DETERMINATION OF NANOMOLAR CONCENTRATIONS OF INDIVIDUAL DISSOLVED LOW-MOLECULAR-WEIGHT AMINES AND ORGANIC-ACIDS IN SEAWATER

A concentration technique using diffusion of amines and organic acids across a hydrophobic membrane was developed for the measurement of these compounds in seawater. Using this approach, the amines and organic acids are concentrated from seawater and also are separated from inorganic salts and most other dissolved organic compounds. Amines or organic acids in the concentrated sample are then quantified by gas chromatography. Concentration factors up to 1000 can be achieved. Natural concentrations of amines and most organic acids of 10 nM can be measured in 500 mL of seawater. For acetic acid, measurable levels are higher (about 750 nM) because of the higher blanks. Lower detection limits can be achieved using a circulation diffusion method with larger volumes of water. Concentrations of various amines and organic acids obtained using this method are reported for coastal and estuarine seawater, sediment pore waters, and a freshwater lake.