Monitoring Trazines and their Precursors Using Fiber Optic-based, UV-Vis Spectroscopy

Guided Wave's product line includes a UV-Vis spectrophotometer, Model 508. This application note discusses the use of Guided Wave hardware and software tools for the measurement of various trazines and synthetic precursors using fiber optic-based, UV-Vis spectroscopy. UV-Vis spectroscopy can be applied in real time directly in process monitoring or as a laboratory procedure. In either case UV-Vis spectroscopy is a time and money saving alternative to traditional chemical methods.

Background

Atrazine, a triazine, is a restricted use pesticide in the United States. It is one of the most commonly used herbicides in the US particularly in the mid-western “corn belt”. It is considered slightly toxic, believed to be an endocrine disruptor and is a suspect carcinogen. Atrazine is a common contaminant in ground and surface water where it is slow to degrade.

Agricultural runoff is the major source of surface water contamination. The US EPA Maximum Containment Level Goal (MCLG) for drinking water is 3ppb. The UV-Vis region of the electromagnetic spectrum displays electronic transitions and is particularly useful for viewing conjugated and aromatic molecules. By measuring the UV spectra of a series of samples of known atrazine or atrazine derivative concentration, a quantitative model can be developed which will allow the measurement of future samples based only on their UV spectrum.

Guided Wave analyzer systems use fiber optics to allow the sample probe to be located in remote locations away from the spectrophotometer itself, potentially reducing the level of operator intervention and providing real-time sample assessment.

Analysis

To find the best wavelength for the atrazines determinations, the correlation coefficient for each type of atrazine was
calculated at each wavelength. These correlation coefficient curves were plotted together to find one wavelength with a high correlation for all atrazines that could be used for concentration predictions (Figure 2). The wavelength with the best overall correlation was 241 nm. The average absorbance at 241 nm was used with the atrazine concentrations in a simple linear regression for each atrazine type (Figure 3). These linear regressions were used to calculate the predicted concentration of each atrazine from the sample spectra. The RMSEC values range from 2.7 to 13.4 wt/wt ppb. The root mean square error of prediction (RMSEP) values ranged from 3.3 to 8.6 wt/wt ppb.

Discussion

The measurement of ppb level atrazine concentrations in water using UV spectroscopy is both fast and reliable utilizing the Guided Wave model 508. This method minimizes the need for laboratory sample collection. Results are available in real-time (seconds) for atrazine concentrations in aqueous streams.For more detailed information regarding system specifications please contact a Guided Wave technical sales specialist.

Absorbance Spectra of Atrazine baseline corrected at 330 and 530nm Figure 1
Correlation coefficients for various atrazines by wavelength Figure 2

Experimental

The atrazines were initially diluted in isopropanol and then serially diluted with deionized water. The UV spectra were
measured using a Guided Wave Model 508 process UV-Vis spectrophotometer in a 100mm path length sample cell.
Isopropanol is UV transparent. The unit was referenced using water, allowing the spectral features attributed to the atrazines to be more easily seen. Figure 1 shows the absorbance spectra collected for atrazine itself baseline corrected at
330 and 350nm.

Concentration vs Absorbance for Various Atrazines at 241nm Figure 3