standard nitrate solution to get the colorimeter calibration curve

[Charles Silva]

Hi all

How can I make a saltwater standard nitrate solution with 1 ppm ?
The plan is preparing a set of different nitrate concentrations then using Red Sea nitrate reagents test it in a colorimeter to get the calibration curve and finally determine my reef concentration.
Any special recommendation for the wavelight or drawbacks with this method for nitrate determination in saltwater ?


Thanks in advance
Charles Silva
Rio de Janeiro - Brazil

 

[Randy Holmes-Farley Verified Community Expert]

The first step is to make a zero or very low nitrate seawater standard, then spike nitrate into it.

How you'd go about that depends on what you have available (chemicals to make your own seawater, a commercial brand you are convinced has much less than 1 ppm nitrate, etc.).

 

[Charles Silva]

Thanks Randy.
For the zero standard can I make it using DI/RO water then mix my salt with S=35 like I prepare my water changes ? Or this new solution might have some nitrate trace that can mask my zero calibration ?
In terms of alternatives to make the calibration solutions what can I use instead Potassium Nitrate ?

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Randy.
For the zero standard can I make it using DI/RO water then mix my salt with S=35 like I prepare my water changes ? Or this new solution might have some nitrate trace that can mask my zero calibration ?
In terms of alternatives to make the calibration solutions what can I use instead Potassium Nitrate ?

The concern is the assumption that the salt mix has much less than 1 ppm nitrate. It might, but you couldn't necessarily be sure.