calibrating Refractometer for hyposalinity!?

[zheka757]

got this refractometer:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
also got Standard Seawater 35 ppt Refractometer Calibration Solution
calibrated using this solution, then tested ro/di water and it was off by .002
spend over hour online reading different comments as to what is should be calibrated to and got confused at to whats accurate.
i still dont have a good answer if i should calibrate refractometer to seawater solution or ro/di water for hyposolinity of 1.009?

[top shelf]

I've never done hypo but I would imagine you would still want to calibrate it to the 35ppt of your calibration solution. Maybe someone with more knowledge on it can chime in.

As for the fluctuation are you following the instructions for the ATC? That looks just like the one I have and mine says to wait 30sec before you can get an accurate reading.

[zheka757]

Yes i wait for almost a minute, but i dont see any difference in reading when checking right away and 45 seconds later.

[Rover88]

Originally Posted by zheka757

got this refractometer:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
also got Standard Seawater 35 ppt Refractometer Calibration Solution
calibrated using this solution, then tested ro/di water and it was off by .002
spend over hour online reading different comments as to what is should be calibrated to and got confused at to whats accurate.
i still dont have a good answer if i should calibrate refractometer to seawater solution or ro/di water for hyposolinity of 1.009?

The answer to calibrating is always to calibrate in your measurement range.

If you have a desired point of 35 ppt, you should be calibrating at 35 ppt. The reason is because of hysteresis or linearity. In essence, the further you are away from the point you calibrated at, the less likely you are to know if you are actually accurate.

I work industrial instrumentation. When we calibrate an instrument for the field, we usually do a two point calibration. One a little above and one a little below. When I was in college, we calibrated a multipoint instrument at every 10%, and it was overkill.

But the downside of doing just a single point is for all you know your 'line' of accuracy is skewed. You might be +5% at the top and -5% at the bottom.

So, if you are measuring 1.009, I'd calibrate with whatever known amount you have closest to that; IE: RODI water at 1.000. If you had 1.009 cal fluid, use that, but if you don't? RODI is better then a cal fluid that is 1.026 (I think thats where 35 ppt lands you?)

If you are measuring for 1.026, use the 1.026 cal fluid, or whatever known number you have closest to that.

[Tripod1404]

Mix equal volumes (be very precise) of RoDi water and calibration fluid. That should give you a new calibration solution with 1.013. Use that to calibrate. Or you can mix 1 part calibration solution with 2 parts of RODI, that would give something like 1.0086. Again you need to be very precise.

If you have access to pipetman, you can prepare calibration solution with 1.009 ppt by mixing specific volumes of calibration fluid and RODI.

[zheka757]

Tripod thats a smart advise I will try that.

[shaginwagon13]

Originally Posted by Rover88

I'd calibrate with whatever known amount you have closest to that; IE: RODI water at 1.000. If you had 1.009 cal fluid, use that, but if you don't? RODI is better then a cal fluid that is 1.026 (I think thats where 35 ppt lands you?)

+1

I did hypo and calibrated with RO water. You want to calibrate to a solution closest to where you are trying to match. When calibrating for 1.026 you use calibration solution. For Hypo when your trying to run 1.009 - 1.008 you want to calibrate with RO water.

[nereefpat]

Originally Posted by Tripod1404

Mix equal volumes (be very precise) of RoDi water and calibration fluid. That should give you a new calibration solution with 1.013. Use that to calibrate. Or you can mix 1 part calibration solution with 2 parts of RODI, that would give something like 1.0086. Again you need to be very precise.

If you have access to pipetman, you can prepare calibration solution with 1.009 ppt by mixing specific volumes of calibration fluid and RODI.

Good advice. The first part is what I was going to suggest.

And who is this Pipetman you speak of, a lab superhero?

[zheka757]

Originally Posted by nereefpat

And who is this Pipetman you speak of, a lab superhero?

Lol

[Tripod1404]

Originally Posted by nereefpat

Good advice. The first part is what I was going to suggest.

And who is this Pipetman you speak of, a lab superhero?

Yep, you can even see the cape

[nereefpat]

Ha!

I'm an eppendorf man.

But yes, if you have access to micropipettes, than make your own standards by diluting.