Hey! I've been working on this problem - I think it would be easy for a chemist to answer. If anyone can help me out, I'd appreciate it! Suppose I want to create a pH gradient from 3 to 9, in increments of 0.5: pH = (3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9) Each pH is in a different test tube. I also want to buffer the pH in each test tube. Therefore, in the pH=4 test tube, I would use a buffer with a pKa~4, and in the pH=8 test tube, I would use a buffer with a pKa~8. However, it's important that I construct this gradient in such a way that aside from pH, everything else is held constant. In other words, if I add a phosphate buffer to one test tube, it would be best if I could add the same amount of phosphate to all test tubes. Therefore, I was hoping I could use a mixture of buffers with different pKas. Each test tube would have every buffer, and to adjust the pH, I would only vary the amount of HCl I add to the solution. The idea is that different buffers will be active in different test tubes, depending on the amount of HCl I add. So my main question is: *Is this possible?* I was also curious if anyone knows how to calculate the pH of a multi-buffered solution like this? Is there an extension of the Henderson-Hasselbalch equation I can use? I could also look at buffers that have multiple dissociation constants. For example, phosphate buffer has pKas at 2.15, 6.86 and 12.32. This exceeds the range I am interested in, but perhaps there is another buffer that I could use? Just a thought. If anyone can help I'd really really appreciate it. Thanks!