Nutrient pollution remains one of the greatest threats to water quality and imposes numerous public health and ecological concerns. Phosphate, the most common form of phosphorus, is one of the key nutrients necessary for plant growth. However, phosphate concentration in water should be carefully monitored for environmental protection requirements. Hence, an easy-to-use, field-deployable, and reliable device is needed to measure phosphate concentrations in the field. In this study, an inexpensive dip strip is developed for the detection of low concentrations of phosphate in water and seawater. In this device, ascorbic acid/antimony reagent was dried on blotting paper, which served as the detection zone, and was followed by a wet chemistry protocol using the molybdenum method. Ammonium molybdate and sulfuric acid were separately stored in liquid form to significantly improve the lifetime of the device and enhance the reproducibility of its performance. The device was tested with deionized water and Sargasso Sea seawater. The limits of detection and quantification for the optimized device using a desktop scanner were 0.134 ppm and 0.472 ppm for phosphate in water and 0.438 ppm and 1.961 ppm in seawater, respectively. The use of the portable infrared lightbox previously developed at our lab improved the limits of detection and quantification by a factor of three and were 0.156 ppm and 0.769 ppm for the Sargasso Sea seawater. The device’s shelf life, storage conditions, and limit of detection are superior to what was previously reported for the paper-based phosphate detection devices.
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Infrared Lightbox and iPhone App for Improving Detection Limit of Phosphate Detecting Dip Strips. Int. J. Chem. Mol. Eng. 2020, 14 (7), 179–185.
In this paper, we report the development of a portable
and inexpensive infrared lightbox for improving the detection limits
of paper-based phosphate devices. Commercial paper-based devices
utilize the molybdenum blue protocol to detect phosphate in the
environment. Although these devices are easy to use and have a long
shelf life, their main deficiency is their low sensitivity based on the
qualitative results obtained via a color chart. To improve the results,
we constructed a compact infrared lightbox that communicates
wirelessly with a smartphone. The system measures the absorbance
of radiation for the molybdenum blue reaction in the infrared region
of the spectrum. It consists of a lightbox illuminated by four infrared
light-emitting diodes, an infrared digital camera, a Raspberry Pi
microcontroller, a mini-router, and an iPhone to control the
microcontroller. An iPhone application was also developed to
analyze images captured by the infrared camera in order to quantify
phosphate concentrations. Additionally, the app connects to an online
data center to present a highly scalable worldwide system for tracking
and analyzing field measurements. In this study, the detection limits
for two popular commercial devices were improved by a factor of 4
for the Quantofix devices (from 1.3 ppm using visible light to 300
ppb using infrared illumination) and a factor of 6 for the Indigo units
(from 9.2 ppm to 1.4 ppm) with repeatability of less than or equal to
1.2% relative standard deviation (RSD). The system also provides
more granular concentration information compared to the discrete
color chart used by commercial devices and it can be easily adapted
for use in other applications.
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- Award ID(s):
- 1655221
- NSF-PAR ID:
- 10248600
- Date Published:
- Journal Name:
- International Journal of Chemical Engineering
- Volume:
- 14
- Issue:
- 7
- ISSN:
- 1687-806X
- Page Range / eLocation ID:
- 179-185
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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