Solvent-free mechanochemical preparation of graphene oxide-Fe3 O4 and its application in magnetic dispersive solid-phase extraction of illegal dyes in food samples.

A simple, green, and efficient mechanochemical approach was developed herein to prepare tunable magnetic graphene oxide nanoparticles. The obtained nanoparticles were successfully used as adsorbents in a magnetic dispersive solid-phase extraction method to extract three cationic dyes (i.e., thioflavine T, auramine-O, and basic orange 2) found in food samples. Our proposed approach also utilized high-performance liquid chromatography with ultraviolet detection. Several key variables affecting the extraction recovery were investigated. These included the sample pH, amount of extractant, extraction time, sample volume, elution solvent type and volume, and the stability and reusability of the magnetic graphene oxide nanoparticles. Under optimized conditions, the calibration curve was linear at a concentration range of 0.005-1.0 µg/mL with a correlation coefficient of 0.9992-0.9996. Moreover, the limits of detection were determined at 0.97-1.35 µg/mL. The extraction mechanism was investigated via ultraviolet-visible spectrophotometry and zeta-potential analyses. The developed method was used to analyze the above-mentioned cationic dyes in bean products and yellow fish samples. Notably, satisfactory spiked recoveries ranging from 90.7 to 104.9% were achieved.

Auramine O in foods and spices determined by an UPLC-MS/MS method.

Auramine O (AO) is a banned food additive and has been classified as an illegal colourant. Therefore, the presence of AO in food should be strictly monitored. In this study, a sensitive UPLC-MS/MS method was applied to monitor AO in 211 food and spice samples. The optimised separation was achieved with a mobile phase consisting of 100 mM ammonium formate at pH 2.9 and acetonitrile, reversed-phase CORTECS T3 column (2.7 µm, 2.1 × 100 mm) operated at 40ºC with a gradient time of 20.0 min (0-95% methanol) at a flow rate of 0.3 mL/min. Limit of detection (LOD) and limit of quantification (LOQ) of the method were 0.1 µg/kg and 0.5 µg/kg, respectively. The results showed that 27.0% of samples were contaminated with AO. Considering the common consumption of sour bamboo shout and turmeric powder by so many consumers, AO exposure is significant and should be decreased.

Optimal fluorescent-dye staining time for the real-time detection of microbes: a study of Saccharomyces cerevisiae.

AIMS: To provide information on the time-dependent behaviour of microbe staining by fluorescent dyes in the order of seconds, which is important in terms of the recent rapid and online techniques for microbe measurements and/or environmental microbe analysis. METHODS AND RESULTS: For combinations of yeast (Saccharomyces cerevisiae) and typical dyes, including DAPI (4',6-diamidino-2-phenylindole) and Auramine-O, a suspension of yeast cells in ultrapure water was injected into a dye solution in a micro cuvette placed inside a spectrofluorometer and the fluorescence intensity of the resulting solution was measured at 1 s intervals, starting immediately after the mixing and continued until the time for the maximum intensity using various concentrations of yeast and dyes. The relaxation time τ, which corresponds to ~63·2% of the maximum fluorescence intensity, was shown to decrease to below 1 s with increasing DAPI concentration, whereas it remained constant for 2-3 s with increasing Auramine-O concentration, for example at a yeast concentration of 100 µg ml-1 . CONCLUSIONS: For the conditions of yeast >10 µg ml-1 , DAPI >1 µg ml-1 and Auramine-O >0·1 µg ml-1 , τ could be adjusted to below 5 s to achieve a rapid and stable staining. SIGNIFICANCE AND IMPACT OF THE STUDY: Design and operating conditions for rapid and online measurements of microbes can be optimized.

[Identification of the impurity in auramine O by high performance liquid chromatography-ion trap-time of flight mass spectrometry and preparation of the auramine O reference standard by preparative high performance liquid chromatography].

A novel and effective method was established for the qualitative analysis of impurities in auramine O samples of illegal food additives using high performance liquid chromatography-ion trap-time of flight mass spectrometry (HPLC-IT-TOF-MS). An impurity was identified in the auramine O sample using the optimized HPLC-IT-TOF-MS method. According to the exact mass of each fragment ion measured by multistage MS, the structure of the impurity was determined to be that of 4-(imino (4-(methylamino) phenyl) methyl)-N,N-dimethylaniline hydrochloride. The synthetic route of the auramine O and the source of the identified impurity were proposed. Simultaneously, a preparative high performance liquid chromatography (prep-HPLC) technique was successfully applied for the purification of the auramine O from complex samples. Prep-HPLC columns with particle sizes of 10 µm and 5 µm were used for the separation and purification with injection volumes of 1 mL and 500 µL, respectively. Finally an auramine O reference standard with 99.52% purity was obtained by secondarily purification and determined by the analytical HPLC area normalization method. Deducting the 0.34% moisture content and 0.13% ash content, the final purity of the sample was 99.05%, as determined by mass balance method. The chemical structure was examined using UV, IR, LC-MS, and NMR. The developed method is simple and efficient, and can be applied for the preparation of reference standard materials for other illegal food additives.

