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.
Portable spectrophotometric device using a digital microscope. A: digital microscope; B: 3D printed support of the digital microscope, cell and light source; C: cuvette; D: Head for LED; E: regulated voltage power supply; F: USB digital microscope connection; G: USB regulated voltage power source connection. Display omitted
•A cheap, simple and portable spectrophotometric system has been developed using a digital microscope.•Two USB ports of a laptop are used to power the microscope and the radiation source.•A simple electronic device connected to an USB port has been used to power different kind of LEDs used as radiation source.
•A microfluidic paper-based analytical device was developed for the determination of nitrite and nitrate ions.•Zinc cannot reduce 100% of nitrate to nitrite.•Zinc reduced nitrite and nitrate to ...ammonia.•Zinc decreased the sensitivity to nitrite.•The microfluidic paper-based analytical device permitted the determination of nitrite and nitrate ions.
We used a microfluidic paper-based analytical device (μPAD) to investigate the influence that zinc reduction exerts on the determination of nitrite and nitrate ions in natural water samples. The μPAD consists of layered channels for the reduction of nitrate to nitrite with zinc powder and the subsequent detection of nitrite with Griess reagent. The amount of zinc, number of layers, and reaction time for the reduction were optimized to obtain an intense signal for nitrate. Initially, the sensitivity to nitrate corresponded to 55% that of nitrite, which implied an incomplete reduction. We found, however, that zinc decreased the sensitivity to nitrite in both the μPAD and spectrophotometry. The sensitivity to nitrite was decreased by 48% in spectrophotometry and 68% in the μPAD following the reaction with zinc. One of the reasons for the decreased sensitivity is attributed to the production of ammonia, as we elucidated that both nitrite and nitrate produced ammonia via the reaction with zinc. The results suggest that the total concentration of nitrite and nitrate must be corrected by constructing a calibration curve for nitrite with zinc, in addition to developing curves for nitrate with zinc and for nitrite without zinc. Using these calibration curves, the absorbance at different concentration ratios of nitrite and nitrate ions could be reproduced via calculation using the calibration curves with zinc for nitrite and nitrate. Eventually, the developed μPAD was applied to the determination of nitrite and nitrate ions in natural water samples, and the results were compared with those using a conventional spectrophotometric method. The results of the μPAD are in good agreement with those of conventional spectrophotometry, which suggests that the μPAD is reliable for the measurement of nitrite and nitrate ions in natural water samples.
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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.
Schematic representation of the spectrophotometric system. Display omitted
•A cheap, simple and potable spectrophotometric system has been developed using a webcam.•Two USB ports of a laptop are used to power the webcam and the radiation source.•A simple electronic device connected to an USB port has been used to power different kind of LEDs used as radiation source.•All image treatment programs used for this device may be free download from internet.
The program WinMLR has been developed to quantify sorbic and benzoic acids in soft drinks, fruit juices, and soy sauce by making a multilinear regression treatment of experimental data to a linear ...combination of standard signals. The spectra of sorbic and benzoic acid and samples were obtained from a conventional spectrophotometer, which has been saved in an ASCII file to be applied with the WinMLR program. Before to determine sorbic and benzoic acids in samples, the wavelength validation and calibration parameters were studied. Standard solutions of sorbic and benzoic acids were used for the calibration parameters to measure the individual analyte. If the sample has simultaneously both compounds, it is better to choose the synthetic mixture for the calibration parameters. This technique provides a good recovery in the range of 80.4–104.8% without a complicated and expensive instrument.
Laccase is a lignin-degrading enzyme that is expected to move industrial applications to a greener form of biotechnology. Here, we used 2,2'-azinobis(3-ethylbenzthiazolin-6-sulfonic acid) (ABTS) as a ...mediator and N-benzoyl leucomethylene blue (BLMB) as a substrate to develop a fluorometric assay that we used to measure laccase activity in mushroom extracts. We then compared this novel approach to conventional absorption spectrophotometry. With this novel approach, laccase oxidizes ABTS to produce ABTS radicals that show an absorption maximum at 415 nm. The ABTS radicals oxidize BLMB to generate fluorescent methylene blue that is measured by fluorometry while absorption spectrophotometry directly measures the absorbance of the ABTS radicals at 415 nm. Under the optimal conditions, the fluorometric assay showed a linear calibration curve with limits of detection and quantification of 1.0 × 10-2 mg mL-1 and 3.2 × 10-2 mg mL-1, respectively, and those values are 1.4-fold lower than the results using conventional absorption spectrophotometry to measure ABTS radicals. Laccase activity of extracts from species of mushrooms that include eryngii and shiitake were successfully determined via both fluorometry and absorption spectrophotometry. The eryngii extract showed the highest level of activity, which was followed by the shiitake extract, but laccase activity was not observed in the shimeji extract.
