Air in syringe

Cory · Jun 16, 2017

After watching this:

I wonder are you supposed to take the air out of the 5ml syringe? I always leave it in because the instructions dont say take it out on the salifert.

Ocelaris · Jun 16, 2017

As long as you have the right volume without air, it doesn't matter if there is air at the top. If there was for some reason air in the tip I could see why you'd want to purge the air.

JimWelsh · Jun 16, 2017

Of course you are supposed to remove the air from the 5 mL syringe. This guy failed to do that. Even though he correctly pointed the syringe up and tapped it, he then failed to actually depress the plunger to expel the air at 1:11, and so even though he had just said, "make sure to get all the air bubbles out of it", he did not do so! As a result, he left appx. 0.5 mL of air (look closely at around 1:17 to 1:20 in the video) in his sampling syringe, so instead of taking 4 mL of tank water, he only took appx. 3.5 mL. No wonder the test produced a low result!

Cory · Jun 16, 2017

That was exactly what i was thinking lol

Cory · Jun 16, 2017

JimWelsh said:
Of course you are supposed to remove the air from the 5 mL syringe. This guy failed to do that. Even though he correctly pointed the syringe up and tapped it, he then failed to actually depress the plunger to expel the air at 1:11, and so even though he had just said, "make sure to get all the air bubbles out of it", he did not do so! As a result, he left appx. 0.5 mL of air (look closely at around 1:17 to 1:20 in the video) in his sampling syringe, so instead of taking 4 mL of tank water, he only took appx. 3.5 mL. No wonder the test produced a low result!

So the whole syringe in the 5ml syringe must be full of water including the tip correct?

Breadman03 · Jun 17, 2017

Edited out..I stand corrected

JimWelsh · Jun 17, 2017

^^^ Nonsensical poppycock.

JimWelsh · Jun 17, 2017

Cory said:
So the whole syringe in the 5ml syringe must be full of water including the tip correct?

You must deliver 4 mL of tank water as the sample material for this test. That is the goal. If there is air in the syringe when the plunger is at the 4 mL mark, and you deliver the sample to the testing vial, then you are not delivering 4 mL of tank water, because the air bubble displaces some of that 4 mL of volume. This should be painfully obvious. The sampling syringe must be absolutely free of air bubbles when delivering the sample.

FWIW, this is an entirely different issue from the question of the bubble of air in the syringe that contains the titrant. We are discussing how to properly deliver the sample in this thread.

Cory · Jun 17, 2017

If the pluger is completely down and i put it in tank water and pull back the plunger to the 4ml mark, there is always a small air bubble. Salifert doesnt say anything about the importance of thr 5ml syringe not having air present, but does about the 1ml for acid. So I assumed it wasnt a problem. Salifert should change their instructions because most are getting low readings then.

So does the tip of the 5ml syringe count towards the sample?

GoVols · Jun 17, 2017

Just checked my alk with the Red Sea Pro kit.
Test one with tip on and air bubble hit the same results as test 2 with the tip off and no air bubble.
So from what I can tell. The fluid that is in the tip makes up the difference for the bubble.

JimWelsh · Jun 17, 2017

Cory said:
If the pluger is completely down and i put it in tank water and pull back the plunger to the 4ml mark, there is always a small air bubble. Salifert doesnt say anything about the importance of thr 5ml syringe not having air present, but does about the 1ml for acid. So I assumed it wasnt a problem. Salifert should change their instructions because most are getting low readings then.

So does the tip of the 5ml syringe count towards the sample?

If you are only talking about the tiny bubble that results from the void in the very tip, then I agree that this is of little consequence. My earlier response was to the HUGE bubble the guy in the video had in his syringe, since that appeared to be what the question was about.

Randy Holmes-Farley · Jun 17, 2017

However much air is in the tip between the zero mL mark and the tippy end of the tip will correctly produce an air bubble in the syringe and is not impacting the result (unless this is a very unusual syringe that has 0 mL at the tip end and not at the full depression of the plunger).

So it is normal and expected to have that volume of air in the syringe and still dispense the correct volume of water. In this case, the tip has air in it at the end.

It is also correct to overfill the syringe with water and blow out the air while upside down to reach the 4 mL mark with the plunger. In this case, the tip has water in it at the end.

Both are correct if done properly.

Cory · Jun 17, 2017

JimWelsh said:
If you are only talking about the tiny bubble that results from the void in the very tip, then I agree that this is of little consequence. My earlier response was to the HUGE bubble the guy in the video had in his syringe, since that appeared to be what the question was about.

Yes thats what i was talking about. Yes i seen the huge bubble he had lol. Sorry i should have been more specific.