A novel portable microchip electrophoresis system for rapid on-site detection of soil nutrient ions

Abstract

The conventional techniques for soil nutrient ion detection face challenges, including prolonged preparation periods and the necessity for distinct instruments tailored to each specific ion. To address these issues, we have engineered a cutting-edge soil nutrient ion detection apparatus: the Microchip Electrophoresis Soil Nutrient Ion Portable Detection System (ME-SNI-PDS). This system, leveraging microchip electrophoresis with a capacitively coupled contactless conductivity detector (ME-C4D), simplifies the detection process with user-friendly touchscreen controls. Our system is capable of simultaneous detection of key soil nutrient ions—ammonium (NH4 +), calcium (Ca2+), magnesium (Mg2+), potassium (K+), nitrate (NO3 −), and dihydrogen phosphate (H2PO4 −)—in a swift 180 s, facilitated by precise voltage regulation. We have refined the buffer solution, consisting of 20 mM 2-(N-morpholinyl)-ethanesulfonic acid and L-histidine, with the addition of 0.01 mM cetyltrimethylammonium bromide and 10 mM 18-crown-6, to ensure the complete resolution of soil nutrient ions. Following this, we established highly accurate peak height-to-concentration correlations for the six aforementioned ions, each with a coefficient of determination (R2) exceeding 0.99. The detection limits for these ions stand at a remarkably low concentration of 0.05 mM, translating to 0.9 mg l−1 for NH4 +, 2.0 mg l−1 for Ca2+, 1.2 mg l−1 for Mg2+, 1.96 mg l−1 for K+, 3.1 mg l−1 for NO3 −, and 4.85 mg l−1 for H2PO4 −. Subsequent soil leachate analysis via the ME-SNI-PDS has yielded ion content data that, upon comparison with results from continuous flow analyser (CFA) and inductively coupled plasma atomic emission spectrometry, confirm the system’s exceptional integration, compactness, portability, speed, and efficiency. The ME-SNI-PDS shows immense promise for application in precision agriculture and the prevention of surface soil pollution. It is poised to make a significant impact in the realm of crop fertilization and environmental stewardship.