How to Make NO3 and PO4 Reference Solutions

Here's a way to make 10, 20, 30 and 40 ppm NO3 reference solutions:

Add 1.631 g of KNO3 to 1 L DI/RO water. This makes a 1000 ppm NO3 solution. (It's really a 1000.29 ppm solution.)

Add 2 mL of the 1000 ppm solution to 18 mL of DI/RO water. This makes 20 mL of a 100 ppm NO3 solution.

Add 15 mL of the 100 ppm solution to 15 mL of DI/RO water. This makes 30 mL of a 50 ppm NO3 solution.

To make a 10 ppm NO3 solution:
Add 2 mL of the 50 ppm solution to 8 mL of DI/RO water. This makes 10 mL of a 10 ppm NO3 solution.

To make a 20 ppm NO3 solution:
Add 4 mL of the 50 ppm solution to 6 mL of DI/RO water. This makes 10 mL of a 20 ppm NO3 solution.

To make a 30 ppm NO3 solution:
Add 6 mL of the 50 ppm solution to 4 mL of DI/RO water. This makes 10 mL of a 30 ppm NO3 solution.

To make a 40 ppm NO3 solution:
Add 8 mL of the 50 ppm solution to 2 mL of DI/RO water. This makes 10 mL of a 40 ppm NO3 solution.




Here's a way to make 1.0, 2.0, 3.0, 4.0 and 5.0 ppm PO4 reference solutions:

Add 1.433 g of KH2PO4 to 1 L DI/RO water. This makes a 1000 ppm PO4 solution. (It's really a 1000.09 ppm solution.)

Add 1 mL of the 1000 ppm solution to 9 mL of DI/RO water. This makes 10 mL of a 100 ppm PO4 solution.

Add 2 mL of the 100 ppm solution to 18 mL of DI/RO water. This makes 20 mL of a 10 ppm PO4 solution.

To make a 1.0 ppm PO4 solution:
Add 1 mL of the 10 ppm solution to 9 mL of DI/RO water. This makes 10 mL of a 1.0 ppm PO4 solution.

To make a 2.0 ppm PO4 solution:
Add 2 mL of the 10 ppm solution to 8 mL of DI/RO water. This makes 10 mL of a 2.0 ppm PO4 solution.

To make a 3.0 ppm PO4 solution:
Add 3 mL of the 10 ppm solution to 7 mL of DI/RO water. This makes 10 mL of a 3.0 ppm PO4 solution.

To make a 4.0 ppm PO4 solution:
Add 4 mL of the 10 ppm solution to 6 mL of DI/RO water. This makes 10 mL of a 4.0 ppm PO4 solution.

To make a 5.0 ppm PO4 solution:
Add 5 mL of the 10 ppm solution to 5 mL of DI/RO water. This makes 10 mL of a 5.0 ppm PO4 solution.

Left C

Hey Tom, doesn't it makes 20ml of a 20ppm solution?!?

We have a 1000ml of a 1000ppm solution, so taking 2ml of it and adding to 18ml of water there should be a 20ppm solution, not a 100ppm solution...
Is it right?!?
Thanks Tom!
Bye!

I think the 2's got you here..........

whether it's 2mls added to 18mls of DI, or if you divide by 1/2-> 1 ml into 9 mls of DI water............the dilution is still 1ml of 1000ppm into 10mls total.
Or 2mls of the stock 1000 ppm into 18mls of DI, or 3mls into 27, or 100mls of stock solution into 900mls of DI

Or 1000 ppm to 100ppm, you just made 20s, not 10mls............

You can make 10mls if you want.........

This is just Left C's version.

I think you mixed up 20mls with 20ppm.


Regards,
Tom Barr

hehehe
Yeah, I've got the wrong calcs in here...
I refeered 2ml as 200ppm of the solution (don't know the hell why I did it!), but it's still a 1000ppm solution, this 2ml added to 18ml would really be 100ppm! (simple division as it said in the case of 1ml for 9ml)
I messed the whole thing! hehehehe
Thanks again Tom!
Bye!

well, figuring out what someone else did wrong is often hard, and are if they are right

Regards,
Tom Barr

Just curious if there is a guide based on the use of things like teaspoon, etc... I have a gram/ounce postal scale (up to 5#) but unfortunately it is not accurate enough for this kind of precision. I dont mind if it requires the use of a larger amount of water to get more accuracy (I know its hard to dose 1/64 of a teaspoon or something like that!) but a couple of gallons of DI water from wallmart for 59c is cheaper than buying a new scale.

20-30$ ought to give accuracy to 0.01 gram from ebay, you might get 0.001 accuracy for a reasonable amount also.

Regards,
Tom Barr

So I take it thats a no then on using volume for measurement as opposed to weight.

If you want to use weight instead of volume I suggest weighing about 10 teaspoons of each fertilizer, then dividing the weight by 10 to get the weight per teaspoon. The accuracy you could get this way would be limited, partly because measuring spoons are not very accurate. I have maybe 4-5 sets of measuring spoons made of different materials, by different manufacturers. If you have that too, measure a teaspoon using each of those, weigh the total weight of them and divide to get a slightly more accurate weight per teaspoon. Or, to get perhaps a little more accurate, measure using the half teaspoon, teaspoon and tablespoon (3 teaspoons), and do the same.

But, of course, as soon as you buy some more KNO3, KH2PO4, etc. the weight per teaspoon will likely be at least a little bit different.

I guess it depends on how precise you want your calibration solutions to be. There's no need for them to be any more precise than the color key that comes with your test kit unless you're using a spectrophotometer.

If you're feeling really thrifty and have a loose sense of ethics you could certainly buy a digital kitchen scale at Target or Walmart, use it, and then return it. Those scales can be precise to the gram. You only need to make a reference solution once, right?