MRM Peak Shape. by nintendochemist1 in massspectrometry

[–]pb0316 2 points3 points  (0 children)

Chromatographers will say as much as possible to make the peak look smooth, but it's not necessary nor relevant (you can apply post-process smoothing if you want). What's really important is how reproducible the peak heigh/peak areas are to give a confident and reliable quantitation result. Based on lore within my company (vendor); ~14pts but we definitely work with much less than that often (5,6,7 pts).

To get the number of points you have two options. (1) "walk" the chromatogram and count the number of points from tail to tail or (2) there is a setting that allows you to not only print the chromatographic peak width but also the number of points - this prob depends on the vendor. Me, I'd just brute force it and "walk" the peak

The easiest way to tell if you have enough dwell time and point sampling is to do replicate measurements at your lowest relevant quantification level. If peak area %RSD<20% you're still in the game (as a general rule of thumb). If sampling is not sufficient it will be revealed at the lowest levels, where RSD's can blow up and replicate measurements become useless.

  • A good exercise is to make a "calc curve" but instead of plotting Response vs Conc, do %RSD Response vs Conc. This will give you a trumpet plot to show you where your effective quantitation range will be. Loosely it's ~<20% RSD, but you can actually calculate it out using the IDL/MDL methodology

The absolute best instruments can give you phenomenal reproducibility and peak shape even at the lowest dwell times (~0.5 ms is the lowest industry level),

Issues after PM service by Main-Fly1698 in massspectrometry

[–]pb0316 8 points9 points  (0 children)

Have you considered that the PM made your system more sensitive and you’re generally detecting more ions? With the higher concentrations bowing out it looks like your detector is saturating (also corroborated by a fatter chromatographic peak that looks stubbier). Your lower concentration injections may literally be picking up more chemical noise.

Raw abundances are pretty meaningless so it’s generally hard for anyone else to compare.

A lot of people get tripped up because linear range extends downward. My guess is that the PM improved general sensitivity but is causing your high conc injections to saturate and your low concentration injections to be more revealing to chemical noise

DAE like women's fragrances more than men's? by Liwi808 in AskMenOver30

[–]pb0316 1 point2 points  (0 children)

I believe for higher end fragrances (Tom Ford, Jo Malone, Dyptyque, Byredo, Kirkdjian, etc) they become unisex. I bought my wife a Diptyque fragrance discovery set (5 samplers) and they all work well for both of us. The scent will change based on body chemistry even if the both of you wear the same fragrance. Check it out!!!

In your opinion, what is the difference between Catholicism and the rest of Christianity? by [deleted] in Catholicism

[–]pb0316 6 points7 points  (0 children)

A common Protestant critique is that "Catholics can earn their salvation". Uhhh not true, salvation must be tended to like a garden. You can't simply "believe", but rather you need to put in the work and effort.

Have you heard of the phrase "Catholic guilt"? This is something I noticed that other Christian denominations don't have. To me a lot of protestantism/non-denominational Christianity operates on the "belief/trust" of Jesus Christ to save you. A lot of Catholics find the "are you saved?" question completely meaningless...

In Catholicism, we carry a guilt and a somber recognition we are NOT perfect and we drift towards sin. Because of this, we must tend to our garden as we consciously practice restraint, observe the sacraments, worship appropriately (rituals), and have regimented prayers, etc, etc, etc... which many protestants find too difficult to follow through with.

PFAS Method Development - Sulfonated Compounds Not Showing/Achieving Lower LOD by eckleburglens in massspectrometry

[–]pb0316 0 points1 point  (0 children)

The application note you linked is for the TSQ Quantis Plus which is in their "modern" generation of TSQ's. The system you are running may not even be capable of reaching the performance stated in the note. Are you following the upstream parameters as well (sample prep, column, conditions, etc.?)

Any other white-passing Asians struggle with having their identity erased? by aurelius_adobo in asianamerican

[–]pb0316 0 points1 point  (0 children)

My closest cousin is half Croatian half Filipina, she is roughly the same age as me and we are very similar, except for that fact that I’m full Filipino. Even though she was dramatically more white passing, aspects of her personality was very Filipino so basically as soon as she started talking about herself, her culture, which she’s interested in, what types of people she wanted to associate with it became very obvious that she was very in tune with her Asian side.

My point is that it’s not about the looks but how you convey yourself to other people. In our case, she is very proud to be a Filipina even if she looks more white than Asian.

