Homemade Calibration Standards

[nrannalli]

I wanted to make my own calibration fluid for calibrating my refractometer. Just had a quick question about this article from Randy back in June 2004. I made all of the solutions to test on my refractometer and the Refractometer Standard & Conductivity Standard calibrated ruffly the same on the refractometer is this suppose to be the case because the Specific Gravity Standard was noticeably higher than the other two. Did I mix them wrong? I used the weight method.
http://www.reefkeeping.com/issues/2004-06/rhf/index.php

Thanks
Nick

[bertoni]

They should be fairly close. What were the actual measurements?

[nrannalli]

Refractometer & Conductivity standard were right at 35ppt if I used one to calibrate the other. But if I calibrated with the Refractometer standard first then the Specific Gravity Standard was about 36-37ppt based off of the Refractometer standard.

[KevChem]

They are not cross-checkable: The RI standard is made to have the same refractive index as S=35 seawater. However, it does not necessarily have the same conductivity. Likewise the conductivity standard is made to have the same conductivity as S=35 seawater while it will not necessarily have the same refractive index.

Look at how they are made - different amounts of sodium chloride thus different actual "salinities". Remember that we never actually directly measure salinity - we use refractive index or conductivity as a surrogate measurement.

Kevin

[nrannalli]

<a href=showthread.php?s=&postid=15083897#post15083897 target=_blank>Originally posted</a> by KevChem


Look at how they are made - different amounts of sodium chloride thus different actual "salinities". Remember that we never actually directly measure salinity - we use refractive index or conductivity as a surrogate measurement.

Kevin

While true they use different amounts of sodium chloride they also use different amounts of water about half 96.35ml and 182ml the refractive reading was slightly lower which makes sense since it had more water as a ratio to salt. But the only one that was noticeably different as far as ratios and comparison was the Specific Gravity so I expected it to be slightly higher... which it was but I didn't want to trust the calibration unless I was sure these readings were correct.

Nick

[bertoni]

Those numbers sound reasonable to me. :)

[Boomer]

Nick

Refractometer & Conductivity standard were right at 35ppt if I used one to calibrate the other. But if I calibrated with the Refractometer standard first then the Specific Gravity Standard was about 36-37ppt based off of the Refractometer standard.

That can correct as that is what the Pinpoint 53mS does also. We use it for refractometers aand conductivity meters. IIRC it also works with SG. It is all in the mixing. But that does not mean they will always be. Other stds not be close to each other on all 3.