Phosphate: ICP test vs Hanna tester discrepancy

[CHSUB]

I think i do a good job with hanna phosphate testing, I take a couple different precautions for consistency as follows:

After i use vials i wash them out rather quickly with tap water. (Not rodi bc it’s not convenient.)

I also make sure to wipe the vials carefully before using.

I ensure the amount of water in the vial is the same and consistent each time.

When cutting open reagent packages, i make sure to get as much out of it as possible..

Very consistent mixing motion once reagent is added.

I test twice consecutively every time i test phosphates.

I’ve found that i tend to get different results every time. Usually results are .07-.09 and something like .13-.15.

Theyre not insanely discrepant so i generally treat the phosphate by whatever number is in the middle of the two tests….

Is there anything significant i may be missing based on that? I’m considering buying a new phosphate tester bc ive had this one for 4+ years used relatively often and maybe it’s having issues…

Looks good. Couple things I learned in the video

- I cut the packet open and place the powder on an index card so every speck goes in vial every time
-I never touch the vial, use a micro cloth
-I time the 2 minute shake to insure exactly the same time every time
-clean the vial with Ro/di and then with a Q tip, allow air dry completely before putting away. Not that it would make much of a difference but Hanna recommends not using tap water. Maybe buy a gallon of distilled to use for cleaning vials?

 

[Malcontent]

Looks good. Couple things I learned in the video

- I cut the packet open and place the powder on an index card so every speck goes in vial every time
-I never touch the vial, use a micro cloth
-I time the 2 minute shake to insure exactly the same time every time
-clean the vial with Ro/di and then with a Q tip, allow air dry completely before putting away. Not that it would make much of a difference but Hanna recommends not using tap water. Maybe buy a gallon of distilled to use for cleaning vials?

Tap water can have phosphate in it for corrosion control. I always clean with RO/DI or distilled.

I would skip the Q-tip step if rinsing with DI or distilled since it would probably air dry cleaner than if dried with a Q-tip.