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

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$begingroup$

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 purposes of m/z ratio), and assuming the difference in mass for an isotope is ~1 Da (with each additional neutron for an analyte at a charge of +1 in positive ionization mode) and assuming there is only one additional isotope, would the difference in weight for two isotopes each with a charge +10 be 0.1 Da?

mass-spectrometry

share|improve this question

asked Jun 30 at 4:28

James HongJames Hong

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3

$begingroup$

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 purposes of m/z ratio), and assuming the difference in mass for an isotope is ~1 Da (with each additional neutron for an analyte at a charge of +1 in positive ionization mode) and assuming there is only one additional isotope, would the difference in weight for two isotopes each with a charge +10 be 0.1 Da?

mass-spectrometry

share|improve this question

asked Jun 30 at 4:28

James HongJames Hong

7688 bronze badges

$endgroup$

add a comment | 

$begingroup$

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 purposes of m/z ratio), and assuming the difference in mass for an isotope is ~1 Da (with each additional neutron for an analyte at a charge of +1 in positive ionization mode) and assuming there is only one additional isotope, would the difference in weight for two isotopes each with a charge +10 be 0.1 Da?

mass-spectrometry

share|improve this question

asked Jun 30 at 4:28

James HongJames Hong

7688 bronze badges

$endgroup$

share|improve this question

asked Jun 30 at 4:28

James HongJames Hong

7688 bronze badges

share|improve this question

asked Jun 30 at 4:28

James HongJames Hong

7688 bronze badges

asked Jun 30 at 4:28

James HongJames Hong

7688 bronze badges

asked Jun 30 at 4:28

James HongJames Hong

7688 bronze badges

2 Answers
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3

$begingroup$

would the difference in weight for two isotopes each with a charge +10 be 0.1 Da?

Short answer: yes

Long answer: You said

assuming there is only one additional isotope

This is a weird assumption, as it is often not true. Molecules containing both $ceH$ atoms and $ceC$ atoms will have isotopic contributions from $ceH$, $ceD$, $ce^13C$, and $ce^12C$. Anything that has a sulfur atom will have contributions from $ce^32S$, $ce^34S$, $ce^33S$, and $ce^36S$. However none of those things really affect the answer to your question as I understand it. Isotopes are separated by almost 1 (or 2) Da increments.

The key is almost. Ions with a +10 charge would have isotopologues that were almost 0.1 Da apart, but not exactly. If the ion in question were only made of carbon, then a more exact value would be 0.10034 Da apart. Not all instruments can resolve a mass difference of 0.1 Da from 0.10034 Da, but some can.

share|improve this answer

answered Jun 30 at 5:12

Curt F.Curt F.

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add a comment | 

4

$begingroup$

More realistically if you have a molecule with Br, then the distance between isotopes:

• Will be 2 $m/z$ units in case of 1 charge


• And 1 $m/z$ units in case of 2 charges

You can use this information to determine if there are molecules ionized twice — their isotopes appear closer than expected.

Eventually since ESI/APCI adds $ceH+$ for each charge, given original EMW was 100 Da, then:

• 
  $m/z$ in case of 1 charge: $(100+1)/1=101$ and $(102+1)/1=103$
  


• 
  $m/z$ in case of 2 charges: $(100+2)/2=51$ and $(102+2)/2=52$
  

Or in case of negative ionization you'll need to subtract 1 and 2 Da, respectively.

share|improve this answer

edited Jun 30 at 8:54

answered Jun 30 at 5:31

Stanislav BashkyrtsevStanislav Bashkyrtsev

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3

$begingroup$

would the difference in weight for two isotopes each with a charge +10 be 0.1 Da?

Short answer: yes

Long answer: You said

assuming there is only one additional isotope

This is a weird assumption, as it is often not true. Molecules containing both $ceH$ atoms and $ceC$ atoms will have isotopic contributions from $ceH$, $ceD$, $ce^13C$, and $ce^12C$. Anything that has a sulfur atom will have contributions from $ce^32S$, $ce^34S$, $ce^33S$, and $ce^36S$. However none of those things really affect the answer to your question as I understand it. Isotopes are separated by almost 1 (or 2) Da increments.

The key is almost. Ions with a +10 charge would have isotopologues that were almost 0.1 Da apart, but not exactly. If the ion in question were only made of carbon, then a more exact value would be 0.10034 Da apart. Not all instruments can resolve a mass difference of 0.1 Da from 0.10034 Da, but some can.

share|improve this answer

answered Jun 30 at 5:12

Curt F.Curt F.

16.5k11 gold badge3939 silver badges9393 bronze badges

$endgroup$

add a comment | 

3

$begingroup$

would the difference in weight for two isotopes each with a charge +10 be 0.1 Da?

Short answer: yes

Long answer: You said

assuming there is only one additional isotope

This is a weird assumption, as it is often not true. Molecules containing both $ceH$ atoms and $ceC$ atoms will have isotopic contributions from $ceH$, $ceD$, $ce^13C$, and $ce^12C$. Anything that has a sulfur atom will have contributions from $ce^32S$, $ce^34S$, $ce^33S$, and $ce^36S$. However none of those things really affect the answer to your question as I understand it. Isotopes are separated by almost 1 (or 2) Da increments.

