Simultaneous determination of multiclass illegal dyes with different acidic–basic properties in foodstuffs by LC-MS/MS via polarity switching mode

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.

Smartphone-based procedure to determine content of single synthetic dyes in food using the Arata-Possetto extraction method

The use of additives, including dyes, is common in the preparation of food products. The analytical control of artificial food dye content is relevant since some, such as azo dyes, may produce cancer and attention deficit disorders and hyperactivity in children. Consequently, the maximum permitted concentration of azo dyes in food is regulated by current legislation. Therefore, it is of interest to find simple and fast procedures for the control of these compounds. The aim of this study is to determine the concentration of azo dyes in food samples by the Arata-Possetto method - based on the extraction of azo dyes employing natural wool -, followed by the analysis of an image captured by a smartphone camera. After experimentally determining the optimal extraction conditions, the calibration curves for standard solutions of different food dyes and the color of the dyed wool were obtained. Results from dyed wool image processing were compared with the absorbance spectra of the solutions before extraction as measured by a diode array spectrophotometer. The spectrophotometric and the image processing procedures were employed to obtain the calibration curves for different food dyes, which were subsequently employed to analyze food samples. Statistical treatment shows that the results of both methods are comparable.

Rapid determination of 61 acid dyes in chili paste, hotpot seasoning, and bearnaise using double liquid-liquid extraction and UHPLC-Q-Orbitrap-MS

The aims of this study were to establish a novel method for simultaneously determining 61 acid dyes in chili, hotpot seasoning, and bearnaise sauce using double liquid-liquid extraction (d-LLE) technology. A mixture of water, methanol, and dichloromethane (1:3:1, v/v/v) was used as the extraction solution, which was actively separated into aqueous and organic phases at a fixed ratio. The clean-up step was initially completed by discarding the organic phase layer, which contained abundant lipophilic compounds. Subsequently, the aqueous phase was further separated by salting out, which effectively removed interference from the highly hydrophilic compounds. As a result of these two purification steps, the matrix suppression effect was significantly reduced by a minimum of 16.9%. Finally, the extract was analyzed using an ultrahigh-performance liquid chromatography-quadrupole Orbitrap mass spectrometer (UHPLC-Q-Orbitrap-MS), and the characteristic ion fragments (SO3 - , m/z 79.9557) of the acid dyes were utilized for the preliminary qualitative analysis. The results showed that the 61 acid dyes showed a good linear relationship in the range of 0.01-0.2 µg/mL, and the limit of quantification (LOQ) was 0.01 mg/kg. The average recoveries were 74.3%-99.7%, with relative standard deviations (RSD) ≤10%. The proposed method can rapidly identify and quantify acid dyes in complex foods at a low cost, with high sensitivity and reliability.

Chitosan-alginate sponge with multiple cross-linking networks for adsorption of anionic dyes: Preparation, property evaluation, mechanism exploration, and application

A chitosan-alginate sponge (CAS) with multiple cross-linking networks was developed using chitosan, sodium alginate, polyvinyl alcohol, and glutaraldehyde to adsorb and enrich the anionic dyes form the food samples. The multiple networks in CAS refer to the electrostatic cross-linking network, hydrogen bonding cross-linking network, and covalent cross-linking network. Compared with pure chitosan and alginate sponges, the CAS showed better three-dimensional network structure, mechanical behavior, and stability, which is benefit by multiple cross-linking networks. The physical and chemical properties of CAS were systematically studied by a series of characterizations. The adsorption performance of CAS on anionic dyes was inspected with different dye concentration, time, temperature, and pH conditions. CAS exhibited a good and stable adsorption property to amaranth, carmine, and sunset yellow with the saturation adsorption capacity of 94.34, 111.5, and 80.05 mg∙g-1, respectively. Furthermore, CAS performed outstanding selectivity to anionic dyes with the selectivity factor up to 16.99. Through electrostatic potential analysis, it is inferred that CAS mainly adsorbs anionic dyes through electrostatic interactions. CAS showed satisfactory reusability, maintaining 97 %-99 % of adsorption performance after six cycles of recycling. Finally, CAS was combined with high-performance liquid chromatography for the enrichment and detection of anionic dyes in candy and cocktail samples, achieving the enrichment factor up to 84.77.

