Question on testing

[vijaym85]

Just wanted to make sure I am doing things correctly. So when I am doing one of those color change titrations I notice that there is always some reagent that gets traped in the tip of the syringe. Albeit, a miniscule amount, but still wanted to know if this is normal. I notice this when I go to replace the extra reagent back in the bottle. I also see this when I have a test that is off the charts and the plunger is all the way down but I can still see some residual amount in the tip of the syringe. So I just wanted to know if this is normal or if it might be skewing my results.
thanks

 

[Randy Holmes-Farley]

There should not be any significant reagent in the tip when the plunger is pushed all the way down. There should be air above the liquid in the syringe when held tip down, and you should not invert the syringe in an attempt to get the air out. This air will displace the reagent when you push the plunger all the way.

That said, tiny amounts of liquid remaining in syringes is unlikely to be important in most kits.

Which kits specifically are you asking about?

 

[vijaym85]

Hey Randy,
Well I am currently using the alk, ca, and mag kits by Salifert. When I place the pointed plastic tip on the syringe I notice traping of some reagent in it. So for instance when I replace the excess reagent back in the bottle I see some of it is stuck within the tip with the plunger pushed all the way down. So it makes me wonder if my readings are slightly lower or higher than what they should be. I do see the air level when I draw back to the 1ml mark, but if I cant ever use the complete 1ml and some of it is left within the tip it makes me wonder about the reading. I am sure it's not anything too major as its only a small amount. Just was curious if this is a common occurance and if that air line level would take this extra traping into account to correct for it OR if you should draw back slightly beyond the 1ml mark to correct for it? The later seems a bit more risky as it's hard to tell how much extra to go beyond without measuring this tiny volume, not to mention there are no gradations beyond 1ml.

 

[Randy Holmes-Farley]

You should draw up reagent with the tip in place already.

Is that what you do?

When you do that, there should be just enough air to blow everything out when you fully depress the plunger.