Smartphone-based colorimetric sensing with reference calibration and ensemble machine learning for enhanced detection of nitrite and ammonium ions - Trung Nguyen Quoc; Minh-Vuong Phan; Khoi Pham Dang; Huy Ngo Huu Gia; Phuc Nguyen Tran Thien; Vinh Truong Hoang; Thanh-Long Do; Thai-Binh Tran; Manh-Huy Do; Le-Kim-Thuy Nguyen; Thanh-Danh Nguyen (Analytica Chimica Acta, 2026)