Continuous Monitoring Of Trace Contaminants In Water
Using On-Line Membrane Extraction
Dawen Kou and Somenath Mitra*
Department of Chemistry and Environmental Science
New Jersey Institute of Technology
Newark, NJ 07102
Membrane extraction for continuous, on-line monitoring of trace contaminants in
water is presented. Figure 1 shows a schematic diagram of such systems. Water flows
continuously on the feed side of the membrane. The membrane serves as a selective
barrier while allowing organic contaminants to permeate through. They are transported
by a gas or a liquid to a concentration device prior to analysis. The range of compounds
tested by these techniques includes small molecules such as chlorinated solvents to large
molecules such as pesticides. Toxic compounds important to the homeland defense can
be continuously monitored by these techniques.
Membrane fiber
Water
Analyte flux
Concentration
Detection
Figure 1. Schematic diagram of membrane extraction
Gas Injection Membrane Extraction (GIME) has been developed for real-time
monitoring of volatile organic compounds, where a gas in used to inject an aliquot of
water into the membrane. This system is able to analyze organics at ppt level on a
continuous basis. A prototype was developed and field-tested at the Naval Engineering
Station in New Jersey.
Membrane Extraction with Liquid Chromatography (ME-LC) has been developed
for the monitoring of semivolatile organic compounds. The operations are automated, and
carried out on-line with high selectivity and high sensitivity. Research continues on this
technique to optimize operations and expand the range of compounds to include organic
acids. The Method Detection Limits (MDLs) for all organics are at ppb or sub-ppb levels.
The Relative Standard Deviations (RSDs) are consistently below 3%. These techniques
provide simple and effective tools for continuous, real-time water monitoring.
References
1. Kou, D.; San Juan, A.; Mitra, S. Gas Injection Membrane Extraction For Fast OnLine Analysis Using GC Detection, Anal. Chem. (2001), 73(22), 5462-5467
2. San Juan, A.; Guo, X; Mitra, S. On-Site And On-Line Analysis Of Chlorinated
Solvents In Ground Water Using Pulse Introduction Membrane Extraction Gas
Chromatography (PIME-GC). J. Sep. Sci. (2001), 24(7), 599-605.
3. Guo, X.; Mitra, S. On-Line Membrane Extraction Liquid Chromatography For
Monitoring Semi-volatile Organics In Aqueous Matrices, J. Chromatogr. A. (2000),
904, 189-196