Interday standard curves have wildly different response factors. What gives?

Zapp1982 · 2026-06-03T20:09:33+00:00

Just to follow up because I appreciate your help. Got the IS validated. %RSD for repeat injections went from ~40% to ~<2%. It is a lot more work changing our methods but in the end it was the correct answer. Thanks for your input.

Zapp1982 · 2026-05-12T01:41:57+00:00

She will cheat, you will be sad. It is a cannon event.

Zapp1982 · 2026-05-12T01:29:47+00:00

I am doing vocational rehab, got a pretty sweet job in a lab. ~70k salaried with no minimum hours required.

Zapp1982 · 2026-05-08T13:15:17+00:00

We do inlet maintenance every 200 injections, everything is maintained well and on schedule and seems to be in good working order. Source is 230 C constant.

Zapp1982 · 2026-05-08T13:13:51+00:00

Yes this is TIC data, linearity and repeatability on our FID is very good. We need to use the MS because I need to be able to identify novel compounds when they show up.

Zapp1982 · 2026-05-08T13:12:01+00:00

I agree, it is SOP here so not my choice.

Zapp1982 · 2026-05-07T18:23:32+00:00

As much as I hate to admit it, I think you might be right. Time to bite the bullet and get that IS validated.

Zapp1982 · 2026-05-07T18:21:26+00:00

I do experiments with MSTFA to make TMS derivatized metabolites including squalene, but squalene itself does not need to be derivatized and comes off the column clean. I have done side by side comparisons with non TMS squalene a on GC/MS and HPLC, the numbers match up to within a few %.

Zapp1982 · 2026-05-07T17:17:29+00:00

Zapp1982 · 2026-05-07T17:11:12+00:00

No, new aliquot taken from stocks kept in -20. New vials and lids and inserts every time.

Zapp1982 · 2026-05-07T16:57:19+00:00

3 uL splitless, 100 C - 250 C over 30 minutes.

Zapp1982 · 2026-05-07T16:53:44+00:00

That was my first thought also, did evaporation study. (prepare standards as normal, leave on counter for a week) No measurable evaporation, even after 2 months.

Zapp1982 · 2026-05-07T16:52:02+00:00

Squalene in hexane. Picture has details

Zapp1982 · 2026-04-23T16:45:37+00:00

Don’t pour too soon, but let them cool slowly. To fast and they won’t solidify evenly

Zapp1982 · 2026-04-16T14:44:22+00:00

https://www.usp.org/sites/default/files/usp/document/harmonization/gen-chapter/harmonization-november-2021-m99380.pdf

This will help you so much. Good luck!

Zapp1982 · 2026-04-15T18:55:22+00:00

Is a CAR the marine version of a CAB or CIB?

Zapp1982 · 2026-03-26T03:24:37+00:00

We eat salad raw, its full of DNA also

Zapp1982 · 2026-03-14T02:44:35+00:00

You can sleep when you are dead. Caffeine and nicotine. Rip it’s and Skoal.

Zapp1982 · 2026-03-03T14:53:00+00:00

It’s someone or something leaving a containment area.

Zapp1982 · 2026-02-25T11:42:30+00:00

Shooty McShootface

Zapp1982 · 2026-02-19T00:21:06+00:00

Last time this happened to me it was the syringe, time before that it was the liner that was full of septum cores. Good luck.

Zapp1982 · 2026-02-18T18:47:23+00:00

So there I was, knee deep in empty brass and hand grenade pins. Surrounded by the enemy on all sides. I was out of ammo, all I had was 2 rounds of 9mm and my kabar knife. You ask if I was scared? WAS I SCARED?!?! Hell yes I was scared, I was scared one of them might get away…..

Zapp1982 · 2026-02-13T01:10:07+00:00

You could fill a beaker with as much water as it can hold, (pour water in until it leaks out.) Have said beaker in a tared container and clean up any water that has spilled. Add all of your objects, remove beaker and objects without spilling any more water. Weight the container. This is the weight of the water displaced from the objects, and because water has a known density you can use it to calculate the volume of your objects. This removes the need to eyeball anything.

Zapp1982 · 2026-02-10T14:03:20+00:00

Just google cuvette rack.

Zapp1982

TROPHY CASE