You are here:
RAMAN SPECTRAL ANALYSIS OF PERCHLORATE CONTAMINATION IN COMMONLY-USED FERTILIZERS
Citation:
Williams, T. L. AND T W. Collette. RAMAN SPECTRAL ANALYSIS OF PERCHLORATE CONTAMINATION IN COMMONLY-USED FERTILIZERS. Presented at Federation of Analytical Chemistry and Spectroscopy Societies Conference, Vancouver, Canada, October 23-29, 1999.
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
Raman spectroscopy (RS) was used for qualitative and quantitative analysis of perchlorate (ClO4-1) in 30+ commonly-used fertilizers. Perchlorate contamination is emerging as an important environmental issue since its discovery in water resources that are widely used for drinking, crop irrigation, and recreation in the western U.S. Perchlorate contamination of substances ingested by humans is a potential health concern because it inhibits iodide uptake by the thyroid, resulting in increased thyroid hormone production.
Perchlorate contamination is also found in crops. One potential explanation is that crops bioaccumlate perchlorate from contaminated irrigation water. However, it is also known that perchlorate occurs in Chilean nitrate, which has been widely used in fertilizers. Based on this concern, we and others have analyzed a wide variety of commercial fertilizers, in order to determine the extent of contamination. Perchlorate was typically present at high levels (>500 ppm) in most of these fertilizers.
Ion chromatography (IC) with conductivity detection is the recommended method for perchlorate analysis. IC is sensitive (limit of detection of 4 ppb for perchlorate), but exhibits numerous problems for analysis of many environmental samples. They include -- 1) interferences from total dissolve solids (TDS), 2) column fouling, 3) retention time migration with column deterioration and relatively short column life, 4) detector hystersis for gradient elution separations, and 5) qualitative determination based solely on retention time matching.
We recently applied RS to the determination of perchlorate in fertilizers and in plant extracts. Most of the problems with IC (or any other chromatographic technique) are not encountered with RS. For example, RS does not exhibit interferences from TDS. If the pH of the sample is below 10.5, then peaks from common fertilizer components (nitrate, sulfate, phosphate, and urea) do not obscure the L1 perchlorate peak at 934 cm-1. In addition, because RS has no upper concentration limits, the time- consuming dilution procedures required of IC are unnecessary for RS. Direct analysis of solid samples is possible. These attributes of RS allow for a short total analysis time to be achieved, and thus RS is better adapted for high-throughput sample analysis. Analysis times for perchlorate determination are ~ 5 min, as compare to ~ 30 min for IC. Finally, qualitative determination by the information-rich vibrational technique of RS is far superior to the retention time matching method.
The problems that IC encounters in perchlorate determination are greatly intensified in the more complex matrix of plant extracts. Although the more complex matrix impacts RS as well, the detrimental effect is not nearly as severe. For example, we can readily identify bioaccumlated perchlorate in lettuce extracts that have been exposed to fertilizers and water contaminated with perchlorate.