Trace Determination of Rhodamine B and Rhodamine 6G Dyes in Aqueous Samples by Solid-phase Extraction and High-performance Liquid Chromatography Coupled with Fluorescence Detection

Direct immersion single-drop microextraction combined with fluorescence detection using an optical probe. Application for highly sensitive determination of rhodamine 6G

The use of an optical probe for fluorescence detection combined with direct immersion single-drop microextraction has been demonstrated as an innovative approach. The optical probe served both as a drop holder for extractant and as a measuring device which made it possible to eliminate the use of cuvettes. A laser and a light emitting diode (LED) were tested as possible light sources. Both of them showed comparable results. However, given the much smaller half-band width of the laser radiation, its use has proven to be preferable since background correction can be eliminated. Direct immersion single-drop microextraction of an ionic association complex of rhodamine 6G with picric acid with subsequent fluorescent detection (λex was 532 nm and 525 nm for laser and LED, respectively; λem was 560 nm for both laser and LED) was used a model system to evaluate the new approach. The extractant phase was a 55 μL amyl acetate microdrop fixed in the optical part of the probe. LOD, LOQ and linear calibration range were found as 0.14, 0.48 and 0.5-10 nmol L-1, and 0.15, 0.50 and 0.5-5 nmol L-1 for laser and LED light sources, respectively. The accuracy of the method was assessed by analyzing real water samples.

Metal-organic framework functionalized with deep eutectic solvent for solid-phase extraction of Rhodamine 6G in water and cosmetic products

An NH2 -MIL-53(Al)-DES(ChCl-Urea) nanocomposite was synthesized for extraction and determination of Rhodamine (Rh) 6G from environmental and cosmetic samples. The deep eutectic solvent (DES) was prepared by mixing choline chloride and urea in a mole ratio of 1:2. NH2 -MIL-53(Al)-DES(ChCl-Urea) nanocomposite was synthesized using the impregnation method at a ratio of 60:40 (w/w). The optimum conditions were determined after NH2 -MIL-53(Al)-DES(ChCl-Urea) characterization was performed. The optimum conditions were determined as pH 8, adsorbent amount of 15 mg, total adsorption-desorption time of 6 min, and enrichment factor of 20. The recovery values of the solid-phase extraction method for water and cosmetic samples under optimum conditions were between 95% and 106%. NH2 -MIL-53(Al)-DES(ChCl-Urea) nanocomposite was an economically advantageous adsorbent because of its reusability of 15 times. All analyses were performed using the ultraviolet-visible spectrophotometer. The linear range, limit of detection, and limit of quantification of the method were 100-1000, 9.80, and 32.68 μg/L, respectively. The obtained results showed that the synthesized nanocomposite is a suitable adsorbent for the determination of Rh 6G in water and cosmetic samples. The real sample applications were verified with the high-performance liquid chromatography system.

An accuracy improved ratiometric SERS sensor for rhodamine 6G in chili powder using a metal-organic framework support

Internal standard molecule 4-mercaptobenzoic acid (4-MBA) embedded Au core-Ag shell nanorods (Au-MBA@Ag NRs) were prepared by a seed-mediated growth method, then loaded on octahedral MIL-88B-NH₂ to obtain a novel ratiometric SERS substrate of Au-MBA@Ag NRs/PSS/MIL-88B-NH₂ (AMAPM) for detecting rhodamine 6G (R6G) in chili powder. The porous structure and excellent adsorption ability of MIL-88B-NH₂, allowed for increased loading of Au-MBA@Ag NRs, thereby shortening the distance between adsorbed R6G and the "hot spot" resulting from local surface plasmon resonance (LSPR) of Au-MBA@Ag NRs. Based on the SERS characteristic peak ratio of R6G to 4-MBA, the ratiometric SERS substrate displayed improved accuracy and excellent performance for R6G detection, with a wide linear range of 5-320 nM and a low detection limit of 2.29 nM as well as fine stability, reproducibility and specificity. The proposed ratiometric SERS substrate offered a simple, fast and sensitive sensing strategy for R6G detection in chili powder, which demonstrated potential applications in food safety and the analysis of trace analytes in complex matrices.

