My setup is a refrigerator with a logger and a small work area I wipe down, nothing more.
I have worked this out and I would like someone to find the error, because I suspect there is one.
My working so far, for the record, is below, and I am fairly sure the error is in the unit conversion rather than the algebra.
Where is my error, and what is the correct working?
The switch to a low-dead-space syringe nearly doubles your usable vial, which is better than switching suppliers if you are looking for cost savings.
The complete rule: fix the syringe architecture first, and then the reconstitution volume becomes a free choice you can make on stability grounds rather than on economics.
| Configuration | Dead volume | Loss at 5 mg/mL | Over 20 draws |
|---|---|---|---|
| Fixed-needle insulin syringe | 3–5 µL | 15–25 µg | 0.3–0.5 mg |
| Low-dead-space, detachable | <2 µL | <10 µg | <0.2 mg |
| Standard luer-lock + 30G | 35–60 µL | 175–300 µg | 3.5–6 mg |
| Luer-lock + 21G drawing needle | 70–100 µL | 350–500 µg | 7–10 mg |
Corollary that follows immediately: changing needle gauge or length barely changes your losses.
The World Health Organisation guidance on injection equipment adopted the same high-versus-low dead-space distinction, using a low-dead-space threshold in the low single-digit microlitres.
One qualification: the dead space does not affect the dose accuracy if the hub was full of solution at the start of the draw.
The switch nearly doubles your vial, which is better than most other optimisations combined.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsSpecifically, at 100 µL draws the dead-space penalty with a luer-lock is 84 per cent per draw — the cost is genuinely catastrophic.
Be sceptical of anything advertised as low dead space that retains a conventional plunger tip: if you can look into the fitting with the plunger fully forward and see an open conical void, that void is your dead space.
Low-dead-space syringe designs either have the needle bonded directly to the barrel — a fixed-needle syringe, which is the cheapest route — or add a moulded projection on the plunger tip that fills the luer cone.
If cost matters, this is the first thing to change, not the last.
More usefully, dead space is irreducible with a high-dead-space syringe, which is why the hardware matters more than any technique.
At 5 mg/mL that is 15 to 25 µg lost per draw on the insulin syringe and 175 to 500 µg on the luer-lock — which over ten draws is the difference between losing a rounding error and losing half a milligram.
Worth being precise here: configuration A — 1 mL luer-lock plus detachable needle, dead space 84 µL: each draw removes 100 + 84 = 184 µL. Draws available from 2,000 µL = 2000 / 184 = 10.87, so 10 full draws.
Published inter-laboratory comparisons of dead-space measurements on identical syringes show good agreement, suggesting the numbers are reliable.
Buy the right syringe — a fixed-needle insulin syringe is cheap and solves the problem.
edited 7 Sept 2025 by tabular_nums — tightened the wording; no substantive change
Worth being precise here: dead space is the volume trapped in the syringe hub and needle after the plunger bottoms out, and it is the reason your 10 mg vial yields only 9.5 mg of usable draws.
Dead space quantified: a fixed-needle insulin syringe holds roughly 3 to 5 µL in the hub and needle after the plunger bottoms out. A luer-lock syringe with a detachable needle holds 35 to 100 µL depending on the hub design.
Write the arithmetic on the vial label. It costs nothing and it removes the step where you reconstruct it from memory at an inconvenient moment.
To be exact about it, this is arithmetic, so let us do the arithmetic and see where the losses actually are.
The needle lumen volume is under a microlitre in a typical fine-gauge configuration, so the needle is not the problem.
The practical summary: fine gauge, gentle swirl, diluent down the wall, room temperature before drawing, and check the syringe scale against the barrel rather than against your assumption.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.