Direct Quantitation Of Haloacetic Acids By Surface Enhanced Raman ScatteringEPA Grant Number: R825363
Title: Direct Quantitation Of Haloacetic Acids By Surface Enhanced Raman Scattering
Investigators: Natan, Michael J.
Institution: Pennsylvania State University
EPA Project Officer: Hiscock, Michael
Project Period: November 4, 1996 through November 3, 1998
Project Amount: $163,609
RFA: Drinking Water (1996) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Description:A new approach is described to direct quantitation of haloacetic acids (HAAs). The new method is based on surface enhanced Raman scattering (SERS), and has several enormous advantages over existing methodologies, including: (1) the absence of any extraction steps; (2) the absence of any separation steps; (3) the capability of simultaneously detecting all nine HAAs as well as 2-chlorophenol; (4) excellent detection limits (< 0.1µg/L) for all ten of these compounds; (5) the absence of procedures involving hazardous materials; and (6) in situ capability. SERS detection can also be used in conjunction with established separation methods such as high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). SERS detection will be demonstrated on laboratory samples of individual HAAs, mixtures, and on disinfected waters from a variety of sources. It is expected that protocols developed in the proposed work will ultimately replace EPA 552 and 552.1. In principle, these can be carried out with a minimum of expertise, with very high throughput, with no danger to the analyst, and at a low cost per analysis. Moreover, the proposed method is pollution-free, requiring no organic solvents. Real-time, on-site analysis with portable instrumentation is also possible. Finally, and perhaps, most importantly, the equipment and substrates used in this work can be easily adapted to a host of other ultratrace analyses in aqueous samples.
The attraction of Raman spectroscopy as a technique for HAA is based upon the fact that each HAA has a unique spectrum, and each has at least one strong vibration that is spectrally well-resolved from the others. Thus, each compound in this table can be identified directly, without any separation required. In contrast to extraction/GC, HPLC, and CE, this is truly a direct measurement, since all compounds are detected simultaneously on the basis of their molecular structure.
Using SERS as an analytical method for HAAs is predicated upon the availability of inexpensive, reproducible substrates, a long standing problem we recently solved in our laboratories. The development of Au and Ag colloid-based surfaces constitute a significant advance in the practice of SERS, and will permit a dramatic simplification of the procedure to monitor HAAs; with these substrates and with a portable Raman instrument, on-site HAA quantitation by individuals without extensive technical training becomes possible.