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In this study, we investigated the main constituent, the predominant class and biological activity of the essential oil extracted from the leaves of Pimenta dioica and the pattern of the major constituent against larvae in the third stage of Aedes aegypti. For this reason, we extracted the oil by hydrodistillation, identified its components by gas chromatography coupled with mass spectrometry (GC/MS) and calculated the lethal concentration (LC50) of the larvicidal activity using the Reed-Muench method. The results show that the oil consists mainly of eugenol, in which the phenylpropanoid class predominated and the lethal concentration, LC50, was 38.86 μg mL-1at a confidence level of 2.25 μg mL-1, while the eugenol standard presented LC5079.75 μg mL-1at a confidence level of 2.10 μg mL-1. Given the facts, we conclude that the oil is more active than the standard and that it has the potential to replace chemical larvicides.

This worlk proposes a rapid, sensitive and accurate flow-batch digital image colorimetric (FB-DIC) system to zinc oxid determination in ointments. The method was based on the reaction between Zn(II) ions and zincon at pH = 9.0. The Zn(II)-zincon complex was formed and detected in the mixing chamber. It was designed with two opposite glass windows: one for the webcam and other for the ultra-bright LED. Absorbance was calculated by the norm of the vector in the RGB space. The method had a linear range between 1.0-8.2 mg L–1 with R2 = 0.9998 (n=8) and limit of detection estimated as 5.7 mg L–1. The relative standard deviation (RSD) and sample throughput were estimated at 0.06% and 109 samples h-1, respectively. Ointment commercial samples were analyzed by FB-DIC and the refference method. The results shown no statistically significant difference between them, when was applied the paired t-test at the 95% confidence level. According to green analytical chemistry (GAC) principles the FB-DIC system can be considered eco-driendly due to its low samples and reagents consumption as its low waste generation.

Este trabalho propõe um método colorimétrico por imagens digitais para determinação de metanol em bebidas alcoólicas. O método é baseado na oxidação do metanol a formaldeído, seguido da reação com ácido cromotrópico produzindo um composto púrpura. Imagens digitais do produto de reação são capturadas usando um scanner e as estas são tratadas usando o programa ImageJ. As condições experimentais foram otimizadas e uma curva analítica, usando o índice colorimétrico de imagens digitais como resposta analítica, foi construída na faixa de 0,0100%-0,1000% v/v de metanol. Os limites de detecção e quantificação foram 1,95 x 10-³% e 6,50 x 10-³% v/v, respectivamente. A viabilidade do método é ilustrada na aplicação em amostras de cachaça e licor. Em comparação com a espectrometria ultravioleta-visível, os resultados não mostraram diferenças estatisticamente significativas mediante aplicação do teste-t emparelhado ao nível de confiança de 95%. Em comparação com outros métodos semelhantes, o proposto apresentou uma sensibilidade superior. Tal característica vantajosa é atribuída à natureza trivariada da detecção do scanner.

This work evaluated the molluscicidal activity of the essential oil of the Zingiber officinale Roscoe rhizomes in with of the Biomphalaria glabrata species. The essential oil was isolated q...

RESUMO A pesquisa descreve a reação espectrofotométrica do complexo Cu(II)-PAN (1-(2-piridilazo)-2-naftol) e determina a concentração de cobre (II) em aguardente de mandioca (Tiquira). Para isso, dimensionamos a reação para os estudos de absorção do complexo, pH, estabilidade, proporção estequiométrica, interferentes, correlação e recuperação. Após essa etapa, determinamos a concentração de cobre(II) em cinco amostras de bebidas destiladas artesanalmente de cinco municípios do Estado do Maranhão. O resultados mostram que o complexo absorve em 548 nm em pH 6, é estável em um tempo de 7 horas em proporções estequiométrica mínima de 1:1 do ligante e metal, possui limite de detecção em 3,3 X 10-2 mg L-1, faixa de linearidade de 1 X 10-6 a 1 X 10-5 mol L-1, correlação (R2= 0,9990), desvio padrão=0,0035 e recuperação em 104,54 ± 7,01 e os principais íons interferentes são o ferro (III) e o cobalto (II). Na aguardente, constatamos que o teor de cobre está acima do permitido pela legislação brasileira. SUMMARY The search describes the spectrophotometric reaction of the Cu (II)-PAN (1-(2-pyridilazo) -2-naphthol) complex and determines the concentration of copper (II) in manioc spirit (Tiquira). For this, we dimensioned the reaction for the studies of complex absorption, pH, stability, stoichiometric ratio, interferences, correlation, and recovery. After this step, we determined the concentration of copper (II) in five samples of beverages distilled artisanal from five municipalities of the State of Maranhão. The results show that the complex absorbs at 548 nm at pH 6, is stable at a time of 7 hours in minimum 1:1 stoichiometric proportions of the binder and metal, has a detection limit in 3.3 X 10-2 mg L-1, range (R2= 0.9990), standard deviation= 0.0035 and recovery at 104.54 ± 7.0, and the main interfering ions are iron (III) and cobalt (II). In the brandy, we find that the copper content is above that allowed by Brazilian legislation.

