Dead space in syringes is throwing off my dosing

[ultima thule]

I'm kicking off this thread because something's been bugging me whenever I get down to the final dose in a vial.

Each time I reach the end of a vial, that last shot ends up bigger than it should be. Take this: I mix 30mg of peptide with 3ml of bac water, which should give me 6 doses of 5ml each (or 5ml doses, whatever). I draw 5 shots of 50units using my 1ml syringe, but that final one always exceeds 50units—by around 10 units, give or take.

At first I figured it was just me being sloppy with measurements when only a few doses remain, causing the last one to run high. But the same pattern shows up with 10mg peptide in 1ml of bac, divided into just 2 doses.

So I dug into it and learned that the 2.5 or 3ml syringes I use for mixing have what's called dead space. That's the little tip area where liquid gets trapped and goes to waste. However, when I'm mixing peptide in a vacuum-sealed vial, all the bac water gets pulled in because the vacuum empties the syringe completely. So in the end, we're adding more bac water than we realize, just going by what the syringe markings say.

Next time I mix, I'll use 10 units less bac and check if my theory holds up.

Has anyone else run into this, and found a trick to prevent overfilling with bac water?

 

[BNLFL]

Is there any filtering going on?

 

[woundcarping]

The lyophilized puck itself takes up space—usually somewhere between .1 and .2ml. That lines up precisely with the extra "10 units" you're seeing.

If precision matters to you, then you compensate by changing how much bac water you add, factoring in that puck volume. That way, both your final volume and your concentration come out correct.

 

[Skidude]

ultima thule said:

I'm kicking off this thread because something's been bugging me whenever I get down to the final dose in a vial.

Each time I reach the end of a vial, that last shot ends up bigger than it should be. Take this: I mix 30mg of peptide with 3ml of bac water, which should give me 6 doses of 5ml each (or 5ml doses, whatever). I draw 5 shots of 50units using my 1ml syringe, but that final one always exceeds 50units—by around 10 units, give or take.

At first I figured it was just me being sloppy with measurements when only a few doses remain, causing the last one to run high. But the same pattern shows up with 10mg peptide in 1ml of bac, divided into just 2 doses.

So I dug into it and learned that the 2.5 or 3ml syringes I use for mixing have what's called dead space. That's the little tip area where liquid gets trapped and goes to waste. However, when I'm mixing peptide in a vacuum-sealed vial, all the bac water gets pulled in because the vacuum empties the syringe completely. So in the end, we're adding more bac water than we realize, just going by what the syringe markings say.

Next time I mix, I'll use 10 units less bac and check if my theory holds up.

Has anyone else run into this, and found a trick to prevent overfilling with bac water?

I've come across reports of people getting inconsistent measurements, and I've also run into situations where certain powders contribute extra volume. Take Glutathione as an example: for a 2 ml volume after reconstitution, I'd use 1.75ml.

 

[Herkimer P Shagnasty]

You could try an experiment using tap water plus a vial that's empty. Put water in, measuring it with the syringe you use for reconstituting, then pull the water back out using your injection syringes. Check whether the amounts line up that way.

 

[BNLFL]

An Easy Touch 1ml syringe that is typical retains roughly 0.003mL (3 μL) in its dead space.

 

[Skidude]

BNLFL said:

An Easy Touch 1ml syringe that is typical retains roughly 0.003mL (3 μL) in its dead space.

Weren't there a chart from you showing how to measure using a 3ml?

Someone posted one. That's yet another spot where folks struggle to measure correctly when they use bigger reconstitution cylinders.

Even though the math checks out, this applies when dealing with Tirz or a small amount of powder.

woundcarping said:

The lyophilized puck itself takes up space—usually somewhere between .1 and .2ml. That lines up precisely with the extra "10 units" you're seeing.

If precision matters to you, then you compensate by changing how much bac water you add, factoring in that puck volume. That way, both your final volume and your concentration come out correct.

 

[BNLFL]

Skidude said:

BNLFL said:

An Easy Touch 1ml syringe that is typical retains roughly 0.003mL (3 μL) in its dead space.