Determination of restricted dyes in textile raw material solid wastes by ultra-high performance liquid chromatography-tandem mass spectrometry

A rapid and highly sensitive method for the quantification of 34 restricted dyes (including acid, basic, disperse, direct, and azo dyes) in solid textile raw material wastes was developed by employing ultrasonic extraction coupled with ultra-high performance liquid chromatography-tandem mass spectrometry(UHPLC-MS/MS). More specifically, the proposed method employed methanol as the extraction solvent, while the mobile phases consisted of acetonitrile and 10 mmol/L ammonium acetate + 0.05% ammonia. A good linearity was achieved over the concentration range of 0.01-200 ng/mL with correlation coefficients (R) between 0.991-0.999, limits of detection (LODs) of 0.25-40.0 µg/kg (S/N = 3) and limits of quantification (LOQs) of 0.84-133.4 µg/kg (S/N = 10). 34 dyes were recovered at three levels ranging from 84.5 to 106.9% with relative standard deviation (RSDs) ranging from 0.59% to 10.61%. Further, the method was applied for the accurate analysis of 32 counts of cotton yarn, waste cotton, and printed fabrics within 15 min. The dyestuffs accurately quantified by this rapid chromatographic procedure covered a wide range of carcinogenic and allergenic dyestuffs listed in the Oeko-Tex Standard 100 (version 02.2023) colourants. The ultrasound technique combined with the ultra-high performance liquid chromatography-tandem mass spectrometry method proposed in this work is thus suitable for the rapid screening, confirmation, and quantitative detection of industrial synthetic dyes within solid waste originating from textile raw materials.

Simultaneous qualitative and quantitative determination of 104 fat-soluble synthetic dyes in foods using disperse solid-phase extraction and UHPLC-Q-Orbitrap HRMS analysis

Public exposure to synthetic dyes through foods has attracted ongoing and serious attention. Here we developed and validated a simultaneous screening and quantitation method for the analysis of fat-soluble synthetic dyes that most frequently found in foods, using C₁₈ d-SPE clean-up and UHPLC-Q-Orbitrap HRMS on Full-MS/dd-MS² mode. During a single run, 104 dyes including 6 pairs of isomers were distinguished based on chromatographic separation and unique product ions. The method showed satisfactory linearity (R > 0.99), recoveries (61.3 %-118.8 %), precision (<20 %) and limit of quantification (0.05-0.5 mg/kg). For 98 % of test dyes, screening detection limits ranged from 2.5 to 25 μg/kg. The validated method was successfully applied to real commercial foodstuffs revealing the presence of two selected illegal dyes in three samples.

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.

Eco-toxicological effect of a commercial dye Rhodamine B on freshwater microalgae Chlorella vulgaris

In this study, the acute toxicity effects of a fluorescent xanthene dye, Rhodamine B (RhB), widely used in textile, paper, and leather industries was investigated on a freshwater microalgae Chlorella vulgaris. The acute toxicity of RhB on C. vulgaris was determined by examining the growth, cell morphology, pigment production, protein content, and the activities of oxidative stress enzymes. Based on the results of the toxicity study of 24-96 h, the median inhibitory concentration (IC₅₀) values ranged from 69.94 to 31.29 mg L^-1. The growth of C. vulgaris was conspicuously inhibited by RhB exposure, and the cell surfaces appeared to be seriously shrunk in SEM analysis. The growth of C. vulgaris was hindered after exposure to graded concentrations (10-50 mg L^-1) of RhB. A significant reduction in growth rate, pigment synthesis (chlorophyll a, chlorophyll b, and carotenoid), and protein content was recorded in a dose-dependent manner. After 96 h exposure of C. vulgaris to 50 mg L^-1 RhB, chlorophyll a, chlorophyll b, carotenoids, and protein contents were reduced by 71.59, 74.90, 65.84, and 74.20%, respectively. The activities of the antioxidant enzymes peroxidase (POD), and catalase (CAT) also increased markedly in the presence of RhB. A notable effect was observed on oxidative enzymes catalase and peroxidase, indicating that oxidative stress may be the primary factor in the inhibition of growth and pigment synthesis. Consequently, the experimental acute toxicity data were compared to the QSAR prediction made by the ECOSAR programme. Results showed that the experimental acute toxicity values were 67.74-fold lower than the ECOSAR predicted values. The study provides convincing evidence for the metabolic disruption in the ubiquitous microalgae C. vulgaris due to the RhB dye toxicity.

