DIY Hydros Salinity Probe Calibration Fluid

[timqmana]

I have a Hydros Salinity kit, which uses a High-range K-10 Conductivity Probe. It comes with 28ppt and 35ppt calibration solution in the kit, but only to be used one time per their instructions. They are charging $15 for each bottle if you wanted to get additional calibration fluid, which I think is ridiculous.

What formula would I use to create my own 28ppt and 35ppt conductivity probe calibration fluid?

 

[SliceGolfer]

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[timqmana]

Thanks! So the formula below for S=35.

But what about S=28?

To make a 3.29 weight percent sodium chloride solution, dissolve 1 teaspoon (6.20 grams) of Morton's Iodized Salt in 182 mL (182 g) of fresh water (making a total volume of about 184 mL after dissolution of the salt). This solution can be scaled up as desired.

For a rougher measurement in the absence of an accurate water volume measurement:

1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified fresh water (about 2104.4 g)
4. Add 3 tablespoons of purified fresh water (about 45 g)
5. Dissolve the total salt (73.1 g) in the total water volume (2149.4 g) to make an approximately 3.29 weight percent solution of NaCl. The volume of this solution is larger than the Coke bottle, so dissolve it in another container.

 

[Randy Holmes-Farley]

Thanks! So the formula below for S=35.

But what about S=28?

To make a 3.29 weight percent sodium chloride solution, dissolve 1 teaspoon (6.20 grams) of Morton's Iodized Salt in 182 mL (182 g) of fresh water (making a total volume of about 184 mL after dissolution of the salt). This solution can be scaled up as desired.

For a rougher measurement in the absence of an accurate water volume measurement:

1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified fresh water (about 2104.4 g)
4. Add 3 tablespoons of purified fresh water (about 45 g)
5. Dissolve the total salt (73.1 g) in the total water volume (2149.4 g) to make an approximately 3.29 weight percent solution of NaCl. The volume of this solution is larger than the Coke bottle, so dissolve it in another container.

There should be no need for 28 ppt unless it’s a weird electronic requirement. Two point calibration doesn’t really make sense for a device that must read 0 at no conductivity (say, air).

But in any case, if you must, I believe you can just use 28/35 = 0.8 times as much salt as the above recipe to make a 28 ppt standard.