A flow-injection spectrometric method for determination of sodium diclofenac in pharmaceutical formulations was developed on this work. Sodium diclofenac solutions were injected into a stream of deionized water that reacted with potassium permanganate on acid medium producing Mn2+ ions whose exhibit maximum absorbance at 450 nm. The methodology used optimize experimental parameters was 33 factorial design and response surface. The proposed method obeyed the Beer’s Law over the range 25-160 mg L-1, applied in tablets and ampoules samples. Results were compare with the reference method. It was verified at the 95% confidence level, through paired t -test application – there is no statistic difference between them. The detection limit was valued in 2.6 mg L-1, relative standard deviation for 10 consecutive injections was 1.5% (100.0 mg L-1 sodium diclofenac solution) and the sample throughput was 80 samples h-1. Regarding optimization of operational conditions, the FIA spectrometric method presented analytical performance as good as other elaborated flow analyzers. Offers a simple and inexpensive way to this drug indirect determination aiming quality control on pharmaceutical industry’s assembly line. However, it can not be used for adulteration screening analysis due to non-selectivity and non-specificity of redox reactions.

This study addresses the challenge of performing fast and accurate titrations with end points that are difficult to identify. In this sense, the combination of digital movies (DMs) with a flow-batch analyzer (FBA) has shown to be a promising analytical tool. In a digital movie-based automatic titrator (DMB-AT), a DM is recorded by a webcam as the titrant is added in the mixing chamber (MC). The DM is then decompiled into frames that are ordered sequentially. In the first frame, the region of interest (ROI) of 257 × 255 pixels is defined. The red (R) component is used to calculate the Pearson's correlation coefficient (r) between the first frame and each subsequent one. The titration curve is obtained in real time by plotting r values and the opening time of the titrant valve. The experimental titration curve is fitted in a sigmoidal regression, and the new titration curve is used to estimate the end point by means of the second derivative method. A software program written in Adobe AIR for a desktop platform programmed in ActionScript 3.0 controlled the opening time of the solenoid valves, gathered the analytical signal and carried out the analytical procedure in real time. The feasibility of the method was confirmed by determining the total hardness and the total alkalinity in mineral waters. The results were compared with classical batch titration and did not exhibit statistically significant differences when the paired t-test at the 95% confidence level was applied. The proposed method is able to process approximately 67 and 86 samples h− 1 for total hardness and total alkalinity, respectively. Its precision was confirmed by overall relative standard deviation (RSD) values of less than 1.0% in both applications.

Neste trabalho foi desenvolvido um sistema de multicimutacao em fluxo para determinacao de diclofenaco de sodio, acido acetilsalicilico e fluoretos em injetaveis, comprimidos e aguas de torneira, respectivamente. Para diclofenaco de sodio o metodo usado foi baseado em sua reacao com permanganato de potassio (20 - 80 mg L -1 ). Para acido acetilsalicilico o metodo usado foi baseado na reacao de Trinder apos hidrolise alcalina do analito (25 - 100 mg L -1 ). Para ions fluoreto o metodo usado foi o bem conhecido SPADNS (0.4 - 1.6 mg L -1 ). Resultados foram comparados com seus respectivos metodos de referencia e, aplicando o teste- t emparelhado, nenhuma diferenca estatisticamente significativa foi verificada entre eles ao nivel de confianca de 95%. Apos a otimizacao das variaveis do sistema analitico, ele foi capaz de analizar 80, 72 e 68 amostras h -1 contendo diclofenaco de sodio, acido acetilsalicilico e fluoretos, respectivamente com geracao de residuos reduzida de acordo com os principios basicos da quimica verde.