Rapid determination of 93 banned industrial dyes in beverage, fish, cookie using solid-supported liquid-liquid extraction and ultrahigh-performance liquid chromatography quadrupole orbitrap high-resolution mass spectrometry

Banned industrial dyes are composed of a large number of chemicals with diverse physical and chemical properties, making their simultaneous determination a challenging task. A one-step extraction and purification of 93 banned industrial dyes from beverage, fish and cookie sample methods was proposed by using solid supported liquid-liquid extraction (SLE). The extract was analyzed by ultrahigh-performance liquid chromatography quadrupole orbitrap high-resolution mass spectrometry (UPLC-Q-Orbitrap-HRMS). The quantitative and qualitative mode adopts Q-Orbitrap-HRMS full scan MS (full scan MS¹) and data-dependent MS/MS (dd-MS²) acquisition mode. The mass resolution was screened under 70,000 FWHM for full-scan MS¹ and 35,000 FWHM for dd-MS². Linearity was observed in the range of 0.01 ∼ 0.5 μg/mL and the limits of quantification were 0.04 ∼ 0.2 mg/kg for 93 dyes. The average recoveries were 70.5-105.8%, with RSD ≤ 10%. The proposed method has the ability to simultaneously screen many banned dyes in foods with high throughput, sensitivity and reliability.

Application of Advanced Analytical Techniques in Organic Cultural Heritage: A Case Study of Ancient Architecture Relics in the Palace Museum (Beijing)

Multilayer objects with different interfaces are quite typical for architectural heritage, and from them may be inferred the age, production process, and deterioration mechanism through analyzing characteristic compositions with advanced analytical techniques. The Meiwu ceiling in the Hall of Mental Cultivation of the Palace Museum was found to contain many paper-based layers during conservation. Once several surface strata were detached, a colorful layer of printed fabric textile was discovered integrally. Through microscopic observation and micro-attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) imaging, the overall structure consisted of 11 layers, namely, bast paper, cotton wiring, xuan paper, cotton printed fabric, two yellow board papers, bamboo paper, three wood pulp paper and surface coatings, and starch was considered as an organic adhesive. For identification of the printed fabric’s color palette, ultra-performance liquid chromatography (UPLC) combined with high-resolution quadrupole time-of-flight (QTOF) technology, non-invasive macro X-ray fluorescence (MA-XRF) and desorption electrospray ionization mass spectrometry imaging (DESI-MSI) were applied in situ. Seven industrial synthetic dyes, including auramine O, malachite green, and eosin Y with corresponding by-products, as well as chromium-based pigments considered as dark draft line, were confirmed. By X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), and micro Fourier transform infrared spectroscopy (micro FTIR, other results showed chalk soil and talc for the outermost coating. According to the synthetic time of industrial dyes and degradation degree of paper, there were at least four occurrences and their specific time periods were speculated.

Magnetic Solid-Phase Extraction Based on Magnetic Sulfonated Reduced Graphene Oxide for HPLC-MS/MS Analysis of Illegal Basic Dyes in Foods

In this study, a magnetic solid-phase extraction (MSPE) method coupled with High-Performance Liquid Chromatography Mass Spectrometry (HPLC–MS/MS) for the determination of illegal basic dyes in food samples was developed and validated. This method was based on Magnetic sulfonated reduced graphene oxide (M-S-RGO), which was sensitive and selective to analytes with structure of multiaromatic rings and negatively charged ions. Several factors affecting MSPE efficiency such as pH and adsorption time were optimized. Under the optimum conditions, the calibration curves exhibited good linearity, ranging from 5 to 60 µg/g with correlation coefficients >0.9950. The limits of detection of 16 basic dyes were in the range of 0.01–0.2 µg/L. The recoveries ranged from 70% to 110% with RSD% < 10%. The results indicate that M-S-RGO is an efficient and selective adsorbent for the extraction and cleanup of basic dyes. Due to the MSPE procedures, matrix effect and interference were eliminated in the analysis of HPLC–MS/MS without the matrix-matched standards. Thus, validation data showed that the proposed MSPE–HPLC–MS/MS method was rapid, efficient, selective, and sensitive for the determination of illegal basic dyes in foods.

