ensuring constant ionisation of transition metals using plasma ionisation for accurate mass spec

Mass spectrometry depends on separation of the analyte based on mass to charge (m/z). ICP-MS is used to detect metals, but under the plasma conditions many of these metals could be ionised multiple ...
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1answer
32 views

Why do impacting electrons have a low probability of causing ionization?

In a section on ionization efficiency and ionization cross section, my mass spectrometry textbook, Mass Spectrometry by Jürgen Gross [1, pp. 38–39], says the following: The ionization energy ...
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2answers
51 views

What is the difference in Da of ESI analytes with multiple charges?

This is a follow-up question to Why are isotopes an issue in reading mass spectra? A follow-up question: electrospray ionization (ESI) produces multiply charged species and charge can be >40 (for the ...
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I need to identify the peaks in this boron mass spectrum

As part of a bigger project we were given this image. Its a mass spectrum produced in an accelerator with a Boron cathode. It was implanted in diamond. I assume the first peak is just $B^-$ but I have ...
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30 views

Calculating Sensitivity in Mass Spectrometry

My mass spectrometry textbook gives the following example: Calculating sensitivity Magnetic sector instruments are specified to have a sensitivity of about $4 \times 10^{-7} C \ \mu g^{-1}$ for the ...
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682 views

Why are isotopes an issue in reading mass spectra?

It is my understanding that the isotope distribution for carbon and hydrogen, for example, are skewed heavily toward one species, i.e., one isotope accounts for ~99% of the abundance of the element in ...
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1answer
53 views

why do atoms need to be ionised in a mass spectrometer? [closed]

why do atoms need to be ionized in a mass spectrometer? why can't you determine the mass of the atoms when they are not ionised? Also what is the mass-to-charge ratio
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1answer
105 views

What do we learn from an isotope peak (or M+2 peak) in a mass spectrum?

Mass spectrum of a molecule showed molecular ion peak and its isotopic peak in 1:1 ratio. What is the possibility of the atom present in the molecule? Since it is mentioned that it has a ...
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2answers
75 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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45 views

Ionisation of a gas - from gas to plasma

Is it possible to ionise a gas such as Carbon Dioxide? If you continue to heat up a gas eventually the electrons from the gaseous atoms are stripped away and those e- gain energy (endothermic reaction)...
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1answer
42 views

Can amide bonds fragment in ESI-MS?

Electrospray Ionization Mass Spectrometry(ESI-MS) is a technique in mass spectrometry to get an idea about molecular ion peak. In the ESI-MS spectra of an amide compound, I observed that the molecular ...
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28 views

Isotope labeled experiment analysis

I'm analyzing a dataset generated with LC-MS from cells that were fed $\ce{^13C}$-Glucose. There are 3 groups in total each with a different media conditions. My goal is to identify differences ...
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1answer
31 views

Determine Empirical Formula from Molar Mass? [closed]

I am trying to write a computer program that predicts the empirical formula of a compound based only on that compound's mass, like what you would get from a high resolution mass spec. I have the ...
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17 views

Finding Pressure of M in a Charge Exchange

Ar (RE = 15.5 eV) is the reagent gas in a charge exchange experiment. If Ar+ reacts with anisole with a rate constant of 2.26x10-10cm3 molecules-1/s-1 and 65% of the Ar ions react in 25 milliseconds, ...
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41 views

Kinetic Shift of Simple Cleavage

What is the kinetic shift for the simple cleavage fragmentation if the ion source residence time is 100 microseconds, the time to reach the detector after leaving the ion source is 10 microseconds? (...
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1answer
43 views

Determining ratio of competing fragmentation processes in mass spectrometry

In a photoionization experiment, three photons of wavelength 266 nm were absorbed by a neutral molecule of 6-methyl-2-heptanone. If the kinetic energy of the electron removed during ionization is 1.4 ...
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1answer
38 views

Defining sensitivity of TOF Mass Spec - Does the detector play a role?

