Accuracy Of Api Test Tubes

[Paul70]

Has anyone else noticed that their api test tubes as supplied in the master test kit may not be an accurate 5ml?

I have started using a medical syring to draw up tank water and when I draw up 5ml tank water and put it in the test tube it goes above the marked 5ml line. when I add water up to the marked line it is only something like 4.5ml.

Should I continue to fill to the marked line or use the 5ml as measured in my syringe? I have not made a mistake with drawing the water as I am experienced with these syringes being a registered nurse.

I have emailed API for advice also and will let you know what they say but for the meantime I am unsure about the accuracy of my water results now.

 

[ian]

saying that...are you using a luer lock or bladder syringe. We had some discrepancy with methadone at work and we audited the problem and it actually came from people using a bladder syringe over the luer lock. The luer locks are more accurate.

 

[Paul70]

it is a luer lock syringe. I personally am not keen on bladder syringes for the reasons you state and will always use a luer lock syringe if they are available when drawing up medication.

 

[Paul70]

I have received a reply from the API helpdesk. I am particularly impressed with this as it is sunday!!

I have copied and pasted the text below:

Thank you very much for contacting us regarding our products. All of your comments and questions are valuable. We use your feedback to create the most effective line of aquarium and pond products available.

Paul you can use either the line or the 5ml of tank water from the syringe. There is a margin of error built into the kits so if slightly too much water added to the test tube or if not enough is added to the tube you still will receive the correct reading for your test.

If you have any other questions or wish to discuss this further, please email back or give us a call at 1-800-847-0659.

Best Regards,

Nathan Fekula
Technical Service and Research
Mars Fishcare

So it seems then that you don't have to be absolutely bang on with your measuring for the kits to give an accurate result. That's all I wanted to know.

 

[Dodders]

That is impressive, and a very useful bit of information - thanks!

 

[Aqua Tom]

I have used a medical syringe to put water in the API test tubes & they where spot on.

???

 

[BIG BAD BARRY]

Looks like you contacted the US part of the company.
I was just as impressed by the UK section when i contacted them.
Really helpful.

 

[chrisrm]

that makes me glad i just spent 5 mins getting a ph test bang on!!!

 

[CletePurcel]

Should I continue to fill to the marked line or use the 5ml as measured in my syringe? I have not made a mistake with drawing the water as I am experienced with these syringes being a registered nurse.

Are you filling so the water at the side of the tube hits the marked line or the bottom of the meniscus (curved water surface) in the centre of the tube hits the marked line?

I vaguely remember from chemistry in college that you are supposed to look through the centre of the tube and when the bottom of the meniscus hits the line that is the correct amount. This might explain a 0.5ml difference perhaps.

 

[Paul70]

I am measuring to the meniscus level as you should when measuring liquids. the meniscus effect would account for 0.01ml anyway I think. anyway it looks like it doesn't matter that much because of the margin of error that they build in.

 

[Geoff-]

I vaguely remember from chemistry in college that you are supposed to look through the centre of the tube and when the bottom of the meniscus hits the line that is the correct amount. This might explain a 0.5ml difference perhaps.

that is correct. the convention for measuring liquids is that the amount is correct when the horizontal part of the meniscus is level with the mark on the measuring device.