API test tube line not actually 5mL o.0

Hey all, I am a registered nurse, so I decided to grab a 5mL syringe at work so I could stop trying to fill the test tubes just right and simply have it be the same everytime.

What I ran into is interesting, the API test tubes 5mL line is about 2mm below actual 5mL. It is like this on all the tubes both from my master kit and my kh kit. The syringe I use is medical grade, ie it is what we draw up highly dangerous cardiac medications for administration through iv to humans. Needless to say I believe the 2 medical syringes that I have tried over the API test tube. I used needle to remove down to the API line and then measured the rest by drawing it up into syringe with a needle. If you add the water to the TOP of the API line it is 4.8 mL if you add to the bottom of the line it is 4.7mL.


The question comes down to however, should I fill the tubes to their 5ml line or should I fill with an actual 5ml for accurate results? I'd think fill with an actual 5mL because that's how the test is made and the tubes are probably lowest bidder Chinese garbage. I'm not sure though, input?


Filled with 5mL:



Syringe used with 5mL:



Remainder drawn up when filled to top of API line:

 

Hi,
I've noticed it before too.

Doesn't particularly bother me whether it's 4.7, 4.8 or 5.0. The API kits are not science/medical grade precision, and they serve their purpose really well.

So for me, I just go by the line on the tube

 

I'm to ocd for that lol. I guess more to the point if I neutral regulate if my ph is above 7.4 I just wonder how much that .3ml makes a difference if any... or if it could make 0 ammonia look like .25 etc.

 

I'm to ocd for that lol. I guess more to the point if I neutral regulate if my ph is above 7.4 I just wonder how much that .3ml makes a difference if any... or if it could make 0 ammonia look like .25 etc.

With the test kits, I doubt it will make a difference.

If you really want to put OCD to rest, then a digital pH tester is probably more your style

 

Long Version:
Even if the line was placed at a calibrated 5ml you still have variables such as the temperature of the water being tested, the chemical make up of the water being tested, if you reading it from eye level at the bottom of the concave meniscus curve at the top or bottom ot the test tube line? However id think since were doing a color of a chemistry result in visual comparison to a color printed from a chinese printer (calibrated or not) on glossy paper. maybe there is s good margin curve for user error, manufacturing inconsistencies, and what not.

Short Version:
close enuff for guverment werk!


PS.
if your going to go that OCD make sure your Digital Meter has "NIST Traceable Calibration" or else the readings it gives can't be trusted anyway.