Salifert alk, cal, mag question

[slythy]

Should the 2 and 5ml syringes have a bubble in them when drawn? sometimes I get a bubble and sometimes I dont. Im assuming since 0 starts above the tip I should have a little one that occupies that space.

What do you guys do?

Thanks,

 

[DanyL]

The markings consider this space as part of the volume.
What I usually do is to pump water in and out a few times before filling the syringe until it is full of water, eliminating all bubbles.

That being said, all titration methods count the amount left so you can safely just ignore what's inside (bubble or not) and look at the markings.

 

[Crofty]

Yes, in my opinion the bubble should be there, especially for the cheap all plastic plunger syringes. If it isn't, when the plunger snapps closed it will expell the extra liguid that would otherwise remain in the tip. This results in up to an extra -0.1 ml. I tested this out of curiosity.
But in reality, it's probably best to just be consistent in how YOU do it. If your results are biased a few percent high or low who cares, as long as you have consistent results you will know how things are trending.

 

[DanyL]

While you are correct to say that in theory it adds some extra liquid when fully drained, it shouldn’t, because the part where the Bubble is can’t physically be dosed without pushing it with air, that is if the seal isn’t broken.

I’ve been taught by my father (which occasionally works in a lab as part of his job, reefer as well) that it is in fact how they use syringes in the lab, but as I mentioned earlier he also said what logically is true - that in practice it doesn’t really matter, probably because the only impact it has is on surface tension differences.

 

[DanyL]

As for consistency and what hung for trends - couldn’t agree more!

 

[Crofty]

While you are correct to say that in theory it adds some extra liquid when fully drained, it shouldn’t, because the part where the Bubble is can’t physically be dosed without pushing it with air, that is if the seal isn’t broken.

I’ve been taught by my father (which occasionally works in a lab as part of his job, reefer as well) that it is in fact how they use syringes in the lab, but as I mentioned earlier he also said what logically is true - that in practice it doesn’t really matter, probably because the only impact it has is on surface tension differences.

I was only talking about the 2 and 5ml syringes used for measuring out the sample water volume. I think you are talking about the 1ml titration syringe, which as you said, isn't fully evacuated so that's a different situation.

On a side note: it's impressive how well the Salifert test kits actually perform, considering how dirt cheap they are. And their results compare very well with more accurate testing methods. The biggest weakness of course being the kits that rely on color gradient visual interpretation. That's coming from years of experience working as a chemist doing all kinds of analytical testing methods.

 

[DanyL]

Well, as a good practice I do it for both 2/5ml and the 1ml syringes, but it would certainly matter most with the syringe used for titration.

I totally agree with you about the quality of the kits, all titration based kits work very well with consistent results, they wouldn't shame any professional equipment, considering the cost and resolutions we work with of course.
I think it's mostly thanks to the fact that Salifert designed the testing process towards hobbyists, simplifying and streamlining it as much as possible to prevent user errors.