portuguesEste trabalho descreveu e comparou quatro estudos entre si que utilizaram metodos automaticos em fluxo com deteccao espectrofotometrica e a reacao de oxidacao do diclofenaco para determinar diclofenaco em formulacoes farmaceuticas e fluidos corporais. Para isso, utilizamos os seguintes artigos: Versatility of a multicommuted flow system in the spectrometric determination of three analytes, Sequential injection spectrophotometric method for the assay of anti-inflammatory diclofenac sodium in pharmaceutical preparations, Screening of conditions controlling spectrophotometric sequential injection analysis e Sequential injection spectrophotometric determination of diclofenac in urine and pharmaceutical formulations e detalhamos as metodologias empregadas, os resultados, conclusoes obtidas e comparamos entre eles os limites de deteccao, desvio padrao relativo e a frequencia analitica. Os resultados mostraram diferencas significativas entre metodos empregados e a utilizacao do Sistema automatico do tipo Analise por Injecao Sequencial, apesar deste possuir menor frequencia analitica. EnglishThis study described and compared four studies that used automatic flow methods with spectrophotometric detection and the oxidation reaction of diclofenac to determine diclofenac in pharmaceutical formulations and body fluids. For this, the following articles were used: Versatility of a multicommuted flow system in the spectrometric determination of three analytes, Sequential injection spectrophotometric method for the assay of anti-inflammatory diclofenac sodium in pharmaceutical preparations, Screening of conditions controlling spectrophotometric sequential injection analysis and Sequential injection spectrophotometric determination of diclofenac in urine and pharmaceutical formulations and we detail the methodologies used, the results, the conclusions obtained and compare the limits of detection, relative standard deviation and analytical frequency. The results showed significant differences between the employed methods and the use of the Automatic System of the Sequential Injection Analysis type, although this one has a lower analytical frequency.

This paper proposes a method to perform rapid and sensitive graphite furnace atomic absorption spectrometry (GFAAS) determination of Cr(VI) in vinegar samples without wet digestion. Taking into account low levels of Cr(VI) and the presence of several concomitants in the sample matrix, the proposed method uses single-phase liquid-liquid extraction (SPLLE). The method is automated, employing a flow-batch analyzer (FBA) which uses a mixing chamber designed to emulate a separation funnel promoting the formation/break of the single-phase solution, reaction and extraction. The Cr(VI) extraction procedure was performed by proportioned mixing of the vinegar sample (aqueous phase), amyl alcohol (organic phase), and ethanol (consolute) to form a single-phase solution. The chelating reagent sodium diethyldithiocarbamate (DDTC) dissolved in the consolute reacts rapidly with Cr(VI), in the single phase to produce a stable Cr-DDTC complex. The single-phase break step is performed by adding an excess of Britton-Robinson buffer, and then the organic phase enriched with Cr(VI) was analyzed by GFAAS. Factors such as extraction steps, single-phase composition, pH, chelating agent concentration, and flow-batch parameters were optimized. The FBA-SPLLE-GFAAS was evaluated in vinegar samples showing satisfactory analytical features in terms of limit of quantification (0.86 μg L −1 ), precision (RSD

The advantages of chemiluminescence, digitally captured movies, magnetic solid-phase extraction (MSPE) and a robotized Flow-batch system were united to develop a new automated luminometer. This digital movie-based robotized Flow-batch luminometer was successfully applied for in-line MSPE, and sensitive, selective determination of Cu2+ in Cachaca (a distilled spirit made from fermented sugarcane juice). Magnetic Fe3O4@Al2O3 nanoparticles immobilized with 1-(2-pyridylazo)-2-naphthol and sodium dodecyl sulfate were employed as magnetic adsorbents. The catalytic effect of Cu2+ on luminol oxidation using H2O2 in alkaline medium was employed to generate the chemiluminescent signals, which were measured via digital movies. The method presented satisfactory analytical features when compared with previous studies, yielding: LOD = 7 μg L−1, recovery rates = 94.8–106.5%, RSD

