text: PIPES has two pKa values. One pKa (6.76 at 25 °C) is near the physiological pH which makes it useful in cell culture work. Its effective buffering range is 6.1-7.5 at 25 °C. The second pKa value is at 2.67 with a buffer range of from 1.5-3.5.  PIPES has been documented minimizing lipid loss when buffering glutaraldehyde histology in plant and animal tissues. Fungal zoospore fixation for fluorescence microscopy and electron microscopy were optimized with a combination of glutaraldehyde and formaldehyde in PIPES buffer. It has a negligible capacity to bind divalent ions.