Syringe Dead Space and Dosing Confusion with Peptide Vials

Did you post a diagram earlier showing how to read the 3 ml syringes? Some people struggle with those larger ones too. The math makes sense especially with lower-volume powders.

It was probably just a reconstitution calculator.

In one case the powder added an extra 0.2 ml. I put in 3 ml of bac water, drew out 3.2 ml, moved it to a larger vial, and then added another 0.3 ml to reach a final 3.5 ml.

If the numbers are right you are actually getting about 91 percent of the intended dose. The effect grows when you combine several vials into one container. Using a larger total volume of water, such as 2 ml per vial, would bring the accuracy above 95 percent, or you could simply raise the amount you draw.

You could also reduce the bac water by roughly 0.1 ml for each of those vials.

Math really does matter here.

Filtering is another option, though it always seems to leave several units behind.

Removing liquid that stays in the filter does not change the concentration of what remains.

The person combined three vials, but the point still holds.

I am surprised anyone can detect a few percent difference. I do not worry about variations that small.

I only have 5 ml sterile vials and combined four of them total. Now that I understand the volume issue I can dose more accurately for everyone involved. We all noticed this batch felt weaker. Being nearly 10 percent under what we expected was noticeable enough that we considered increasing the draw by a unit or two. I had calculated 0.227 mg per unit at the time. This is exactly why I keep checking the forum. I would have just assumed the batch was under-strength and kept going. Combining three vials with 4 ml of water changed the math by about 0.021 mg per unit. A couple of us are very sensitive to dose changes.

When three vials are combined the extra volume reaches 0.3 to 0.4 ml. In a 3 ml total that is roughly a 9 percent error, and even with 4 ml it stays around that level. In my own test I ended up with 3.5 ml total for 140 mg, giving 40 mg per ml. Without correction the concentration would have been about 5 percent low. The claim that typical dosing error is 0.05 to 0.1 ml seems overstated for a 0.3 ml syringe whose marks are only 0.005 ml apart. Plunger placement within one or two marks is realistic, and bubbles are usually no larger than a single mark.

Have you verified the actual delivered volume of your mixing syringes? Some models have printing tolerances up to 10 percent. These are not precision lab instruments.

I had not checked that, but I plan to. I will follow the empty-vial test suggestion. I bought the syringes from a medical supply store rather than online, so I assumed they would be accurate, but maybe that trust was misplaced.

It is not really about trust. These syringes are made to show broad differences, not fine measurements. Labs use calibrated pipettes for small volumes. Because we work at small scale with different tools, we run into these volume issues. If the difference matters, lowering concentration or correcting the final math helps, but some liquid will always remain in the syringe or vial. It is like the residue left in a mixing bowl; you cannot recover everything.

I usually try to keep concentration at 10 mg per 1 ml when possible. In that case an extra 10 units changes the dose by 1 mg, which is significant. I will still test the syringes to see what is happening.

Two- or three-dose vials are still multi-dose vials; the label does not change anything here. The powder occupies space regardless. Withdrawing the entire contents is a separate choice from what the actual concentration is. If it helps, simply draw a little extra on the first dose and the last one will land where you expect. Adding 3 ml to a powder that contributes 0.15 ml will always give more than 3 ml total.

My earlier math and reading were off by a factor of ten because I missed how the vials were combined. Dose accuracy should be within 0.01 ml or better; it is easy to misplace a decimal.

That matches what happened to me recently. I reconstituted one vial with 1.6 ml and planned 40-unit doses, but the fourth draw came out at 55 units. I just used it anyway and later realized the powder volume was the likely reason.

That explanation fits the extra volume at the end. Are the mixing and injection syringes accurate enough for the volumes involved?

I used two 0.5 ml syringes for a 10 mg vial, both the same brand.

So 0.5 ml and 1 ml versions of that brand? What about the syringe used to add the water, and are you filtering?

The unit markings are the same across sizes. I actually used a 1 ml syringe to add the water and 0.5 ml syringes to draw doses.

No filtering.