Hi RG reserchers, recently our lab purchased a liquid chromatography coupled with mass spectrum brand “LC/MS-2020 shimadzu, Nexera XR/ LC 20AD”. When we operated it using phenolic extracts, we discover that the resulted picks appear without mentioning the name of the pick compounds or even a proposed name of the potential compound (like GC/MS). The mass spectrum fragmentations appear but without proposing a name of the compound. So, I am wondering if some of you have before used this apparatus and have faced this issue? also, does this apparatus need NIST or Wily bibliographies to identify the compounds? If so, where we can bay them?
You have not done your homework to understand the basic fundamentals of how an HPLC or LC-MS system operates yet (or maybe have been watching too many of those TV shows or Movies). There is no similar library ability with HPLC-MS as their is with electron impact detectors (hard ionization) used in GC-MS system. When a proper GC method is coupled to a GC based MS (EI) detector, then one or more applicable libraries may be used, along with actual standards, to make qualitative assignments. For HPLC, there are far too many variables involved in the methods themselves (which determine selectivity for the compounds), the detectors themselves and the settings used (esp. for Mass detectors which have many critical setting that must be optimized, for each sample) which can create, change or make data disappear. And, as each instrument is different, similar methods may generate different data too.
- LC Mass detectors are NOT universal detectors.
- LC Mass detectors do not detect everything (compounds that do not ionize well or at all, are unseen).
- HPLC analysis and LC Mass detectors take many years of training just to achieve a basic proficiency in use. A well developed HPLC method must first be developed for use with the detector and sample. Changing the energy levels used (gas, temperature, flow rates, LC method) changes the results obtained so a lot of training is needed to optimize the settings and interpret the data. Any one can use these tools to generate "peaks", but those peaks (and the data obtained) may not be real or scientifically valid.
You have not done your homework to understand the basic fundamentals of how an HPLC or LC-MS system operates yet (or maybe have been watching too many of those TV shows or Movies). There is no similar library ability with HPLC-MS as their is with electron impact detectors (hard ionization) used in GC-MS system. When a proper GC method is coupled to a GC based MS (EI) detector, then one or more applicable libraries may be used, along with actual standards, to make qualitative assignments. For HPLC, there are far too many variables involved in the methods themselves (which determine selectivity for the compounds), the detectors themselves and the settings used (esp. for Mass detectors which have many critical setting that must be optimized, for each sample) which can create, change or make data disappear. And, as each instrument is different, similar methods may generate different data too.
- LC Mass detectors are NOT universal detectors.
- LC Mass detectors do not detect everything (compounds that do not ionize well or at all, are unseen).
- HPLC analysis and LC Mass detectors take many years of training just to achieve a basic proficiency in use. A well developed HPLC method must first be developed for use with the detector and sample. Changing the energy levels used (gas, temperature, flow rates, LC method) changes the results obtained so a lot of training is needed to optimize the settings and interpret the data. Any one can use these tools to generate "peaks", but those peaks (and the data obtained) may not be real or scientifically valid.
Dear Adel Benarfa, unfortunately for you, William Letter is right. I fully agree with all his answer, even if I think the harshness of his comment is excessive. Indeed, you should be aware that only EI ionisation (used only in GC/MS) gives reproducible fragmentations which can be used in library search. Instead, all HPLC/MS ionisation techniques (regardless it is ESI, APCI, APPI or whatever) give fragmentations which depend on a number of factors (e.g. ionisation parameters but also elution parameters) and you cannot use commercially available libraries.
Dear William Letter, thank you for your valuable information and your scientific harshness comments which I accept them, you're right it seems that I didn't do well my homework. Thank you so much.
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