We use the Milipore MiliQ system, which reliably delivers 18+ MOhm water. I'm not sure about the total organic content though, which may be something you want to consider. Most important though, in my eyes, is the resistance. There are modular pH meters these days, where you can swap the pH probe with alternate probes, and one of them can be a resistance probe. That'll allow which would allow you to do the measurements yourself. Your best bet is to simply find a neighboring lab that has an ultrapure water system if you don't have enough funds to buy one yourself.
We use the MiiiQ system also, which would require an upfront investment but it may be worth it. I would think that any molecular grade water will be good. As Christoph Lossin states above, pH is important. Additionally, we check the Osmolarity, but at my old lab we did not do this. If I were really concerned about my water, I would check my liquid junction potential.
Thanks for the answers! We were of course using Mili iQ. I discovered by exclusion that the issue was with one of the salts which contained (presumably) contaminants. Problem now solved! Without a baseline (as was new MiliQ plant and moved labs) its very difficult to work through such a problem, if you are not sure your water is OK. Thanks
We use a Nanopure system. In the past I have also used the MilliQ. Both deliver 18 MOhm water. I don't find the water to be so much of an issue for patch clamp solutions as for culture media. On the other hand, for patch clamp solutions the purity of the salts and organic compounds is key. Organic compounds, such as TEA and choline chloride, often degrade, releasing toxic substances or substances that appear to interfere with obtaining gigaseals. Make sure that they are fresh, and consider whether they should be stored in the freezer and/or in a dessicant container. It pays to buy the highest quality reagents. Some salts, such as CsCl are contaminated with heavy metals, unless you pay for the highest grade reagent. Heavy metals can block ion channels, and they can be toxic, even at submicromolar concentrations. If you can't avoid using a lower grade reagent, it may help to put a few micromolar EDTA to sop up heavy metals ions.
After several years of off and on problems which we vaguely thought was due to variations in the quality of the water coming from our Departmental purification system, we switched to bottled water and the problems forever vanished (knock on wood). The problem as we saw it was not that the system itself was faulty, but that, being a departmental system, it was not consistently maintained. As it turns out, the bottled water is quite a bit less expensive than buying and maintaining one's own system. We use Fisher Scientific HPLC-grade water, Cat # W5-4. Everyone might not have the same cost/benefit experience as we do. Stanford has an agreement with Fisher, so we get it at a heavily discounted price.
Interesting! I switched to HPLC water during my PhD, and all my problems with patching seemed to go away. But, the problem was that I changed so many other parameters that I was never sure whether it was the change to the HPLC water or other measures that made the difference.
This is a very interesting discussion. I would agree about the shared resources not being maintained evenly. Ive had this problem in the past with milliq plant (variable periods for servicing and no control over when it happens) hence my question. Also agree with comments about the salt quality. I always keep back some 'good' internal solutions in the deep freeze. When things go 'wrong' it is easier to go back and check quickly. If the salts are the same, you can determine if it is a water quality issue. Problem was that in moving labs I did not have old stocks anymore. Even though problem is now solved I will try the HPLC quality water now. Thank you.
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