Ultraviolet absorption of contaminants in water

Abstract

Contaminants in water were studied using ultraviolet absorption with light emitting diode and deuterium lamp sources, and a thresholding detector. The absorption spectra of potassium hydrogen pthalate, clothianidin, tryptophan, thiamethoxam, uric acid and metaldehyde were obtained in the range 200-360 nm. Only metaldehyde was not suitable for detection in this range. For the other contaminants, and mixtures of pairs of compounds, the transmitted signal could be approximately described with a simple spectral model of the source-absorption-detector system. Combined measurements at two wavelengths could allow relative concentrations in certain mixtures to be determined, and real-time absorption measurements were demonstrated in a flume.

Figure 1

Absorption spectra for metaldehyde, clothianidin, tryptophan, thiamethoxam, potassium hydrogen pthalate (KHP) and uric acid, at 10 mg/L for 10 mm optical path.

Figure 2

Spectral characteristics of the UV transmission apparatus. Panel (a) shows the transmittance and detector quantum efficiency, while (b) shows the spectral response of the light source–cuvette–detector system for three LEDs and a deuterium lamp.

Figure 3

Total transmittance for KHP in water at different concentrations using a 250 nm LED and a deuterium lamp. Solid lines are from the model. Experimental error bars in both transmission and concentration are within the size of the symbols.

Figure 4

Transmittance data (symbols) and model (lines) for two mixtures of contaminants in water, with total concentration 10 mg/L and using 250 nm (blue) and 280 nm (red) LEDs. The mixtures are (a) KHP and clothianidin, and (b) tryptophan and thiamethoxam.

Figure 5

Photograph (a) of the sensor setup in a flume. The plot (b) shows a time series of sensor output. The pronounced dip at 10–12 s is due to arrival of uric acid solution deposited into the flume.