Metal Oxide Nanoparticle-Assisted Microextraction Coupled with Smartphone Digital Image Colorimetry for the Determination of Rhodamine B in Water Samples

A metal oxide nanoparticle-based microextraction method was developed and optimized for the determination of Rhodamine B in aqueous samples. During the method development stage, the effects of adsorbent amount, extraction medium pH, elution solvent type and volume, ionic strength, extraction time, and elution time were systematically investigated and optimized. After the microextraction procedure, quantitative determination of Rhodamine B was carried out using smartphone digital image colorimetry. Furthermore, in colorimetric measurements, optimum measurement conditions were determined by investigating the distance between the detector (smartphone camera) and the sample, as well as the brightness of the light source, in a specially designed measurement box used for colorimetric measurements. The analytical performance of the proposed method was evaluated under optimized conditions. The limit of detection (LOD) and limit of quantification (LOQ) were determined as 0.013 µg/mL and 0.043 µg/mL, respectively. Method precision was assessed by analyzing water samples spiked with 0.3 µg/mL Rhodamine B five consecutive times within the same day, yielding an intra-day relative standard deviation (RSD) of 3.1%. Inter-day precision was evaluated by repeated analyses performed on different days, and the inter-day RSD value was calculated as 4.5 %. The applicability of the method was further validated by analyzing different water samples, and relative recovery values were found to be in the range of % 98.0-100.2. The results indicate that the developed metal oxide nanoparticle-assisted microextraction combined with smartphone digital image colorimetry is a simple, sensitive, and reliable analytical method for the determination of Rhodamine B in water samples.