I tracked dead-space loss across 3 syringe types for 8 weeks

Low-dead-space syringes are the only reason I switched. My 0.5mL fixed needles lost less than luer lock, but I never weighed it. Did you prime the luer hub before zeroing?

Wait, you're including the needle prime? Tha'ts not dead space, that's just priming volume. If you zero after priming, luer lock should look much closer.

I did zero after priming. Still saw about 0.04mL difference. Air bubbles in the hub were the wild card.

0.001g scale is not enough for 0.02mL. That's 20mg, assuming water density. You need 0.0001g or repeat 20 draws.

Agreed on scale resolution. Could you weigh 10 draws together and divide? That's what I do for my bac water storage logs.

I ran a similar test with 1mL slip tips and 0.3mL insulin pins over 6 weeks, weighing ten draws at a time on a 0.0001g scale. My average loss was 0.07mL for slip tip and 0.015mL for the fixed needle. Biggest factor was how far I inserted the needle into the vial; if I stopped at the shoulder, I pulled more air. Also, vial pressure after adding water changed the draw. Not saying your numbers are wrong, but technique swamped the syringe difference in my case. Did you keep insertion depth and venting identical?

Insertion depth is a good call. I also warm the vial in my hand for a minute, which seems to reduce bubbles.

Warming might help bubbles, but for storage I care more about rubber stopper coring than 0.02mL. Anyone seen more cores with 31g after multiple draws?

Ran a 5-week bench version of this with a 0.001g scale, 12 draws per setup, and landed on almost your exact split—0.018mL on the 0.5mL fixed-needle vs 0.071mL on the 1mL luer locks. The surprise was weighing the vials before and after instead of the syringes: the week-to-week error from eyeballing the draw line came out at ±0.09mL, which is bigger than the dead-space gap itself. So low-dead-space syringes are real, but the sloppier leak was just not drawing to the same mark every time and losing track of how much bac water had already gone in. Now every vial gets a piece of tape with the date and running total mL, and the 12-vial waste estimate dropped from about 1mL to 0.4mL. What size luer lock are you using, and are you weighing the vial or the syringe?

hi, I’m only week one and this might be a silly question, but did you weigh the vial before/after instead of the syringe? I tried that with my 0.01g scale for two draws and couldn’t see anything—too noisy. Wondering if 0.001g is truly necessary, or if you ever get static drift on the scale. Also, do you tare a fresh empty syringe each time? I’m still learning and don’t want to mess up my little notes.

night shift here. Weigh the syringe dry, wet, then after a full purge. That separates true dead space from leftover film. I did a colored-water test: 31g hub holds almost nothing, but the luer collar keeps a visible bead even when the plunger bottoms out. Also ceck scale

Fellow spreadsheet nerd: my trendline says yes, but it's a rounding error unless you're stretching every last drop.

This is the kind of spreadsheet nerdery I’m here for 😂

Honestly, i love this. One thing I’d add: at those volumes, evaporation and scale drift can masquerade as dead space. I started capping the syringe tip and weighing within 10 seconds, plus noting room temp/humidity on my log. My 0.001g scale also drifts if the AC kicks on, so I re-tare before each draw. Did you randomize the order of syringe types? If all the luer locks happened later in the session, water temp/evap could skew it. Not saying your trend is wrong—just a gentle confound check.

New variable: the receiving vial. Weigh it before and after each draw, then subtract by difference. That measures what actually lands in storage and ignores whether the leftover is dead space, film, or a bubble clinging to the plunger. Also, if you’re drawing from the same vial, internal pressure drops as you pull; later draws may underfill slightly even with identical technique. Are you randomizing draw order? If not, your 8-week average may be partly vial-pressure curve, not syringe geometry.

Hi! Very new here (week one), so take this with a grain of salt. Could your 31g fixed needles have a different needle length