Simultaneous and rapid screening and determination of twelve azo dyes illegally added into food products by using chemometrics-assisted HPLC-DAD strategy

Screening method for the analysis of Rhodamine B in chili powder

Rhodamine B is a synthetic dye known to enhance the visual appearance of chili powder. Due to its toxicity and carcinogenicity, chromatographic methods have been developed to monitor its presence in adulterated chili powder, but their assays are laborious, time consuming and expensive for screening purposes. The present studies propose an alternative for screening Rhodamine B in chili powder samples. The method combines thin layer chromatography (TLC) to solid surface room-temperature fluorescence spectroscopy. The scrape-dissolution procedure common to the instrumental analysis of TLC procedures was replaced with a fiber optic probe coupled to a commercial spectrofluorometer. The determination of Rhodamine B on the chromatographic plate is based on its retardation factor and maximum excitation and emission wavelengths. The limit of detection (1.9 ng.mL-1) and the limit of quantitation (5.2 ng.mL-1) are well below the usual contamination of Rhodamine B in adulterated foods.

Highly sensitive fluoroprobe for detecting Sudan dyes in paprika utilizing carbon dot-embedded zeolitic imidazolate framework-8

In this manuscript, we synthesized CDs@ZIF-8 through a one-step, in-situ method by integrating green-emitting carbon dots (CDs) with zeolitic imidazolate framework-8 (ZIF-8). The resulting CDs@ZIF-8 was utilized as an ultrasensitive probe for detection, leveraging the inner filter effect. The analysis demonstrated the capability to detect Sudan dyes. Sudan I, for example, could be detected within a concentration range spanning from 0.25 to 70 μM, achieving a remarkable detection limit of 76.56 nM. This established method was effectively employed for detecting Sudan I in paprika. Compared with CDs, CDs@ZIF-8 exhibited a 3.32-fold increase in sensitivity and a wider detection range. This enhanced performance was attributed to the porous ZIF-8, which allowed for the enrichment of targets around CDs and avoided the aggregation of CDs. Additionally, embedding the CDs in ZIF-8 improved their pH stability. Our study provides a new approach for using CDs under limited conditions by leveraging metal-organic frameworks.

TiO2 nanorod arrays@PDA/Ag with biomimetic polydopamine as binary mediators for duplex SERS detection of illegal food dyes

Based on TiO2 nanorod arrays@PDA/Ag (TNRs@PDA/Ag), a better surface-enhanced Raman scattering (SERS) sensor with effective enrichment and enhancement was investigated for duplex SERS detection of illicit food dyes. Biomimetic PDA functions as binary mediators by utilizing the structural characteristics of polydopamine (PDA), which include the conjugated structure and abundant hydrophilic groups. One PDA functioned as an electron transfer mediator to enhance the efficiency of electron transfer, and the other as an enrichment mediator to effectively enrich rhodamine B (RhB) and crystal violet (CV) through hydrogen bonding, π-π stacking, and electrostatic interactions. Individual and duplex detection of illicit food dyes (RhB and CV) was performed using TNRs@PDA/Ag to estimate SERS applications. Their linear equations and limits of detection of 1 nM for RhB and 5 nM for CV were derived. Individual and duplex food colour detection was successfully accomplished even in genuine chili meal with good results. The bifunctional TNRs@PDA/Ag-based highly sensitive and duplex SERS dye detection will have enormous potential for food safety monitoring.

Combination of smartphone digital image colorimetry and UV-Vis spectrophotometry as detection systems with solidified floating organic drop microextraction as preconcentration method for the quantification of methyl red in wastewater samples

In this study, a portable smartphone-based digital image colorimetric system (SDIC) was designed and integrated with a solidified floating organic drop microextraction method (SFODME) for the quantification of methyl red in textile wastewater samples. The RGB (red, green, and blue) data were evaluated for each captured image, and the green channel was selected for quantification due to its linear response for the analyte. Under optimal conditions, an acceptable linear range was recorded for the analyte. The proposed method recorded a limit of detection (LOD) value of 0.046 mg/L. The developed microextraction method was also combined with UV-Vis spectrophotometry, which recorded an LOD value of 0.012 mg/L. Real sample analysis was carried out with textile wastewater samples to check the applicability/accuracy of the developed method, using a matrix matching calibration strategy to enhance quantification accuracy. Satisfactory percent recoveries in the range of 93.3%-114.3% and 92%-92.7% were recorded for the SFODME-SDIC and SFODME-UV methods, respectively.