The specifics, since they change the answer: an 18G drawing needle · 6.67 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 6.67 mg/mL every microlitre left behind is 6.67 µg, so a 50 µL hub costs 0.334 mg per draw and a 5 µL fixed-needle barrel costs 0.0333 mg. Multiply by the draws, not by the doses: ten draws through a 50 µL dead space is 3.33 mg gone, which at 6.67 mg/mL is 0.5 mL of solution you paid for and never administered. Against a 2 mg dose that 50 µL is 16.7 per cent; against a 0.25 mg dose it is 133.4 per cent, which is why the loss matters most at exactly the doses where you can least afford it. an 18G drawing 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.
The underlying point is that dead space is irreducible with a high-dead-space syringe, which is why the hardware matters more than any technique.
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.
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.
Published inter-laboratory comparisons of dead-space measurements on identical syringes show good agreement, suggesting the numbers are reliable.
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.
Buy the right syringe — a fixed-needle insulin syringe is cheap and solves the problem.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsChanging syringe architecture changes everything, while changing needle gauge changes almost nothing.
Corollary that follows immediately: changing needle gauge or length barely changes your losses.
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.
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.
If cost matters, this is the first thing to change, not the last.
edited 8 Sept 2024 by t_oyelaran — added the placebo-arm figures
The short answer is that dead space is small in absolute terms and huge as a fraction of a small dose, which is why it feels like a rounding error and behaves like a systematic loss.
Draws available = 2000 / 102 = 19.6, so 19 full draws. Delivered peptide = 19 x 0.5 mg = 9.5 mg. Lost to dead space = 19 x 2 µL = 38 µL x 0.005 = 0.19 mg. Yield = 95 per cent.
More usefully, 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.
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.
The switch nearly doubles your vial, which is better than most other optimisations combined.
The single most important fact about dead space is that it is almost entirely in the hub cone, not in the needle, which is why changing needle gauge or length barely changes your losses.
The luer cone of the syringe plus the needle's own plastic hub accounts for the vast majority of the dead space.
The general principle here — that peptides adsorb and denature at air–liquid and solid–liquid interfaces — is standard formulation science, and it is why licensed presentations contain a surfactant such as polysorbate 20 or 80. A research vial does not, which is precisely why handling matters more, not less.
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.
The distinction that resolves most of these questions is understanding that dead space is a fixed volume — typically 3 to 5 µL in a fixed-needle syringe and 35 to 100 µL in a luer-lock — and its cost scales with how small your draws are.
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.
Worth noting: draw size matters enormously — the smaller your draws, the more the syringe architecture matters.
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.