Search

Photogeneration of silver chloride nanoparticles (AgCl-NPs) in fuel ethanol was used as a sensor for the spectrophotometric determination of chloride. A low-power UV radiation source (germicidal lamp) was placed close to a flow-batch chamber and a 3D-built support for the reaction chamber was used to couple fiber optic cables in the orthogonal direction with the UV-lamp beam, allowing the monitoring of nanoparticle formation in real-time using a spectrophotometer. The nanoparticles were characterized via high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and UV–vis spectroscopy. Most of the particles exhibited a spherical shape with an average diameter of 18 nm. The absorbance maximum was observed at 440 nm and was used for chloride determination in fuel ethanol. Under the optimized working conditions, the system exhibited a linear response from 0.05 to 0.8 mg L−1 chloride, with a limit of detection (95%) and coefficient of variation (n = 8) were estimated to be 12 μg L−1 chloride and 2.2%, respectively. The intra- and inter-day precisions (coefficient of variation) were 2.4% and 2.8%, respectively. This working range (0.05–0.8 mg L−1) for the determination of chloride at low concentrations met the limit required by Brazilian legislation (limit of 1.0 mg kg−1). Analyses of fuel ethanol were performed without sample treatment and the obtained results were compared with those obtained by ion-chromatography. No significant differences were observed between the two methods at the 95% confidence level.

A simple, accurate, and fast flow-batch procedure employing photometric detection for the determination of sulfate in fuel ethanol was developed. After the formation of soluble barium sulfate in alcoholic medium, the remaining barium forms a product with dimethylsulfonazo III (DMS), the absorbance of which was monitored at 655 nm directly in the reaction chamber. The proposed procedure does not require any sample treatment such as dilution. Under the optimized conditions, the technique offers the advantages of low waste generation (

Aiming at determination of anionic surfactants as milk adulterants, a novel procedure based on simultaneous protein precipitation and liquid-liquid microextraction (LLME) of the ion-pair formed between the analytes and methylene blue is described. Sample treatment, ion-pair extraction, and photometric detection with a smartphone camera were carried out in a single vessel, thus significantly simplifying the procedure and minimizing risks of contamination and analyte loss. The chloroform volume for both sample treatment and extraction of the ion-pair was only 150 μL and usual drawbacks of LLME, such as the need for phase isolation and dilution of the extract before spectrophotometric measurements were avoided. By using sodium dodecylsulfate as a model surfactant, and only 100 μL of sample, 25 μg of methylene blue, and 2.9 mg of EDTA, a linear response was achieved from 10 to 50 mg L−1, r = 0.999 (n = 5), with detection limit (99.7% confidence level) and coefficient of variation of 2.2 mg L−1 and 1.9% (n = 10), respectively. The proposed procedure is a simple, fast, cost-effective, and environmentally friendly approach for detection of milk adulterations by surfactants.

OZONE APPLICATIONS AND IMPLICATIONS FOR INDUSTRY, ENVIRONMENT, AND HEALTH. Stratospheric ozone is an efficient filter for ultraviolet radiation, which damages organisms’ lives exposed to sunlight. In the troposphere, ozone is essential to oxidate volatile organic compounds, but its effects are harmful to animals and plants, particularly humans. The high reactivity of ozone with some organic compounds makes it a promising agent for several applications, such as microbiological control and the medical field. However, their contact with surfaces containing unsaturated substances and other compounds can result in the formation of products that are harmful to human health or distort the organoleptic and structural properties of food. The results available in the literature are often divergent as to their safety and economic viability. Despite this, there are many cases of dermatological applications, and as sanitizing agents in several environments. Antiviral and bactericide properties were that guided the expansion of ozone application in the current coronavirus pandemic (COVID-19). However, more studies should be carried out to comprove its effectiveness, considering possible damages resulting from these applications.

