LC-MS/MS

[N.V.V.S.S. RAMAN]

Hai Friends,

I would like to buy an LC/MS/MS system for our impurity profiling and structural conformation purpose. Can anybody suggest which technique is suitable whether Ion trap or Triple quadropole

ur suggestions are highly helpful to me to decide the machine

Thank Q
Raman

[james little]

We have a triple quadrupole and a TOF. Both are Waters instruments (Quattro Micro and LCT TOF). We use the triple quadrupole for quantitative and qualitative. The TOF we use for only qualitative.

Like the mass resolution and sensitivity of the TOF for full scan acquisitions. Also, at times the accurate mass data is useful.

Normally for qualitative analyses, we run 5 experiments in one analysis, just use multifunctions within the same analysis. One function is low collision voltage in the source for MW in pos ion, the second function is higher collision energy in the source in positive ion for fragmentation (substuctural information). The same two approaches are take in negative ion mode. The fifth function is the diode array.

Can get a lot of information in just one run. We add the high energy negative and positive ion fragmentation data to a NIST library for searching. The library also includes the structure. The database can be searched by best hit to either structure or spectrum.

See the approach in surfactant section on my website for multifunction experiment. THe website also has another section on using the NIST library.

http://users.chartertn.net/slittle/default.htm

We don't have an iontrap, but have seen nice things done to obtain good substructural fragmentation data.

[N.V.V.S.S. RAMAN]

thank you james little
U have given a very good information.
Thanks again

raman

[pillin]

Hi,
I am also searching for an MS-system for impurity profiling and structural confirmation purpose.
James little wrote in his reply that he uses collision induced dissociation, which is taking place in the source of his MS/MS system, for structural confirmation. So I have three questions:
Is it possible to do the same experiments with an single quad-system?
Are the fragmentation data reproducable enough for database searching and reliable enough for structural confirmation?
What is the best way to get fragmentation data for struct. confirmation - CID in a source or fragmentation taking place in a collision cell of an MS/MS detector?

best regards

[richa_malhotra]

ion trap is fading away and most of the scientists are moving towards triple quads & tofs for both quantitation, qualitation & exact mass measurements.

i am a user of triple quad from micromass , uk and i am very happy with thier system performance and especially thier software which has no comparisions with any of the ms manufacturers.

my honest suggestion is to go for a triple quad and which can be used for multiple applications ranging from qualitative to quantitation and off course stuructural elucidation as well.

if you have enough funds simply go for waters lctof beacuse of thier lockspray option which is very unique with them.

[N.V.V.S.S. RAMAN]

Thank you Richa

can we establish the relation between the compounds on Quad. Ie, I have an unknown impurity eluting in one of our drug. Can I establish the relation between the impurity and the drug.

raman

[james little]

I use both in[source CID and tandem (in collision cell, triple quad).

Nice to have both. The CID allows us to do the survey runs easily with 4 functions, 2 pos, 2 neg. The pos run at low in-source energy to get MW, the other pos at high to get fragments. Same for negative, then also the diode array.

Generate a lot of data in one run.

Upside to CID in-source, get a lot of fragments that are useful without having to decide which ions to monitor, no loss of isotope information.

Downside of CID in-source is that must separate components by chromatography so no infusion of mixtures. Other downside is that can get solvent adducts. For example compounds containing benzyl group give m/z 91 ion which is real and then an ion adduct for acetonitrile plus benzyl ion at m/z 132. Acetonitrile seems to be the worst for givnig ion adducts with fragments, haven't note any for methanol.

Also for in-source and tandem, hard to tell fragmentation pathway. Would be better defined in ion-trap.

Mathcing of libraries not like EI. We have 40,000 EI spectra in our corporate library and they almost always are reproducible between instruments. We also have 5000 CID library entries. Not as reproducible between instruments, but still very valuable.

THe database searchable by structure and by spectrum and both sorted by hit value. Very useful for finding model compounds.

Lot of papers in the literature on CID (tandem and in-source). Some people average several different energies, some say ion traps superior for reproducibility. Bottom line, current CID spectra are not as reproducilbe as electron impact, but definitely very useful and offer wealth of substructural information.

The only limitation to our TOF is that it can't see ions below m/z 59 with good sensitivity. Probably just a design attribute. I often scan the quad down to m/z 10 at high collision energies and see useful information. At high energies can scan low since sovlent clusters are greatly diminished.

For example, have used quad to look for chlorinated compounds by plotting m/z 35 at high energies. Wouldn't see the m/z 35 on my TOF.

[james little]

Some references to creating CID libraries..

. “Comparison of Product ion Spectra Obtained by Liquid Chromatography/Triple-Quadruple Mass Spectrometry for Library Search,â€