Water quality analysis - a challenge for spectroscopy technologies

Traditional methods for assessing water quality parameters include chemical, biological, and physical approaches. While chemical methods require bulky and expensive equipment and a large number of reagents, biological methods suffer from lower accuracy and sensitivity.

Physical methods, on the other hand, include spectral remote sensing technology in the UV and visible wavelengths, such as UV-Vis spectrophotometry, which is increasingly utilized for rapid water quality assessment.

Single-wavelength and multiwavelength detectors

There are two types of spectral sensors used in water analysis: single-wavelength (SW) sensors and spectrophotometers.

SW sensors generally consist of a bandpass-filtered single photodetector and a light source that emits in the targeted wavelength and is absorbed by the substance to be detected.

Spectrophotometers use a broadband light source, a diffractive grating that separates light into its wavelengths components and directs it towards a linear array photodetector.

Generally, when comparing the performance of full-spectrum and SW sensors, the latter can measure parameter variations during certain periods but may not compensate for the particle effect accurately, specifically when comparing the results with the standard laboratory procedures and measurements. Spectrophotometers, however, provide better particle compensation and can be calibrated to specific locations with higher accuracy. They are better for precise applications, such as real-time water and treatment process monitoring.

Light sources for UV-Vis spectroscopy

When using a UV-Vis spectral or full-spectrum sensor, it is crucial to choose the most suitable broadband light source. The light source needs a suitable spectrum, brightness, reliability, short to no warm-up time, long lifetime, low power consumption and compactness.

Although LEDs are widely used in many applications, they are not as useful in UV-Vis spectrophotometry due to their narrow-spectrum light and limited available wavelengths. Instead, broadband emitters like Deuterium Lamps and Xenon Flash Lamps are preferred.

Deuterium Lamps have a limited emission spectrum and require long warmups but are preferred for lab-based benchtop devices due to lower peak-to-peak variation. Xenon Flash Lamps offer a wider wavelength range, allowing for the detection of a higher number of water parameters to be detected simultaneously.

Hamamatsu’s Xenon Flash lamps for portable spectrophotometers

Using their unique know-how in vacuum device fabrication and electronics integration, Hamamatsu Photonics developed the most advanced Xenon Flash Lamps for UV-Vis-NIR portable spectrophotometry and online water monitoring.

These devices are available as stand-alone emitters or modules with an integrated trigger socket and power supply for easy integration.

Hamamatsu’s Xenon Flash lamps feature instantaneous high peak output, a compact design, low heat generation, and a continuous emission spectrum from 160 nm up to mid-infrared wavelengths making it the ideal light source for miniaturized instruments.  These lamps have a guaranteed lifetime of 10 billion flashes and offer output powers spanning from 2 W up to 60 W.

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