Molecular Absorption Spectrophotometry Research Articles

Nutritional and phytochemical profile of a traditional beverage made from roasted roselle (Hibiscus sabdariffa) seeds

The consumption of locally available and affordable food with high nutritional properties is a recommended solution to prevalent undernutrition in low-income countries. The objective of this study was to investigate the nutritional and phytochemical profile of a traditional beverage made from roasted green or red roselle seeds. Proximate composition was determined using AOAC standard methods. Minerals and phytochemicals were quantified by atomic and molecular absorption spectrophotometry, respectively. The bioavailability of iron, zinc, and calcium was estimated using phytates/mineral molar ratios. A sensory analysis was conducted to evaluate the acceptability of the studied beverages, and their contribution to the Recommended Daily Intake of proteins, energy, iron, zinc, and calcium was also assessed. The beverage made from roasted green roselle seeds presented the highest content of proteins, fats, total fibres and energy, while the beverage made from roasted red roselle seeds was more concentrated in carbohydrates. Both beverages had similar contents of total phenols, oxalates, ascorbic acid but exhibited different phytates and carotenoids contents that were higher in the beverage made from roasted red roselle seeds. The mineral composition revealed higher contents of sodium, potassium, magnesium, phosphorus, zinc, and copper in the beverage made from roasted red roselle seeds, while iron and manganese were more concentrated in the beverage made from roasted green roselle seeds. A good bioavailability was observed for iron and zinc in the beverage made from roasted red roselle and green roselle seeds, respectively. An unfavourable calcium bioavailability was exhibited by both beverages. The consumption of 500 mL of the studied beverages, which were positively appreciated by the sensory test panel, could cover more than 100% of the Recommended Daily Intake of proteins, energy, zinc, and more than 50% of that of iron, for children up to 3 years old. The consumption of beverages made from roasted roselle seeds could be an efficient and affordable solution to undernutrition in low-income countries.

Improvement in the Chromium(VI)-Diphenylcarbazide Determination Using Cloud Point Microextraction; Speciation of Chromium at Low Levels in Water Samples.

A reliable, rapid, and low-cost procedure for determining very low concentrations of hexavalent chromium (Cr) in water is discussed. The procedure is based in the classical reaction of Cr6+ with diphenylcarbazide. Once this reaction has taken place, sodium dodecylsulfate is added to obtain an ion-pair, and Triton X-114 is incorporated. Next, the heating of the mixture allows two phases that can be separated by centrifugation to be obtained in a cloud point microextraction (CPE) process. The coacervate contains all the Cr6+ originally present in the water sample, so that the measurement by molecular absorption spectrophotometry allows the concentration of the metal to be calculated. No harmful organic solvents are required. The discrimination of hexavalent and trivalent forms is achieved by including an oxidation stage with Ce4+. To take full advantage of the pre-concentration effect inherent to the coacervation process, as well as to minimize reagent consumption and waste generation, a portable mini-spectrophotometer which is compatible with microvolumes of liquid samples is used. The preconcentration factor is 415 and a chromium concentration as low as 0.02 µg L-1 can be detected. The procedure shows a good reproducibility (relative standard deviation close to 3%).

Sobreingesta de boro durante la época precolombina en las poblaciones de Arica

In some valleys in northern Chile, the natural water reservoirs used for human consumption contain high levels of boron (> 25 mg/L). In local Pre-Colombian populations, this resulted in overexposure which is harmful to human health, causing gastrointestinal and other issues. Boron levels vary regionally, with the Lluta and Camarones Valleys presenting higher mean values (14 and 25 mg/L, respectively) than the Azapa Valley (1 mg/L). To estimate concentrations in northern Chile’s pre-Columbian populations, we used molecular absorption spectrophotometry to analyze rib samples of 211 individuals from these valleys. All the ancient rib samples presented mean boron values approximately 7 to 23 times higher than the 10.2 mg/Kg reported for modern bone tissue. Levels were highest in inhabitants of the Lluta Valley (235.52 mg/Kg) and Camarones Valley (119.09 mg/Kg), followed by those from the Azapa Valley (69.97 mg/Kg). We conclude that boron overexposure significantly impacted northern Chile’s ancient populations, and the discussions of pre-Columbian settlements and biocultural trajectories should consider water quality.