In this paper, a flow-batch analysis (FBA) system, hydride generation (HG), and atomic fluorescence spectrometry (AFS) are coupled for the first time to develop a fast and sensitive FBA–HG–AFS method for automated inorganic antimony speciation in waters, whether from the sea, mineral water, tap water, or lakes. Unlike previous automated flow methods that use confluent fluids and complex devices, the main advantage of the proposed FBA-HG-AFS method is an innovative use of a simple laboratory made flow-batch chamber to simultaneously perform mixing, homogenization, reactions, antimony hydride formation, and gas–liquid separation. The FBA-HG-AFS method was optimized using two–level full factorial and Box–Behnken designs, and validated on the basis of real repeated measurements and analysis of variance, yielding a satisfactory working range (100–2000 ng L−1), precision (RSD = 4%), sensitivity, and limit of detection (6 ng L−1) for the water samples analyzed. Accuracy was evaluated by recovery tests and analysis of a standard reference material (SRM 1643e) of trace elements in water (NIST, USA), resulting in recovery rates of from 90 to 114%, and relative error = 0.7%. The high sampling throughput (54 speciations h−1), together with low waste generation, low costs, low reagent and sample consumption make this FBA-HG-AFS method an interesting proposal for fast large-scale analysis in routine laboratoy according to the principles of green analytical chemistry.

A new method referred to as microemulsion-based Dispersive Magnetic Solid-Phase Extraction (MDM-SPE) is presented for use in the extraction and preconcentration of metal ions from complex organic matrices. MDM-SPE combines the features of magnetic nanoparticles (MNPs) and microemulsions. It was successfully applied to the extraction of copper(II) from gasoline prior to its determination by Graphite Furnace Atomic Absorption Spectrometry (GF-AAS). The material for use in MDM-SPE was obtained by first functionalizing MNPs of the type Fe3O4@Al2O3 with sodium dodecyl sulfate and the chelator 1-(2-pyridylazo)-2-naphthol (PAN) dispersed in 1-propanol. The resulting functionalized magnetic MNPs were dispersed in a microemulsion prepared from gasoline, buffer, and 1-propanol. After waiting for 5 s (during which the formation of the copper complex on the MNPs is complete), the MNPs are magnetically separated. The complex was then eluted with 2 mol L−1 HNO3, and the eluate submitted to GF-AAS. Various parameters were optimized. Copper(II) can be quantified by this method over a linear range that extends from 2.0 to 10.0 μg·L−1. Other figures of merit include (a) a 37 ng·L−1 detection limit, (b) a repeatability of 1.1%, (c) a reproducibility of 2.1%, and (d) an enrichment factor of nine. The high surface-to-volume ratio of the microemulsion containing the dispersed magnetic sorbent warrants an efficient contact for reaction between copper(II) and the complexing agent, and this results in fast (about 40 s) extraction and pre-concentration of copper(II). MDM-SPE is accurate, precise and efficient. Microemulsions do not break down, and phase separation, heating, laborious, and time-consuming sample preparation, and incorporation of impurities into the graphite furnace (which can generate inaccuracies in GF-AAS analysis) are not needed.

The pleasant taste and flavor of coffee are responsible for making it one of the most preferred and consumed beverages around the world. Industrial coffee plants usually roast both coffee and adulterants together, which affects directly the quality of the product, specially the sensorial characteristics of the drink. Therefore, this work aims the identification of adulterations in ground roasted coffees (due to the presence of husks and sticks) using ultraviolet–visible spectroscopy and the Successive Projections Algorithm for variable selection in association with Linear Discriminant Analysis (SPA-LDA). For this purpose, extracts of ground roasted coffees prepared in hot water alone (representing the final product as ingested by the consumers) were then analyzed. The proposed methodology obtained a 100% classification in both training and test sets, providing a simple and fast analysis of the aqueous extracts of ground roasted coffees. Moreover, it can also afford security to coffee consumers and regulatory agencies, preventing the fraudulent labeling.

