I'm testing the dry ice wash on an MHRB extract dissolved in hexane. It certainly worked to separate the solvent from the vessel,

as gas expansion overwhelmed the container. Good thing it was a small test. The remaining half of solution was hazy for a minute but there doesn't appear to be anything that precipitated, goo or otherwise. I freeze-precipitated a large amount of crystals within the solution last night, then re-dissolved them today, so I know the solvent is loaded. I was surprised by how much gas a small piece of dry ice created, I think it is fair to say if there was NMT it had its chance. I wasn't necessarily expecting NMT from MHRB, but I've heard a rumor about traces. I've already done a couple A/B's and many washes on this extract though, so any NMT could have been removed long before I got around to dry ice.
I may have spoke too soon. I treated the rest of the solution with dry ice because it didn't seem to hurt anything. There wasn't any noticeable precipitation, but then I wondered how it might look if it's just a trace amount. Like, would the nmt carbamate deposit as a very thin film, or maybe even stay caught in the non polar solvent.
I looked closely at the solvent and it was swirling. I think I was seeing convection currents in the solvent, but can only really imagine what's going on at the molecular level. Maybe high amounts of dissolved CO
2 make the convection more visible? or trace carbamates in suspension?
I wanted to give any potential carbamates an exit point, I figured water, but didn't want to expose the freebase to carbonic acid, so I used NaOH. I'm not sure if carbamate can dissolve in alkaline water though so I doubt that was the right idea for separating suspended carbamates. But I figured it wouldn't hurt to do one more alkaline wash on the NPS.
After thoroughly mixing, both solvents in solution remained hazy, and as things settled overnight there was a bit of something at the interface between alkaline water and hexane. Maybe a few concretions of oil, and a thin white film. I'm not sure why there would be anything at all, but maybe the DMT had started to precipitate and was just having a hard time with the water below it.
I used a 0.22 micron inline PTFE membrane filter, tygon tubing, peristaltic pump - to pull the hexane off the water. In case the haziness is from suspended water molecules, the PTFE membrane should deny those, I believe. A few strange things happened that I don't understand.
1. On the downstream side of the intake filter there was bubble generation. The entire filter was submersed, so I think the bubbles had to be coming from the solution. I was reading about de-gassing solutions this afternoon and coincidentally saw a couple suggestions to start with 0.22 micron filtering. The membrane filter did seem to be separating the dissolved gas, and once the gas molecules got grouped together on the other side of the filter they eject up the line as a stream of bubbles.
2. As the hexane was being transferred to the other container, through the filter, the remaining solution waiting to be filtered started to become more clear. Not as clear as what was coming out the outtake, but clearer than before I started the filtered transfer. I'm wondering if there was a large amount of dissolved CO
2 from the dry ice, and whether the filter was somehow sucking the dissolved gas out of the hexane faster than the hexane itself? And less gas = more clear?
3. The outtake half of the line was fitted with a second filter. Between the pump head and the outtake filter, a lot of precipitate formed in-line. It eventually clogged the outtake filter and I had to swap it. This was unexpected too, but since the pump is manipulating pressure, that must have something to do with it. When the line is fitted with filters it tends to build up a vacuum on the intake and positive pressure on the out line. Maybe pressure was precipitating the spice out as the solvent passed through this higher pressure section of line. Or maybe something about the way the peristaltic pump releases pressure for a split second before the next roller catches vacuum. The line develops a pulse from the beat of the pressure slips.