Development of clinoptilolite zeolite-coated magnetic nanocomposite-based solid phase microextraction method for the determination of Rhodamine B in cosmetic products

Green synthesis of clinoptilolite zeolite/Fe₃O₄ nanocomposite (MZNC) was carried out using Laurus Nobilis L. leaf extract. Characterization of this MZNC was performed using Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, X-Ray Diffraction and Vibrating Sample Magnetometer. According to the VSM analysis results, the saturation magnetization of 23 emu/g and coercivity of 23.5 Oe indicate that the synthesized magnetic nanocomposite is superparamagnetic. A new ultrasonic assisted clinoptilolite zeolite-coated magnetic nanocomposite-based solid phase microextraction (MZNC-SPME) method combined with high performance liquid chromatography was developed for the extraction and determination of Rhodamine B. The preconcentration factor for the MZNC-SPME method was found to be 40 under optimal conditions. Under optimal conditions, the linear range, correlation coefficient (R²), limit of detection (LOD), and intra- and interday relative standard deviation (RSD) were found to be 1.00-100.00 ng mL^-1, 0.9995, 0.16 ng mL^-1, 1.89% and 2.49%, respectively. The developed method was successfully performed to determine Rhodamine B in 6 different cosmetic samples. 6 ions and 5 different dyes were added to the sample solution to show the selectivity of the method. The obtained results show that the determination of Rhodamine B is possible in the presence of these ions and dyes. In order to determine the accuracy of the MZNC-SPME method, two different concentrations of Rhodamine B concentration in cosmetic samples were added as 10 and 50 ng mL^-1. Extraction recoveries were found in the range of 92.03-101.52% and these results are quite satisfactory. It is seen that the developed method for the extraction and determination of Rhodamine B from cosmetic samples is applicable due to the easy synthesis of the sorbent and the short, simple, environmentally friendly and low cost of the method.

Ag Nanoparticles Decorated ZnO Nanorods as Multifunctional SERS Substrates for Ultrasensitive Detection and Catalytic Degradation of Rhodamine B

Industrial wastewater containing large amounts of organic pollutants is a severe threat to the environment and human health. Thus, the rapid detection and removal of these pollutants from wastewater are essential to protect public health and the ecological environment. In this study, a multifunctional and reusable surface-enhanced Raman scattering (SERS) substrate by growing Ag nanoparticles (NPs) on ZnO nanorods (NRs) was produced for detecting and degrading Rhodamine B (RhB) dye. The ZnO/Ag substrate exhibited excellent sensitivity, and the limit of detection (LOD) for RhB was as low as 10⁻¹¹ M. Furthermore, the SERS substrate could efficiently degrade RhB, with a degradation efficiency of nearly 100% within 150 min. Moreover, it retained good SERS activity after multiple repeated uses. The interaction between Ag NPs, ZnO, and RhB was further investigated, and the mechanism of SERS and photocatalysis was proposed. The as-prepared ZnO/Ag composite structure could be highly applicable as a multifunctional SERS substrate for the rapid detection and photocatalytic degradation of trace amounts of organic pollutants in water.

Urea-linked covalent organic framework functionalized polytetrafluoroethylene film for selective and rapid thin film microextraction of rhodamine B