In this paper, we propose a new methodology to identify adulterations in ground roasted coffees (due to the presence of husks and sticks) using digital images and the successive projections algorithm for variable selection in association with linear discriminant analysis (SPA-LDA). A simple document scanner was used for capturing the images, and a Petri dish support with eight circular holes (one for each sample) to be scanned was employed. Color histograms in the hue-luminosity-saturation (HLS) channels extracted from the digital images were used as input data and statistically evaluated using supervised pattern recognition techniques. For comparison with SPA-LDA, soft independent modeling by class analogy (SIMCA) and partial least squares discriminant analysis (PLS-DA) were also used. In general, SPA-LDA provided significantly better performance than the other classification models, reaching a mean accuracy of 92.5 % for both the training and test sets, while SIMCA and PLS-DA attained only 71.5 and 85.5 %, respectively. More specifically, all of the models presented high rates (above 90 %) for sensitivity and specificity (in the test set samples classification), except SIMCA, which presented a specificity rate of 76 %. Moreover, the SPA-LDA model generally showed the lowest classification error rates. As such, it is a more adequate chemometric tool for discriminating pure coffee samples and adulterated by husks and sticks. The proposed strategy avoided laborious sample preparation, and additional operational costs, assessing coffee adulteration by husks and sticks.

This paper proposes combining Multiple Linear Regression (MLR) and Digital Image-Based Flame Emission Spectrometry (DIB-FES) to overcome the inherent spectral interference in Flame Emission Spectrometry (FES) when sodium and calcium are present in the same sample. Metals in the air–butane flame emit radiation which is revealed in the digital images captured by a webcam (detector), on the basis of the Red-Green-Blue (RGB) color system. MLR calibration models for sodium and calcium were both developed and validated. In order to illustrate the feasibility of this proposal, the validated models were applied for the determination of sodium and calcium in powder milk. The results were compared with those obtained using Flame Atomic Absorption Spectrometry (FAAS) as the reference method. No statistically significant difference was observed between the results for both metals by using the paired t-test at a 95% confidence level. The accuracy of the models was also attested to by their recovery factors which fell between 97 and 103% for both metals. The results confirm the models' discriminating power in isolating each analyte's information from a single digital image, even with spectral interference.

This study proposes a digital image-based flow-batch analyzer (DIB-FBA) for aluminum (III) and chromium (VI) determinations in natural water. A webcam with a CCD sensor and RGB data are used. The method for determining aluminum is based on an Al(III) ion, quercetin, and cetyltrimethylammonium bromide (CTAB) reaction which yields a yellow colored complex in an acetate buffer medium (pH 5.5). The determination of chromium is based on a Cr(VI) ion with 1,5-diphenylcarbazide (DPC) reaction whose product is a violet colored complex. Digital images present the color of the emergent (complementary) radiation to that absorbed by the complexes formed in each analysis. RGB data were employed to build the analytical curves. All standard solutions were prepared in-line, and all analytical processes were completed by simply changing the operational parameters in the DIB-FBA control software. The working ranges were from 10 to 600 μg L − 1 for Al(III) with r = 0.9994 (n = 5), and 10 to 300 μg L − 1 for Cr(VI) with r = 0.999 (n = 5), the limits of detection were 3.97 and 2.65 μg L − 1 respectively for Al(III) and Cr(VI). The relative standard deviation (RSD %) and sampling rate were estimated at 1.5% and 137 h − 1 and at 1.7% and 134 h − 1 for Al(III) and Cr(VI), respectively. Comparing with the reference method, no statistically significant differences were observed when applying the paired t -test at a 95% confidence level.

The traditional flow chemiluminescence (CL) systems typically use flow cells in spiral shape mounted in front of a photomultiplier tube (PMT). The sample is transported by using carrier fluids, undergoes dispersion, and mixes with reagents and CL reaction occurs before reaching the flow cell. As a consequence, the maximum of the chemiluminescence intensity is not exploited and the sensitivity is significantly diminished. In this work, these drawbacks were overcome by using a flow–batch approach and a large area silicon photodiode instead of PMT in order to build a simple and automatic luminometer for CL measurements. The feasibility of the proposed flow–batch luminometer was demonstrated in the determination of vitamin B 12 in injection ampoules, yielding limits of detection and quantification (0.11 and 0.36 μg L − 1 , respectively), recovery rates (between 97.8 and 102.1%), relative standard deviations (RSD − 1 ). Thus, it was possible to both project and build a simple, flexible, versatile and automatic luminometer, while keeping the excellent characteristics of the previous flow–batch analyzer such as: low reagent and sample consumption and minimal waste generation.

