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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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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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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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29 views

log K vs Internal Energy Question

In a photonionization experiment the neutral molecule absorbed three 266 nm photos. If the kinetic energy of the electron removed during ionization is 1.4 eV, what is the ratio of the simple cleavage ...
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28 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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396 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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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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23 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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46 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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26 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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20 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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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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91 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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155 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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168 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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52 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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28 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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68 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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56 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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89 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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395 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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148 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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146 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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48 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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74 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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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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255 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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92 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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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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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 ...
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Would cerium(III) in solution be oxidized to cerium(IV) in ESI mass spectroscopy?

During ESI (assuming positve ion mode for now), we apply a strong voltage ($1.0{-}\pu{5.0 kV}$) to induce ionization. Therefore, it is common to see oxidation of metal ions (e.g. $\ce{Cu^{+I} -> ...
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230 views

In TOF Mass Spectrometry how does the detector 'know' the difference between ions of different elements?

After the positive ions have been accelerated, I know that they travel through the drift zone at different speeds due to their masses. But surely, a heavier ion/element that enters the drift zone ...
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157 views

Batch conversion of Waters mass spectrometry file formats

Are there any free tools for converting raw mass-spectrometry files into open formats? In particular, is there any way to convert Water's .raw MS files into a readable format in a batch-wise fashion (...
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2k views

How many peaks of HCl are found in a mass spectrum?

In a mass spectrometer some hydrogen chloride molecules will split into atoms. Chlorine has two isotopes. The hydrogen involved here is the isotope $\ce{^1_1H}$ only. How many peaks does a mass ...
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303 views

What is the difference between a time of flight mass spectrometer and a spectrometer that uses a magnetic field?

Traditional mass spectrometers used electromagnets to deflect isotopes of different masses which allowed only a certain isotope to reach the detector. But how is the TOF MS different besides the fact ...
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564 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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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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385 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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Mass spectrometry: systematic mathematic transformation for calibration

Given a NaI mass calibration in the m/z 300-2000 range on a QTOF instrument as shown below: and given any uncalibrated mass spectrum that has been measured with the same instrument settings. What ...
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51 views

Mass Spectrometry for detection of a chemical from a distance

I want to know if mass Spectrometry to detect a chemical compound from a long distance, say, a 100 meters away from the device. Is this possible ? If not, then what can be used to fulfill this ...
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1answer
86 views

Compare concentrations using LC/MS

Suppose I run a reaction and then pass the results through LC/MS to find the conversion. One idea could be to compare the peaks of the reactants to the peak of the product. But: MS peak will depend ...
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How exactly are ions in a Mass Spectrometer accelerated?

After a molecule is ionised, the ion is accelerated by an electric plate up to a certain kinetic energy by the attraction of the ion to the electric plate. However, after the ion has passed the ...
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860 views

Why does 2-chloropropane's mass spectrum have a peak at 27?

I have noticed that all halogenoalkanes of the form 2-Xpropane seem to have a mass spec peak at 27, implying that a $\ce{C2H3+}$ ion is being formed. Forming a $\ce{C2H3+}$ ion, however, would mean ...
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264 views

Mass spectrum analysis [closed]

When finding ions which correspond to certain fragments on a mass spectrum; there are multiple possible ions that can correspond to the same fragment; How should I know which one is the correct one?
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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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315 views

Determining Structure of molecule based on IR Spectra and HNMR data [closed]

I have been given the following data and am asked to determine what the structure is. So far based on the IR spectra given I (think) I have identified a $\ce{C-O}$ bond, $\ce{sp^3}$ $\ce{C-H}$ bond ...
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496 views

Why is it that the number of nucleon in an element is the mass of the element

Why is it that the number of nucleon in an element is the mass of the element for example the mass of oxygen is 32g and the nucleon number is 32.
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Why is the relative atomic mass numerically equal to the gram atomic mass of the Atom? [duplicate]

Why is it that the relative atomic mass of an atom is numerically equal to gram atomic mass? For example,Relative Atomic Mass of Oxygen= 16 u So,Gram atomic mass of Oxygen=16 g.