Levels of Heavy Metals Contamination (As, Cd, Hg, Pb) in Some Human Consumption Water Sources in Agbangnizoun and Za-Kpota Town Halls, Southern Benin

In the current decades, the increasing presence of metallic contaminants in water for human consumption has become a major public health concern. This concern is even more pronounced in rural areas such as in the Town Halls of Agbangnizoun and Za-Kpota where the majority of households use surface water, wells and tanks to satisfy their daily drinking water needs, without any prior treatment, due to the low level of access to drinking water supplied by the State. This study aims at assessing the levels of contamination of these resources in mercury (Hg), cadmium (Cd), lead (Pb) and arsenic (As). The mercury was determined using the cold vapor technique by the Direct Mercury Analyzer (DMA-80) while lead and cadmium were analyzed by molecular absorption spectrophotometry by the DR 3900. The Arsenic was extracted by distillation using the silver diethyldithiocarbamate method then measured by molecular spectrophotometry technique. The results show that surface waters contain great quantities of metals than well and cistern waters. Lead (220.97 ± 9.45 µg/L) and cadmium (20.13 ± 0.17 µg/L) in surface waters have levels above WHO guidelines and Bénin standards. On the other hand, there is no significant difference between the metal concentrations of well and cistern waters at the 5% threshold compared to the borehole water (witness sample). Significant correlations are established between toxic metals (Pb and Cd) and physical parameters (turbidity and suspended matters) at the threshold of 1 %. As for mercury (Hg) and arsenic (As), the concentrations are very lower than these of Cd and Pb and below the quantification limit of the device. These results confirm that the surface waters consumed by the populations of the Town Halls of Agbangnizoun and Za-Kpota do not respect drinking water standards.

SÍNTESE DE NANOPARTÍCULAS DE OURO E SENSORIAMENTO COLORIMÉTRICO DO SULFATIAZOL: UMA PRÁTICA EXPERIMENTAL PARA AULAS INTERDISCIPLINARES

SYNTHESIS OF GOLD NANOPARTICLES AND COLORIMETRIC SENSING OF THE SULFATHIAZOLE: AN EXPERIMENTAL PRACTICE FOR INTERDISCIPLINARY CLASSES. Students undertaking courses in the field of sciences and engineering need to learn practical skills and conceptual knowledge, and the experimental classes are the best moment for this. In this paper, we propose a practical experiment to aid nanotechnology learning by synthesizing gold nanoparticles (AuNPs) and their application as a colorimetric sensor of sulfathiazole. AuNPs were prepared using sodium citrate as a reducing and capping agent. The existence of the synthesized AuNPs was detected using the Tyndall effect while their optical properties were investigated by molecular absorption spectrophotometry. The gold nanoparticles exhibit spherical-like shape morphology and an average size of 13.6 nm, determined by transmission electron microscopy. The AuNPs were applied as a colorimetric sensor for the detection of sulfathiazole in mixed water/ethanol solution by simple visual inspection and using molecular absorption spectrophotometry. Due to the simplicity of the experimental steps, this activity is well-suited for a hands-on introduction of nanoparticles synthesis and its application as a molecular sensor. In addition, the experiment encompasses knowledge from different fields being suitable for interdisciplinary classes.

