A simple and green ion-pairing extraction colorimetric determination of chlorhexidine employing coconut oil as a natural solvent with image processing

Abstract

A cost-effective, simple, and green determination of chlorhexidine is proposed. A commonly available bromothymol blue serves as a reagent. The ion-pairing of chlorhexidine and bromothymol blue in an aqueous solution can be extracted into an organic phase of coconut oil, which is proposed as an alternative natural green solvent, replacing the conventional toxic organic solvents. An investigation of the chlorhexidine-bromothymol blue ion pair was made spectrophotometrically and via image processing using a smartphone camera. Downscaling is operated for the extraction of 500 μL of an aqueous mixture containing chlorhexidine and bromothymol blue in phosphate buffer (pH 7.5, 5 mmol/L) with 500 μL of coconut oil for 3 min by hand-shaking. A set of 12 extraction tubes can be operated in one run. After phase separation by centrifuging (3000 rpm, 3 min), the 12 tubes are photographed in one shot using a smartphone. Images of both aqueous and organic phases are evaluated for red-green-blue (RGB) color intensity system. Linearity equations: R intensity = 1.205 [Chlorhexidine] – 23.6 (r2: 0.9795), and ΔB intensity = 1.525 [Chlorhexidine] – 36.75 (r2: 0.9907), are obtained for aqueous and organic phases, respectively. The limits of detection (LOD) and quantitation (LOQ) were 12 and 40 mg/L for aqueous, while 11 and 34 mg/L for organic phases, respectively. The proposed procedure was applied to real samples of active pharmaceutical ingredients (API), disinfectant cleaner, and mouthwash. The results obtained by the proposed procedure agree with the high-performance liquid chromatography (HPLC) reference method that utilizes a UV detector. In evaluations using the green analytical procedure index (GAPI) and analytical greenness (AGREE), the proposed procedure was found to be the greenest compared to the conventional spectrophotometric method and HPLC. The proposed procedure involved the UN-SDGs #3, #4, and #12 and scored the highest value of the need, quality, and sustainability (NQS) index. The proposed procedure encourages sustainable chemistry and pharmacy.