A novel and simple electroanalytical method for the determination of Cu2+ in biodiesel samples by stripping voltammetric analysis was developed. The method employs a carbon paste electrode (CPE) modified with Vulcan carbon, previouly functionalized with carbazone (CBZ). The CPE/Vulcan-CBZ sensor promoted a significant increase in the analytical signal obtained from copper as compared to unmodified CPE, and the CPE modified with Vulcan carbon (CPE/ Vulcan). Vulcan-CBZ, Vulcan and CBZ materials were characterized by Fourier transform infrared spectroscopy (FTIR) technique. The electrochemical behavior of the sensor was evaluated using cyclic voltammetry (CV) and square-wave anodic stripping voltammetric (SWASV) techniques. The CPE/Vulcan-CBZ modified electrode showed excellent response and was able to detect Cu2+ at nanomolar levels. The electrochemical method is based on preconcentration of Cu2+ ions on the CPE/Vulcan-CBZ at 0.35 V vs. Ag/AgCl(sat) in 0.2 mol L-1 ammonium sulfate solution ((NH4)2SO4), pH 3.5, during 120 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu2+ concentrations in the range from 6 to 190 nmol L-1 (r = 0.998), with a detection limit of 1.2 nmol L-1. The sensor was successfully applied for the determination of Cu2+ in biodiesel and the average recovery varied between 97.0 and 102.8% for the soybean biodiesel samples and between 109.6 and 111.0% for the babassu biodiesel samples showing a good accuracy for the proposed method.

This work deals with a fully automated multicommuted flow analysis setup employing a homemade syringe pump for fluid propulsion and solenoid valves for solution handling, assembled to carry out photometric titrations using a homemade LED-based photometer. The data acquisition and control software was designed to perform titrations following the binary search concept, in which the course of titration is decided based on previous measurements. The operation conditions were optimized and the setup efficiency was then evaluated by analyzing samples of fruit juice, vinegar, and wine. Furthermore, in order to assess the accuracy, the samples were also analyzed using an independent method. Upon applying the paired t -test to the results, no significant differences at the 95% confidence level were observed. Other useful features are also reported, such as intraday precision of 1.2%, relative standard deviation of 0.9% for an acetic acid solution with a concentration of 0.106 mol L − 1 , and a titration range of 0.036 to 0.176 mol L − 1 .

A spot test was developed for indirect determination of iodine value in biodiesel by using digital images taken by a smartphone. The procedure is based on the iodine consumption in the halogenation reaction of unsaturated compounds in biodiesel. The remaining reagent was determined after complex formation with starch, thus circumventing the background absorption inherent to biodiesel samples. The images were captured using the cell phone camera in a paper support and converted to RGB values using free application software (PhotoMetrix® 1.1.1). The reflectance values from the red channel were inversely proportional to the color intensity because of the complementary color of the iodine-starch complex. Hexane was used for diluting a biodiesel reference sample, whose iodine value was predetermined by the Friedman method for constructing the calibration curves. A linear response was observed in the range 10–106 g I2/100 g of biodiesel, as described by the equation S = 155 + 0.722C (g I2/100 g), r = 0.990. Coefficient of variation and the detection limit were estimated as 4.9% (n = 10) and 8 g I2/100 g, respectively. The spot test consumed only 49 μg of I2 and generated 64 μL of effluent per determination. Analytical responses for biodiesel derived from different sources were in agreement, thus demonstrating the absence of matrix effects. These results agreed with those of the iodometric reference procedure at the 95% confidence level. The proposed procedure, which is the first application of a spot test for biodiesel analysis, is practical, inexpensive, and robust. Moreover, it uses less toxic chemicals and minimizes reagent amount and waste generation in relation to the usual methods for iodine value determination.

This paper describes an environmentally friendly procedure for the determination of losartan potassium (Los-K) in pharmaceuticals. The photometric method was based on the light scattering effect due to particles suspension, which were formed by the reaction of Los-K with Cu (II) ions. The method was automated employing a multicommuted flow analysis approach, implemented using solenoid mini-pumps for fluid propelling and a homemade LED based photometer. Under the optimized experimental conditions, the procedure showed a linear relationship in the concentration range of 23.2–417.6 mg L –1 ( r =0.9997, n =6), a relative standard deviation of 1.61% ( n =10), a limit of detection (3.3*σ) estimated to be 12.1 mg L –1 , and a sampling rate of 140 determinations per hour. Each determination consumed 12 µg of copper (II) acetate and generated 0.54 mL of waste.