Amoxicillin Trihydrate Characterization and investigative adsorption using a Brazilian montmorillonite

The objective of this work was to investigate the adsorptive potential of a previously benefited and characterized brazilian montmorillonite sample, regarding amoxicillin trihydrate removal, a zwitterionic species, present in aqueous solutions. 500 mg capsule of antibiotic was properly characterized by XRD, FTIR, SEM/EDS and surface charge measurement through Zeta potential. Amoxicillin aqueous solution and supernatants from adsorption essays were characterized by Molecular Absorption Spectrophotometry in Ultraviolet-Visible Region (UV/VIS), from 200 to 400 nm. Three investigative essays were performed, varying montmorillonite mass (0.050, 0.525 and 1.000 g) and contact time between substances (10, 95 and 180 min). Amoxicillin sample is crystalline, morphologically prismatic, essentially composed of carbon, nitrogen, sulfur, hydrogen and oxygen. Its zwitterionic character was confirmed by Zeta potential, presenting positive (pH 2 to 4), relatively neutral (pH 4 to 6), and negative (above pH 6) surface charges. Test results indicated that the highest removals (21.4 and 41.8 %) were for the largest clay mineral masses (0.525 and 1.000 g, respectively), with pHs close to amoxicillin pka1 (2.68). Larger clay mineral masses have more adsorbent sites, which, associated with components opposite charges in desired pH range, promote a greater interaction. Thus, brazilian montmorillonite can promote amoxicillin removal from aqueous solutions.

DEVELOPMENT AND OPTIMIZATION OF A SPECTROPHOTOMETRIC METHOD WITH CLOUD POINT EXTRACTION FOR DETERMINATION OF GADOLINIUM

This work describes a simple, sensible, and low-cost analytical method, based on cloud-point extraction (CPE) of the surfactant (1,1,3,3-Tetramethylbutyl)phenyl-polyethylene glycol (Triton X-114), for the efficient extraction and sensible determination of gadolinium after its complexation with 1-(2-pyridylazo)-2-naphthol (PAN) and subsequent determination by ultraviolet-visible molecular absorption spectrophotometry at the wavelength of 556 nm. Full two-level and Doehlert experimental designs were applied to investigate and optimize the variables (pH, complexing concentration, and TX-114 concentration) involved in the extraction efficiency of Gd3+. The CPE was satisfactory for the determination of gadolinium with limits of detection (LoD) and quantification (LoQ) of 1.0 and 3.2 µg L-1, respectively, as well as an enrichment factor of 9.4. Accuracy was confirmed by spike tests with recovery values between 98.4 and 78.3%. The precision was expressed as relative standard deviation (%RSD, n =3), being found: 2.3% (10 µg L-1) and 2.7% (100 µg L-1). The proposed analytical method is suitable for the determination of Gd in tap water and contrast agent solutions.

Evaluation of Metallic Trace Elements Content (Cadmium, Copper, Zinc and Lead) in the Water of Lake Azili in the Municipality of Zangnanado (Centre-Benin)

This study focuses on the assessment of the level of contamination in metallic trace elements (cadmium, copper, zinc and lead) in the waters of lake Azili in the municipality of Zangnanado. The methodology adopted to achieve these results is the method of molecular absorption spectrophotometry. Four sites were sampled at the beginning of November 2020 (period of the long dry season). The results obtained show that the copper content varies between 1.04 mg/l and 1.67 mg/l. The zinc content between 0.2 mg/l to 0.62 mg/l and those of lead recorded are all above 0.05 mg/l. As for their cadmium concentration, they are all above 0.001 mg/l. These results from water analysis of Azili lake show that the sources of this type contamination of the lake are due on the one hand to human activities (dumps of household waste, use of motorized boats) and others other hand to the contributions of the effluents of the lake carrying pesticides. The water quality of Lake Azili is therefore influenced by these various metallic trace elements found there. These results show that the waters of lake Azili are at their beginning of pollution even if it is not yet alarming at the time of our study. Under these conditions, if nothing is done to mitigate it, the pollution will be critical over time.

