An Infrared Evanescent Wave Sensor for Detection of Ascorbic Acid in Food and Drugs

An infrared evanescent wave sensor was developed to accurately detect ascorbic acid (vitamin C) in food and drugs. The sensor was fabricated by tapering and bending of As
₂
S
₃
infrared fibers. Due to the broad transmission range (5000–1500 cm
⁻¹
) of the infrared fibers, covering the characteristic absorption peak of ascorbic acid (C = O at 1760 cm
⁻¹
and C = C at 1690 cm
⁻¹
), the sensor is capable of accurately identifying and detecting the concentration of ascorbic acid. Experimental results demonstrated that a conically tapered fiber sensor with a waist diameter of 50 μm, waist length of 30 mm, and a radius of 2 mm achieved a maximum sensitivity of 0.1257 (a.u./(mg·ml
⁻¹
)) and a limit of detection (LoD) of 0.917 mg/ml. Furthermore, the application of this fiber sensor in various vitamin C-containing tablets and juices validated its high accuracy and minimal measurement deviation (as low as 0.19 mg/ml). Compared to traditional detection methods, the sensor not only provides a faster and cost-effective solution to identify the substance but also maintains high accuracy. It offers a new approach to quantitative and qualitative analysis of food and drugs.