A new approach for photometric measurements in procedures involving liquid–liquid extraction is proposed. It is based on the direct acquisition of the digital image of the sample extract in a conical tube by using a smartphone and a free application to convert the image to RGB values. The approach avoids the drawbacks of UV-vis spectrophotometric measurements caused by the restricted volume of the sample extract, such as reduction of the optical path or the need for dilution. Moreover, the need for phase isolation and thus losses of the extract before measurements is avoided. The feasibility of the procedure was demonstrated by (i) dispersive liquid–liquid microextraction aimed at the determination of anionic surfactants in freshwaters by the methylene blue (MB) method and (ii) cloud point extraction for the determination of free chlorine in tap waters by the N,N-diethyl-p-phenylenediamine (DPD) method. The values of the RGB channels were taken as the analytical signal. For the MB method, a linear response was achieved within 10.0 and 70.0 μg L−1, with a detection limit of 2.6 μg L−1. With the proposed strategy, the consumption of chloroform was 1000-fold reduced (only 100 μL is required per determination) in comparison to the conventional procedure. Good recoveries (within 87.8 and 99.7%) and agreement with the reference method were observed. The DPD method yielded a linear analytical response within 0.1 and 2.0 mg L−1, with a detection limit of 70 μg L−1, and results in agreement with the reference procedure. For both procedures, the coefficient of variation was estimated at 4.0% (n = 10).

Herein, a multicommuted flow-batch setup and a photometric procedure for the determination of mercury at the ppb level in aqueous samples are described. The setup was designed to implement a versatile solvent extraction and pre-concentration strategy by combining flow-batch and multicommuted flow analysis approaches. The photometric method was based on Hg(II) reaction with dithizone in a chloroform medium, which was also used as the extracting organic solvent. The flow analysis system was composed of a homemade syringe pump module, a set of solenoid valves, two Aquarius mini-pumps, and a flow-batch chamber. The homemade photometer was comprised of a light emitting diode (LED), photodiode, and homemade flow cell (50 mm length). The flow system and photometer were controlled using an Arduino Due board, running custom-written software. After optimizing the operational conditions, the effectiveness of the developed system was evaluated for the determination of the mercury concentration in drinking water. For accuracy assessment, samples were analyzed using a spiking methodology and an independent method, yielding a recovery ranging from 92% to 108%. Other important characteristics of the proposed method were found as follows: linear response range, 0.5–10.0 μg L−1 (r = 0.9984); limit of detection 0.38 μg L−1 Hg(II); consumption of dithizone and chloroform, 1.85 μg L−1 and 0.8 mL per analysis, respectively; coefficient of variation, 2% (n = 10); sampling throughput, 20 determinations per h.

A novel approach for the detection of hydrogen peroxide as a milk adulterant via a colorimetric spot test and smartphone-based photometry is proposed. The procedure is based on analyte oxidation of iron(II) followed by formation of a red iron(III)-thiocyanate complex. The acid medium required for complex formation doubles as a protein precipitation solution, while digital images are taken directly in disposable microtubes under controlled illumination conditions without sample pretreatment. Determination of the adulterant takes about 2 min and generates as little as 350 μL of waste per determination. A linear response was attained from 2.5 to 25.0 mg L−1, with a limit of detection of 1.7 mg L−1 at a 95% confidence level. Repeatability and reproducibility, expressed as coefficients of variation, were 4.8% and 6.8%, respectively. Due to these characteristics, along with the portability and wide availability of smartphones, the proposed method is attractive for determination of hydrogen peroxide adulterant at different stages of production chain.