CAFÉ COM QUIMIOMETRIA: UMA APLICAÇÃO DO PLANEJAMENTO FATORIAL FRACIONÁRIO 25-1

COFFEE WITH CHEMOMETRIC: AN APPLICATION OF 25-1 FRACTIONAL FACTORIAL DESIGN. Chemometrics is a subfield of chemistry that emerged from advances in analytical instrumentation and computing. When seeking to solve chemical problems that depend on many concomitants experimental variables, chemometrics can be employed in order to extract as much information as possible in the least possible number of experiments. In addition, it is possible to evaluate the important effects and interactions among the variables to understand the processes being monitored in each system. In this sense, this article aimed to develop a didactic experiment of caffeine extraction using an espresso machine, applying the 25-1 fractional factorial design. The variables studied were temperature (75 and 78 ºC), pressure (2 and 15 bar), granulation (bean and ground), type of coffee (special and traditional) and period of the day (morning and afternoon) to obtain maximum extraction of caffeine. The coffee extracts obtained were analyzed using UV-Vis molecular absorption spectrophotometry. The developed experiment showed the potential to spread the application of chemometrics in the academic environment and to facilitate the teaching of fractional factorial design.

Comparative Study of the Nutritional Value of Unripe and Ripe Arils of Blighia sapida (K. D. KOENIG)

B. sapida arils are of great socio-economic importance in West Africa due to their food uses. Several studies have focused on mature arils but few studies have focused on immature ones. The objective of this work was to assess the nutritional potential of mature and immature arils of these species. The arils were collected in Kara (Northern-Togo) and in Lome (Southern-Togo). The organic substances contained in the arils were determined according to the methods of AOAC while the minerals were determined by flame atomic absorption spectrophotometry for sodium, potassium, calcium and magnesium and by molecular absorption spectrophotometry for phosphorus. The main results showed that the mature and immature arils of B. sapida contain alkaloids, tannins, reducing compounds and carbohydrates and are a good source of proteins, fats, carbohydrates and minerals. Furthermore, immature arils showed a better dietary fiber content compared to mature arils. The metabolisable energy of the two types of arils were 526.78 ± 39.87 and 615.95 ± 33.90 Kcal/100 g of dry matter, respectively for the unripe arils and the ripe ones. All these results show that these arils have an appreciable nutritional value and can contribute to food safety. This justifies their food uses.

Iron Forms Fe(II) and Fe(III) Determination in Pre-Roman Iron Age Archaeological Pottery as a New Tool in Archaeometry.

This article presents studies on iron speciation in the pottery obtained from archaeological sites. The determination of iron forms Fe(II) and Fe(III) has been provided by a very simple test that is available for routine analysis involving the technique of molecular absorption spectrophotometry (UV–Vis) in the acid leachable fraction of pottery. The elemental composition of the acid leachable fraction has been determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Additionally, the total concentration of the selected elements has been determined by X-ray fluorescence spectrometry with energy dispersion (EDXRF). The results of the iron forms’ determinations in archaeological pottery samples have been applied in the archaeometric studies on the potential recognition of the pottery production technology, definitely going beyond the traditional analysis of the pottery colour.

Production of High Purity Samarium Acetate for Use in Nuclear Area

Samarium is currently used in many applications, such as catalysts, lasers and metal alloys. Samarium is also employed to absorb neutrons in nuclear reactors. In medicine, samarium is used in the form of radioactive 153Sm to produce radiopharmaceuticals. A simple process for the preparation of pure samarium acetate was studied. The raw material, which was used in the form of rare earth carbonates was produced industrially from the chemical treatment of Brazilian monazite. Ion exchange chromatography was performed using a strong cationic resin to fractionate rare earth elements (REE). Under these conditions, 99.9% pure Sm2O3 and yield greater than or equal 60% was eluted by ammonium salt of ethylenediaminetetraacetic acid (EDTA) solution in controlled pH. The EDTA-samarium complex was transformed into samarium oxide, which was subsequently dissolved in acetic acid to obtain the samarium acetate. Molecular absorption spectrophotometry was used to monitor the samarium and sector field inductively coupled plasma mass spectrometry was used to certify the purity of the samarium acetate. The solid salt was characterized by chemical analysis, thermal analysis, infrared spectroscopy and X ray diffraction. The analytical data collected allowed to conclude that stoichiometric formula for the samarium acetate obtained is Sm(CH3COO)3.4.H2O.Keywords: Samarium, Ion exchange, Rare Earth.

