Solid-phase Extraction (SPE) Combined with Digital Colorimetry as an Eco-friendly Method for the Separation and Quantification of Cephalexin in Pharmaceutical Preparations

Abstract

The aim of this study was to develop a simple and green analytical method for the determination of cephalexin, based on solid-phase extraction (SPE) followed by digital image colorimetry (DIC) as an environmentally friendly alternative to conventional chromatographic methods. Initially, a C18 cartridge was activated using 3 mL of methanol and then equilibrated with 3 mL of distilled water. After passing 10 mL of the aqueous sample through the cartridge, the active compound was eluted with a small volume (2 mL) of methanol. The eluate was evaporated and the residue was reconstituted in 50 µL of sodium hydroxide. The colorimetric reaction was then performed on filter paper by adding 10 µL of the reagent and 10 µL of the sample, and the resulting color was recorded using an LED light (1A, 12V) and captured with a mobile phone camera.

The results demonstrated that the developed method provides accurate and reliable analysis with an acceptable linear range of 1–16 µg/mL and good correlation coefficients (R² > 0.9917). The limit of detection (LOD) was 0.027 µg/mL, and the limit of quantification (LOQ) was 0.088 µg/mL. The method showed good precision, with relative standard deviation (RSD%) values not exceeding 0.56% for intra-day precision and 1.52% for inter-day precision. Recovery values ranged from 100.16–101% for the Cefalex S2 syrup sample and 98.25–101.6% for the Cefalex C2 capsule sample, with a notable reduction in organic solvent and energy consumption. The total penalty points (PPs) for the green assessment of the developed method were only 6, compared to 26 points for the reference HPLC method, confirming its superiority in terms of environmental friendliness and sustainability.