Preparation of a sustainable magnetic sorbent for the extraction and preconcentration of progestogens in natural water samples.

A film composed of agarose and graphene (G) and magnetic nanoparticles (G-MNPs) is proposed as a sorbent for the extraction and determination of medroxyprogesterone (MED), levonorgestrel (LEV), norethisterone (NOR) and progesterone (PRO) in natural water samples. Both the preparation of the film and the extraction procedure were optimized. The optimal extraction parameters were as follows: isopropyl alcohol as activation solvent, sample pH value of 3.0, extraction time of 30 min, 1.00 mL of acetonitrile as eluent, elution time of 5 min and sample volume of 100.00 mL. HPLC with photodiode array detector was used for the separation and determination. The method presented a linear range between 2.50 and 75.0 µg L-1 for all analytes, and the LODs were between 1.40 and 1.80 µg L-1. The method was applied to natural water samples, obtaining satisfactory recovery values (75-111 %). In conclusion, for the immobilization of the G-MNPs, agarose was used, which is a non-toxic, renewable and biodegradable material. The G-MNPs-agarose film was reused up to 70 times, without losing its extraction capacity significantly and presenting excellent sorbent properties, which allow the extraction and preconcentration of the progestogens under study.

Preparation of a single and reusable biopolymer-based film for the extraction and preconcentration of anti-inflammatory drugs from environmental water samples.

One of the main goals of green chemistry is to reduce the use of toxic materials and the generation of hazardous waste, both during method development and in the synthesis of the materials used. Thus, a biodegradable, single and reusable material composed of agarose and multi-walled carbon nanotubes was proposed. The film preparation was carefully optimized in order to obtain a one-piece sorbent, with high extraction efficiency and the possibility of reuse. The film was tested in the simultaneous extraction and preconcentration of three non-steroidal anti-inflammatory drugs (ketorolac, ketoprofen and piroxicam) from environmental water samples. The optimal extraction parameters were as follows: isopropyl alcohol as the activation solvent, a sample pH value of 3.0, extraction time of 30 min, 2.00 mL of acetonitrile as the eluent, an elution time of 5 minutes, and a sample volume of 250.00 mL. Under these conditions, the film was reusable 50 times without losing its extraction capacity significantly. HPLC with a photodiode array detector was used for the separation and determination. The method presented a linear range between 0.10 and 1.2 µg L-1, good sensitivity with limits of detection between 0.0075 and 0.0089 µg L-1, and quantification between 0.025 and 0.030 µg L-1. In addition, low RSD values (0.46-3.13%) were obtained demonstrating satisfactory precision. Stream water samples were analyzed, and recoveries between 82.0 and 109.0% were obtained.

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.

An inner filter effect based sensing system for the determination of caffeine in beverage samples.

In this work, the inner filter effect (IFE) of caffeine (CF) over the fluorescence signal of glibenclamide (GLB) was used for the determination of CF in beverage samples. The system worked in a turn-off mode since the absorption spectrum of CF overlaps the excitation band of GLB resulting in a decline in its fluorescence signal (λexc = 234 nm, λem = 350 nm). No changes in the fluorescence lifetime of GLB (0.29 ns) were observed in the presence of CF up to 127.6 mg L-1 concentration. The parameters that affect the fluorescence intensity were investigated, such as fluorophore concentration (16 mg L-1), pH (3.2) and temperature (25 °C). Under optimized conditions, the IFE-based approach can determine CF in a range between 1.00 and 100.0 mg L-1, with a detection limit (LOD) of 0.10 mg L-1. The relative standard deviation (% RSD) values for the intra-day and inter-day precision were 0.75 and 1.24, respectively. The new method was successfully tested in the determination of the target analyte in beverage samples without previous treatment. The results were compared with those obtained by a reference method, leading to the conclusion that there were no significant differences at the studied confidence level (α = 0.05).

Flow-batch analysis of clenbuterol based on analyte extraction on molecularly imprinted polymers coupled to an in-system chromogenic reaction. Application to human urine and milk substitute samples.

A fully automated spectrophotometric method based on flow-batch analysis has been developed for the determination of clenbuterol including an on-line solid phase extraction using a molecularly imprinted polymer (MIP) as the sorbent. The molecularly imprinted solid phase extraction (MISPE) procedure allowed analyte extraction from complex matrices at low concentration levels and with high selectivity towards the analyte. The MISPE procedure was performed using a commercial MIP cartridge that was introduced into a guard column holder and integrated in the analyzer system. Optimized parameters included the volume of the sample, the type and volume of the conditioning and washing solutions, and the type and volume of the eluent. Quantification of clenbuterol was carried out by spectrophotometry after in-system post-elution analyte derivatization based on azo-coupling using N- (1-Naphthyl) ethylenediamine as the coupling agent to yield a red-colored compound with maximum absorbance at 500nm. Both the chromogenic reaction and spectrophotometric detection were performed in a lab-made flow-batch mixing chamber that replaced the cuvette holder of the spectrophotometer. The calibration curve was linear in the 0.075-0.500mgL-1 range with a correlation coefficient of 0.998. The precision of the proposed method was evaluated in terms of the relative standard deviation obtaining 1.1% and 3.0% for intra-day precision and inter-day precision, respectively. The detection limit was 0.021mgL-1 and the sample throughput for the entire process was 3.4h-1. The proposed method was applied for the determination of CLB in human urine and milk substitute samples obtaining recoveries values within a range of 94.0-100.0%.

