Publishing type：Research paper (scientific journal)  

In this paper, a field-deployable method for the spectrophotometric determination of iron after a simple preconcentration procedure in column is proposed. A 3D-printed portable system, housing a small spectrophotometer with a CCD detector and a LED as homemade light source is used for spectrophotometric detection. The entire system is powered through two USB outputs of a notebook. The Fe (III) preconcentration is based on a solid phase extraction with a column packed of Chelex-100 chelating resin. The Fe (III) eluted in the cuvette was reduced to Fe (II) and the iron concentration was determined using the o-phenanthroline method. Preconcentration factors between 9.7 and 98 were obtained. Under optimized conditions, linear calibration curves without and with preconcentration were constructed (R2 > 0.9992). Low LD (5 µg L−1) and LQ (10 µg L−1) were achieved, and good values for intra-day and inter-day precision were obtained (RSD ≤ 2.9% and RSD ≤ 9.6%, respectively). Recoveries of spiked iron in local tap water, sea water, well water, leachate and supernatant of anaerobic digester were ranged from 93 to 106%. The validation of method was also carried out by successfully analyzing a river water reference material SLRS-4.

DOI： 10.1016/j.microc.2021.106774

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Publishing type：Research paper (scientific journal)  

This work presents a simple, low cost, and portable spectrophotometer based on a digital microscope as a detector for the determination of the antioxidant activity and total phenolic content (TPC). The antioxidant activity was expressed as ascorbic acid equivalents (AAE) using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) assay. The TPC value was measured using the Folin-Ciocalteu method. The color of the products was captured using a digital microscope powered through the USB output of a laptop. A digital microscope, held in a 3D printing device was used to take photos of the reaction product that was illuminated with the stable light source of the digital microscope. The pictures were analyzed for quantitation. For the DPPH assay, the developed method provided a working range from 0.6 to 6 mg L−1 of ascorbic acid with a limit of detection (LOD) of 0.2 mg L−1 and a relative standard deviation (RSD) of 2.2%. The TPC method provided a working range from 4.6 to 100 mg L−1 for gallic acid, with a LOD of 1.4 mg L−1 and a RSD of 1.3%. Results of the proposed system agree well with a conventional spectrophotometric method and have been successfully applied to measure the antioxidant activity and TPC of local Thai tea samples.

DOI： 10.1080/00032719.2021.1886304

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

A new automated system based on a multi-pumping flow system (MPFS) for the spectrophotometric determination of total iron in various wine samples is presented. This analytical protocol is based on the complex formation between Fe (II) and 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP). The addition of ascorbic acid allows the determination of total iron by reducing the Fe (III) present in the samples to Fe (II). Several physical and chemical parameters, including the mixing coil length, the sample volume, the chromogenic reagent concentration, the pH, and the ascorbic acid concentration have been characterized in order to optimize the analytical conditions. The limits of detection and quantification were 34 mu g L-1 and 114 mu g L-1 respectively. The developed procedure requires minimal sample preparation.

DOI： 10.1080/00032719.2020.1758710

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

A Multi-Syringe Flow Injection Analysis (MSFIA) fluorometric system based on a 3D printing device hosting a CCD detector has been designed for the determination of quinine in soft drinks. A LED controlled by an electronic circuit was used as a radiation source. The entire system is connected to two USB outputs of a computer. The AutoAnalysis program has been used for data acquisition and treatment. The results are more accurate and precise than those obtained with a manual method using a conventional spectrofluorometer. This developed system is a viable alternative to reduce the consumption of reagents, the impact on the environment and reduce measurement costs.

DOI： 10.1016/j.talanta.2020.121163

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

A simple, cheap and portable spectrophotometric system is described. It is based on the use of a cheap digital microscope housed from a 3D printed device which simultaneously supports a LED as a light source and a flow cell. A simple electronic device to power the LED is also described using electronic smd components. Both the digital microscope and the power source required to light the LED are connected to the USB ports of a notebook in order to avoid the need of any power source to complete the portable system. This method was applied to make the determination of Fe2+ with o-phenanthroline as chromogenic reagent. The reaction provided the red complex which is used to monitor the analytical response with the digital microscope.

