Analytical Design of an Automated Microfluidic System and Its Application for the Determination of Nitrite Ions in Environmental Samples

This study describes the development of a fully automated microfluidic spectrophotometric system for detecting various pollutants, including nitrite, in the Shatt al-Arab River in the Basra governorate of southern Iraq. The proposed system offers a simple, effective, and efficient analytical approach characterized by high sample throughput, low reagent consumption, and minimal sample volume requirements. The custom-fabricated microfluidic chip has a total volume capacity of 25 μL and a length of 10cm. It consisted of three microchannels, two channels with individual volumes of 10 μL, and the third with a volume of 5μL. Three Arduino-controlled peristaltic pumps were employed, supported by in-house developed software to control the flow rates of both reagent introduction and sample loading. Data acquisition was performed by recording peak heights corresponding to sample concentrations using the Microsoft Excel 2016 program. Application of the system to real samples from the Shatt Al-Arab River revealed the nitrite concentration ranging from 0.006 to 0.06 μg mL^-1. The method demonstrated a detection limit of 1×10^(-4) μgmL^-1 and exhibited excellent precision, with a relative standard deviation (RSD%) of 0.379% for ten replicate measurements at a concentration of 0.1 μg/mL. Linearity was established in the range of (0.01-0.1) μgmL^-1, yielding a correlation coefficient (R²) of 0.9998 based on ten data points. Each analysis of a sample required only 50µl of reagents, resulting in a total reagent consumption of 30 mL for 600 analyses within an hour. Consequently, this system is eco-friendly due to its minimal waste levels.