On-line membrane preconcentration for continuous monitoring of trace pharmaceuticals

Membrane pervaporation is presented as a method for on-line concentration and monitoring of trace analytes in a simulated pharmaceutical process stream. Pervaporation involves the selective transport of volatile organics across a membrane and into a gas stream. Experiments were carried out using a polar solvent-permeable Nafion membrane and several model pharmaceutical compounds. Solvent reductions greater than 90% and enrichment factors in excess of 7.9 were observed. Residence time and temperature were found to be important operating parameters. Interaction with membrane bound sulfonic acid residues resulted in the loss of reactive analytes such as 1,2-diphenylhydrazine. The concentrated stream was monitored using HPLC and UV/vis detection. Method detection limits were 0.5-1.2 μg/mL and the relative standard deviation for six repeat injections was 3.9-6.2%.