Gum xanthan-psyllium-cl-poly(acrylic acid-co-itaconic acid) based adsorbent for effective removal of cationic and anionic dyes: Adsorption isotherms, kinetics and thermodynamic studies.

The present work highlights the synthesis of the adsorbent based on Gum xanthan-psyllium hybrid backbone graft co-polymerized with polyacrylic acid-co-polyitaconic acid chains for the rapid sequestration of auramine-O (Aur-O) and eriochrome black-T (EBT) dyes from the aqueous fluid. The excellent dye removal efficiency of 90.53% for EBT and 95.63% for Aur-O was found at initial dye concentration of 30mgL-1 (EBT) and 15 mgL-1 (Aur-O) 40mL-1 with an adsorbent dose of 600mg within time duration of 5h and 323K temp. The adsorption isotherm data fitted well with Langmuir isotherm and Freundlich isotherm for Aur-O and EBT dyes (R2 ≥ 0.90), respectively. The adsorption kinetics depicted that pseudo-second order kinetics was followed simultaneously with intra-particle diffusion for both the dyes. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were also calculated and confirmed the spontaneity, randomness and endothermic nature of the adsorption process. Further, the adsorbent exhibited good recyclability efficiency for the capture of Aur-O and EBT from aqueous solution with minimal activity decline after six and three cycles, respectively. So, the synthesized adsorbent could be used successfully by the textile industries for the treatment of dye contaminated water with excellent competency.

Quantitative determination of Auramine O by terahertz spectroscopy with 2DCOS-PLSR model.

Residues of harmful dyes such as Auramine O (AO) in herb and food products threaten the health of people. So, fast and sensitive detection techniques of the residues are needed. As a powerful tool for substance detection, terahertz (THz) spectroscopy was used for the quantitative determination of AO by combining with an improved partial least-squares regression (PLSR) model in this paper. Absorbance of herbal samples with different concentrations was obtained by THz-TDS in the band between 0.2THz and 1.6THz. We applied two-dimensional correlation spectroscopy (2DCOS) to improve the PLSR model. This method highlighted the spectral differences of different concentrations, provided a clear criterion of the input interval selection, and improved the accuracy of detection result. The experimental result indicated that the combination of the THz spectroscopy and 2DCOS-PLSR is an excellent quantitative analysis method.

A Simple and Sensitive Method for Auramine O Detection Based on the Binding Interaction with Bovin Serum Albumin.

A simple, rapid and effective method for auramine O (AO) detection was proposed by fluorescence and UV-Vis absorption spectroscopy. In the BR buffer system (pH 7.0), AO had a strong quenching ability to the fluorescence of bovin serum albumin (BSA) by dynamic quenching. In terms of the thermodynamic parameters calculated as ΔH > 0 and ΔS > 0, the resulting binding of BSA and AO was mainly attributed to the hydrophobic interaction forces. The linearity of this method was in the concentration range from 0.16 to 50 µmol L(-1) with a detection limit of 0.05 µmol L(-1). Based on fluorescence resonance energy transfer (FRET), the distance r (1.36 nm) between donor (BSA) and acceptor (AO) was obtained. Furthermore, the effects of foreign substances and ionic strength were evaluated under the optimum reaction conditions. BSA as a selective probe could be applied to the analysis of AO in medicines with satisfactory results.

LED fluorescence microscopy in the diagnosis of tuberculosis: Fading and restaining of smears for external quality assessment.

Blinded rechecking is a method proposed for external quality assurance (EQA) of auramine-stained acid-fast bacilli (AFB) smears using fluorescence microscopy (FM), however, this procedure is not well developed and slides fading over time could compromise its implementation. Since bleaching of fluorescent molecules involves temperature-dependent chemical reactions, it is likely that low temperatures could slow down this process. We stored auramine-stained slides under different environmental conditions, including -20°C, and examined them over time. The slides stored in all the environments faded. At -20°C, fading was not reduced in relation to room temperature. Restaining and re-examining smears after five months showed that the slides containing saliva and storage at -20°C were associated with failure in AFB reappearance. In conclusion, the practice of freezing slides until they are viewed should be discouraged as it has a negative effect on blinded rechecking by reducing reading concordance after restaining. Specimen quality should be considered when interpreting FM-EQA results.

Preparation and evaluation of a novel molecularly imprinted SPE monolithic capillary column for the determination of auramine O in shrimp.