Weren't there a chart from you showing how to measure using a 3ml?

Someone posted one. That's yet another spot where folks struggle to measure correctly when they use bigger reconstitution cylinders.

Even though the math checks out, this applies when dealing with Tirz or a small amount of powder.

woundcarping said:

The lyophilized puck itself takes up space—usually somewhere between .1 and .2ml. That lines up precisely with the extra "10 units" you're seeing.

If precision matters to you, then you compensate by changing how much bac water you add, factoring in that puck volume. That way, both your final volume and your concentration come out correct.

I believe it's only a calculator for reconstitution.

 

[woundcarping]

Skidude said:

BNLFL said:

An Easy Touch 1ml syringe that is typical retains roughly 0.003mL (3 μL) in its dead space.

Weren't there a chart from you showing how to measure using a 3ml?

Someone posted one. That's yet another spot where folks struggle to measure correctly when they use bigger reconstitution cylinders.

Even though the math checks out, this applies when dealing with Tirz or a small amount of powder.

woundcarping said:

The lyophilized puck itself takes up space—usually somewhere between .1 and .2ml. That lines up precisely with the extra "10 units" you're seeing.

If precision matters to you, then you compensate by changing how much bac water you add, factoring in that puck volume. That way, both your final volume and your concentration come out correct.

After mixing, the R140 came out to .2ml more than the puck alone.

I wrote this down in a different thread on here:

"3ml of BAC went into the vial that came with it. I pulled out 3.2ml, put that into a 5ml vial, then put in .3ml of bac so the total ended up at 3.5ml."

 

[sheilarae74]

I’ve never reconstituted something and ended up with the exact dose count the vial was meant to yield. My assumption has always been that the filter eats some of it. Maybe the filler content in the powder plays a role too. I’m not a lab tech, so I really don’t know.

 

[HereKittyKitty]

For that exact reason, I recently picked up a few low dead space luer locks. I'm curious to test them out and figure out what the deal is.

 

[bbbilly]

I'd considered this before but assumed it wouldn't matter much (the puck), since it dissolves like a powder with lots of empty space. Hearing others mention it contributes .1ml to the total volume explains a lot about why my current batch (3, t30s into a new sterile vial) seems a bit weak.

Without realizing, I added an extra .3-4ml and messed up the math.

 

[Herkimer P Shagnasty]

bbbilly said:

I'd considered this before but assumed it wouldn't matter much (the puck), since it dissolves like a powder with lots of empty space. Hearing others mention it contributes .1ml to the total volume explains a lot about why my current batch (3, t30s into a new sterile vial) seems a bit weak.

Without realizing, I added an extra .3-4ml and messed up the math.

Assuming your calculations and premises hold up, you'd actually be receiving 91% of the intended dose. This gets worse when you use small water volumes and combine several vials into a cartridge or another container.

To reduce the problem, you could increase the water, for instance 2ml for each vial. That would bring you above 95% of the dose.

Alternatively, simply tweak the dose...

 

[woundcarping]

Herkimer P Shagnasty said:

bbbilly said:

I'd considered this before but assumed it wouldn't matter much (the puck), since it dissolves like a powder with lots of empty space. Hearing others mention it contributes .1ml to the total volume explains a lot about why my current batch (3, t30s into a new sterile vial) seems a bit weak.

Without realizing, I added an extra .3-4ml and messed up the math.

Assuming your calculations and premises hold up, you'd actually be receiving 91% of the intended dose. This gets worse when you use small water volumes and combine several vials into a cartridge or another container.

To reduce the problem, you could increase the water, for instance 2ml for each vial. That would bring you above 95% of the dose.

Alternatively, simply tweak the dose...

Alternatively, for each T30 vial you reconstitute, cut back on the bac water by roughly .1ml.

 

[Herkimer P Shagnasty]

woundcarping said:

Herkimer P Shagnasty said:

bbbilly said:

I'd considered this before but assumed it wouldn't matter much (the puck), since it dissolves like a powder with lots of empty space. Hearing others mention it contributes .1ml to the total volume explains a lot about why my current batch (3, t30s into a new sterile vial) seems a bit weak.

