Abstract
Spectrophotometers are commonly used to measure the concentrations of a wide variety of analytes in drinking water and other matrixes; however, many laboratories with limited resources cannot afford to buy these very useful instruments. To meet this need, an accurate, precise, and affordable light emitting diode (LED) spectrophotometer was designed and built using best engineering practices and modern circuit design. The cost and performance of this LED spectrophotometer was compared against 4 common commercial spectrophotometers. More specifically, the performance of these spectrophotometers was evaluated from the upper limits of linear range, upper limits of operational range, calibration sensitivities, R2 values, precisions of standards, estimated limits of detection, and percent calibration check standard recoveries for the determinations of iron (Fe), manganese (Mn), and fluoride (F-) in drinking water. This evaluation was done in the United States (U.S.) and India. Our LED spectrophotometer costs $63 United States Dollars (USD) for parts. The 4 commercial spectrophotometers ranged in cost from $2,424 to $7,644 USD. There are no practical differences in the upper limits of linear range, upper limits of operational range, R2 values, precisions of standards, and estimated limits of detection for our LED spectrophotometer and the 4 commercial spectrophotometers. For 2 of the 3 analytes, there is a practical difference in the calibration sensitivities our LED spectrophotometer and the 4 commercial spectrophotometers. More specifically, the calibration sensitivities for Mn and F- using our LED spectrophotometer were 65.2% and 67.0% of those using the 4 commercial spectrophotometers, respectively. In conclusion, this paper describes the design, use, and performance of an accurate, precise, and extremely affordable LED spectrophotometer for drinking water and other testing with limited resources.
Highlights
The small blank voltages (V0) of the total F− analyses most likely gave small signal to noise ratios and the large spread of upper limits of linear range for the light emitting diode (LED) spectrophotometer (Table 4; Fig 14). These results suggest that the LED spectrophotometers have upper limits of linear range that are generally comparable to those of the 4 commercial spectrophotometers used in this study (Tables 2–4; Figs 8–14) and would be sufficient for comparisons to World Health Organization (WHO) guidelines for drinking water quality or health-based values for these analytes [44, 45]
The small blank voltages (V0) of the total F− analyses most likely gave small signal to noise ratios and the large spread of upper limits of operational range for the LED spectrophotometer (Table 4; Fig 14). These results suggest that the LED spectrophotometers have upper limits of operational range that are generally comparable to those of the 4 commercial spectrophotometers used in this study (Tables 2–4; Figs 8–14) and would be sufficient for comparisons to WHO guidelines for drinking water quality or health-based values for these analytes [44, 45]
The estimated limits of detection for the LED spectrophotometer ranged from 0.006 to 0.03 milligrams per liter (mg/L) for total F− (Table 4). These results suggest that the LED spectrophotometer has estimated limits of detection that are generally comparable to those of the 1 commercial spectrophotometer used in India (Table 4) and would be sufficient for comparisons to WHO guidelines for drinking water quality or health-based values for these analytes [44, 45]
Summary
They are used to measure the concentrations of a wide range of inorganic, organic, and biological chemicals. They are used to measure the concentrations of harmful metals in drinking water [1, 2], active ingredients in pharmaceutical products [3], and clinically important molecules in humans [4]. Commercial spectrophotometers typically cost over $2,000 United States Dollars (USD), a sum which can make these instruments unattainable for organizations with limited resources. In this project, we describe the development of a spectrophotometer which can be built by laboratory technicians or others competent in basic electronics for $63 USD in parts. This spectrophotometer has performance characteristics comparable to 4 commonly used commercial spectrophotometers
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