Reef Chemistry Question of the Day #161 Using a Syringe

[Rjramos]

If anyone has used a Salifert kit and read the directions that come with it, it tells you to read at the plunger. Don't worry about the air, so 2.9 is the definate answer. Randy?

 

[twilliard]

I think after the answer Randy should write up his next article, sticky it and clear all this confusion up.
I love being married to a nurse

 

[Randy Holmes-Farley]

And the answer is...B. 2.9 mL

Here's how to think about how a syringe works:

When the plunger is pushed all the way in, the leading edge of the plunger aligns with the zero mL marking. That is true of nearly every syringe I've seen. When you begin to use it, the tip and barrel are empty, with the tip containing air and the barrel occupied by the plunger.

As you draw back the plunger with the tip in a liquid, the plunger creates a vacuum between it and the liquid, drawing in the liquid. The movement of the plunger draws in exactly the amount of liquid equal in volume to the travel of the plunger backwards (or upwards). So you can track how much fluid is taken up exactly by the travel of the plunger against the volume markings, regardless of what you see with the fluid (assuming it is functioning properly).

Some of the drawn in liquid will be in the tip, and some (or perhaps none, if it is all in the tip) will be in the barrel of the syringe. If the volume of the tip is larger than the volume indicated by the movement of the plunger, none will show in the barrel. Many modern pipettes work this way to avoid contaminating the barrel of the device. The device stays clean and the tip is discarded after each use.

Now, when you go to dispense the liquid, the plunger is pushed in, and all of the liquid is dispensed and the air is pushed back into the tip.

If you mistakenly tipped the syringe upward during dispensing, and blew out the air before the liquid, then when you push the plunger all the way in, there will still be liquid in the tip, and you probably won't know how much so you end up with a mismeasurement.

In the medical world, it can be super important to not inject air into a patient's bloodstream. In that case, the syringe must first be overfilled. It is then tipped up and all of the air blown out and some liquid may be blown out until the end of the plunger is exactly aligned with the volume marking you want to dispense. The syringe in total now contains the amount you want to inject, plus the volume of the the needle. Then you inject and when done, the needle is still full of liquid in the exact amount as before injection, and like before, the amount dispensed is exactly determined by the movement of the plunger. So this situation is no different except that you start and end with a full tip/needle. In a non-injection setting, you start and end with an air-filled tip.

So it doesn't matter how much liquid you see in the barrel. Only the movement of the plunger is important, whatever the use.

 

[Jlobes]

this thread had me interested, a lil laughing and feeling a bit terrible for some folks tanks. Honestly, this was a great topic and it was really interesting to see how many folks, really dont know how to use a syringe. Makes me wonder, how often the posts about bad test kits, off parameters, etc are really just user error.

thanks for the enlightening query and accompanying answer.

 

[Paul B]

This was great. I don't believe it but it was great anyway.

OK say you have a tank. An army tank, and it is traveling down a road at 20mph. The top of the track is going 40mph. How fast is the bottom track going? If he runs over a puddle of seawater and a syringe on the way, this could be called a chemistry question, but forget that for now and answer the question.

 

[Jlobes]

This was great. I don't believe it but it was great anyway.

what do you not believe? the answer, the method?

 

[joshkirkland83]

This was great. I don't believe it but it was great anyway.

OK say you have a tank. An army tank, and it is traveling down a road at 20mph. The top of the track is going 40mph. How fast is the bottom track going? If he runs over a puddle of seawater and a syringe on the way, this could be called a chemistry question, but forget that for now and answer the question.

I like french toast.

 

[Randy Holmes-Farley]

OK say you have a tank. An army tank, and it is traveling down a road at 20mph. The top of the track is going 40mph. How fast is the bottom track going? If he runs over a puddle of seawater and a syringe on the way, this could be called a chemistry question, but forget that for now and answer the question.

53 million femptofeet per nanosecond.

 

[Reflective]

This was great. I don't believe it but it was great anyway.

OK say you have a tank. An army tank, and it is traveling down a road at 20mph. The top of the track is going 40mph. How fast is the bottom track going? If he runs over a puddle of seawater and a syringe on the way, this could be called a chemistry question, but forget that for now and answer the question.

0 mph

 

[Jlobes]

I like french toast.

yum!
now I know what im having for lunch!!

 

[Habib(Salifert)]

This was great. I don't believe it but it was great anyway.

OK say you have a tank. An army tank, and it is traveling down a road at 20mph. The top of the track is going 40mph. How fast is the bottom track going? If he runs over a puddle of seawater and a syringe on the way, this could be called a chemistry question, but forget that for now and answer the question.

Depends on where the observer is. Like throwing a ball up in a moving train. The observed velocity of the ball will depend on wether the observer is in the train or outside.

 

[SethOF]

Reef Chemistry Question of the Day [HASHTAG]#160[/HASHTAG]

I have just drawn tank water into a syringe with a tip (shown below, including a blowup of the barrel). The blue coloration shows where the fluid is.

When I started to draw fluid in, the tip and syringe were empty and the plunger was all the way in. Now I am going to dispense the fluid into my test vial.

How much fluid will be dispensed by pressing the plunger all the way back in?

A. 3.6 mL
B. 2.9 mL
C. 2.2 mL
D. 1.6 mL
E. Cannot be determined because of the air present

Good luck!

.

D. 1.6 mL

 

[Randy Holmes-Farley]

D. 1.6 mL

Sorry.

See post #83.

 

[Paul B]

what do you not believe? the answer, the method?

Yes.

53 million femptofeet per nanosecond.

Close, but no cigar

0 mph

That is correct.

Depends on where the observer is. Like throwing a ball up in a moving train. The observed velocity of the ball will depend on wether the observer is in the train or outside.

That has nothing to do with it. Unless you have that syringe and you stick it in your arm with a hallucinogenic.

That's like saying "Caution 53,000,000 Ohms"

 

[Jlobes]

well, believe it or not, this is how its done. if youre doing it differently, youre doing it wrong.

 

[Bunnee911]

This was great. I don't believe it but it was great anyway.

OK say you have a tank. An army tank, and it is traveling down a road at 20mph. The top of the track is going 40mph. How fast is the bottom track going? If he runs over a puddle of seawater and a syringe on the way, this could be called a chemistry question, but forget that for now and answer the question.

Green bananas

 

[markalan]

Hey Randy, thank you for all your time that you put into this forum.

 

[saltyphish]

Yes.


Close, but no cigar


That is correct.



That has nothing to do with it. Unless you have that syringe and you stick it in your arm with a hallucinogenic.

That's like saying "Caution 53,000,000 Ohms"

Resistance is futile!!!!

 

[Ontheway]

There are many people, especially beginners easily confused on this syringe usage. Knowing the following clarifies all questions:

When you bring the piston all the way in, look what part of piston stays on "zero" line.
And when you start pulling, be sure same part of the piston comes to the number you want.
In other words, while filling the syringe, follow the point of the piston which were formerly showing zero in the fully injected position, before you start pulling.
(Mods are free to correct above, if there is a better way of saying this. This is all, with my English)

 

[Reduck]

Thanks Randy for making me think. This was a cliffhanger of a question.