Incorporation of highly selective and stable adsorbent with facile extraction technology is desired in practical analysis. Here we show the rational preparation of a urea-linked covalent organic framework functionalized polytetrafluoroethylene film (COF-117-PTFE) with ordered porous structure, rich functional groups, and large surface area-to-volume ratio as the effective adsorbent for convenient, selective and rapid thin film microextraction (TFME) of rhodamine B (RB). The COF-117-PTFE based TFME coupled with high performance liquid chromatography-fluorescence detector (HPLC-FLD) successfully realized the determination of RB with the limit of detection of 0.007 μg L^-1, the linear range of 0.1 - 100 μg L^-1. The relative standard deviation (RSD) of intraday (n = 5) and interday (n = 5) for the determination of 10 μg L^-1 RB were 2.3% and 6.8%, respectively. The absolute recoveries were 80.3%, 71.2% and 67.9% in river water, chili powder and Sichuan pepper powder, respectively. The recoveries for RB spiking in complicated real samples (dry chili, chili powder, dry Sichuan pepper, Sichuan pepper powder and river water) ranged from 90.4% to 107.5%. The developed COF-117-PTFE based TFME-HPLC-FLD method is promising in practical application. This work reveals the high potential of functionalized COF film as the adsorbent for effective extraction of trace contaminants in complicated samples.

Voltammetric Behaviour of Rhodamine B at a Screen-Printed Carbon Electrode and Its Trace Determination in Environmental Water Samples

The voltammetric behaviour of Rhodamine B was studied at a screen-printed carbon electrode (SPCE), by cyclic and differential pulse voltammetry. Cyclic voltammograms exhibited two reduction peaks (designated R1 and R2) generated from the reduction of the parent compound through, first, one electron reduction (R1) to give a radical species, and then a further one-electron, one-proton reduction to give a neutral molecule (R2). On the reverse positive-going scan, two oxidation peaks were observed. The first, O1, resulted from the oxidation of the species generated at R2, and the second, O2, through the one-electron oxidation of the amine group. The nature of the redox reactions was further investigated by observing the effect of scan rate and pH on the voltammetric behaviour. The developed SPCE method was evaluated by carrying out Rhodamine B determinations on a spiked and unspiked environmental water sample. A mean recovery of 94.3% with an associated coefficient of variation of 2.9% was obtained. The performance characteristics indicated that reliable data may be obtained for Rhodamine B measurements in environmental water samples using this approach.

Rapid and sensitive detection of Rhodamine B in food using the plasmonic silver nanocube-based sensor as SERS active substrate

The use of dye in food is harmful to human health and is prohibited nowadays. However, it is still used because of the benefits, such as cheap prices and abundant resources. Rhodamine B is usually used as the colorant in food such as chili powder, chili oil, etc. It is colorless at very low concentration 10^-7 M. The sensitive detection of RhB at ultra-low concentration help to prevent some risk for human. Surface-enhanced Raman scattering (SERS) is a great technique to detect the analytes at ultra-low concentration and provide the molecule's information as a fingerprint. In this study, silver nano-cube was facilely synthesized by reducing Ag⁺ in ethylene glycol and upgraded to thin-film as a SERS active substrate. RhB was detected at 10^-10 M by a silver nano-cube sensor. The dynamic linear regression between the Raman intensity and RhB concentration over seven orders of magnitude (from 10^-4 to 10^-10 M) was excellent with high reliability (R² = 0.99). Moreover, the substrate can be used after storing in a dark area for 60 days. This proposed nano-cube silver could serve as a potential substrate for detecting RhB in food at very low concentration.

Multiple adverse effects of textile effluents and reactive Red 239 dye to aquatic organisms

