PERFORMANCE-CHARACTERISTICS OF GEL PROBES USED FOR MEASURING THE CHEMISTRY OF PORE WATERS

Polyacrylamide gel probes provide a rapid, simple procedure for measur ing iron and manganese in pore waters at sub-millimeter resolution by diffusional equilibration in thin films (DET). Fe(II) and Mn(II) diffu se freely within the gel matrix, and with a 0.4 mm thick gel, complete equilibration is achieved in 6 min. Gels must be deoxygenated prior t o deployment, and exposure to air limited to 15 s to avoid overestimat ion of iron. Treatment with 10 mmol L(-1) NaOH or KOH quantitatively i mmobilizes Fe and Mn as their insoluble oxyhydroxides and brings about a diffusional transfer of Fe and Mn to the edges of the gel. The time from removal from the sediment to fixing or slicing the gel is the gr eatest limit to resolution. Fixing within 20 s should allow good resol ution at a millimeter scale, but to achieve 250-mu m resolution, fixin g within 1-2 s in a 250 mu m thick gel is required.