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Mohammed
07/30/2017, 10:53 AM
Hi,

I usually place the 1ml syring with pink attachment below the liquid level then pull up and depress all before I fill to the 1ml mark including the air gap (I do not try to rid the syringe of the air bubble, and I get repeatable results) . I have been testing like this for years and it recently dawned on me that once I titrate the test I depress the remainder back into the bottle and chuck the syringe back into the box.

Is it at all plausible that the tiny bit of liquid still retained in the pink tip evaporates a bit and when retrieving the next amount in the manner I do above im returning the slightly evaporated liquid back into the bottle thus making the results skewed. The amount of liquid still in the tip could vary depending how often I use the kit.

Could this be the reason that guys get lower readings on newly opened kits and usually evaporation is usually offered as a possible reasons.

How do you guys do it?

I could rinse the syringes after every test but am I over thinking about this?

billdogg
07/30/2017, 11:34 AM
I just pull the plungers back a couple times to expel whatever is left as best as I can. Then I put them away and have never given it another thought

Until now.

Thanks:frog:

Vinny Kreyling
07/30/2017, 11:45 AM
If it were to be a problem I'm sure we would have heard about it by now.
Not to worry!

Dan_P
07/30/2017, 12:57 PM
Strictly speaking, we all use less than a disciplined approach performing analytical chemistry procedures. At the same time, asking "so what" to a very disciplined approach is important to avoid over spending time and money on precision.

A drop of reagent, approximately 0.02 mL, that evaporates completely and then mixes with 1 mL fresh reagent would increase the concentration of the reagent in the syringe by about 2%. This results in adding less reagent to achieve an endpoint and the conclusion drawn would be the water sample has a lower concentration of what you are testing for than it really does. In general, the variance in results of a hobby test kit is likely larger than 2% and you might not be able to detect that 2% error.

Solvent evaporation and contamination of the reagent are potentially bigger sources of error. For this reason, it is always unwise to return unused reagent in the syringe to the reagent bottle. I imagine most people do it though. Keeping the reagent bottles tightly capped is key to minimizing evaporation.

LobsterOfJustice
07/30/2017, 01:32 PM
I rise the small syringe with tip, large syringe, and test tube with tap water and then RODI after each use.


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FullBoreReefer
07/30/2017, 03:36 PM
I squirt it back in the bottle and move to the next...

bertoni
07/30/2017, 06:49 PM
I agree that it's probably safest to discard the unused reagent, but if you use only the syringe for that reagent, and avoid using the syringe for anything else, that's probably safe enough for us. Keeping the bottles capped as much as possible is a good idea, too.

Vinny Kreyling
07/31/2017, 09:07 AM
Switching tests with the same syringe, in my book anyway is a NO NO.

devastator007
08/01/2017, 08:21 AM
I agree that it's probably safest to discard the unused reagent, but if you use only the syringe for that reagent, and avoid using the syringe for anything else, that's probably safe enough for us. Keeping the bottles capped as much as possible is a good idea, too.

another +1 to the advice. I do strive for the most accurate results possible, so I personally discard unused reagent, but it likely isn't a big deal to return to the bottle. The biggest issue I could see potentially happening is the tip of the syringe coming in contact with the fluid being tested, and returning contaminate to the reagent bottle. This is why I discard. I also have many syringes that I keep separate for each test. Syringes are dirt cheap and if it saves you one small screw up with adjusting perameters in your tank than it's money well spent.

I also discard the reagent because the other chemicals used in the test kits are measured with the assumption that you'll be using the full amount of reagent, so you'll just end up having an excess of reagent when the kit is used up, if you even use up a kit before it's expired.

FullBoreReefer
08/01/2017, 11:53 AM
I squirt it back in the bottle and move to the next...

I should reiterate, that when I say I move to the next, I mean NOT using the same syringe for the "next" test...

Sk8r
08/01/2017, 01:46 PM
Do not mix equipment for tests, as a general rule. This includes spoons, stirrers, etc. You can return unused reagent to the bottle, but in general, once the first element of a kit is done-for, toss the kit. There is no economy in risking wrong readings or expired tests.

One thing: you may wash and save metric measures: they're hard come by in the US, in small enough utensils. A horse syringe serves me for mg, eg. And a NoPoX cup is a treasure. But do dedicate them to a specific purpose, is the best rule.

Mohammed
08/02/2017, 01:29 AM
Thanks for all the responses. I usually keep all my test kits boxed so I only use the vials and syringes for that particular kit.

bertoni
08/02/2017, 02:08 PM
That should be fine. :)

d0ughb0y
08/03/2017, 11:04 AM
if you are really ocd about this, you can toss the syringe tip and use a new one each time.
you can get them on ebay for like $2 for 100pcs.

http://www.ebay.com/itm/100PC-Glue-Liquid-Syringe-Needle-Tube-Plastic-for-Plastic-hesive-Dispenser-AD-/111940677188?hash=item1a102f2e44:g:3~4AAOSwa~BYTi1J

http://i.ebayimg.com/images/g/zbUAAOSwOtdYTi1M/s-l500.jpg

or for extreme ocd, you can use a brand new syringe and tip each time you test.