Looking at TOF MS systems, my current understanding is that temporal resolution results in mass resolution - so by controlling the flight time (with distance) and sampling rate, you can start to ...
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509 views

Why is a very small peak with larger m/z not considered to be the molecular ion?

With regards to the following spectrum: When asked for the M/Z for the molecular ion, the peak at 58 was taken, not 59. What causes the peak at 59, and why isn't it taken as the molecular ion?
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Why is it vital that atoms in the same sample are all given the same charge? Mass spectrometry

When being tested in the spectrometer why is it vital that the atoms in the same sample are given the same electrical charge e.g all are c+1 or all are +2 etc
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105 views

How to identify the structure of an organic acid based on its reactivity, mass and NMR spectrum?

Taken from OCR A Chemistry Unified Chemistry Sample Paper. Information about a monobasic organic acid D is shown below. D reacts by both electrophilic substitution and electrophilic ...
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1answer
35 views

Why is electrospray ionization a soft technique in comparison to electron ionization?

I know that electrospray ionization (ESI) is a soft ionization technique and that electron ionization (EI) is not, because it causes a great amount of fragments in a fast time due to the fact that a ...
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2answers
47 views

Is there a way to search for adducts by exact mass? [closed]

We found an unknown of exact mass 217.082. Is there a tool that one can search by an exact mass get a list of possible compounds. We have considered desmethylnaproxen as a possibility, but found its ...
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Impediments to GC-MS characterization of petroleum products

In an attempt to characterize, and sometimes to 'match' oil on feathers of birds, a laboratory utilize gas chromatographic - mass spectrometry. Persons likely to encounter oiled birds are advise to ...
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1answer
23 views

How do electrostatic analysers act as kinetic energy analysers?

Consider a mass spectrometer. The ions produced are accelerated across a potential V. Now, the kinetic energy of an ion with charge q is given by qV. When it enters the analyser with electric field ...
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22 views

Comparing collision energy formats in the NIST 17 MS/MS library

In the NIST 17 MS/MS library, collision energy can be represented as a positive integer (i.e. 1,2,3,...), a percentage (i.e. 35%), or a floating point number (i.e. 7.3 eV). How can I compare these ...
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1answer
110 views

Predict NMR spectra from the Mass Spectrometry

Imagine, you have a tissue and the Mass Spectrometry for it. How would you get the corresponding NMR spectra knowing only the Mass Spec? Is there is a special formula or a well-known technique? I ...
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2answers
415 views

Exceptions to the Nitrogen Rule in mass spectrometry

The Nitrogen Rule in mass spectrometry states that (organic) molecules containing no or an even number of nitrogen atoms will have even masses, and molecules containing an odd number of nitrogen atoms ...
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1answer
333 views

How can I interpret the CH4+ structure?

I am trying to teach myself about Electron Ionization, and am very confused about the formation of the CH4+ Ion. Do the dotted lines between the C and the H, and between the two Hydrogens indicate a ...
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1answer
57 views

How do I get Mass spectrometry graph, history, and Infra-red spectroscopy graph for Secnidazole?

My chemistry teacher wants me to create an academic poster for a recently-discovered biologically important organic molecule with chirality that is relatively small and is also recent. Secnidazole (...
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35 views

Can catecholamines be quantified by HPLC-MS/MS at high pH?

It seems that most HPLC-MS/MS methods used for quantitation of catecholamines (epinephrine, norepinephrine and dopamine, specifically) operate at low pH (commonly 3.0), and therefore demand the ...
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1answer
105 views

Where can I find example MS, IR, NMR spectra for teaching molecular spectroscopy?

I am teaching a course on analytical chemistry, and I would like to give my students MS, IR and NMR spectra to practice with. It would be ideal if they could analyze spectra in a more "realistic" way ...
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How does the “sample type” selection on the MassHunter software for Agilent 7900 ICP-MS affect the quantitative results?

