One day when we made our regularly used medium, we noticed the initial pH was much higher than usual (above 6.0. usually it is around 4.0). It seems it only happened in our lab. The neighbor lab doesn't have problems. I have tried to test the initial pH using the water from our lab (B16) and the neighbor lab (B12). When I made LB medium, the initial pH was comparable with water from both labs; however, when making other media containing salts, vitamins, hormones, and sucrose, they showed different readings. The pH using water from neighbor lab was similar as our previous records while that using our lab was abnormally higher. I also used pH strips. The pH for water from the neighbor lab has been consistent, but that from our lab varied. Occasionally, it was similar; but most time shown in the attached file (shown in the attached file). Now my concern is what caused the high pH of this water. Is it toxic for our tissue culture? Any suggestions for figuring out the problem? Any information will be appreciated.
Seems pretty clear that your water treatment equipment is not working the same as previously. A normal pH of 4.0 for your water is fairly acidic; do you have pH treatment of your lab water in addition to a deionizer? Can easily measure the electrical conductivity of lab water to see if your deionizer is working effectively; then you likely need to check on the maintenance of your lab water treatment equipment (perhaps something as simple as changing out cartridge on your deionizer).
James C. Trask Thanks for your comments. The pH 4.0 is not for the DI water. It is for the plant media after we add all chemicals before adjusting the pH to an ideal value. We don't have additional treatment for the DI water. It used to work well without any problems. The cartridges are changed regularly. I am going to test the conductivity.
Hello Qingzhen--the pH above 6.0 for your media solution sounds suspiciously like a carbonate-buffered solution; the pK for protonated/nonprotonated bicarbonate ion is around 6.4, so such a solution would tend to buffer around pH 6.4. Perhaps bicarbonate and/or carbonic acid is making it thru your DI treatment, either due to spent cartridge or leakage in your dI system plumbing.
Hi James, thank you again for this valuable information. The weird thing is that we share the same source of DI water (cartidge/tank) with other labs. Our neighbor lab (B12) has the DI water with consistent pH while ours (B16) started to suddenly have the abnormal pH since that day we noticed. The pH strips shown here are for the water from both labs (no any additives). I bought a conductivity meter and I will check the water quality when we have it. I am wondering if there is a leak somewhere in the pipe leading to our lab only.
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