DOI： 10.1016/j.talanta.2020.120977

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

The program WinMLR has been developed for the quantification of mixtures of several components by making a multilinear regression treatment of experimental data to a linear combination of standard signals. Data may be obtained with any multichannel detector having more measuring channels than components to be resolved. For a correct resolution, a linear relationship between the signal of every channel and the component concentration is required. The data must be located into ASCII files, one file for each standard or sample measurement, which contain the X and Y values in separated columns.The program allows three types of calibration methods: single standard, multiple standards and multiple standards addition. In the first case, the program requires to measure one standard per component. In the second case, the user can employ standards of both pure compounds and known mixtures under the sole constraint that the set of standards must include all components in different proportions. Similarly, the multiple standard addition method (more known as general standard addition method) requires the data obtained by adding known amounts of one or several mixture components to the sample so that all of them are included in the assays. In the multiple standards and multiple standards addition procedures, once the calibration has been done, the program allows the mixture to be resolved by weighted or unweighted regression.

DOI： 10.1016/j.talanta.2020.120830

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

The development of a simple and economical spectrophotometric system based on the use of a device created by 3D printing and the electronics necessary to control the intensity of the radiation source was described. The measurements are made with a low-cost digital webcam. The entire system is only powered through the USB outputs of a computer, which makes the portable and really practical system for the measurements in the field. This method was applied to determine iron (II) in waters using o-phenanthroline as chromogenic reagent giving a red complex, and also to hypochlorite determination using tetramethylbenzidine as the reagent providing a yellow color. The calibration curves were built using a mathematical algorithm making a RGB deconvolution. The intense of colors obtained from a webcam in each concentration of analyte had a relationship with the absorbance values. In order to confirm the accuracy and precision of this method, a traditional spectrophotometer was used for validation.

DOI： 10.1016/j.talanta.2019.120250

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

The spectrophotometric determination of uranium (VI) has been developed using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). This reaction has been adapted to apply a multisyringe flow injection analysis (MSFIA) system with spectrophotometric detection. The ternary complex of uranium (VI)-(Br-PADAP)-F has been measured at 578 nm. The procedure was optimized using univariate method and two-level full factorial. Four variables (concentrations of Br-PADAP, CyDTA, NaF and sample volume) were regarded as factors in the extraction optimization. Results of the two-level full factorial design, showed that only two factors (concentration of Br-PADAP and CyDTA) are statistically significant. The calibration curve is linear over the range 0.3-5 mg L-1 uranium (VI) with a relative standard deviation of 4.0% (1 mg L-1 uranium (VI), n=10). The recoveries of uranium in water samples were between 80 and 102%.

DOI： 10.1016/j.microc.2019.104148

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

A conductometric system with a multipumping module and a gas-diffusion cell has been developed to determine free and total sulfur dioxide (SO2) in wine. The developed method has two protocols to determine both types of SO2 using the same system. For free SO2, sulfite is converted to H2SO4 by acidification and diffusion with H2O2 in an acceptor channel. The sample was previously hydrolyzed by mixing the sample with NaOH and heated at 70 degrees C prior making the determination of total SO2 in order to break the bonds of the combined SO2. Free and total SO2 were determined in the ranges of 2.5-25.4 and 10.2-76.2 mg L-1 with a sample throughput of 13 and 12 h(-1), respectively. The calibration curves of free and total SO2 were in the range of Delta G (mS cm(-1)) = (-1.0242 +/- 0.2871) + (0.6613 +/- 0.0201) [SO2, mg L-1], r(2) of 0.997 and Delta G (mS cm(-1)) = (-0.5850 +/- 0.1678) + (0.1236 +/- 0.0033) [SO2, mg L-1], r(2) of 0.997. The proposed automated method is simple and easy to apply for the determination of SO2 in wine using simple reagents.

DOI： 10.1080/00032719.2018.1539742

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

This work presents a multisyringe flow injection analysis (MSFIA) system for the automatic spectrophotometric determination of total iron in wine. The reaction is based on the complexation of Fe(II) with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP). Ascorbic acid was used as reducing reagent for Fe(III) to Fe(II) and, in this way, to determine the total iron content in wine. The absorbance of the Fe(II)-(Br-PADAP)(2) complex was measured at 748 nm. The proposed method provided a working rage from 0.36 to 5 mg L-1 of Fe(II), with a detection limit of 0.11 mg L-1 of Fe(II), a relative standard deviation of 0.42% (3 mg L-1 of Fe(II), n=10), and a 46 h(-1) injection throughput. The system is very simple, rapid and selective, and has been successfully applied to determine total iron in red, rose and white wine without any need for sample pre-treatment steps. The results agree well with ICP-AES, which used as a reference method.

