Hydroxyethylcellulose- and Chitosan-Modified 3D-Printed Carbon Electrodes for Indole-3-Acetic Acid and Salicylic Acid Determination

Abstract This study describes the development of a 3D-printed carbon black (3D-CB) electrode modified with hydroxyethylcellulose (HEC) and chitosan (CH) layers, applied to the simultaneous quantification of indole-3-acetic acid (IAA) and salicylic acid (SA) in plant samples. Measurements were performed by square-wave voltammetry (SWV) under optimized conditions, enabling rapid and resolved detection of phytohormones. The method exhibited linear responses for both analytes, with correlation coefficients (r) of 0.999. Limits of detection (LOD) were 0.446 μM for IAA and 0.335 μM for SA. Good precision was obtained, with RSD values for both intraday and interday analyses not exceeding 4.70%. The applicability of the method was evaluated in real plant samples, including roots and leaves of soybean and maize, as well as roots, leaves, and green fruits of strawberry. For IAA, mean recoveries for the three extracts ranged from 96.82% to 101.37%, with RSD values between 2.74% and 5.27%. For SA, recoveries ranged from 98.13% to 102.98%, with RSD values between 1.92% and 4.01%. The absence of a statistically significant difference between added and found concentrations confirmed the accuracy and reliability of the proposed method. Owing to its simple fabrication, rapid SWV response, low operational cost, and use of environmentally friendly materials, the proposed 3D-CB/HEC–CH platform represents an alternative for efficient monitoring of IAA and SA in agricultural matrices.