salifert test kit question

[kevensquint]

Hello, when I do the last step in my Ca,Mg or Alk salifert test, I'm supposed to draw in the tritation liquid to the syringe so the plunger goes all the way up, then adjust the bottom of the plunger to 1ml and start from there. BUT, the liquid does not always go up to the same level when I draw it in. I'm assuming I need to get the liquid level to 1ml, then adjust the base of the plunger to 1ml to then start the dropping. Is this correct?

[downbeach]

There is always going to be a little air between the plunger and the top of the fluid in the syringe because the tip piece will hold some of the fluid, in addition to what's in the syringe itself. So, when you get the plunger to the 1ml mark you will see a gap.
I have had a bad, or loose tip that would suck a little air once in a while, which would give you less liquid than you should have. Make sure your tip is on tightly, if you still have a problem replace the syringe.

[disc1]

Nope. There should be an air gap between the liquid and the plunger. There is some volume in the tip and that's made up for by the air gap. You're really only interested in how much was actually delivered so you're really only going to use the difference between the starting and ending position of the plunger. It really doesn't matter how much air is there or not.

[Sport507]

The air bubble is caused by what the syringe tip holds. So you are really getting 1ml of tritation.

[kevensquint]

Ya, I think I explained too vaguely. I understand about the air gap which compensates for the long tip :)...but, my air gap is variable, sometimes its 1ml even, sometimes I have about 1.5 ml of air at the top, this affects my final reading. Exactly what is the correct amount of air to have in the gap between the bottom of the plunger and the top of the liquid? thanks

[disc1]

Ya, I think I explained too vaguely. I understand about the air gap which compensates for the long tip :)...but, my air gap is variable, sometimes its 1ml even, sometimes I have about 1.5 ml of air at the top, this affects my final reading. Exactly what is the correct amount of air to have in the gap between the bottom of the plunger and the top of the liquid? thanks

You can't have 1.5ml of air at the top it is only a 1 ml syringe.

You were perfectly clear. It doesn't matter how much air you have. You are only concerned with the difference. If you start with the plunger at 1ml and the level of the liquid is at .85ml and you push down until the plunger is at .5ml and the liquid is at .35ml you've delivered half a mil of titrant. Same story if the liquid level starts at .75 and goes to .25 . It is still half a ml. The difference is what matters, not how much started in the syringe.

There is no exactly how much air to have. The only thing you should care about is how far it changed from beginning to end and the air gap plays no part in that.

[downbeach]

There is always going to be a little air between the plunger and the top of the fluid in the syringe because the tip piece will hold some of the fluid, in addition to what's in the syringe itself. So, when you get the plunger to the 1ml mark you will see a gap.

I have had a bad, or loose tip that would suck a little air once in a while, which would give you less liquid than you should have. Make sure your tip is on tightly, if you still have a problem replace the syringe.

You will have some air in the syringe, but it should be the same amount of air each time. Make sure that your syringe is fully/constantly in the fluid while you're drawing it into the syinge. Make sure there isn't a crack in the tip, or it's not loose as mentioned above.