A simple, sensitive and selective spectrophotometric method for determining iron in water samples

We proposed a procedure for determining iron in various water samples employing molecular absorption spectrophotometry. The ligands used are 1-Nitroso-2-naphthol-3,6-disulphonic acid disodium salt (Nitroso R Salt) and Hexadecyl trimethyl ammonium Bromide (CTMAB). Iron can be determined by chromogenic reaction without redox pretreatment. The effects of temperature, acidity and the amount of reagent on the color reaction were studied. The linear correlation coefficient between iron concentration and absorbance is 0.9997. The limits of detection and quantification of method are 6.7 × 10−8 and 2.0 × 10−7mol/L, respectively. The molar absorption coefficient is 0.8 × 105 L. mol−1cm−1. Under selected conditions, common co-existing ions generally do not interfere with the determination of iron in water samples. Ten repeated determinations of Fe standard solution (8.0 × 10−6 mol/L) have shown that the relative standard deviation (RSD) is 0.61%. In the determination of the trace iron in actual samples, the RSDs are less than or equal to 3.1% (n = 4), and the recovery rate of standard addition method is between 92.8% and 108%. The proposed method is simple, economical, rapid, sensitive, accurate and highly selective, and can be used to determine iron contents in various water samples without pretreatment.

Short Strong Hydrogen Bonds can Hinder Complex Formation: A Stability and Structure Study of Copper(II) Alkyl-N-iminodiacetic Acid Complexes in Aqueous Systems and Solid State

In the present study the solution and coordination chemistry of copper(II)–alkyl-N-iminodiacetate systems are studied in aqueous solution by potentiometry, using ion selective copper and pH electrodes, EXAFS (extended X-ray absorption fine structure) and dye probe molecular absorption spectrophotometry. Alkyl-N-iminodiacetates with varying alkyl chain length, methyl (CH3–), n-hexyl (C6H13–), n-dodecyl (C12H25–) and n-octadecyl (C18H37–) were used to tune the amphiphilic properties of the ligands. The polar head groups have both oxygen (hard Lewis base) and nitrogen donor (border-line Lewis base) atoms. This means that metal ions with different bonding characteristics may bind these ligands differently. Furthermore, the chelating properties of the polar head group may be regulated by pH as the acid–base properties of the imine and carboxylic acid groups are different. Copper(II) forms two stable complexes with alkyl-N-iminodiacetates with short alkyl chains, present as monomers in aqueous solution, log10β1 = 11.10(2), log10β2 = 19.5(2) for methyl-N-iminodiacetate, and log10β1 = 12.22(4), log10β2 = 21.9(2) for n-hexyl-N-iminodiacetate. n-Octadecyl-N-iminodiacetic acid, present as large aggregates in acidic aqueous solution, has short strong hydrogen bonds between carboxylic acid and carboxylate groups in the surface of the aggregates, which hinder complex formation at pH values below 4, obstructs it in the pH region 4–7, while the complex formation behaves as for short-chained alkyl-N-iminodiacetates at pH > 7. The structure around copper in copper(II)–alkyl-N-iminodiacetate complexes in aqueous solution and solid state formed at different pH values and copper(II):alkyl-N-iminodiacetate ratios has been determined by EXAFS. The coordination chemistry of copper(II) shows four strong bonds in the equatorial plane, and two different Cu–O/N bond distances, ca. 0.2 Å apart, in the axial positions of a non-centrosymmetric tetragonally elongated octahedron.

Study of a more than a hundred years old theriac jar' content: A famous thousand-year-old counter-poison.