This work proposes the use of digital image-based method for determination of total acidity in red wines by means of acid-base titration without using an external indicator or any pre-treatment of the sample. Digital images present the colour of the emergent radiation which is complementary to the radiation absorbed by anthocyanines present in wines. Anthocyanines change colour depending on the pH of the medium, and from the variation of colour in the images obtained during titration, the end point can be localized with accuracy and precision. RGB-based values were employed to build titration curves, and end points were localized by second derivative curves. The official method recommends potentiometric titration with a NaOH standard solution, and sample dilution until the pH reaches 8.2-8.4. In order to illustrate the feasibility of the proposed method, titrations of ten red wines were carried out. Results were compared with the reference method, and no statistically significant difference was observed between the results by applying the paired t-test at the 95% confidence level. The proposed method yielded more precise results than the official method. This is due to the trivariate nature of the measurements (RGB), associated with digital images.

A fast, reliable, and low cost biamperometric flow‐injection method, with an error of 1.3% and an analytical throughput of 55 samples h−1, for determination of tetracycline hydrochloride in pharmaceuticals capsules is proposed. The analytical curve was linear (r=0.998) in the range 10 to 50 mg l−1 using Fe(CN)6 3− and NaOH solutions as reagent and carrier stream/supporting electrolyte, respectively. A relative standard deviation of 1.6% (10 sequential injections of 30.0 mg l−1) was verified with detection and quantification limits of 0.6 and 3.4 mg l−1, respectively.

This study proposes the use of digital movies (DMs) in a flow–batch analyzer (FBA) to perform automatic, fast and accurate titrations. The term used for this process is “Digital movie-based on automatic titrations” (DMB-AT). A webcam records the DM during the addition of the titrant to the mixing chamber (MC). While the DM is recorded, it is decompiled into frames ordered sequentially at a constant rate of 26 frames per second (FPS). The first frame is used as a reference to define the region of interest (ROI) of 28×13 pixels and the R , G and B values, which are used to calculate the Hue ( H ) values for each frame. The Pearson's correlation coefficient ( r ) is calculated between the H values of the initial frame and each subsequent frame. The titration curves are plotted in real time using the r values and the opening time of the titrant valve. The end point is estimated by the second derivative method. A software written in C language manages all analytical steps and data treatment in real time. The feasibility of the method was attested by application in acid/base test samples and edible oils. Results were compared with classical titration and did not present statistically significant differences when the paired t -test at the 95% confidence level was applied. The proposed method is able to process about 117–128 samples per hour for the test and edible oil samples, respectively, and its precision was confirmed by overall relative standard deviation (RSD) values, always less than 1.0%.

The exploitation of digital images obtained from a CCD camera (WebCam) as a novel instrumental detection technique for titration is proposed for the first time. Named of digital image-based (DIB) titration, it also requires, as a traditional titration (for example, spectrophotometric, potentiometric, conductimetric), a discontinuity in titration curves where there is an end point, which is associated to the chemical equivalence condition. The monitored signal in the DIB titration is a RGB-based value that is calculated, for each digital image, by using a proposed procedure based on the red, green, and blue colour system. The DIB titration was applied to determine HCl and H3PO4 in aqueous solutions and total alkalinity in mineral and tap waters. Its results were compared to the spectrophotometric (SPEC) titration and, by applying the paired t-test, no statistic difference between the results of both methods was verified at the 95% confidence level. Identical standard deviations were obtained by both titrations in the determinations of HCl and H3PO4, with a slightly better precision for DIB titration in the determinations of total alkalinity. The DIB titration shows to be an efficient and promising tool for quantitative chemical analysis and, as it employs an inexpensive device (WebCam) as analytical detector, it offers an economically viable alternative to titrations that need instrumental detection.

A lab-made interface for acquisition of instrumental analog signals between 0 and 5 V at a frequency up to 670 kHz at the parallel port of a microcomputer is described. Since it uses few and small components, it was built into the connector of a printer parallel cable. Its performance was evaluated by monitoring the signals of four different instruments and similar analytical curves were obtained with the interface and from readings from the instrument' displays. Because the components are cheap (~U$35,00) and easy to get, the proposed interface is a simple and economical alternative for data acquisition in small laboratories for routine work, research and teaching.