•A novel fluorometric assay for laccase activity is developed.•The fluoromentric assay is applicable to the measurement of laccase activity.•The fluoromentric assay was comparable with absorption spectrophotometry.•Eryngii mushrooms showed higher laccase activity than shiitake and shimeji mushrooms.
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•N-Benzoyl leucomethylene blue is a novel substrate in enzyme assays using horseradish peroxidase in paper-based analytical devices.•This is the first demonstration of paper-based ...analytical devices using colorimetric detection for glutamate determination.•The device permits the analysis of glutamate, which is related to diseases and allergies.•The paper-based analytical devices successfully assessed the glutamate content in several food samples.•The paper-based analytical devices determined glutamate in food samples without special tools such as a micropipette.
A paper-based device (PAD) capable of colorimetric detection was developed to determine the presence of glutamate in various food samples. The PAD employs an enzymatic reaction with glutamate followed by an oxidation reaction with N-benzoyl leucomethylene blue (BLMB) in the presence of horseradish peroxidase. The designed PAD consists of a sample introduction zone connected to a channel that transports a sample solution to three detection zones. The detection zones contain pre-deposited reagents: glutamate oxidase, horseradish peroxidase, BLMB, a phosphate buffer, and poly(acrylic acid). The PAD is perpendicularly immersed into a sample solution and bent at a right angle using a 3D-printed holder to allow the sample to simultaneously flow into three different detection zones. When the PAD is immersed into a sample containing glutamate, glutamate oxidase produces hydrogen peroxide, which changes the pale blue color of BLMB to a deep blue color in the presence of horseradish peroxidase. Under the optimum conditions, the calibration curve between the logarithm of the glutamate concentrations and the color intensity was linear within a range of from 5 × 10-6 mol L-1 to 10-2 and with a correlation coefficient of 0.994. Using this system, the PAD successfully determined glutamate in soup stocks, sauces, snacks, and tomato juice without the need of complicated sample pretreatment. These results agreed with those of a commercially available glutamate assay kit, which was employed as a certification method (tstat = 1.95, tcrit = 2.57). The developed PAD is simple, easy to fabricate, portable, and could be used outside of equipped laboratories to determine the presence of glutamate in food samples.
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.
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•Software program for the simultaneous quantification of several components in mixtures.•May be applied to spectrophotometry, fluorimetry or differential pulse polarography.•Allows single standard, multiple standards and multiple standards addition calibration methods.
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.
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•Automatic determination of quinine in soft drink with multisyringe flow injection analysis.•A fluorometric system based on 3D printing device has been designed to host a CCD detector.•The AutoAnalysis program has been used for data acquisition and treatment.•Better accuracy and precision are than with a conventional spectrofluorometer.
•Paper-based isoelectric focusing was applied to the separation and fractionation of amino acids.•Ampholytes were used to form a pH gradient in the folding paper.•Formation of a pH gradient was ...confirmed using pH indicators.•HPLC confirmed the separated amino acids following extraction from the paper.
We demonstrated the fractionation of two amino acids, glutamic acid and histidine, separated via isoelectric focusing (IEF) on filter paper folded and stacked in an origami fashion. Channels for electrophoresis were fabricated as circular zones acquired via wax printing onto the filter paper. An ampholyte solution with amphiphilic samples was deposited on all the circle zones, which was followed by folding to form the electrophoresis channels. IEF was achieved by applying an electrical potential between the anodic and cathodic chambers filled with phosphoric acid and sodium hydroxide solutions, respectively. A pH gradient was formed using either a wide-range ampholyte with a pH of 3 to 10 or a narrow-range version with a pH of 5 to 8, which was confirmed by adding pH indicators to each layer. The origami IEF was used to separate the amino acids, glutamic acid and histidine, by mixing with the ampholytes, which were deposited on the layers. The components in each layer were extracted with water and measured by high-performance liquid chromatography using pre-column derivatization with dansyl chloride. The results indicated that the focus for glutamic acid and that for histidine were at different layers, according to their isoelectric points. The origami isoelectric focusing achieved the fractionation of amino acids in less than 3 min using voltage as low as 30 V.
