Development of a liquid membrane technique to measure the temporal variation in “bioavailable” copper and nickel in the South San Francisco Bay
A supported liquid membrane (SLM) technique for the determination of free and labile copper in estuarine and coastal water was developed. The SLM consisted of 10 mM Lasalocid, a naturally occurring carboxylic polyether ionophore, dissolved in o-nitrophenyl octyl ether (NPOE), immobilized on a thin microporous solid membrane. The solid membrane was sandwiched between two aqueous phases: (1) a source or sample solution containing the analyte (in this case free/labile copper) to be extracted and (2) a strip or acceptor solution into which the analyte(s) is trapped. The membrane support was clamped between two circular Teflon blocks each with circular groves like an Archimedes spiral.
The SLM was used to extract free and labile copper from water samples collected from two sampling stations, Dumbarton Bridge and San Bruno Shoals in South San Francisco Bay The copper concentration in the SLM extracts was determined off-line by GFAAS.
Between 90-97% of the total dissolved copper was bound to organic ligands, and therefore not “bioavailable” to phytoplankton. Thus only about 5-10% of the total dissolved copper existed as inorganic and/or labile organic copper species. The measurements were consistent with earlier copper speciation measurements that were made in South San Francisco Bay using electrochemical methods.