An automatic titration setup exploiting flow analysis was proposed for the evaluation of the copper complexation capacity of highly opaque substances (milk and humic substances). The binary search approach was implemented in a flow-batch analyzer, in order to add the in-line selected titrant (e.g. copper ions) volumes to the sample. When the titration end-point was surpassed, the free metal ions catalyzed the reaction of luminol with hydrogen peroxide, yielding the chemiluminescence, which was quantified even in solutions of high opacity. Accuracy was assessed through addition/recovery tests involving classical complexing species (EDTA, DTPA and DTTC), and recoveries ranged from 96% to 115%. The proposed system requires low amounts of reagents and samples (0.42 mg of luminol, 82 μg H2O2, 1.10 mL of sample) per titration run, meaning ca. 12 mL of effluent per titration, and yields precise results (5% r.s.d.) at a sampling throughput of 43 h−1.

An automatic photometric titration procedure was developed to determine the acidity of fuel ethanol. The procedure was implemented by using a binary search algorithm and a multicommuted flow analysis approach. Solution-handling setup included a homemade syringe pump and a set of solenoid valves, which were assembled to treat the solution-handling as a time function controlled by a microcomputer. Photometer detection was performed using a compact homemade light emitting diode (LED)-based photometer. Aiming to evaluate the accuracy, samples were analyzed by employing the methodologies recommended by the Brazilian Association of Technical Standards (ABNT) and the American Society for Testing and Materials (ASTM). Accuracy was assessed by applying the Student’s t-test for paired samples at the 95% confidence level (n = 4), which shown that there is no significant difference between results. Other useful features included relative standard deviation of < 1% and waste generation volume ten times lower than those produced by ABNT and ASTM methods.

This paper describes a new technique for the determination of captopril in pharmaceutical formulations, implemented by employing multicommuted flow analysis. The analytical procedure was based on the reaction between hypochlorite and captopril. The remaining hypochlorite oxidized luminol that generated electromagnetic radiation detected using a homemade luminometer. To the best of our knowledge, this is the first time that this reaction has been exploited for the determination of captopril in pharmaceutical products, offering a clean analytical procedure with minimal reagent usage. The effectiveness of the proposed procedure was confirmed by analyzing a set of pharmaceutical formulations. Application of the paired t-test showed that there was no significant difference between the data sets at a 95% confidence level. The useful features of the new analytical procedure included a linear response for captopril concentrations in the range 20.0–150.0 µmol/L (r = 0.997), a limit of detection (3σ) of 2.0 µmol/L, a sample throughput of 164 determinations per hour, reagent consumption of 9 µg luminol and 42 µg hypochlorite per determination and generation of 0.63 mL of waste. A relative standard deviation of 1% (n = 6) for a standard solution containing 80 µmol/L captopril was also obtained. Copyright © 2015 John Wiley & Sons, Ltd.

This paper presents an analytical procedure for the determination of folic acid employing commutation flow analysis process and detection by chemiluminescence. The procedure is based on the reaction of hexacyanoferrate(III) with folic acid, followed of luminol oxidizing reaction in alkaline medium, resulting in emission of radiation at 425 nm. After optimization the experimental variables, the proposed procedure afforded the following useful features. A linear response ranging from 0.1 to 1.00 mg mL-1 folic acid (R2= 0.993), a detection limit (3σ criterion) 0.046 mg mL-1, a sampling rate of 156 determination per hour, a relative standard deviation less than 0.5% (n = 6) for a 0.6 mg mL->1 folic acid standard solution and a waste generation of 0.86 mL per determination.

This paper describes a procedure based on multicommutation in flow analysis system for photometric determination of hydroquinone in pharmaceutical gel formulations. The procedure involves oxidation of hydroquinone by Fe (III) and subsequent reaction between the generated Fe (II) species with 1,10-phenanthroline, producing a complex detected at 510 nm. Under optimized conditions, the proposed system showed a linear response in the range between 5 to 120 µmol L-1 (r = 0.9995), a limit of detection (3σ) 0.52 µmol L-1 and a relative standard deviation (RSD) of 1.5% for a 80 µmol L-1 hydroquinone standard solution. Others profitable features such as an analytical frequency of 72 samples per hour; a reagent consumption of 0.432 and 0.117 mg 1-10-phenantroline and FeCl3.6H2O per determination, respectively; and a waste generation of 4.0 ml per determination were also achieved.

