A simple method to quantify azo dyes in spices based on flow injection chromatography combined with chemometric tools.

Para Red (PR) and Sudan dyes have been illegally used as colorants to adulterate certain foods by enhancing their red/orange colour. In addition, they are toxic and carcinogenic. This work presents the development of a simple flow injection chromatographic method combined with chemometric tools to perform the determination of PR, Sudan I (SI) and Sudan II (SII) in food samples. The flow chromatographic system consisted of a low-pressure manifold coupled to a reverse phase monolithic column. A Partial Least Square (PLS) model was applied to resolve overlapped absorption spectra registered for each dye at the corresponding retention time. The relative errors of calibration (RMSECV, %) were 0.49, 0.85 and 0.23, and the relative errors of prediction (RMSEP, %) were 1.12, 0.75 and 0.33 for PR, SI and SII, respectively. The residual predictive deviation (RPD) values obtained were higher than 3.00 for all analytes. The method was successfully applied to quantify the dyes in six different commercial spices samples. The results were compared with the HPLC reference method concluding that there were no significant differences at the studied confidence level (α = 0.05). The proposed method can be used to rapidly determine the analytes in a simple, reliable, low-cost and environmentally-friendly manner. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-021-05299-8.

Oxidized carbon nanotubes as sorbent for miniaturized solid-phase extraction of progestins from environmental water samples prior to their determination by HPLC-UV.

A solid-phase extraction method is presented for micro-extraction of three progestins (levonorgestrel, 19-norethisterone acetate and medroxyprogesterone acetate) from water samples. A mini-column was packed with 60 mg of oxidized multiwalled carbon nanotubes and coupled to a flow injection assembly. The extraction parameters, such as washing solution, eluent type, eluent volume, flow rate and sample volume, were optimized. Separation and determination were performed by HPLC with UV detection. The method has a good linear range (0.90-9.0 µg L-1), acceptable limits of detection (0.05-0.14 µg L-1) and low RSDs (0.8-4.6%). Attractive features of the method include low consumption of organic solvents and preconcentration factors of up to 100. The method was applied to analyze stream, underground and effluent water samples, and recoveries between 74 and 121% were obtained. Graphical abstractSchematic representation of the flow injection assembly couples to an ox-MWCNTs extraction column used to perform the solid phase extraction procedure of progestins in environmental water samples.

Ionic liquid mediated extraction, assisted by ultrasound energy, of available/mobilizable metals from sediment samples.

A new extraction method for metals from sediment samples was developed. In this procedure, the chelating agent EDTA was combined with a minimal amount of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (Bmim[BF4]), assisted by ultrasound energy. The available analytes -Cd, Cr, Cu, Ni, Pb and Zn- were extracted under optimal conditions for a 12.5 ratio (extractant volume/sample mass) with 0.005molL-1 EDTA solution, 0.1molL-1 NaHCO3, 5.0mmolL-1 Bmim[BF4] and 7.0min of sonication time, using an ultrasonic bath (output power of 160W). The best extractions were obtained with 100W (power dissipated in the liquid). These conditions were obtained applying the univariate method. It is important to highlight that the conventional method (extraction with 0.05molL-1 EDTA solution only) consumes 6h to extract available metals from sediment samples selectively, and with the proposed procedure the extraction time is noticeable reduced to 7.0min. Extractable metal concentrations obtained were measured by flame atomic absorption spectrometry. The results showed good agreement with those obtained by the conventional method using a Student's paired t-test.

Second order advantage in the determination of amaranth, sunset yellow FCF and tartrazine by UV-vis and multivariate curve resolution-alternating least squares.

A direct spectrophotometric method for the determination of three artificial colors--amaranth, sunset yellow FCF and tartrazine--in beverages samples is proposed. The spectra were recorded between 359 and 600 nm. The spectra of the samples (just filtrated), pure dyes (concentrations ranged between 0.01 and 1.8 mg L(-1) for amaranth, 0.08 and 4.4 mg L(-1) for sunset yellow and 0.04 and 1.8 mg L(-1) for tartrazine) and synthetic mixtures were disposed in a column-wise augmented data matrix. This kind of data structure, analyzed by multivariate curve resolution-alternating least squares (MCR-ALS) makes it possible to exploit the so called 'second order advantage'. MCR-ALS algorithm was applied to the experimental data under the non-negativity and equality constraints. As a result, the concentration of each dye in the samples and their corresponding pure spectra were obtained. The results were validated using internal reference materials and no significant differences were found (alpha=5%) between the reference values and the ones obtained with the proposed method. The second order advantage made it possible to obtain unbiased results even in the presence of interferences.

Fast chromatographic method for the determination of dyes in beverages by using high performance liquid chromatography--diode array detection data and second order algorithms.

A fast chromatographic methodology is presented for the analysis of three synthetic dyes in non-alcoholic beverages: amaranth (E123), sunset yellow FCF (E110) and tartrazine (E102). Seven soft drinks (purchased from a local supermarket) were homogenized, filtered and injected into the chromatographic system. Second order data were obtained by a rapid LC separation and DAD detection. A comparative study of the performance of two second order algorithms (MCR-ALS and U-PLS/RBL) applied to model the data, is presented. Interestingly, the data present time shift between different chromatograms and cannot be conveniently corrected to determine the above-mentioned dyes in beverage samples. This fact originates the lack of trilinearity that cannot be conveniently pre-processed and can hardly be modelled by using U-PLS/RBL algorithm. On the contrary, MCR-ALS has shown to be an excellent tool for modelling this kind of data allowing to reach acceptable figures of merit. Recovery values ranged between 97% and 105% when analyzing artificial and real samples were indicative of the good performance of the method. In contrast with the complete separation, which consumes 10 mL of methanol and 3 mL of 0.08 mol L(-1) ammonium acetate, the proposed fast chromatography method requires only 0.46 mL of methanol and 1.54 mL of 0.08 mol L(-1) ammonium acetate. Consequently, analysis time could be reduced up to 14.2% of the necessary time to perform the complete separation allowing saving both solvents and time, which are related to a reduction of both the costs per analysis and environmental impact.