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  #1  
Old 08/25/2002, 12:41 PM
bpelkey bpelkey is offline
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Seachem Calcium Test pipette

I need help.

When I use the Seachem Calcium test I never am sure that I got the corrrect water amount in the pipette. My method - as for the other Seachem test kits with smaller pipettes - is to squeeze the bulb of the pipette and put the bottom of the pipette into the aquarium water, then release the bulb pressure gradually while watching the water come up to the 1 ml (?) mark. When I see it's at the proper level, I try to pull the pipette out of the water while maintaining the same bulb pressure, but unlike the smaller pipettes provided with other Seachem kits, the larger pipette's water level lowers as soon as I lift it from the water. I can't seem to get the water level to lock at the proper mark.

What am I doing wrong, or what should I try?

Thanks very much!

Brian
  #2  
Old 08/25/2002, 04:22 PM
Randy Holmes-Farley Randy Holmes-Farley is offline
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I've not used this kit in many years, so I'm not experienced with it, but here's a general comment on such things:

You are doing fine when you get to 1 mL and pull the bulb from the water. Then, unless the water rises all of the way into the bulb itself, there is no reason to try to hold it at exactly 1 mL. It is OK to suck up a little air below the fluid, let the fluid rise a bit above 1 mL, and then just blow it all out when using it (I'm presuming that you use the 1 mL all at once; if not, it is trickier).
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  #3  
Old 08/26/2002, 02:36 AM
Goofnut Goofnut is offline
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What I do is immediately release the pressure on the bulb after I pull it out of the water and then invert the pipette as air lifts the water up into the bulb. I use the same method you do to get the water into it intially.

The biggest problem I had with this kit is getting all of the air bubbles out of the syringe when pulling titrant out of the bottle. What I do now is to leave that small amount of titrant in the tip of the syringe after a test and then cap it tightly with the syringe cap. The next time I use it, I just dip it in the titrant bottle and pull up. Voila! No more air bubbles!
  #4  
Old 08/27/2002, 02:25 PM
Dman Dman is offline
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Goofnut,
I not entirely sure of this, but I was under the impression that the cylinder of the syringe is calibrated to 1ml, and space outside of the cylinder below the plunger and subsequently the air bubble is not figured into the equation. No need to store that tritant in the tip, it's just displacing space not required in the equation.
Dman
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  #5  
Old 08/27/2002, 10:51 PM
Goofnut Goofnut is offline
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I had to break out the instructions to be sure - I believe after reading them that the syringe tip is not directly used in calculating the volume, but since some titrant remains in the tip when fully depressing the plunger, it is essentially a filler taking up the "void" space.

The kit indicates that there should not be any air bubbles in the syringe when filling it from the titrant bottle. After ensuring that the bubbles are removed, it instructs you to pull the plunger up to the 1.0cc marking. It later states "Once true blue color is obtained, withdraw into the syringe any titrant hanging from the tip of syringe so that titrant is flush with the tip before reading volume of titrant used in titration."
  #6  
Old 08/27/2002, 10:55 PM
Goofnut Goofnut is offline
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Sure, you can do it with air in the "void" space as well. It's just more complicated -air trapped in a liquid doesn't behave very predictably
  #7  
Old 08/27/2002, 11:41 PM
Dman Dman is offline
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I don't suppose it really makes much of a difference as your counting out or measuring the tritant used from the backend so to speak, just so long as when you push 1cc of tritant out of the syringe,1cc actuall does come out. It would be irrellevant until you got to the point where you had exhausted the syringes' contents, even then it wouldn't matter as the space from the tip to the beginning of the cylinder isn't part of the measurement, so if it was filled with air or tritant it still wouldn't come out, sorry just typong out loud
Dman
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