Textile dyeing consumes high volumes of water, generating proportional number of colored effluents which contain several hazardous chemical. These contaminants can implicate in significant changes in aquatic environmental, including several adverse effects to organisms in different trophic levels. The present study was developed to assess the ecotoxicological effects of textile effluent samples and reactive Red 239 dye (used in cotton dyeing) to aquatic organisms Vibrio fischeri bacteria, Daphnia similis crustacean, and Biomphalaria glabrata snail (adults and embryos). Chronic assays with lethal and sublethal effects for Daphnia similis were included and performed only for textile effluents samples. The mutagenicity was also evaluated with Salmonella/microsome assay (TA98, TA100, and YG1041 strains). V. fischeri bacteria was the most sensitive to reactive Red 239 dye (EC50 = 10.14 mg L^-1) followed by mollusk embryos at all stages (EC50 = 116.41 to 124.14 mg L^-1), D. similis (EC50= 389.42 mg L^-1), and less sensitive to adult snails (LC50= 517.19 mg L^-1). The textile effluent was toxic for all exposed organisms [E(L)C50 < 15%] and B. glabrata embryos showed different responses in the early stages of blastulae and gastrulae (EC50 = 7.60 and 7.08%) compared to advanced development stages trochophore and veliger (EC50 = 21.56 and 29.32%). Developmental and sublethal effects in B. glabrata embryos and D. similis were evidenced. In the chronic assay with effluent, the EC10/NOEC = 3% was obtained. Mutagenic effects were not detected for dye aqueous solutions neither for effluents samples. These data confirmed the importance of evaluating the effects in aquatic organisms from different trophic levels and reinforce the need for environmental aquatic protection.

Removal of organic pollutants in water using water hyacinth (Eichhornia crassipes)

Globally, water hyacinth is recognized as an invasive species that threatens the survival of aquatic organisms. Its removal from water is performed manually or physically to avoid the secondary water pollution that results through the usage of chemically synthesised herbicides for its control, thus generating solid waste. Among other things, scientists have proposed the conversion of this waste into adsorbents that can be utilized for the remediation of water resources. This is essentially significant as the quality of water remains a necessity in all spheres of life. In this paper, the remediation strategies that have been proposed for the remediation of water resources through the removal of organic pollutants using water hyacinth are reviewed. Phytoremediation and removal of organics through adsorption using water hyacinth have been extensively investigated. From this review, it can be observed that the majority of the reviewed work focussed more on the removal of organic dyes from water. In this context, the mechanisms involved during the adsorption processes are discussed. In the end, future research that is likely to assist in the environmental management of water resources through their remediation with water hyacinth is suggested.

A comprehensive review on magnetic carbon nanotubes and carbon nanotube-based buckypaper for removal of heavy metals and dyes

Industrial effluents contain several organic and inorganic contaminants. Among others, dyes and heavy metals introduce a serious threat to drinking waterbodies. These pollutants can be noxious or carcinogenic in nature, and harmful to humans and different aquatic species. Therefore, it is of high importance to remove heavy metals and dyes to reduce their environmental toxicity. This has led to an extensive research for the development of novel materials and techniques for the removal of heavy metals and dyes. One route to the removal of these pollutants is the utilization of magnetic carbon nanotubes (CNT) as adsorbents. Magnetic carbon nanotubes hold remarkable properties such as surface-volume ratio, higher surface area, convenient separation methods, etc. The suitable characteristics of magnetic carbon nanotubes have led them to an extensive search for their utilization in water purification. Along with magnetic carbon nanotubes, the buckypaper (BP) membranes are also favorable due to their unique strength, high porosity, and adsorption capability. However, BP membranes are mostly used for salt removal from the aqueous phase and limited literature shows their applications for removal of heavy metals and dyes. This study focuses on the existence of heavy metal ions and dyes in the aquatic environment, and methods for their removal. Various fabrication approaches for the development of magnetic-CNTs and CNT-based BP membranes are also discussed. With the remarkable separation performance and ultra-high-water flux, magnetic-CNTs, and CNT-based BP membranes have a great potential to be the leading technologies for water treatment in future.

A New Green In Situ Effervescent CO2-Table-Induced Switchable Hydrophilicity Solvent Extraction Method of Rhodamine B in Food and Soft Drink Samples

BACKGROUND

A new and simple effervescent CO2-table-induced switchable hydrophilicity solvent extraction method (CI-SHS) was used for the preconcentration of rhodamine B (RB).

OBJECTIVE

The main theme of the proposed method to disperse green solvent by in situ CO2-table system overcome on the contamination and to avoid the dispersion by using different chemicals.