DOI： 10.1016/j.foodchem.2018.10.115

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Language：English   Publisher：TAYLOR & FRANCIS INC  

Quite often one of the biggest problems in analytical methods, including spectrometry, resides in the pre-processing of the sample, which usually must be solved manually. To solve these problems, it can be very useful to request the help of the flow techniques, which will allow to automate the methods, decrease the time of the analysis, decrease the consumption of the samples and reagents, increase the reproducibility, the sample throughput and to work continuously for a long period of time.Between the advantages of the low separation flow techniques are their very high versatility facing the application of various treatment techniques, such as photo-oxidation, pre-concentration, clean-up, derivatization, gas diffusion, etc. Since the entire process is carried out in a completely closed system, results are obtained in a faster and more reproducible way.In this contribution, coupling different low-resolution separation flow techniques with several very selective spectrometric instruments, like ICP-AES, ICP-MS, AFS, etc. Hyphenation with different kind of chromatographic and the capillary electrophoretic techniques is also described.

DOI： 10.1080/05704928.2018.1446975

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Language：English   Publisher：ELSEVIER SCI LTD  

Kinetic methods have been widely used in analytical chemistry, generally using spectrophotometric or electrochemical detector. However, although enthalpimetric methods have been scarcely used, they may offer some interesting performances, like to be blind to the color and/or turbidity of the samples. This paper will be related with the description of some enthalpimetric kinetic methods and their instrumentation that could be used in these techniques, making a review on direct injection catalytic enthalpimetry, thermometric titration with catalytic endpoint detection, catalytic enthalpimetric flow injection analysis, continuous flow enthalpimetries, chip calorimetry, and trends of kinetic thermometric detection. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.trac.2017.09.019

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Kinetic-catalytic analytical methods have proved to be very easy and highly sensitive strategies for chemical analysis, that rely on simple instrumentation [1,2]. Molecular absorption spectrophotometry is commonly used as the detection technique. However, other detection systems, like electrochemical or thermometric ones, offer some interesting possibilities since they are not affected by the color or turbidity of the samples. In this review some initial experience with thermometric kinetic-catalytic methods is described, up to our current experience exploiting spectrophotometric flow techniques to automate this kind of reactions, including the use of integrated chips. Procedures for determination of inorganic and organic species in organic and inorganic matrices are presented.

DOI： 10.1016/j.talanta.2017.02.004

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Language：English   Publisher：ELSEVIER SCI LTD  

Kinetic-catalytic analytical methods are simple and highly sensitive strategies for chemical analysis, that rely on simple instrumentation. For that reason, they have been implemented to the quantification of a large number of chemical species such as transition metals, non-metallic anions and organic compounds. Flow techniques are presented as an efficient tool to overcome the main limitations of the kinetic catalytic methods. Solving problems related with sample handling, the reproducible data acquisition, reproducible temperature control and the implementation of different kinetic determination methods (initial rate, fixed time and fixed measure).Herein we review the recent applications of novel approaches to perform fully automated kinetic catalytic methods based on computer controlled flow techniques. We also describe new devices and materials such as chip-based flow injection analyzers and the use of nanoparticles to improve the performance of this class of analytical methodologies. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.trac.2016.08.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A novel spectrophotometric method for the determination of bromide has been developed using the Multisyringe Flow Injection Analysis technique (MSFIA). This method is based on the decolorization of methylene blue by the bromine released from the oxidation of bromide by bromate under acidic conditions. By incorporating a gas-diffusion unit into the MSFIA system the transferred bromine reacts with methylene blue in the acceptor stream. The decrease of the methylene blue absorbance is monitored at 745 nm. The oxidation conditions are not strong enough to oxidize chloride to chlorine, which is a major component of both natural and seawater. The proposed method provides linearity for the determination of bromide over a range of 1 x 10(-5) mol L-1 to 6 x 10(-5) mol L-1 in 5 x 10(-2) mol L-1 of chloride, with a correlation coefficient (r(2)) of 0.9939, and a precision of 3.1% (% RSD for 3 x 10(-5) mol L-1 Br-in 5 x 10(-2) mol L-1 Cl-, n = 10). The limit of detection (3 sigma) is 0.5 x 10(-5) mol L-1. The proposed method has been applied to the determination of Br-in water samples, obtaining recoveries in the analysis of spiked tap, natural, and seawater samples in the range of 90-106%.

DOI： 10.1039/c5ay00202h

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