Multilayered particle-packed column: Evaluation and comparison with monolithic and core-shell particle columns for the determination of red azo dyes in Sequential Injection Chromatography.

A recently presented new type of "multilayered" organic-inorganic hybrid silica particle packed column YMC-Triart C18 (50 mm × 4.6 mm, 5 µm) was used for the development of a sequential injection chromatography method for determination of five azo dyes (Sudan I, Sudan II, Sudan III, Sudan orange G, and para red) in selected food seasonings. The use of a novel sorbent brings attractive features, reduced backpressure, and broader chemical stability together with high separation performance, which are discussed and compared with that of three types of columns typically used in medium-pressure flow chromatography techniques (classic monolithic, narrow monolithic, and core-shell particle columns). The separation was performed in gradient elution mode created by the zone mixing of two mobile phases (acetonitrile/water 90:10, 1.5 mL + acetonitrile/water 100:0, 2.3 mL) at a flow rate of 0.60 mL/min and time of analysis <9.5 min. The spectrophotometric detection wavelengths were set to 400, 480, and 500 nm. The high performance of the developed method with multilayered particle column was well documented and the results indicate a broad capability of sequential injection chromatography.

Application of a fully integrated photodegradation-detection flow-batch analysis system with an on-line preconcentration step for the determination of metsulfuron methyl in water samples.

This work presents the development of a fully automated flow-batch analysis (FBA) system as a new approach for on-line preconcentration, photodegradation and fluorescence detection in a lab-constructed mixing chamber that was designed to perform these processes without sample dispersion. The system positions the mixing chamber into the detection system and varies the instrumental parameters according to the required photodegradation conditions. The developed FBA system is simple and easily coupled with any sample pretreatment without altering the configuration. This FBA system was implemented to photodegrade and determine the fluorescence of the degradation products of metsulfuron methyl (MSM), a naturally non-fluorescent herbicide of the sulfonylurea׳s family. An on-line solid phase extraction (SPE) and clean up procedure using a C18 minicolumn was coupled to the photodegradation-detection mixing chamber (PDMC) that was located in the spectrofluorometer. An enrichment factor of 27 was achieved. Photodegradation conditions have been optimized by considering the influence of the elution solvent on both the formation of the photoproduct and on the fluorescence signal. Under optimal conditions, the calibration for the MSM determination was linear over the range of 1.00-7.20 µg L(-1). The limit of detection (LOD) was 0.28 µg L(-1); the relative standard deviation was 2.0% and the sample throughput for the entire process was 3h(-1). The proposed method was applied to real water samples from the Bahía Blanca׳s agricultural region (Bahía Blanca, Buenos Aires, Argentina). This method obtained satisfactory recoveries with a range of 94.7-109.8%.

Successive projections algorithm applied to spectral data for the simultaneous determination of flavour enhancers.

A novel variable selection strategy for multiple lineal regression (MLR), the successive projections algorithm (SPA), was applied to spectrophotometric data (190-320 nm) for the simultaneous determination of monosodium glutamate (MSG), guanosine-5'-monophosphate (GMP) and inosine-5'-monophosphate (IMP) in dehydrated broths samples. This selection method uses simple operations in a vector space to minimize variable collinearity and has become an interesting variable selection strategy for multivariate calibration. In this work, nine, six and four wavelengths for MSG, GMP and IMP, respectively, were selected to construct calibrations models in order to solve successfully the serious spectral overlapping in samples containing these analytes. The relative errors of prediction (REP) for the validation set were 2.3%, 0.9% and 1.8% for MSG, GMP and IMP, respectively. Commercial samples were analysed and a recovery study was carried out to verify the accuracy of the proposed method with satisfactory results. A continuous flow system was used to develop a simple, cheap and rapid method (sample throughput: 200 h(-1)), without any previous extraction step.

A new automated approach to determine monosodium glutamate in dehydrated broths by using the flow-batch methodology.

The advantages of the flow-batch methodology were exploited to implement a simple system with nephelometric detection for the determination of monosodium glutamate (MSG) in food samples. The method is based on the inhibitory effect of the MSG over the crystallization of L-lysine in an isopropanol/acetone mixture. The calibration curve was prepared on-line. The method was linear over the range of 2.8 x 10(-3) to 1.1 x 10(-2)gL(-1) and a detection limit of 9.7 x 10(-5)gL(-1) was achieved. It was successfully applied to determine the MSG concentration in food samples, without a previous treatment. A recovery study was carried out on real samples and the percentages were between 98 and 106%.