Environmental monitoring using a conventional photographic digital camera for multianalyte disposable optical sensors

The primary interest of this study concerns the use of an inexpensive photographic digital camera as the detection system, using its own flash as the source of light to present a new analytical procedure to measure disposable multianalyte optical sensors for potassium, magnesium, hardness and conventional pH test strips. The camera arrangement was designed in a fixed position over an optical board with controllable ambient conditions. After acquiring the digital image, the analytical information contained in each test zone is analyzed using theRGB colour space. Reflectance measurements were developed to study the colourimetric and spectral characteristics of the test zones. We obtained the following application ranges and precision in terms of relative standard deviation (RSD %): for potassium from 3.2 × 10⁻⁷ to 0.1 M with a precision between 3.3 and 4.0%, for magnesium from 2.7 × 10⁻⁶ to 1.5 M showing a precision between 4.7 and 7.8% and finally for hardness from 4.3 × 10⁻² to 200,000 mg L⁻¹ CaCO₃ and between 5.1 and 7.0%. Moreover, the analytical characteristics of several optical procedures were compared with the results presented here. The proposed method was statistically validated against a reference procedure using samples of water from different sources and beverages, indicating that there are no significant statistical differences at a 95% confidence level.