The aims of the present study were to investigate the relationship of aerobic and anaerobic parameters with 400 m performance, and establish which variable better explains long distance performance in swimming. Twenty-two swimmers (19.1±1.5 years, height 173.9±10.0 cm, body mass 71.2±10.2 kg; 76.6±5.3% of 400 m world record) underwent a lactate minimum test to determine lactate minimum speed (LMS) (i.e., aerobic capacity index). Moreover, the swimmers performed a 400 m maximal effort to determine mean speed (S400m), peak oxygen uptake ([Formula: see text]) and total anaerobic contribution (CANA). The CANA was assumed as the sum of alactic and lactic contributions. Physiological parameters of 400 m were determined using the backward extrapolation technique ([Formula: see text] and alactic contributions of CANA) and blood lactate concentration analysis (lactic anaerobic contributions of CANA). The Pearson correlation test and backward multiple regression analysis were used to verify the possible correlations between the physiological indices (predictor factors) and S400m (independent variable) (p < 0.05). Values are presented as mean ± standard deviation. Significant correlations were observed between S400m (1.4±0.1 m·s-1) and LMS (1.3±0.1 m·s-1; r = 0.80), [Formula: see text] (4.5±3.9 L·min-1; r = 0.72) and CANA (4.7±1.5 L·O2; r= 0.44). The best model constructed using multiple regression analysis demonstrated that LMS and [Formula: see text] explained 85% of the 400 m performance variance. When backward multiple regression analysis was performed, CANA lost significance. Thus, the results demonstrated that both aerobic parameters (capacity and power) can be used to predict 400 m swimming performance.

O presente trabalho tem por objetivo despertar no aluno da educação básica, especialmente do ensino médio, a melhor compreensão da química, enquanto ciência experimental, pela realização de aulas práticas e o registro em vídeo desses experimentos. Para a maioria dos estudantes, a química é reconhecida como uma disciplina de difícil compreensão, que não desperta o interesse quanto à assimilação dos conteúdos, o que vem acarretando resultados negativos em relação à repetência e abandono por parte de uma grande quantidade de alunos matriculados na rede pública do nosso estado. Dessa forma, este trabalho apresenta a química de uma maneira diferente: aplicada, contextualizada, trabalhada pelo aluno, através de experimentos simples, rápidos, gravadas em vídeos para futuras postagens na internet ou para apresentação em sala de aula aos demais alunos da série.Palavras-chave: Química. Ensino médio. Experimentos.VIDEO PRODUCTION AS AN EDUCATION TOOL FOR HIGH SCHOOL CHEMISTRY CLASSESAbstract: This work aims at arousing in students of basic education, especially in high school students, a better understanding of chemistry as an experimental science, by conducting practical classes and video recording of those experiments. For most students, chemistry is recognized as a subject of difficult understanding, that does not arouse interest on the assimilation of the contents, which has been causing negative results regarding failure and abandonment by a large number of students enrolled in public schools of Maranhão State. Thus, this paper presents chemistry in a different way: applied, contextualized, worked by the student through simple experiments, fast, and recorded on video for future posts on the internet or for presentation in classrooms to other students in the grade.Keywords: Chemistry. High School. ExperimentsCLASES DE PRODUCCIÓN VIDEO EDUCACIÓN COMO HERRAMIENTA DE LA QUÍMICA EN LA DISCIPLINA ESCOLARResumen: Este trabajo tiene como objetivo despertar la educación básica de los estudiantes, especialmente en la educación secundaria, una mejor comprensión de la química como un experimento científico, para larealización de las clases prácticas y grabación de vídeo de estos experimentos. Para la mayoría de los estudiantes, la química es reconocido como un tema difícil de entender, no despierta el interés en la asimilación de los contenidos, que ha estado causando resultados negativos con respecto al fracaso y abandono por parte de un gran número de alumnos matriculados en las escuelas públicas de nuestro estado. Por lo tanto, este trabajo se presenta la composición química de una manera diferente: aplicada, contextualizado, elaborado por el estudiante a través de experimentos sencillos y rápidos, grabadas en vídeo para futuros posts en Internet o para su presentación en clase con otros estudiantes en el grado.Palabras clave: Química. La escuela secundaria. Experimentos.