DIY Liquids not measuring correctly

[rickylford]

Hey everyone,

Just curious to see if anyone else has had this problem.. But I bought some 10mL plastic clear bottles from USPlastic and some syringes and dropped bottles, etc. from MyFreedomSmokes a long while back. Well, now that I'm measuring out my liquid, I've noticed that when I use any sort of calculator, especially this one my liquids never measure out correctly. For instance: using that calculator, if I'm making a 10mL mixture using a 60mg nicotine base and cutting it to 36mg with 5% water and 15% flavoring, it gives me this output:

ingredient	ml	drops*	% of total
PG or VG with nicotine	6.0 ml	120 drops	60.0%
PG or VG (no nicotine)	2.0 ml	40 drops	20.0%
Water	0.5 ml	10 drops	5.0%
Flavoring(s)	1.5 ml	30 drops	15.0%

Now, that's all fine and dandy. It adds up to 10mL with no problems. For the 6.0mL ingredient, I'm using my 60mg nicotine base. For the 2.0mL PG/VG no nicotine ingredient, I'm using my VG that I got from Walmart. For the 0.5mL I'm using purified water we got from the local water machine. And for the 1.5mL flavoring ingredient, I'm using Capella flavorings. All of those ingredients equal 10mL, which is great, because that's what I want.

However, when I measure it out using my syringes, etc., when I go to mix it in the bottle, it's as if about .3mL and sometimes .5mL of liquid just "disappears." I tested this out by putting all of my ingredients into a 10mL syringe and it came out to about 9.6mL, not the full 10mL that I had measured out using a smaller 3mL syringe.

So, I must ask.. Do any of you have ANY sort of idea on why this is happening? It blows my mind completely and I can't figure out for the life of me why this keeps happening.

 

[Hoosier]

When you measure with your syringes do you use the point of the plunger or the seal?

 

[Spazmelda]

I think that's about as accurate as you can get with a syringe. They are not the most accurate of measuring instruments. I tried to search for information on acceptable error for syringe, but it seems to depend on the brand, volume, and etc...

I'd think that +/- 0.25 ml for each measurement made would be within the realm of possibility, so if you figure you are making 4 separate measurements and each one could be off by 0.1-0.2 ml, you can see how those could easily add up to 0.3 to 0.5 ml. Also, you don't really know the accuracy of your 10 ml syringe either. It could also be off by a similar amount. So really, getting to within half a ml of your desired final volume is 'close enough', IMO.

 

[Cookster]

how about using a graduated cylinder? That should get you as close as possible, better than a syringe.

 

[rickylford]

When you measure with your syringes do you use the point of the plunger or the seal?

I use the side edge of the black rubber stopper thing. I don't use the very center pointy part of it. Should I?

 

[rickylford]

how about using a graduated cylinder? That should get you as close as possible, better than a syringe.

I probably should upgrade to some better equipment if I want to get in better control of my vaping levels. I looked up some graduated cylinders this evening, but the only ones I could find were like 50mL+. Do you know of a good source to around a 10mL graduated cylinder online? Plastic, glass, doesn't matter to me.

 

[Hoosier]

I use the side edge of the black rubber stopper thing. I don't use the very center pointy part of it. Should I?

Yep. Once you do I bet you'll be less than 1% off.

 

[LucentShadow]

I've never figured out how different needle gauges and lengths could be properly accounted for, or whether they are an issue at all with the proper technique. I suppose that if you just do one slow push, then the needle retains it's own volume in liquid.

Anyway, there was an interesting thread started by a chemist here quite some time ago, that pointed to the possibility that adding liquids of differing densities together could result in a volumetric amount that did not equal the sum of the parts.

I don't know if he ever satisfied his curiosity on that issue, but he makes a seemingly good point about mixing in such a way as to ensure the correct nicotine ratio in that thread.

 

[Spazmelda]

Yep. Once you do I bet you'll be less than 1% off.

Where do you get that info from? Curious really (meaning im not trying to be snotty) because that's not the way I learned how to measure with a syringe. E.g. http://health.prenhall.com/olsen/pdf/Olsen_ch7.pdf, describes the way I was taught to measure with a syringe.

Is there some reason it would be different for DIY liquids?

