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[Micro]

I was making guanidine thiocynate buffer (or GES buffer) for the first time today. I followed the methods outlined in some journal articles except for one part. I filter steriled with a 0.22um instead of a 0.45um filter. The buffer was yellow in colour before filtering and clear after, with a yellow pigment present in the filter. Is this colour change supposed to happen or was using a smaller filter the wrong thing to do?

It is also possible that I didn't heat  the buffer for long enough. It requires heating to 65oC to dissolve the GT crystals. I let it reach 65oC and then removed it immedately. I couldn't see any crystal but is it possible that the crystals were not properly dissolved and got caught in the filter?

Any advice would be greatly appreciated!

Cheers
M

[Micro]

I might have found a problem, either related or unrelated to the colour change. It appears that the lab pH metre is have problems doing its job and my EDTA was pH 6.0 not 8.0 like it should have been. From what I've read the EDTA pH is important to the buffer working properly.