Chromatography Forum

Hi,
Does anyone know if it is possible to copy a MS library from one software device to another MS machine. we have two MS and one of those connected softwares library is out of date and can not identify compounds correctly.

1) Purchased mass spectral libraries are copyrighted materials and when purchased come with the condition that they are to be installed on only one computer.

2) Just because a mass spectral library is old should not make it identify compounds incorrectly – unless you are trying to identify one of the compounds that has been added to a newer version of the library.

3) If you have built the mass spectral library yourself - typically all you need to do is copy the file from one instrument to the other placing the library in the folder containing all of the other libraries on the destination computer.

1) Purchased mass spectral libraries are copyrighted materials and when purchased come with the condition that they are to be installed on only one computer.

2) Just because a mass spectral library is old should not make it identify compounds incorrectly – unless you are trying to identify one of the compounds that has been added to a newer version of the library.

3) If you have built the mass spectral library yourself - typically all you need to do is copy the file from one instrument to the other placing the library in the folder containing all of the other libraries on the destination computer.

Ok, thanks for the help. One last question, I wonder why the MS recognizes my compound as e.g. Methyl ester (90% prbability) when it is actually Isopropyl ester(2% matching probability)? does it mean that the ion library is misguiding the sofware or is not properly written.?

A library search is a mathematical routine and computes ratios of signals and comares them to ratios in the spectrum. It knows nothing of chemistry or fragmentation. The library search provides suggestions - many of them good - and it up to the human, who can understand ionization and fragmentation processes, to figure out the rest.

You can sometimes improve the selection provided by adjusting search parameters.

I am not sure what you are saying about your library search results. Are you saying that you get hits for both the methyl ester and the isopropyl ester when you do a library search of a spectrum that should be that of the isopropyl ester and that the ID probability of the methyl ester is 90% whereas the ID probability is 2%? If this is the case, it is very likely that the spectrum you are searching is that of a methyl ester and not an isopropyl ester.

The mass spectra of ethyl esters of linear saturated fatty acids have a base peak at m/z 74. This peak is not present in the mass spectra of isopropyl esters of linear saturated fatty acids. The spectra of these compounds exhibit odd-electron ion peaks at m/z 102, m/z 60 and an m/z value corresponding to [M – 42]+; however, the base peak is at m/z 43. The spectra of methyl esters exhibit an [M – 43]+ peak whereas the spectra of isopropyl esters exhibit an [M – 59]+ peak.

Look at the spectrum, not just the library search results.