The purpose of this article is to study the content of a 19th century white porcelain pot from the Pochet-Desroche fabric, offered to the National Order of Pharmacists and probably containing theriac. The aim is to identify the active ingredients of any substances that may still be present and to try to determine the preparation period of the panacea. All the analyzes were carried out according to the reference current methods. Liquid / liquid extractions in a separating funnel, high performance liquid chromatography coupled with three-dimensional diode array molecular absorption spectrophotometry and gas chromatography coupled with mass spectrometry have revealed 218 molecules which may belong to the ingredients of a theriac. 29 of these are clearly still present in the opiate studied. Their comparison with the French pharmacopoeias formulas of 1818 and 1884 pleads for manufacture according to the formula of 1884. The originality of our work lies in the rarity of this type of analysis on very old pharmaceutical samples and in the fact that it concerns a mixture of great complexity.

Swelling behavior of acrylamide and sodium acrylate copolymer hydrogel in aqueous solutions of copper (II) chloride with amino acids additives

Swelling of acrylamide and sodium acrylate copolymer polyelectrolyte hydrogel in aqueous Cu(II) chloride solutions with additives of proteinogenic amino acids glycine and L-histidine has been studied. Research relevance is due to the application of such systems in agrochemical products that are supposed to have high water absorption capacity in the presence of microelements ions and amino acids, which are used to prevent nutritional deficiency and make plants resistant to adverse weather conditions and diseases. Gravimetry, atomic absorption spectrometry, FTIR ATR spectroscopy and molecular absorption spectrophotometry were used. The impact of acidity (pH 3, 5 and 7) of aqueous Cu(II) chloride solutions with amino acids additives on the hydrogel swelling degree and Cu(II) ions absorption has been determined. The reasons for changes in the hydrogel swelling degree in aqueous Cu(II) chloride solutions in presence of glycine and L-histidine have been found. The main product of the crosslinked copolymer interaction with the components of 0.01 M aqueous Cu(II) chloride solution with the addition of 0.04 M glycine or L-histidine at pH 3 has been assumed to be a mixed Cu(II) ions complex with functional groups of both copolymer and amino acids.

Evaluation of the bioavailability of potentially toxic metals in surface sediments collected from a tropical river near an urban area

The objective of this study was to evaluate the bioavailability of the metals cadmium, copper, lead, nickel, and zinc from sediment samples collected in the Paraguaçu river between the cities of Cachoeira and São Félix in the state of Bahia in Brazil. The method used was the acid extraction of volatile sulfides and metals extracted simultaneously (AVS-SEM) as described in the literature. For the extraction of sulfide, an argon drag system was used after acidification of the samples with HCl, releasing the volatile sulfides collected in the basic solution. Its determination was made by molecular absorption spectrophotometry using the methylene blue method. For quantification of the metals, the sediment with acid was filtered and the residual solution was analyzed by inductively coupled plasma mass spectrometry (ICP MS) in which the elements that were associated with the sulfide were released in solution. The bioavailability evaluation was done by the relation between the sum of the concentrations of the metals in solution (SEM) and the concentration of sulfide in each sample (AVS). When the ∑SEM/AVS ratio is >1, the medium is considered contaminated by the high bioavailability of the metals to other environmental compartments. In the samples collected in the Paraguaçu river in two campaigns, with an ∑SEM/AVS ratio of 0.007 to 1.082, the last value being the only critical>1, while the other quantities in the metallic phase were not available for a biota. By comparing the metal concentration data with the internationally established tolerance limits, all the values found were below the critical values, presenting no toxic risks to the surrounding ecosystem.

Comprehensive evaluation of radical scavenging, reducing power and chelating capacity of free proteinogenic amino acids using spectroscopic assays and multivariate exploratory techniques.