I'm new to using the instrument, and recently I have tried to measure Cr in both the eluent(1% nitric acid) and a method blank (also 1% nitric acid, but after it has gone through the entire analytical ...
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70 views

Differences between LIBS over LA-ICP-MS? [closed]

Which differences should I consider between the techniques Laser-Induced Breakdown Spectroscopy and Laser Ablation Inductively Coupled Plasma Mass Spectrometry for a geochemistry fingerprint focused ...
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1answer
112 views

organic spectroscopy: n-phenethylacetamide base peak ion [closed]

This is the n-phenethylacetamide mass spectrum His base peak ion is at 104 m/z. I have long been thinking about what its structure might be, but with a m/z ratio of 104 I can not think of anything ...
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1answer
871 views

What is the structure of 92 m/z fragment for aspirin

Aspirin has the following structure: What would the fragment structure be for m/z = 92? Even though $\ce{C6H4O}$ is a molecular structure with mass 92, I don't think this will be formed since two ...
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1answer
205 views

What is the identity of the unknown compound using GCMS and NMR?

I've been asked to identify an unknown compound by performing several analytical techniques on it. The compound was a white powder and had a boiling point of 65 degrees celsius. I have the GC mass ...
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2answers
207 views

Non-Scanning Mass Spectrometry

Does anyone do mass spectrometry with a magnetic sector to separate ions by mass and an array of detectors in a line to measure the ions? If not, why don't they? Something like this this setup for ...
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1answer
51 views

What happens to the “leftover” Ions in the Mass Analyzer

I am very intrigued by what happens to the ions which do not make it to the detector in mass spectrometers, do they just pile up? I have never seen anyone clean our quadrupole, is this done? or do ...
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1answer
87 views

How isotopes atomic mass was defined?

So we say that 1 Amu (u) = 1/12 of the mass of a Carbon 12 atom. Im not sure about this, but I believe that first we measured the mass of 1 carbon 12 atom (This includes the mass defects that occur ...
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2answers
111 views

In the mass spectrum of niacin (3-pyridine-carboxylic acid), what ion corresponds to the peak at m/z = 105?

The mass spectrum can be found here. I am interested to know what ion this is and why the peak at $m/z = 105$ is higher than the peak at $m/z = 106$ (which I believe corresponds to $\ce{C5H4NCO+}$).
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What is the relative size of the (M+2) peak?

The $(M+1)$ peak is often considered in the high-resolution mass spectra of organic molecules as it reveals the number of carbon atoms in the sample. In general, it is known that the ratio of the size ...
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1answer
350 views

Question regarding cone voltage on mass spectrometers

Why is the cone voltage on mass spectrometers +ve for +ve ions? I would have thought that the +ve ions would be attracted to the cone by a -ve potential. Is the voltage, perhaps, indicative of ...
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1answer
115 views

Quadrupole MS: mass as a function of voltage

Every time I see an article about Quadrupole MS (e.g. here), they give formulas like: $$ a_x = \frac {8eU} {m r_0^2 \Omega^2} $$ and $$q_x = - \frac {4eV} {m r_0^2 \Omega^2}$$ I suppose the ...
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2answers
2k views

Why is the probability for the signal at 160 in the bromine mass spectrum twice as high as for the signals at 158 and 162?

The mass spectrum in Bromine, with the molecules $\ce{^{158}Br2+}$, $\ce{^{160}Br2+}$ and $\ce{^{162}Br2+}$: As you can see, the $\ce{^{160}Br2+}$ is almost double in intensity compared to the $\ce{^{...
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1answer
46 views

In ESI-MS, why do we assume that the positive charge on the analyte must come from protonation from the solvent?

In ESI-MS, we ionise the molecules using a high voltage. Why wouldn't this high voltage cause the ejection of an electron from the analyte itself, generating a M+ ion. Why do we have to assume the the ...