Asal Asali

10 Questions 13 Answers 0 Followers

Questions related from Asal Asali

Why are there so many fragment ions in the product ion spectrum?

For LC-MS/MS method development, I performed infusion of my compounds and recorder product ion scan with, obviously, the mass of the molecular ion in the Q1. I usually see a few fragment ions, of...

26 April 2022 6,856 4 View

How to identify possible metabolite from chromatogram?

We have done the analysis for a pre-clinical study and we have observed additional peaks in the chromatograms. We think that these peaks are metabolites. The concentration of the additional peaks...

03 December 2020 6,397 10 View

Why does increasing the internal standard concentration (higher than the ULOQ) improves linearity in LC-MS/MS?

For a while, I have been experimenting with improving the linearity of my method. I have noticed that increasing my deuterium labeled (3x) internal standard to a concentration 2.5 times the ULOQ...

23 March 2020 3,221 7 View

Where are protons in ESI+ formed in LC-MS/MS?

Can anyone help me with peer reviewed papers that explain whether or not ions are formed in the ESI source? Is this what they call 'right-way-round' principle? Then how come that some for some...

11 March 2020 2,831 1 View

How can source saturation occur for one of two analytes in LC-MS/MS at the same retention time ?

I am trying to expand the linearity of my method. There is in-source saturation (detector saturation is excluded by using isotopologues that did not improve linearity). However, at a certain...

23 September 2019 963 2 View

Is it possible to quantify a glucuronide in-source fragment in LC-MS/MS?

My analysis requires a extremely wide concentration range from 1-5000 ng/mL. As expected, the calibration curve flattens out at the higher concentrations. I have ruled out detector saturation (see...

26 August 2019 1,261 5 View

How to distinguish ion-source saturation and detector saturation with LC-MS/MS?

I am trying to develop a LC-MS/MS method for a compound. The calibration curve flattens at the higher concentration points when measuring in the range of 2.5-5000 ng/mL. It is lineair when...

05 June 2019 3,121 7 View

Why is a linear calibration curve preferred?

For bio-analysis with LC-MS/MS, a linear calibration curve is preferred over a quadratic. Why is this? Is it OK to continue method development with a quadratic fit? I have to add that the...

04 March 2019 5,722 13 View

Why do some analytes have a low recovery in Opti-MEM medium?

I have done stability tests in Opti-MEM and I have seen a major decrease in signal (LC-MS/MS) in time. Chemical instability is highly unlikely for this compound. It seems to be related to the...

04 March 2019 3,565 4 View

How to further improve LC-MS/analytical chemistry skills

I finished my masters in analytical chemistry, but there is so much more to learn. My main interest is the hard core fundamentals of chromatography and mass spectrometry. What positions in the...

01 January 1970 9,166 8 View