Sorption–spectroscopic Determination of Chromium (Iii) Ions Using Eriochrome Black T Immobilized on Silk Fibroin Fiber

A sorption–spectrophotometric method for the determination of chromium (III) ions was developed using Eriochrome Black T (EBT) immobilized on silk fibroin fiber. Immobilization markedly enhanced the method’s stability, sensitivity, and selectivity. Complex formation was confirmed by FT-IR spectroscopy (Cr–O band at 607 cm⁻¹), X-ray fluorescence analysis (clear Cr peak), and SEM-EDS (≈ 20 wt % Cr in the complex). Optimal conditions were pH 8, λ = 618 nm, and a universal buffer. The detection limit was 1.2 µg L⁻¹; analysis time, 10 min; calibration linearity, R² = 0.9991 for 5–50 µg Cr(III). Average absorbance at 50 µg was 0.273, and Sandell sensitivity 0.00279 µg cm⁻². Selectivity testing showed that Ni²⁺, Fe³⁺, and Cu²⁺ caused no interference, whereas Al³⁺, Co²⁺, and Cd²⁺ interferences were masked effectively. Validation with industrial wastewater (Navoi Electrochemical Plant, Mubarek Gas Processing Plant, Almalyk Mining and Metallurgical Complex) gave relative errors ≤ 6% and Sr ≤ 0.085. The method therefore offers an economical, rapid, and accurate tool for monitoring Cr(III) ions in environmental waters, suitable for both field and laboratory applications.