Without realizing, I added an extra .3-4ml and messed up the math.

Assuming your calculations and premises hold up, you'd actually be receiving 91% of the intended dose. This gets worse when you use small water volumes and combine several vials into a cartridge or another container.

To reduce the problem, you could increase the water, for instance 2ml for each vial. That would bring you above 95% of the dose.

Alternatively, simply tweak the dose...

Alternatively, for each T30 vial you reconstitute, cut back on the bac water by roughly .1ml.

Turns out my mother and Mrs. Blaylock did have a point.

Math really does matter in everyday life

 

[Herkimer P Shagnasty]

bbbilly said:

I'd considered this before but assumed it wouldn't matter much (the puck), since it dissolves like a powder with lots of empty space. Hearing others mention it contributes .1ml to the total volume explains a lot about why my current batch (3, t30s into a new sterile vial) seems a bit weak.

Without realizing, I added an extra .3-4ml and messed up the math.

Alternatively, filtering is an option. That method consistently appears to consume a few units.

 

[woundcarping]

Herkimer P Shagnasty said:

bbbilly said:

I'd considered this before but assumed it wouldn't matter much (the puck), since it dissolves like a powder with lots of empty space. Hearing others mention it contributes .1ml to the total volume explains a lot about why my current batch (3, t30s into a new sterile vial) seems a bit weak.

Without realizing, I added an extra .3-4ml and messed up the math.

Alternatively, filtering is an option. That method consistently appears to consume a few units.

Getting rid of the leftover reconstituted volume doesn't alter the concentration at all.

 

[lessthanhalf]

I'm not convinced the math checks out. When you add 0.1ml into 3ml of bac water, that's a 1/30 ratio (3.33%), or 1/31, but either way it's close. That means the largest possible error for any given dose is 3.3%. In practice, that's well inside the normal range of error you get from eyeballing doses in a small insulin syringe, and once you factor in tiny air bubbles and similar issues, doses are probably off by even more than that on a regular basis (my guess would be around +/- 0.1ml per dose, or 0.05ml if you're really careful). So my take is that this doesn't actually matter, because it falls within the measurement error you're already dealing with, and there's no method that would make it any more exact. That said, I am somewhat surprised that your dosing was consistent enough for you to pick up on this at all, and a 3% swing in dose is irrelevant, too minor to detect or have any real-world impact.

 

[Herkimer P Shagnasty]

lessthanhalf said:

I'm not convinced the math checks out. When you add 0.1ml into 3ml of bac water, that's a 1/30 ratio (3.33%), or 1/31, but either way it's close. That means the largest possible error for any given dose is 3.3%. In practice, that's well inside the normal range of error you get from eyeballing doses in a small insulin syringe, and once you factor in tiny air bubbles and similar issues, doses are probably off by even more than that on a regular basis (my guess would be around +/- 0.1ml per dose, or 0.05ml if you're really careful). So my take is that this doesn't actually matter, because it falls within the measurement error you're already dealing with, and there's no method that would make it any more exact. That said, I am somewhat surprised that your dosing was consistent enough for you to pick up on this at all, and a 3% swing in dose is irrelevant, too minor to detect or have any real-world impact.

He is combining 3 vials into 1.

Even so, yeah

 

[Herkimer P Shagnasty]

woundcarping said:

Herkimer P Shagnasty said:

bbbilly said:

I'd considered this before but assumed it wouldn't matter much (the puck), since it dissolves like a powder with lots of empty space. Hearing others mention it contributes .1ml to the total volume explains a lot about why my current batch (3, t30s into a new sterile vial) seems a bit weak.

Without realizing, I added an extra .3-4ml and messed up the math.

Alternatively, filtering is an option. That method consistently appears to consume a few units.

Getting rid of the leftover reconstituted volume doesn't alter the concentration at all.

That's correct. It's unexpected that bbbilly picks up on it. A few percent either way doesn't concern me. Still, everyone's different