Post by Lyrebird_Cycles on Feb 15, 2021 18:45:58 GMT 10
No drama. Be aware it might not wash: if you are having to validate the solutions to achieve IANZ certification you'd have to get the calibration curve recognised by the certifying laboratory* so it might not be worth the effort.
Anyway, I found a calibration curve for PEG4000 with added guanidine hydrochloride which looks pretty linear,so hopefully PEG800 behaves similarly.
BTW if you use an Abbe refractometer it will give you direct measurement in ND.
* I have a mate (also a winemaker) who used to be a chemical engineer with Shell. Anything they brought in for the offshore rig had to be challenged with sea water so the engineering team had sea water tablets which they dissolved in distilled water to make certified sea water. Did I mention they were on an offshore oil rig surrounded by billions* of litres of actual seawater? Not good enough for the certifying laboratory.
*Being me, I went and looked this up. About 1.5 sextillion litres ( 1.5 x 10^21) in the oceans.
Post by good4whatalesu on Feb 15, 2021 20:29:02 GMT 10
The psychrometer (and PEG formula Michel 1983?) requires requires a temp calibration (viscosity change?). We run the seed experiments at different temps (eg. 15, 20, 25, 30, 35) so guessing the refractometer curve/ has to be also temp dependent. .. Someone at work smarter than me has put Michels formula in an excel sheet all I do is punch in the desired temp and water potential and it spits out the PEG concentration (grams/grams h2O). But then I have to verify the solution with psychrometer (slow and annoying across town I don't have one).
Post by Lyrebird_Cycles on Feb 16, 2021 20:32:46 GMT 10
Well it involves refractometers so it's vaguely relevant.
You are right, any refractometric measurement will have a temperature coefficient attached. This is captured by the thermo-optical coefficient which is basically dependent on the density of dipoles present in the material changing with temperature (spreading out).