Among others, amino acids can inhibit oxidative processes through multiple pathways including inactivation of reactive oxygen species, scavenging free radicals, chelation of pro-oxidative transition metals, as well as reduction of hydroperoxides. Moreover, they can be a major target for oxidants as a result of their abundance in biological systems. The purpose of the present study is to examine the radical scavenging, reducing power and chelating capacity of the free proteinogenic amino acids, using several analytical assays based on different mechanisms and monitored via molecular UV-vis absorption spectrophotometry. In most of the assays, the highest antioxidant activity is rendered by Cys and Trp, known for their involvement in physiological radical reactions, followed by Tyr, Asn and Arg. The least reactive amino acids with respect to both radical scavenging and reducing power principle were Ala, Met, Thr and Val. The hierarchy of the amino acids based on their antioxidant activity is shifting, depending on the analytical assay employed. Results from the multivariate exploratory techniques-hierarchical cluster analysis and principal component analysis-could point out the methods that are most similar and best connected to each other, thus classifying the investigated amino acids according to their activity. Considering the results of chemometric techniques, the antioxidant methods that best discriminate between amino acids are DPPH bleaching and SORS assays. Not only the comprehensive study of antioxidant activity of amino acids is novel in this study but also the application of the sum of ranking differences to compare and rank the various antioxidant capacity assays. The obtained results will support the development of amino acids based multifunctional formulations with important physiologically relevant implications for both humans and animals, with a possible future use in the food industry.

UN ESTUDIO COMPARATIVO ENTRE LA CALIBRACIÓN MULTIVARIANA Y LA RED NEURAL ARTIFICIAL EN LA CUANTIFICACIÓN DEL BIODIESEL DE SOJA

Biodiesel is an alternative fuel and can be obtained by the transesterification of vegetable oils. Spectrophotometric methods can be used for the quantification of mixtures, associated with chemometric tools, enabling the analysis of overlapping signals. The aim of this work is to apply the multivariate calibration with PLS (partial least squares) and artificial neural network (ANN), to estimate the concentration of esters in the transesterification of soybean oil using molecular absorption spectrophotometry as analytical technique. Absorbance measurements were performed in a spectrophotometer UV/VIS. Synthetic solutions were prepared with standards of the five major compounds of soybean biodiesel and real samples were obtained by the reaction of transesterification of soybean oil with NaOH and enzymatic method was used Lipozyme® IM (Novozymes), as catalysts. Results shows that all components of this reaction medium absorb in the wavelength range of 190-280 nm. Reactions of basic catalysis reached conversions close to 100%, while enzymatic reactions reached lower conversions. For both methods, calibration and validation groups were composed, respectively, by synthetic and real samples. Results showed that the concentrations of esters estimated by ANN model in the real samples are more accurate (R2-0.93), showing the good ability to estimation of ANN.

Determination of ascorbic acid in natural fruit juices using digital image colorimetry

This work proposes a procedure using digital image colorimetry for the determination of ascorbic acid in natural fruit juices. The method was established by measuring the color of the iron(II)-1,2 ortho-phenanthroline complex. The digital images obtained during the experiments were stored in JPEG format, and the region of interest (ROI) was submitted to decomposition in color values according to the RGB additive color model. However, the analytical procedure recommended the employment of the blue channel because it presented higher sensitivity than the red and green channels.The optimization of the parameters of the colorimetric reaction was performed employing a full two-level factorial design. The influence of the distance from the webcam to the cuvette on the sensitivity and precision of the method was also evaluated. This experiment, demonstrated that there was no significant difference between the slopes obtained in the calibration curves under the conditions studied.When utilizing the optimized conditions, the method allows the determination of ascorbic acid in fruit juices with limits of detection and quantification of 0.005 and 0.015 mg L−1, and precision expressed as the relative standard deviation of 1.2% for lemon juice with an ascorbic acid concentration of 24.8 mg/100 g. So, the procedure was applied for the determination of ascorbic acid in lemon, orange, grape, cashew, lime, pineapple, tangerine and mango natural juices. The concentrations found varied from 4.5 to 182.5 mg/100 g. The fruit juice samples were also analyzed by molecular absorption spectrophotometry using a classical method established using 1,2 ortho-phenanthroline. The results obtained were compared using the t-test, which showed that there was no significant difference between the ascorbic acid contents found by the two methods.