Also, I found this info earlier. I couldn't find ISO 7886 without paying for it but this summarizes the accuracy requirements for hypodermic syringes.

"Syringe manufacturers are expected to meet ISO 7886, the standard for Sterile Hypodermic Syringes for Single Use, among other published quality and accuracy guidelines. This standard includes the expected accuracy limits for delivery volumes. These limits are stated as ± 5% at half scale and ± 4% at full scale. According to the standard, therefore, if a syringe is filled manually and its air expelled leaving the plunger position on the 10 mL line, the volume dispensed must be between 9.6 and 10.4 mL. Or, if the syringe contains exactly 10 mL, its plunger position must be between the 9.6 and 10.4 mL graduation lines. Since plastic syringes are injection molded, variations in the molded parts are low, relative to the ISO standard. However, the placement of the graduation lines on the syringe barrel may vary significantly relative to the ISO standard.
Assuming that process variations are normal with very good production capability, (that is, a process capability index or Cpk of 1.3) statistics predict the following results from manual syringe filling of a 10 mL volume, using the graduation marks:
• Less than 67% of the volumes would be within ± 0.1 mL
• Less than 85% would be within ± 0.15 mL
• Less than 95% would be within ± 0.20 mL of the desired volume."

 

[glassmanoak]

This trick might help:
When I draw liquid into the syringe, I draw a bit of air in first, before I start drawing in liquid. That way you measure where the liquid is, not the bottom, side or whatever of the plunger against the marks on the syringe side. The plunger will have absolutely nothing to do with your measurement that way.

In chemistry class, I was always to measure the bottom of the liquid surface, not where is goes up the side. I think this is called the "meniscus".

 

[MiamiMom63]

I prefer to use a 10 ml cylinder. I have a plastic one and glass one. I thought the glass one would help keep the VG from sticking to the sides so much but it doesn't really help alot. You can get them from MyFreedomSmokes.com, or alot of other places. Maybe OneStopDIYShop also. I'm not sure. They are easy to use. I tend to use my syringe mostly for the flavor extracts.

 

[Hoosier]

I'm not reading standards Spaz, just what I've learned with my syringes and graduated cylinder.

Give it a go and see. (if I encounter my stuff off by 1%, or more, I toss the offending syringe, but that's rare.)

 

[chaos-7]

I use the side edge of the black rubber stopper thing. I don't use the very center pointy part of it. Should I?

Yes, you should always use the center point of the plunger.

 

[zengargoyle]

The center point of my syringe looks like 'T' where there's a proboscis that drops down to fill the area that connects the needle tip to the syringe body. Measuring from that would be way wrong. The bottom of the edge of the plunger is even with the bottom edge of the 0ml line when empty, it only makes any sense that the bottom of the edge of the plunger is at 1ml when filled with 1ml.

 

[Cookster]

I probably should upgrade to some better equipment if I want to get in better control of my vaping levels. I looked up some graduated cylinders this evening, but the only ones I could find were like 50mL+. Do you know of a good source to around a 10mL graduated cylinder online? Plastic, glass, doesn't matter to me.

Wizard Labs

 

[glassmanoak]

This trick might help:
When I draw liquid into the syringe, I draw a bit of air in first, before I start drawing in liquid. That way you measure where the liquid is, not the bottom, side or whatever of the plunger against the marks on the syringe side. The plunger will have absolutely nothing to do with your measurement that way.

In chemistry class, I was always told to measure to the bottom of the liquid surface, not where is goes up the side. I think this is called the "meniscus".

I don't think that I'm explaining myself very well, but please try this.
Draw a little air into your syringe, then put the tip of the syringe into the liquid you are wanting to measure. Pull liquid into the syringe past the mark you want to measure. If you look into the syringe from the side, you will see the fluid with an air space above it. It's like reading a graduated cylinder. Push the plunger down until the meniscus of the liquid is at the mark you want. The position of the plunger or the shape of the plunger has nothing to do it.. just the position of the liquid inside the marked syringe.
I hope I've made myself clear. By taking the air into the syringe first, before taking in the liquid, you've turned the syringe into a small graduated cylinder, and,depending on the size of the syringe, you can get a very accurate measurement. You can't expect to measure accurately to .1 ml if you're using a 10 ml syringe. Use a 1 ml syringe or a half ml syringe. The size of the syringe should be close to the amount of liquid you wish to measure.

