I think it's important not to try to overgeneralize. The solution to avoid interferences depends a lot on the technique you are trying to use, what your analyte is, and so forth. Even for very light analytes, exact m/z ratios are not common and resolution may be good enough to separate them. For example, we often analyze for sulfur in our lab, which is roughly isobaric with dioxygen (molecular weight = 32) and a few other potential interferences. But it's not EXACTLY the same. Isotope patterns are different, and the resolution of the ICP-MS may be good enough to resolve in certain instrument modes. In cases where resolution is not good enough to separate ICP-MS interferences, collision cells are used. There's no one "magic bullet" to get rid of an isobaric interference. It all depends on what your analyte is, what your sample is, and what instrumentation you have available. And this is only for ICP-MS. LC/MS, GC/MS, etc., all have many but complex solutions to potential interferences.
I think it's important not to try to overgeneralize. The solution to avoid interferences depends a lot on the technique you are trying to use, what your analyte is, and so forth. Even for very light analytes, exact m/z ratios are not common and resolution may be good enough to separate them. For example, we often analyze for sulfur in our lab, which is roughly isobaric with dioxygen (molecular weight = 32) and a few other potential interferences. But it's not EXACTLY the same. Isotope patterns are different, and the resolution of the ICP-MS may be good enough to resolve in certain instrument modes. In cases where resolution is not good enough to separate ICP-MS interferences, collision cells are used. There's no one "magic bullet" to get rid of an isobaric interference. It all depends on what your analyte is, what your sample is, and what instrumentation you have available. And this is only for ICP-MS. LC/MS, GC/MS, etc., all have many but complex solutions to potential interferences.
No instrument is perfect. Sometimes you just have to deal with interferences.
That said.
In the case of mass spec: first, resolution is better than m/z = 18. The chances of two completely independent chemicals having exactly the same m/z ratio is small. You might be able to resolve them even if they are close. Second, chromatographic separation on the front end (e.g., GC/MS) can provide a lot of additional information and help separate away interferences. Third, in some types of MS (like ICP-MS) collision cells or reaction cells can be used to "react away" interferences that have the same mass number as the analyte of interest. Third, there are fragmentation patterns and other means of getting around interferences. While a parent ion may have an m/z of XX, daughter ions may also result from ionization that have different m/z values. So while one of the ions may have an interference, others may not.
No instrument is perfect. Sometimes you just have to deal with interferences.
That said.
In the case of mass spec: first, resolution is better than m/z = 18. The chances of two completely independent chemicals having exactly the same m/z ratio is small. You might be able to resolve them even if they are close. Second, chromatographic separation on the front end (e.g., GC/MS) can provide a lot of additional information and help separate away interferences. Third, in some types of MS (like ICP-MS) collision cells or reaction cells can be used to "react away" interferences that have the same mass number as the analyte of interest. Third, there are fragmentation patterns and other means of getting around interferences. While a parent ion may have an m/z of XX, daughter ions may also result from ionization that have different m/z values. So while one of the ions may have an interference, others may not.
we often analyze for sulfur in our lab, which is roughly isobaric with dioxygen (molecular weight = 32) and a few other potential interferences.But it's not EXACTLY the same.
So if I have a sample of bromine and I would like to find out the relative abundance of the different isotopes of bromine, will 79Br+ and 79Br-79Br2+ give the same m/z peak? If no, why? If yes, then the second molecular ion is affecting the actual percentage abundance of the79Br isotope and so how does resolution solve this issue?
we often analyze for sulfur in our lab, which is roughly isobaric with dioxygen (molecular weight = 32) and a few other potential interferences.But it's not EXACTLY the same.
So if I have a sample of bromine and I would like to find out the relative abundance of the different isotopes of bromine, will 79Br+ and 79Br-79Br2+ give the same m/z peak? If no, why? If yes, then the second molecular ion is affecting the actual percentage abundance of the79Br isotope and so how does resolution solve this issue?
The chances of two completely independent chemicals having exactly the same m/z ratio is small.
I understand the impact of making assumptions in science can have on formulating plausible models. However, in this particular case, I can't rely on such assumption because it can heavily alter the meaning of the measurement. Your statement could hold a decent degree of truth for large and complex molecules, but for a sample of a monatomic element, I can't see how the chances are small.
So is it imperative that we couple MS with other separation techniques in order to enhance the accuracy of determining the mass of a chemical species?
The chances of two completely independent chemicals having exactly the same m/z ratio is small.
I understand the impact of making assumptions in science can have on formulating plausible models. However, in this particular case, I can't rely on such assumption because it can heavily alter the meaning of the measurement. Your statement could hold a decent degree of truth for large and complex molecules, but for a sample of a monatomic element, I can't see how the chances are small.
So is it imperative that we couple MS with other separation techniques in order to enhance the accuracy of determining the mass of a chemical species?
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That said.
In the case of mass spec: first, resolution is better than m/z = 18. The chances of two completely independent chemicals having exactly the same m/z ratio is small. You might be able to resolve them even if they are close. Second, chromatographic separation on the front end (e.g., GC/MS) can provide a lot of additional information and help separate away interferences. Third, in some types of MS (like ICP-MS) collision cells or reaction cells can be used to "react away" interferences that have the same mass number as the analyte of interest. Third, there are fragmentation patterns and other means of getting around interferences. While a parent ion may have an m/z of XX, daughter ions may also result from ionization that have different m/z values. So while one of the ions may have an interference, others may not.
That said.
In the case of mass spec: first, resolution is better than m/z = 18. The chances of two completely independent chemicals having exactly the same m/z ratio is small. You might be able to resolve them even if they are close. Second, chromatographic separation on the front end (e.g., GC/MS) can provide a lot of additional information and help separate away interferences. Third, in some types of MS (like ICP-MS) collision cells or reaction cells can be used to "react away" interferences that have the same mass number as the analyte of interest. Third, there are fragmentation patterns and other means of getting around interferences. While a parent ion may have an m/z of XX, daughter ions may also result from ionization that have different m/z values. So while one of the ions may have an interference, others may not.
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So if I have a sample of bromine and I would like to find out the relative abundance of the different isotopes of bromine, will 79Br+ and 79Br-79Br2+ give the same m/z peak? If no, why? If yes, then the second molecular ion is affecting the actual percentage abundance of the79Br isotope and so how does resolution solve this issue?
Thanks again.
So if I have a sample of bromine and I would like to find out the relative abundance of the different isotopes of bromine, will 79Br+ and 79Br-79Br2+ give the same m/z peak? If no, why? If yes, then the second molecular ion is affecting the actual percentage abundance of the79Br isotope and so how does resolution solve this issue?
Thanks again.
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VOTE
I understand the impact of making assumptions in science can have on formulating plausible models. However, in this particular case, I can't rely on such assumption because it can heavily alter the meaning of the measurement. Your statement could hold a decent degree of truth for large and complex molecules, but for a sample of a monatomic element, I can't see how the chances are small.
So is it imperative that we couple MS with other separation techniques in order to enhance the accuracy of determining the mass of a chemical species?
Thanks.
I understand the impact of making assumptions in science can have on formulating plausible models. However, in this particular case, I can't rely on such assumption because it can heavily alter the meaning of the measurement. Your statement could hold a decent degree of truth for large and complex molecules, but for a sample of a monatomic element, I can't see how the chances are small.
So is it imperative that we couple MS with other separation techniques in order to enhance the accuracy of determining the mass of a chemical species?
Thanks.
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VOTE