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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47 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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60 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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29 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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27 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
114 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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53 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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32 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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26 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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38 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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33 views

Why do species not absorb an electron in mass spectrometry? [duplicate]

The following is a direct quote from my high-school chemistry text-book regarding mass spectrometry: The ionization process in the mass spectrometer involves an electron from an electron gun ...
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1answer
1k views

What is the difference between TIC and TICC?

I have picked up a textbook on mass spectrometry, and I am finding it did not clearly distinguish between total ion chromatogram (TIC) and total ion current chromatogram (TICC) in the section (1.3 Ion ...
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75 views

Possible ionization and fragmentation of chemicals

Is there any generic method where I can know/calculate/generate the possible ionization and fragmentation of a specific chemical, for example, hydrogen chloride and water? This question is actually ...
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326 views

GC-MS unexpected peaks during 1-octanol quantification

Note: This experiment was performed as part of a teaching lab experiment which has concluded, so I would not be able to alter any experimental conditions. I was also unable to modify any of the ...
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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 ...
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1answer
73 views

How to evenly ionize in mass spectrometry

I know that in mass spectrometry they charge different molecules and then run them through a magnetic field and then see where they land. Depending on this, they calculate their masses relative to ...
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149 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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1answer
3k 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
185 views

Mass Spectroscopy peak assignments in but-3-en-1-ol

i have the mass spectrum for the molecule but-3-en-1-ol. The Mr of this is 72 There are four peaks that are labelled which I have to name the species responsible for forming that peak. The peaks are:...
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1answer
64 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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2answers
76 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
42 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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1answer
66 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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2answers
825 views

GCMS Peak Identification: Online or Open Source / Free Programs?

Suppose I have a GCMS peak graph for a component, what are possible options to figure out what the molecule may be? Any tips about good software that will do this? I do know that for many compounds ...
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1answer
676 views

why do we denature proteins before mass spectroscopy?

I'm learning about mass spectroscopy in particular the use of it in analyzing protein structure. they said we have to use trypsinolysis to cut the protein to segments, but why does the protein have to ...
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1answer
250 views

Relative atomic mass

Is it possible for an element to have a calculated relative atomic mass that is higher than the relative isotopic mass of its most massive component isotope? The equation is: $\mathrm{Relative~...
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2answers
166 views

What is the process involved in performing a mass spectrometry experiment?

I have heard that mass spectrometry is very time consuming: why is this? What is the process involved in performing a mass spectrometry experiment? What steps are the most time consuming?
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51 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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1answer
1k views

Why mass spectra of 2-methylbutane do not show big peak at 71 coming from tertiary carbocation?

Mass spectra of 2-methylbutane show strong peak at 57 by loss of methyl radical to give secondary carbocation while a loss of hydrogen radical from 2-position would form tertiary carbocation with m/z =...
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2answers
97 views

How closely do GCMS spectra typically agree to conclude a match?

I have two unknown peaks on my GC (both with the same MW or rather highest M/Z ratio peak = 98) and I am trying to confirm their identity. Unknown-1 Unknown-2 Based on the expected chemistry I ...
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1answer
146 views

Minimum resolution to acquire exact mass on a spectra from m/z peak

I'm having a little difficulty with finding what the minimum resolution required to obtain the exact mass of a 400 $m/z$ peak in a mass spectrum. I would appreciate any help.
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41 views

How to control the purity and quality of fatty acids or their CoA thioesters?

Background: We are looking into getting a series of cis-mono-unsaturated very-long-chain (C20-C32) fatty acids (with different, specific double-bond positions) — and/or the corresponding acyl-Coenzyme ...
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1answer
60 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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1answer
41 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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32 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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2answers
2k views

How does mass spectroscopy of nicotine work?

Take this nicotine molecule: And this mass spectrum: I'm not sure how to explain all the peaks. This might explain the peak at 42: But can this peek als be explained by something else in the ...
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33 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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56 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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22 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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52 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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18 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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67 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
60 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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38 views

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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140 views

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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86 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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48 views

What is the best way to illustrate the recovery of an extraction method?

I'm currently working on PFAS (perfluoroalkyl compounds) extraction from soils and their analysis by HPLC-MS/MS. I wonder what kind of graph can be the best to illustrate the recovery of the method. ...
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87 views

Influence of rotational degrees of freedom on gas phase stability of ions in CID

In mass spectrometry it is possible to determine the stability of an ion in the gas phase using e.g. collision induced dissociation (CID). In CID, we fragment an ion by colliding it with a neutral ...
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931 views

What is a “tube lens” in a mass-spectrometer ion source and what does it do?

I came across the Russian phrase "Transporting capillary voltage: 85 V" in a text I was translating. The paragraph was describing the operating parameters of an electrospray ionization-based ion ...
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76 views

What causes differences in limits of detection?

I'm wondering what causes the limits of detection (LOD) to vary between different compounds, when calculated from the data obtained from one sample. I've analyzed a 0,1 µg/ml sample, containing ...
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141 views

Mass Spec - What could a loss of 28amu as the first fragmentation be?

I guess 28 could be CO, C2H4 or N2. However I can't work out a mechanism by which CO could be the first fragmentation of any common organic compound. It seems like a diazonium salt could lose N2 as ...