[Meta] the concentration rule is doing its job and people should stop complaining
the concentration rule is doing its job and people should stop complaining — with the counter-argument included, because I find it fairly persuasive.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Asked MKM what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
Spent 24 weeks confused about this until somebody drew the table for me. 10mg, 2mL, 5mg/mL, 2mg is 40 units. That is the whole thing.
Happy to answer the boring questions. Those are usually the ones worth asking.
best — the order this archive was captured in
Adding more water does not change how much peptide is in the vial. It changes the concentration, which changes the volume you draw for the same amount. That is the entire relationship.
The dead space question sent me down a rabbit hole for a week. It is a fraction of a unit and it is the same every draw.
Correction: that gives 5 units, not what you have written. 30mg into 3mL is 10mg/mL and the division follows from there.
The arithmetic in full: concentration is mass over volume, so 30mg into 2mL gives 15mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1.5mg is 1.5 divided by 15 millilitres, which is 10 units.
How many mg in the vial and how many mL are you adding?
Working has to be shown on arithmetic posts. Added a note asking for it rather than removing this one.
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do the arithmetic before you reconstitute, not while holding a syringe
dead space in the needle hub is real and it is small
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
Aim the stream down the wall of the vial rather than into the cake. Reconstitution is a solubility problem, not a mixing problem, and mechanical shear does nothing helpful.
Aim the stream down the wall of the vial rather than into the cake.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
I would not round that figure. At 30mg/mL a rounding error of two units is a real fraction of the intended amount.
Reconstituted at 3mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 10mg/mL on the glass before I put the cap back.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
the number you write down is the number you will trust at 6am
a U-100 syringe reads 100 units to the millilitre, every time
Research-use-only material is not approved for human use, so treat everything in this thread as arithmetic about solutions rather than instructions for a person.
What concentration did you actually reconstitute at, rather than what did you intend to?
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
- 1Adding more water does not change how much peptide is in the vial. It…9 comments in this branch · started by u/priya_weiss
- 2Aim the stream down the wall of the vial rather than into the cake.…9 comments in this branch · started by u/tl_dr_tina