Reef Chemistry Question of the Day #161 Using a Syringe

[Randy Holmes-Farley]

Curious - why use a syringe with a tip at all? (especially like the one in the example where its measuring CC volumes)? There is a risk of air going into the syringe if the tip has a small leak (unless submerged) - especially if its been taken off and put on multiple times.

With expensive pipetors, you always keep all the liquid in the disposable tip, so the device never gets dirty. They do not leak.

In the case of many of our hobby titration kits, i expect a goal is to use a tip with a tiny point so the drop size is smaller.

To be honest, I've never seen a tip/syringe connection actually leak so air goes in. They are usually designed to fit well.

 

[MnFish1]

That was the point I was trying to make

Yes , sorry - I meant to quote your post. I haven't used any reagents that required a tip on the syringe. Unless its on a pipette-like device where all the liquid stays in the actual tip. Now that I think of it some of the Red Sea kits have tips on their small syringes - to make smaller drops I guess for titration. I usually take them off

 

[MnFish1]

With expensive pipetors, you always keep all the liquid in the disposable tip, so the device never gets dirty. They do not leak.

In the case of many of our hobby titration kits, i expect a goal is to use a tip with a tiny point so the drop size is smaller.

To be honest, I've never seen a tip/syringe connection actually leak so air goes in. They are usually designed to fit well.

Thanks you beat me to it - I was just posting about the titration.

 

[orr2003]

Yes , sorry - I meant to quote your post. I haven't used any reagents that required a tip on the syringe. Unless its on a pipette-like device where all the liquid stays in the actual tip. Now that I think of it some of the Red Sea kits have tips on their small syringes - to make smaller drops I guess for titration. I usually take them off

I dont use them either. To expand on my theory some more. I have taken a syringe with the tip on and placed it down into the reagant bottle before with only the point of the tip submerged (lets say only a small amount of reagant left in the bottle, therefore you cant submerge the entire tip) and pulled up to the 1ml mark and the fluid line would be at .85ml. Then push the reagant back into the bottle and pull up again the same way to the 1ml mark and the fluid line read .82ml. My only explanation for the difference is the tip is allowing air to be pulled up at the same time thus the inconsistency and the reason I dont use the tips.

 

[Randy Holmes-Farley]

I dont use them either. To expand on my theory some more. I have taken a syringe with the tip on and placed it down into the reagant bottle before with only the point of the tip submerged (lets say only a small amount of reagant left in the bottle, therefore you cant submerge the entire tip) and pulled up to the 1ml mark and the fluid line would be at .85ml. Then push the reagant back into the bottle and pull up again the same way to the 1ml mark and the fluid line read .82ml. My only explanation for the difference is the tip is allowing air to be pulled up at the same time thus the inconsistency and the reason I dont use the tips.

Ever try that a few times without a tip to see if it matters?

Even without a tip you'll have an air gap.

 

[orr2003]

Ever try that a few times without a tip to see if it matters?

Even without a tip you'll have an air gap.

Not sure I understand the question. If I dont use the tip and expel the air everytime I know I am getting exactly 1ml of reagant. But I am probably just being OCD lol

 

[Randy Holmes-Farley]

Not sure I understand the question. If I dont use the tip and expel the air everytime I know I am getting exactly 1ml of reagant. But I am probably just being OCD lol

Even with no tip, there will be air between the liquid and the syringe plunger bottom if you draw just once. It is from the air present in the syringe bottom end between the plunger bottom and the very end of the syringe barrel.

My suggestion was that the differences you are seeing may not be from air leaking in if you put the tip on correctly (and it is the correct tip). If you drew liquid up without a tip, you might see that small variation too. FWIW, the numbers you quoted are likely within the claimed uncertainty of any but the most expensive syringes (0.85 ml being different than 0.82 mL).

The standard for accuracy of medical syringes is on the order of 4-5%. SO 0.82 and 0.85 is within required accuracy.

 

[orr2003]

Even with no tip, there will be air between the liquid and the syringe plunger bottom if you draw just once. It is from the air present in the syringe bottom end between the plunger bottom and the very end of the syringe barrel.

My suggestion was that the differences you are seeing may not be from air leaking in if you put the tip on correctly (and it is the correct tip). If you drew liquid up without a tip, you might see that small variation too. FWIW, the numbers you quoted are likely within the claimed uncertainty of any but the most expensive syringes (0.85 ml being different than 0.82 mL).

The standard for accuracy of medical syringes is on the order of 4-5%. SO 0.82 and 0.85 is within required accuracy.