A novel method combining molecular imprinting and SPE was developed in a capillary column for the determination of auramine O in shrimp. The capillary monolithic column was prepared by UV-initiated in situ polymerization, using auramine O as template and methacrylic acid and ethylene dimethacrylate as functional monomer and cross-linker, respectively. The properties of the prepared capillary monolithic column were investigated under the optimized conditions coupled with HPLC, and then the morphologies of the inner polymers were characterized by SEM. The calibration curve was expressed as A = 103C + 19.8 (r = 0.9992) with a linear range of 0.25-25.0 µg/mL, and the recoveries of auramine O at different concentrations in shrimp ranged from 90.5 to 92.4% with RSDs ranging from 2.1 to 4.4%. The capacities of the molecularly imprinted polymer and nonimprinted polymer columns were 0.722 and 0.147 µg/mg, respectively, and the LOD (S/N = 3) of auramine O in shrimp was 17.85 µg/kg. Under the selected conditions, the enrichment factors obtained were higher than 70-fold. The results indicate that the prepared molecularly imprinted capillary monolithic column was reliable and applicable to the analysis of auramine O in shrimp.

[Determination of ten basic dyes in meat products by ultra fast liquid chromatography-ion trap time of flight mass spectrometry].

A method was developed for the simultaneous determination of 10 basic dyes in meat products using ultra fast liquid chromatography-ion trap time of flight mass spectrometry (LC-IT-TOF-MS). The target analytes were separated at a flow rate of 0.2 mL/min on a Waters Acquity UPLC BEH C18 (100 mm x 2.1 mm, 1.7 microm) column with a gradient elution. The mobile phase was 5 mmol/L ammonium acetate-acetonitrile (containing 0.1% (v/v) formic acid). The identification and quantification were achieved in positive ion mode with electro spray ionization source. The samples were extracted with a simple procedure using acetonitrile and cleaned up by weak cation exchange (Oasis WCX) solid phase extraction column. Ten basic dyes were determined by LC-IT-TOF-MS, and quantified by external standard method. The developed method showed a good linearity over the wide range of 1.0 - 100.0 microg/L, and the relative standard deviations (n = 7) were less than 8.54%. The average recoveries of the ten basic dyes at three levels (2, 10 and 25 microg/kg) were ranged from 65.39% to 119.18%. Therefore, this method, owing to its simplicity, rapidity and high sensitivity, has a good applicability to the simultaneous determination of dye residues in meat products.

A simple method for simultaneous determination of basic dyes encountered in food preparations by reversed-phase HPLC.

The present method utilizes a simple pretreatment step, cleanup on polyamide SPE cartridges, and HPLC resolution on reversed-phase C18 for the detection of the three basic nonpermitted dyes encountered in food matrixes. Polyamide cartridges were chosen because both acidic and basic dyes can be cleaned up due to their amphoteric nature. Analysis was performed on a reversed-phase C18 micro-Bondapak column using the isocratic mixture of acetonitrile-sodium acetate with a flow rate of 1.5 mL/min and a programmable lambda(max) specific visible detection to monitor colors, achieving higher sensitivity and expanded scope to test multicolor blends. All the colors showed linearity with the regression coefficient, from 0.9983 to 0.9995. The LOD and LOQ ranged between 0.107 and 0.754 mg/L and 0.371 and 2.27 mg/L or mg/kg, respectively. The intraday and interday precision gave good RSDs, and percentage recoveries in different food matrixes ranged from 75 to 96.5%. The study demonstrates that the use of a combination of a simple SPE cleanup and HPLC resolution with UV-Vis end point detection was successful in screening the presence of these three basic nonpermitted dyes individually or in blend, in a variety of food matrixes.

[Spectral and photometric characteristics of different batches of auramine O (OO)]. / Spektral'nye i fotometricheskie kharakteristiki razlichnykh partii auramina O (OO)

The spectra of absorption and fluorescence of Auramine O (OO) specimens in water solution and in cells, stained with Schiff-type auramine-SO2 reagents for DNA, were investigated. Using different specimens of the stain the accuracy and sensitivity of the cytofluorometric method were estimated by the next parameters: the value of the useful signal from the nucleus (no), the value of the production of no by the time constant of fading (tau), the value of proportion of the signal to the background (no/nphi) and, in addition, the value of the variation coefficient under the measurement of the rat liver tetraploid cells. The purity of the dye was shown to interfere largely with accuracy and sensitivity of the above method. Auramine 00 of the Reanal production appeared to have the best photometricl characteristics. For this, the maxima of the absorption spectrum in the 320--700 nm region in the solution and in the cell were 371 and 433 nm, and 375 and 436 nm, resp. The maximum of the fluorescence spectrum was found 521 nm and 526 nm, resp. for the solution (0.02%) and for the Auramine-SO2 treated cells. Moreover, an isomer of Auramine O (00) -- Auramine G can be used for detection and photometrical measurement of DNA and glycogen after the Feulgen and PAS reactions, resp.