METHODS

Switchable hydrophilicity solvent (N, N-Dimethyl cyclohexylamine) was dispersed in an aqueous solution by reaction of CO2-table of sodium carbonate and citric acid to enhance the contact area between two medium, which radically improved the extraction capacity of the RB from aqueous medium to switchable solvent. The phase separation was achieved by simple heating not by centrifugation that makes a change on hydrophilicity to hydrophobicity. The supernatant-enriched RB- N, N-Dimethyl cyclohexylamine phase was withdrawn and injected into the UV glass cells. The absorbance was measured at 542.

RESULTS

Limit of detection and enhancement factor were achieved to be 0.042 and 50 µg/L. Validity and accuracy of the method verified by analysis of real samples by the spiking addition method. The relative standard deviation was obtained at 3.2%. The method was applied to food and soft drink samples.

CONCLUSIONS

This method offers high sensitivity, selectivity, accuracy, and precision for the separation, preconcentration, and spectrophotometric determination of RB. Simple, fast, low-cost, and green extraction method was developed.

HIGHLIGHTS

High enrichment factor and lower detection limits were observed in this microextraction method. Present method is sensitive, selective, very accurate, and precise.

Surface Polymers on Multiwalled Carbon Nanotubes for Selective Extraction and Electrochemical Determination of Rhodamine B in Food Samples

In this study, we combine magnetic solid phase extraction (MSPE), with the screen-printed carbon electrode (SPCE) modified by a molecular imprinted polymer (MIP) for sensitive and selective extraction and electrochemical determination of Rhodamine B in food samples. A magnetic solid phase extraction (MSPE) was carried out using magnetic poly(styrene-co-divinylbenzene) (PS-DVB) and magnetic nanoparticles (MNPs) synthetized on the surface of multiwalled carbon nanotubes (MWCNTs). An MIP was prepared on the surface of MWCNTs in the presence of titanium oxide nanoparticles (TiO₂NPs) modifying the SPCE for the rapid electrochemical detection of Rhodamine B. The MIPs synthesis was optimized by varying the activated titanium oxide (TiO₂) and multiwalled carbon nanotubes (MWCNTs) amounts. The MSPE and electrochemical detection conditions were optimized as well. The present method exhibited good selectivity, high sensitivity, and good reproducibility towards the determination of Rhodamine B, making it a suitable method for the determination of Rhodamine B in food samples.

Colorimetric and fluorescent sensing of rhodamine using polymethacrylate matrix

This is a description of the tracer analysis method involving colorimetric and fluorescent measurements based on solid phase extraction of rhodamine into transparent polymethacrylate matrix. Concentration of rhodamine in PMM is measured as spectrophotometric absorption level at 535 nm and fluorescence at 554 nm. The calibration graphs are linear within the ranges 0.02-0.10 mg∙L^-1 and 0.002-0.06 mg∙L^-1 and detection limits 0.014 mg∙L^-1 and 0.0005 mg∙L^-1 are calculated for colorimetric and fluorescent measurements, respectively. The method has been successfully used for determination of rhodamine in groundwater.

Rapid, simultaneous and interference-free determination of three rhodamine dyes illegally added into chilli samples using excitation-emission matrix fluorescence coupled with second-order calibration method

In this study, a smart and green analytical method based on the second-order calibration algorithm coupled with excitation-emission matrix (EEM) fluorescence was developed for the determination of rhodamine dyes illegally added into chilli samples. The proposed method not only has the advantage of high sensitivity over the traditional fluorescence method but also fully displays the "second-order advantage". Pure signals of analytes were successfully extracted from severely interferential EEMs profiles via using alternating trilinear decomposition (ATLD) algorithm even in the presence of common fluorescence problems such as scattering, peak overlaps and unknown interferences. It is worth noting that the unknown interferents can denote different kinds of backgrounds, not only refer to a constant background. In addition, the method using interpolation method could avoid the information loss of analytes of interest. The use of "mathematical separation" instead of complicated "chemical or physical separation" strategy can be more effective and environmentally friendly. A series of statistical parameters including figures of merit and RSDs of intra- (≤1.9%) and inter-day (≤6.6%) were calculated to validate the accuracy of the proposed method. Furthermore, the authoritative method of HPLC-FLD was adopted to verify the qualitative and quantitative results of the proposed method. Compared with the two methods, it also showed that the ATLD-EEMs method has the advantages of accuracy, rapidness, simplicity and green, which is expected to be developed as an attractive alternative method for simultaneous and interference-free determination of rhodamine dyes illegally added into complex matrices.