See I told you I was just OCD lol.....but to your point about air with no tip, I pull up and down a few times on the plunger while submerged to expel any air in the syringe so I know I am getting exactly 1ml. I am sure this doesnt really matter in the grand scheme of things its just how I have always done it and at least I know I am being consistant in my methodology. I have thought about the droplet size before not using the tiny tip but just use the next drop after I see some color change and have always just stopped there. Definitely not as precise as the tiny droplet.

 

[siggy]

Not sure I understand the question. If I dont use the tip and expel the air everytime I know I am getting exactly 1ml of reagant. But I am probably just being OCD lol

Hanna has a video on using all their kits and explains all this in detail, they expressed not to try and expel the air it will alter the readings. Not sure if .03 would matter with most.

 

[orr2003]

Hanna has a video on using all their kits and explains all this in detail, they expressed not to try and expel the air it will alter the readings. Not sure if .03 would matter with most.

They mean not to expel the air with the tip on. This would definitely cause testing error as you would be drawing up more than 1ml. I expel the air without a tip which gives me precisely 1ml in the syringe. Can not alter the reading this way, impossible.

 

[Randy Holmes-Farley]

See I told you I was just OCD lol.....but to your point about air with no tip, I pull up and down a few times on the plunger while submerged to expel any air in the syringe so I know I am getting exactly 1ml. I am sure this doesnt really matter in the grand scheme of things its just how I have always done it and at least I know I am being consistant in my methodology. I have thought about the droplet size before not using the tiny tip but just use the next drop after I see some color change and have always just stopped there. Definitely not as precise as the tiny droplet.

My concern with such a method is that you have more than 1 full mL in the syringe.

If you just carefully push the plunger down once without any shaking, that will probably only dispense 1 ml and retain some liquid in the end of the syringe, but so if you intentionally or accidentally deliver the liquid that is in the end of the syringe, you will overdose.

 

[Randy Holmes-Farley]

They mean not to expel the air with the tip on. This would definitely cause testing error as you would be drawing up more than 1ml. I expel the air without a tip which gives me precisely 1ml in the syringe. Can not alter the reading this way, impossible.

Not so. You are drawing up more than 1 mL, and must be careful to not expel it all, even without an added tip, because the syringe itself always has volume between the end of the syringe and the zero mL line.

 

[Randy Holmes-Farley]

This is the air/liquid volume I'm discussing in a tipless use:

 

[siggy]

They mean not to expel the air with the tip on. This would definitely cause testing error as you would be drawing up more than 1ml. I expel the air without a tip which gives me precisely 1ml in the syringe. Can not alter the reading this way, impossible.

I was with you on this until I watched the video, I guess they account for the air gap in the syringe tip?
@Randy hit another provocative discussion over something so common, and yes after raising four children and OD-ing them Ill just stick to Brandy for now on

edit: Im always late

 

[orr2003]

My concern with such a method is that you have more than 1 full mL in the syringe.

If you just carefully push the plunger down once without any shaking, that will probably only dispense 1 ml and retain some liquid in the end of the syringe, but so if you intentionally or accidentally deliver the liquid that is in the end of the syringe, you will overdose.

I have thought about that before and try to only use the syringes that have the flat style plunger not the pointy type at the end and usually there is reagant left in the tip. But I see your point and might just start using the tips. I have always just rinsed the syringes out after use but I see the point of the air in the barrel as it expels all the reagant from the force of the air bubble. I need to change my ways!! lol thanks for discussing this with me as I see why to use the tip now.

 

[orr2003]

I was with you on this until I watched the video, I guess they account for the air gap in the syringe tip?
@Randy hit another provocative discussion over something so common, and yes after raising four children and OD-ing them Ill just stick to Brandy for now on

edit: Im always late

HAHA!!! I am going to do a comparison test using the tips and doing it my way without the tip and see what, if any, the difference is. Its possible I could be off on my results. I will do the Hanna checker alk and phosphate, Salifert Nitrate, Alk, Calcium, and Mag test tonight and report back. Not sure it will make a difference but lets see.

 

[Jeff Hall]

The correct answer is 1.6

 

[Jeff Hall]

The correct answer is 1.6ml

 

[Jeff Hall]

The answer is 1.6. I may not know everything about reefing but any half decent nurse knows how to use a syringe...

 

[Jeff Hall]

Actually on second thought, you would have to flip the syringe around to get the accurate amount its definitely not 2.8 mL because there is way to much air in the syringe but it's most likely not 1.6mL either because there is a small amount of fluid still in the tip. If you flipped the syringe around you could accurately measure it.