Unified chromatography - Mass spectrometry as a versatile tool for determination of food dyes

Unified chromatography with mass spectrometric detection was assessed for determination of food dyes. Nineteen substances representing azo, triphenylmethane, xanthone, indigoid, quinoline and polyene classes covering an unprecedented range from nonpolar β-Carotene (logD 13.6) to ionic Tartrazine (logD -7.5) were analyzed simultaneously. The dyes were separated in a single experimental run by an 18-min gradient elution from 98% CO₂ to 100% aqueous-methanolic modifier on a diol column. Isomeric substances were resolved, and Isatin Sulfonic acid was detected as a degradation product of Indigo Carmine. Mobile phase properties reproducibly changed from supercritical to liquid state ensuring stable retention times (inter-day RSD<0.5%). Quantitative analysis of sports drinks after straightforward 10- or 25-fold dilution with dimethyl sulfoxide confirmed the method applicability to real-life samples. Sufficient limits of detection (typically 0.025 mg L^-1 in processed samples, equivalent to 0.25 mg L^-1 in drink) and a wide linear range (typically 0.5-50 mg L^-1 or 1.3-125 mg L^-1 in drink for 10× or 25× dilution, respectively) were demonstrated during validation. A comparison of method performance with competitive liquid chromatography procedures is also provided. Unified chromatography is a promising tool for comprehensive multiclass analysis of dyes in the context of food safety.

Rapid screening of 70 colorants in dyeable foods by using ultra-high-performance liquid chromatography-hybrid quadrupole-Orbitrap mass spectrometry with customized accurate-mass database and mass spectral library

A rapid screening method of 70 colorants for regulatory control in dyeable foods was established using ultra-high-performance liquid chromatography-hybrid quadrupole-Orbitrap mass spectrometry (UHPLC-Q/Orbitrap MS) with customized accurate-mass database and mass spectral library. A rapid, high-throughput, and simple sample pretreatment condition with low reagent consumption and high recovery was developed on the basis of ultrasound-assisted extraction and dispersion solid-phase extraction. Rapid screening was conducted by comparing the experimentally measured exact mass of the parent and fragment ions, the isotope pattern, and the retention time with the accurate-mass database and by matching the acquired MS/MS spectra against the mass spectral library. The performance of the method was evaluated in terms of linearity, limits of detection, limits of quantitation, recovery, repeatability, reproducibility, and matrix effect. The proposed method was applied for simultaneous analysis of 70 colorants in seven kinds of dyeable foods, and it exhibited great potential for broad, sensitive, and reliable.

Modification of screen-printed gold electrode with 1,4-dithiothreitol: application to sensitive voltammetric determination of Sudan II

Objectives

The aim of this study is to investigate the electrochemical behavior of Sudan II (SuII) using a screen-printed gold electrode (SPGE) modified with 1,4-dithiothreitol (DTT) and to determine the amount of Sudan II by voltammetry.

Materials and Methods

A DTT-modified screen-printed gold electrode (DTT/SPGE) was fabricated and its application for differential pulse voltammetric (DPV) determination of SuII was reported. Fourier transform infrared spectroscopy (FT-IR), cyclic voltammetry and electrochemical impedance spectroscopy were used for the characterization of the modified electrode. The effects of instrumental and chemical parameters were optimized for the determination of SuII. The fabricated electrode was used for the analysis of SuII in fortified and real samples. High-performance liquid chromatography was preferred as a reference method for the evaluation of the obtained voltammetric results.

Results

The electrochemical studies and FT-IR demonstrated that the SPGE was modified with DTT. The obtained peak current at DTT/SPGE was 6.67 times higher than that recorded with SPGE. At the optimized conditions of DPV in pH = 2.5 of H2SO4, the oxidation peak current of SuII was proportional to its concentration in range: 0.001–1.500 μmol l–1 with a detection limit of 0.0002 μmol l–1 (S/N = 3). For the analysis of SuII, 101.67%–104.33% of recovery percentage was obtained.

Conclusions

A new electrode was successfully improved for the determination of SuII. This highly selective and sensitive electrode supplied the fast determination of SuII in ketchup, chili sauce and salsa dip sauce. In addition, voltammetric and chromatographic results are found to be consistent.

Optimization of staining with SYTO 9/propidium iodide: interplay, kinetics and impact on Brevibacillus brevis

Fluorophores SYTO 9 and propidium iodide (PI) are extensively applied in medicine, food industry and environmental monitoring to assess the viability of bacteria. However, the actual performance of these dyes remains largely unknown. In addition, their effects on the physiology of cells have not been elucidated. Here we characterized the effects of these two dyes on Brevibacillus brevis under optimized staining. We found that SYTO 9 entered cells continuously while PI tended to adhere to the cell wall before entering the cell. In addition, results showed that a high amount of the dyes altered the physicochemical properties of membranes, improving their breakthrough. These results provide new perspectives and ideas for improving the characterization of bacterial viability using flow cytometry.