A novel and simple deep eutectic solvent based liquid phase microextraction method for rhodamine B in cosmetic products and water samples prior to its spectrophotometric determination

A novel and green deep eutectic solvent based liquid phase microextraction (DES-LPME) methodology has been proposed for the assessment of rhodamine B from cosmetic products and water samples. A deep eutectic solvent (DES) consist of tetrabutyl ammonium chloride-decanoic acid (1:2) as extraction solvent and tetrahydrofuran as emulsification agent were used for the microextraction of rhodamine B. The quantitative recoveries were achieved at pH 3 by using 0.3 mL of DES and 0.3 mL of THF. The rhodamine B concentration in last volume was analyzed by mirco-cuvette UV-VIS spectrophotometer at 550 nm. The limit of detection (LOD), limit of quantification (LOQ), preconcentration factor (PF) and relative standard deviation (RSD %) were found as 2.2 μg L^-1, 7.3 μg L^-1, 25 and 2.3%, respectively. Accuracy and validity of the developed method was verified by addition-recovery studies for water and cosmetic samples.

Application of derivative and derivative ratio spectrophotometry to simultaneous trace determination of rhodamine B and rhodamine 6G after dispersive liquid-liquid microextraction

Two novel methods, first derivative spectrophotometric method ((1)D) and first derivative ratio spectrophotometric method ((1)DR), have been developed for the simultaneous trace determination of rhodamine B (RhB) and rhodamine 6G (Rh6G) in food samples after dispersive liquid-liquid microextraction (DLLME). The combination of derivative spectrophotometric techniques and DLLME procedure endows the presented methods with enhanced sensitivity and selectivity. Under optimum conditions, the linear calibration curves ranged from 5 to 450 ng mL(-1), with the correlation coefficients (r) of 0.9997 for RhB and 0.9977 for Rh6G by (1)D method, and 0.9987 for RhB and 0.9958 for Rh6G by (1)DR method, respectively. The calculated limits of detection (LODs) based on the variability of the blank solutions (S/N = 3 criterion) for 11 measurements were in the range of 0.48-1.93 ng mL(-1). The recoveries ranged from 88.1% to 111.6% (with RSD less than 4.4%) and 91.5-110.5% (with RSD less than 4.7%) for (1)D and (1)DR method, respectively. The influence of interfering substances such as foreign ions and food colorants which might be present in the food samples on the signals of RhB and Rh6G was examined. The developed methods have been successfully applied to the determination of RhB and Rh6G in black tea, red wine and chilli powder samples with the characteristics of simplicity, cost-effectiveness, environmental friendliness, and could be valuable for routine analysis.

Novel electroanalytical platform based on bimetallic oxide nanospheres for the sensitive determination of Rhodamine B

In this work, uniform cobalt and nickel bimetallic oxides were formed by calcining the carbon templates, which were then modified on a glassy carbon electrode (cobalt–nickel oxide/GCE) as a novel system for the preparation of an electrochemical sensing platform. The electrochemical oxidation behavior of Rhodamine B (RB) at the cobalt–nickel oxide/GCE was investigated using differential pulse voltammetry under optimal conditions; the high electrocatalytic activity of the modified electrode toward analysis of RB was indicated. In addition, a linear range of 0.03−1.0 μmol L–1 and a low detection limit of 5.3 nmol L–1 (S/N = 3) for RB detection were obtained. Finally, the developed method with good stability and sensitivity was successfully applied for RB determination in food samples extract.