Hoosier, I hope you try this, because you have a way with describing things to new DIYers.

 

[vsummer1]

I don't think that I'm explaining myself very well, but please try this.
Draw a little air into your syringe, then put the tip of the syringe into the liquid you are wanting to measure. Pull liquid into the syringe past the mark you want to measure. If you look into the syringe from the side, you will see the fluid with an air space above it. It's like reading a graduated cylinder. Push the plunger down until the meniscus of the liquid is at the mark you want. The position of the plunger or the shape of the plunger has nothing to do it.. just the position of the liquid inside the marked syringe.
I hope I've made myself clear. By taking the air into the syringe first, before taking in the liquid, you've turned the syringe into a small graduated cylinder, and,depending on the size of the syringe, you can get a very accurate measurement. You can't expect to measure accurately to .1 ml if you're using a 10 ml syringe. Use a 1 ml syringe or a half ml syringe. The size of the syringe should be close to the amount of liquid you wish to measure.

That ^. Not to be rude, but why would anyone be messing around with chemistry without even knowing how to use basic measuring? It is the same with ANYTHING you measure, including a large measuring cup for cooking, you measure at the meniscus. You wouldn't want to use a big measuring cup to measure something small right?

Meniscus:
A concave surface of a liquid resulting from surface tension. The bottom of the meniscus is used to measure the volume of a liquid in apparatus such as a graduated cylinder.

 

[zoiDman]

When I do DIY, I don’t get too Hung Up on numbers. The Only thing that is Important to me is can a DIY recipe be Repeated with a Reasonable level of Accuracy.

If I do a 10ml DIY mix and when I’m done it has a Total Volume of 9.5ml, that cool. As long as the Next time I do the mix I get the Same Volume and the Same Proportions of Ingredients.

 

[glassmanoak]

vsummer1, you'd be surprised! Look at some of the DIY questions asked

MY point was to draw air into the syringe first. We are usually taught that air in a syringe is absolute evil. Well, it is IF you are injecting someone or something. In this case, it is about turning a syringe into a small graduated cylinder

 

[zengargoyle]

Using the meniscus with air above it to measure in a syringe is just wrong. It may be easier for you to get reproducible results; it is the right method for graduated cylinders, beakers, flasks and the like (which are calibrated to use the meniscus, and calibrated to the meniscus of a specific liquid). But that's not how a syringe works. Using that method, the actual volume of liquid would change depending on the needle attached. That is there is fluid in the needle and the bit that screws to the syringe and there is fluid in the body of the syringe. If you use a bigger or longer needle then there will be more fluid if you just measure by meniscus.

What you do is this (for say 1ml):

draw in 1ml of air into syringe.
insert syringe into bottle and hold upside down.
inject air into bottle.
draw .5ml of fluid. There will be a small air buble at the needle end of the syringe, this is the air that was in the needle tip part. inject this back into the bottle. let's say push .25ml or so + the air back in the bottle.
draw fluid down to 1ml mark. You now have 1ml of fluid in the body of the syringe, and a needle full of fluid, and no air bubbles anywhere.
remove and inject into wherever.
there will still be fluid in the needle bit, that is waste and you just pump it out into a vaper towel or something.

If you measure by meniscus with an air buble between the liquid and the plunger, you'll end up with the liquid in the syringe (1ml) PLUS whatever liquid it takes to fill the needle part. If you change needle tips to a longer or larger bore needle and keep using the meniscus method you'll end up with two different amounts of liquid because there will be more in the needle part.

If you instead do it properly, you'll end up with the same amount of liquid no matter which tip you use. You could have a 3 foot long 1/8" needle and still get the same amount of liquid.

Yes I know I'm being nitpicky and at the scale of things we're measuring something like being off by 0.05ml isn't going to be much of a difference. If you use the same syringe and same needle all the time, the meniscus method will give you the same amount of liquid each time, but it's won't be what you were trying to measure on the scale. Syringes are not closed bottomed cyinders and aren't designed to be read the same way.