The key is almost. Ions with a +10 charge would have isotopologues that were almost 0.1 Da apart, but not exactly. If the ion in question were only made of carbon, then a more exact value would be 0.10034 Da apart. Not all instruments can resolve a mass difference of 0.1 Da from 0.10034 Da, but some can.

share|improve this answer

answered Jun 30 at 5:12

Curt F.Curt F.

16.5k11 gold badge3939 silver badges9393 bronze badges

$endgroup$

add a comment | 

$begingroup$

would the difference in weight for two isotopes each with a charge +10 be 0.1 Da?

Short answer: yes

Long answer: You said

assuming there is only one additional isotope

This is a weird assumption, as it is often not true. Molecules containing both $ceH$ atoms and $ceC$ atoms will have isotopic contributions from $ceH$, $ceD$, $ce^13C$, and $ce^12C$. Anything that has a sulfur atom will have contributions from $ce^32S$, $ce^34S$, $ce^33S$, and $ce^36S$. However none of those things really affect the answer to your question as I understand it. Isotopes are separated by almost 1 (or 2) Da increments.

The key is almost. Ions with a +10 charge would have isotopologues that were almost 0.1 Da apart, but not exactly. If the ion in question were only made of carbon, then a more exact value would be 0.10034 Da apart. Not all instruments can resolve a mass difference of 0.1 Da from 0.10034 Da, but some can.

share|improve this answer

answered Jun 30 at 5:12

Curt F.Curt F.

16.5k11 gold badge3939 silver badges9393 bronze badges

$endgroup$

share|improve this answer

answered Jun 30 at 5:12

Curt F.Curt F.

16.5k11 gold badge3939 silver badges9393 bronze badges

answered Jun 30 at 5:12

Curt F.Curt F.

16.5k11 gold badge3939 silver badges9393 bronze badges

answered Jun 30 at 5:12

Curt F.Curt F.

16.5k11 gold badge3939 silver badges9393 bronze badges

4

$begingroup$

More realistically if you have a molecule with Br, then the distance between isotopes:

• Will be 2 $m/z$ units in case of 1 charge


• And 1 $m/z$ units in case of 2 charges

You can use this information to determine if there are molecules ionized twice — their isotopes appear closer than expected.

Eventually since ESI/APCI adds $ceH+$ for each charge, given original EMW was 100 Da, then:

• 
  $m/z$ in case of 1 charge: $(100+1)/1=101$ and $(102+1)/1=103$
  


• 
  $m/z$ in case of 2 charges: $(100+2)/2=51$ and $(102+2)/2=52$
  

Or in case of negative ionization you'll need to subtract 1 and 2 Da, respectively.

share|improve this answer

edited Jun 30 at 8:54

answered Jun 30 at 5:31

Stanislav BashkyrtsevStanislav Bashkyrtsev

67811 gold badge55 silver badges1212 bronze badges

$endgroup$

add a comment | 

4

$begingroup$

More realistically if you have a molecule with Br, then the distance between isotopes:

• Will be 2 $m/z$ units in case of 1 charge


• And 1 $m/z$ units in case of 2 charges

You can use this information to determine if there are molecules ionized twice — their isotopes appear closer than expected.

Eventually since ESI/APCI adds $ceH+$ for each charge, given original EMW was 100 Da, then:

• 
  $m/z$ in case of 1 charge: $(100+1)/1=101$ and $(102+1)/1=103$
  


• 
  $m/z$ in case of 2 charges: $(100+2)/2=51$ and $(102+2)/2=52$
  

Or in case of negative ionization you'll need to subtract 1 and 2 Da, respectively.

share|improve this answer

edited Jun 30 at 8:54

answered Jun 30 at 5:31

Stanislav BashkyrtsevStanislav Bashkyrtsev

67811 gold badge55 silver badges1212 bronze badges

$endgroup$

add a comment | 

$begingroup$

More realistically if you have a molecule with Br, then the distance between isotopes:

• Will be 2 $m/z$ units in case of 1 charge


• And 1 $m/z$ units in case of 2 charges

You can use this information to determine if there are molecules ionized twice — their isotopes appear closer than expected.

Eventually since ESI/APCI adds $ceH+$ for each charge, given original EMW was 100 Da, then:

• 
  $m/z$ in case of 1 charge: $(100+1)/1=101$ and $(102+1)/1=103$
  


• 
  $m/z$ in case of 2 charges: $(100+2)/2=51$ and $(102+2)/2=52$
  

Or in case of negative ionization you'll need to subtract 1 and 2 Da, respectively.

share|improve this answer

edited Jun 30 at 8:54

answered Jun 30 at 5:31

Stanislav BashkyrtsevStanislav Bashkyrtsev

67811 gold badge55 silver badges1212 bronze badges

$endgroup$

share|improve this answer

edited Jun 30 at 8:54

answered Jun 30 at 5:31

Stanislav BashkyrtsevStanislav Bashkyrtsev

67811 gold badge55 silver badges1212 bronze badges

answered Jun 30 at 5:31

Stanislav BashkyrtsevStanislav Bashkyrtsev

67811 gold badge55 silver badges1212 bronze badges

answered Jun 30 at 5:31

Stanislav BashkyrtsevStanislav Bashkyrtsev

67811 gold badge55 silver badges1212 bronze badges