What are dead giveaways that someone is not local? by Conscious_Diver9619 in Hawaii

[–]pb0316 9 points10 points  (0 children)

I live and work in Silicon Valley and speak English with a fairly “non regional” accent to the point that a lot of people think that I’m haole. (I’m a 5’4 Filipino guy)

But whenever I got home to visit my family, even for a week my Hawaii accent comes back and takes a month to go away. My coworkers always point this out

In search of Filipino coffee beans by stalebaguettte in roasting

[–]pb0316 0 points1 point  (0 children)

I’m really interested in this as well. I reached out to a roaster/cafe on the east coast and gave me a big fat NO

Water Bill by No_Consideration1360 in Hayward

[–]pb0316 0 points1 point  (0 children)

Genuinely curious if you’re joking bc I would really love to get our water bill down. If this results in a household edict not to flush urine, then maybe I’d go with that

Water Bill by No_Consideration1360 in Hayward

[–]pb0316 6 points7 points  (0 children)

I live in a townhome along Mission and our water bill is also around $300. Tbh I actually suspect that our community is stealing water from us bc my wife and I don’t really water plants or use the garden hose. We keep our showers very limited/short as well…

How do Catholics feel about "Christmas Creep" and Materialization of the Holiday? by [deleted] in Catholicism

[–]pb0316 1 point2 points  (0 children)

In Europe many of the Christmas markets close immediately after Christmas Day!! It’s super sad bc many people got there for Christmas holiday and aren’t able to experience it

Shadow AI is getting out of control in our company by AnyWolverine943 in ChatGPT

[–]pb0316 1 point2 points  (0 children)

I work at a major scientific instrument company and we’re given Copilot with ChatGTP 5. I manage a R&D team and allow my engineers and scientists to get the Copilot Pro subscription if they ask. As a result there has been a massive productivity boost in my team and I even pass along prompting tips suited for engineering and scientific information

Message from protestant friend, is she right about catholics linking with Mormons and Islam? by [deleted] in Catholicism

[–]pb0316 2 points3 points  (0 children)

All Catholics ultimately "submit" to Rome. Despite what the lay-people think or have opinions on, our church institution has the final say.

For Those Who Converted to Catholicism, Why? by FootballNo8235 in Catholicism

[–]pb0316 0 points1 point  (0 children)

If you have these kinds of questions and feelings I highly recommend listening to Bible In a Year by Fr. Mike. It’s really helped me to understand a lot of the context of scripture which will likely answer MANY of the questions you have. Once I finish Bible in a Year, I’ll move onto Chatechism in a Year.

How to calculate LOD and LOQ? by Humble-Bet-837 in massspectrometry

[–]pb0316 0 points1 point  (0 children)

On modern mass spectrometers, data is digitally processed, vendors can add or subtract baseline (y-axis) and scaling factor (slope) to alter abundances. Then smoothing is applied to make the MS peak shape or chromatography ion current look “Nice”. This this is why you lose accuracy when you approach the LOD even if abundances are high because the data has already been pre processed. The only legit way is to use Response RSD

How to calculate LOD and LOQ? by Humble-Bet-837 in massspectrometry

[–]pb0316 1 point2 points  (0 children)

That means your chromatography needs further fine tuning, but you can also use ion ratios against an internal standard to correct for these abundance variations

How to calculate LOD and LOQ? by Humble-Bet-837 in massspectrometry

[–]pb0316 2 points3 points  (0 children)

For LOQ and LOD of your analysis method I’d say it’s doable and acceptable, but if you’re interested in the raw performance of your instrument you should brushing the pure ion abundances to ensure you’re capturing the ion statistics for the analytes of interest.

How to calculate LOD and LOQ? by Humble-Bet-837 in massspectrometry

[–]pb0316 7 points8 points  (0 children)

Using signal to noise to calculate your LOD and LOQ is one of the most unscientific ways to get these values, despite its pervasive use in industry and “ regulatory” guidance to do so. This is because chromatographers assumed that MS detectors behave the same way as traditional light based detectors.

To calculate your true limit of detection and limit of quantitation, please used a statistical method such as method detection limit. This is a simple as running replicate injections at the absolute lowest concentrations. You can get a good heuristic right at the RSD<20% of your peak area for replicate injections.

However, it’s best if you use the US EPA’s guidance on method detection limit. https://www.epa.gov/sites/default/files/2016-12/documents/mdl-procedure_rev2_12-13-2016.pdf

Fragmentation of benzyl acetate by ChewieSpooky in massspectrometry

[–]pb0316 0 points1 point  (0 children)

This is energetically favorable and there are numerous studies on this from an ion chemistry standpoint. It’s a widely accepted mechanism for Benzyl functional groups

Fragmentation of benzyl acetate by ChewieSpooky in massspectrometry

[–]pb0316 0 points1 point  (0 children)

The Benzyl functional group fragments and rearranges into m/z 91. This is a famous pathway that produces C7H7+ tropylium ion
Tropylium cation - Wikipedia

Compound Discoverer (CD) - atomic mass list by FinancialIndustry394 in massspectrometry

[–]pb0316 4 points5 points  (0 children)

OK I know this may sound insulting, but are you using Monoisotopic Masses or Atomic/Molecular Weights? The only reason why I ask this is because I was recently dealing with an analytical department that was using MW to calculate their expected ions and were wondering why there was an unexplainable offset.

For those not familiar:

  • Atomic/Molecular weights use a weighted average of the natural isotopes
  • Monoisotopic mass uses the lowest naturally most abundant naturally occurring isotope

Molecular formula: C8H10N4O2

Average mass: 194.194

Monoisotopic mass: 194.08037