For reference: a 29G needle · 2.5 mg/mL.
I would like the arithmetic checked rather than the conclusion asserted.
I have deliberately not used an online calculator because I want to be able to check the result.
Can someone show the working rather than just the answer?
At 2.5 mg/mL every microlitre left behind is 2.5 µg, so a 50 µL hub costs 0.125 mg per draw and a 5 µL fixed-needle barrel costs 0.0125 mg. Multiply by the draws, not by the doses: ten draws through a 50 µL dead space is 1.25 mg gone, which at 2.5 mg/mL is 0.5 mL of solution you paid for and never administered. Against a 2 mg dose that 50 µL is 6.3 per cent; against a 0.25 mg dose it is 50 per cent, which is why the loss matters most at exactly the doses where you can least afford it. a 29G needle has a bore, a hub and a length, and the hub dominates: a fixed-needle insulin barrel has almost none, a luer connection has a measurable one before the needle even starts.
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.
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.
| 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 |
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.
Syringe residual volume has been measured properly, mainly in the infection-control literature, with a median residual of about 84 µL for a conventional 1 mL syringe with a detachable needle and roughly 2 µL for a fixed-needle low-dead-space design.
Buy the right syringe — a fixed-needle insulin syringe is cheap and solves the problem.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemStart from the worked arithmetic: a 10 mg vial reconstituted with 2 mL gives 5 mg/mL. One hundred microliter draws are 0.5 mg each. At 84 µL dead space per draw, half your vial disappears into the hub.
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.
Mechanically, configuration B — 0.5 mL fixed-needle U-100 insulin syringe, dead space 2 µL: volume removed per draw = 100 + 2 = 102 µL.
Published inter-laboratory comparisons of dead-space measurements on identical syringes show good agreement, suggesting the numbers are reliable.
If cost matters, this is the first thing to change, not the last.
Put another way, 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.
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 noting: draw size matters enormously — the smaller your draws, the more the syringe architecture matters.
The switch nearly doubles your vial, which is better than most other optimisations combined.
edited 17 Jan 2026 by dead_volume — added the method parameters
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 luer cone of the syringe plus the needle's own plastic hub accounts for the vast majority of the dead space.
One qualification: the dead space does not affect the dose accuracy if the hub was full of solution at the start of the draw.
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.
edited 18 Apr 2026 by u100_marks — corrected a unit error in the worked example
Changing syringe architecture changes everything, while changing needle gauge changes almost nothing.
Delivered peptide = 10 x 0.5 mg = 5.0 mg. Lost to dead space = 10 x 84 µL = 840 µL x 0.005 = 4.2 mg. Yield = 50 per cent.
The caveat is that dead space is a yield loss and not a dose-accuracy loss, so the person feeling this loss most is the person with the most total draws.
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.