A digital image-based flame emission spectrometric (DIB-FES) method for the quantitative chemical analysis is proposed here for the first time. The DIB-FES method employs a webcam to capture the digital images which are associated to a radiation emitted by the analyte into an air-butane flame. Since the detection by webcam is based on the RGB (red-green-blue) colour system, a novel mathematical model was developed in order to build DIB-FES analytical curves and estimate figures of merit for the proposed method. In this approach, each image is retrieved in the three R, G and B individual components and their values were used to define a position vector in RGB three-dimensional space. The norm of this vector is then adopted as the RGB-based value (analytical response) and it has revealed to be linearly related to the analyte concentration. The feasibility of the DIB-FES method is illustrated in three applications involving the determination of lithium, sodium and calcium in anti-depressive drug, physiological serum and water, respectively. In comparison with the traditional flame emission spectrometry (trad-FES), no statistic difference has been observed between the results by applying the paired t-test at the 95% confidence level. However, the DIB-FES method has offered the largest sensitivities and precision, as well as the smallest limits of detection and quantification for the three analytes. These advantageous characteristics are attributed to the trivariate nature of the detection by webcam.

A portable, microcontrolled and low-cost spectrophotometer (MLCS) is proposed. The instrument combines the use of a compact disc (CD) media as diffraction grid and white light-emitting diode (LED) as radiation source. Moreover, it employs a phototransistor with spectral sensitivity in visible region as phototransductor, as well as a programmable interrupt controller (PIC) microcontroller as control unit. The proposed instrument was successfully applied to determination of food colorants (tartrazine, sunset yellow, brilliant blue and allura red) in five synthetics samples and Fe 2+ in six samples of restorative oral solutions. For comparison purpose, two commercial spectrophotometers (HP and Micronal) were employed. The application of the t -paired test at the 95% confidence level revealed that there are not significant differences between the concentration values estimated by the three instruments. Furthermore, a good precision in the analyte concentrations was obtained by using MLCS. The overall relative standard deviation (R.S.D.) of each analyte was smaller than 1.0%. Therefore, the proposed instrument offers an economically viable alternative for spectrophotometric chemical analysis in small routine, research and/or teaching laboratories, because its components are inexpensive and of easy acquisition.

A new method for metronidazole determination, based on spectrometric monitoring of a diazonium salt produced in-line by alkaline hydrolysis released nitrite ions, was developed and successfully applied to pharmaceutical tablets (r = 0.9993, 2.0-20.0 mg L-1, DL = 0.7 mg L-1) with no interference from common ingredients accompanying the drug. Um novo método para determinação de metronidazol, baseado no monitoramento espectrométrico do sal de diazônio produzido in-line pelos íons nitrito, liberados numa hidrólise alcalina, foi desenvolvido e aplicado com sucesso a comprimidos (r = 0,9993, 2,0-20,0 mg L-1, LD = 0,7 mg L-1), sem interferência de ingredientes comumente presentes.

A microcontrolled, portable and inexpensive photometer is described. It uses six light-emitting diodes (LEDs) as radiation sources and a phototransistor as detector, as well as a microcontroller (PIC - Programmable Controller of Interruption). This device provided total autonomy to the proposed photometer, which was successfully applied to determination of Fe2+ in ferrous syrups and of seven clinical biochemical parameters. As the components are cheap (~U$30.00) and easy to find, the proposed photometer is an economical alternative for routine chemical analyses in small laboratories, for research and teaching. Being portable and microcontrolled, it allows doing field chemical analyses.

This paper proposes a digital image-based flame emission spectrometric (DIB-FES) method for indirect determination of sodium diclofenac, sodium dipyrone and calcium gluconate in injectable forms. The proposed DIB-FES method uses digital images obtained from a webcam, based on the RGB (Red-Green-Blue) system. It offers a simple and inexpensive way to quantify these organic substances using the radiation emitted by the alkaline and earth-alkaline metals present in their formulae. Analytical curves were constructed on the basis of the relationship between RGB values and calibration solution concentrations. The results showed no statistical difference between the proposed and reference methods when applying the paired t-test at a 95% confidence level. The proposed DIB-FES method also performed well in terms of the figures of merit LOD, LOQ, linear range, precision, and the accuracy as revealed by recovery tests.