Evaluation of a range of MRI‐active pH indicators using a multiple‐sample method

A multisample magnetic resonance imaging (MRI) method was used to measure the effects of a range of paramagnetic metal ions and chelating ligands on the T 1 and T 2 values of the protons of water over the pH range of 2 to 12. Copper sulfate and manganese chloride were combined with one or more of the following chelating agents:‐ ethylenediamine, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol‐bis‐tetraacetic acid, D‐penicillamine, or triethylenetriamine; Gd(III)DTPA was used as purchased. The multisample MRI method was also used to determine the sensitivity of aqueous MnEDTA to pH of carrots to demonstrate how the medium under investigation causes an offset to the calibration acquired in vitro. That calibration enabled null‐point T 1 imaging and maps of T 2 values to track the change in pH as acetic acid diffused into the carrot tissue. © 2005 American Institute of Chemical Engineers AIChE J, 2005