All Questions
Tagged with chromatography mass-spectrometry
28
questions
3
votes
0
answers
124
views
What could lead to exaggerated positive LC-MS/MS test for tetrahydrocannabinol?
I was driving with the car and was involved in a minor traffic violation and I was submitted to a drug saliva test. The sample was analysed in the laboratory using liquid chromatography with tandem ...
- 31
3
votes
1
answer
163
views
Are there LCMS compatible buffer systems available for the high pH range 12-14?
I want to perform chemical stability studies for different pH Values. To achieve pH Values from 1 to 6 I can prepare solutions with trifluoric acid and formic acid and ammonium formate and acetate. I ...
- 799
5
votes
1
answer
404
views
How to effectively replace DMSO with LC–MS-compatible solvent for the samples from a well plate?
I want to do LC–MS analysis of the samples from a 384-well plate where each compound (at around 1–10 μM) is dissolved in 10–15 μL of DMSO. I am worried about the DMSO dwarfing the analyte’s signal, as ...
- 441
2
votes
0
answers
58
views
Dynamic equilibrium of Girard T-derivatized oxysterols
This is a question relating to organic chemistry, moreso than chromatography.
I am running LC-MS on various hydroxycholesterols (HC) and dihydroxycholesterols (diHC). To increase ionization efficiency ...
- 341
3
votes
1
answer
129
views
Why can I extract all metabolites from blood plasma with one solvent, but to extract only fatty acids I must use many solvents?
I want to do a metabolite study using GC- without derivatization and UPLC-MS (RP and NP) on samples of plasma and urine. My hypothesis is agnostic about which metabolite will correlate with the ...
- 261
2
votes
1
answer
518
views
Impact of flow rate on peak areas in Mass Spectrometry
As a follow up to the discussion in comments: it's now clear that UV peaks will have larger area if flow rate is decreased, because the same portion of molecules are measured again and again.
With ...
- 1,567
2
votes
0
answers
126
views
Can acetone be used as a GC–MS solvent for a sample containing ammonia?
Сan acetone be used as a GC–MS solvent/diluent for a sample containing ammonia? Will there be a reaction between these two species?
- 41
3
votes
3
answers
616
views
Why do I see two peaks for methyl salicylate in my GC–MS spectrum?
I ran a neat sample of methyl salicylate (CAS: 119-36-8) on the GC–MS and used $m/z~120$ as the quantifier and $m/z~92$ and $152$ as qualifiers. Below is the SIM spectrum for these ions, with two ...
- 39
2
votes
1
answer
4k
views
What are quantifier and qualifier ions in mass spectrometry data for GC-MS or LC-MS?
I've read that one should pick an ion peak that is unique to an analyte for quantification purposes and then pick at least 2 qualifier peaks and use their ratios to identify the analyte (or avoid ...
1
vote
1
answer
71
views
What are the benefits of using zero capillary voltage for discarding fractions in LC–ESI–MS/MS?
In the second episode of The Association for
Mass Spectrometry & Advances in the Clinical Lab (MSACL) podcast, namely Getting going with mass spectrometry : Josh learns chromatography (aired 2021-...
- 38.4k
1
vote
1
answer
195
views
Does using same calibration curve for chemical analysis introduce correlation in sample error/uncertainty values?
I am using a hypothetical case to explain my question
Let us consider a chemical analysis method A (using a certain instrument), which is used to quantify the value of a particular species b. ...
4
votes
1
answer
238
views
Stronger ESI signal for deuterated substances
I observe a constant phenomenon in my ESI measurements, which indicates that deuterated substances give a stronger signal than the same substance in non-deuterated form. Unfortunately I can't make any ...
- 1,257
1
vote
0
answers
663
views
Disadvantages of SIM vs TIC in GC-MS [closed]
In GC-MS what are the relative advantages/disadvantages of using Selected-Ion Monitoring (SIM) vs using Total Ion Chromatograms (TIC)?
I know that SIM offers a better S/N ratio, however if the S/N is ...
- 11
2
votes
1
answer
2k
views
Conditions for choosing quantifying and qualifying ion in LC-MS/MS
In my PhD-work, we are trying to develop LC-MS/MS methods for targeted analysis. Usually, I determine my quantifying ion/fragment based on a few different criteria:
If there is a 13C internal ...
- 23
2
votes
1
answer
144
views
Software platforms with integration of multi vendor mass spectrometer device data?
I know about ACD/Spectrus Processor which is a software platform to integrate analytical chemistry data from multiple mass spectrometer device vendors (e.g. Agilent Technologies, Bruker, Waters) to ...
- 219