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A green, rapid and sensitive automated analytical method with imaging detection for the determination of sulfite in vinegars using the pararosaniline (PRA)–formaldehyde–sulfite reaction is demonstrated. This work proposes the use of a flow-batch analyzer (FBA) in association with digital images (DIs) obtained from a webcam to perform fast and accurate quantification of sulfite in vinegar samples with low waste generation and high sensitivity. The FBA designed for the monitoring of the PRA–formaldehyde–sulfite reaction under non-equilibrium conditions consisted of a mixing chamber (MC) with a lateral glass window and an ultra-bright LED mounted on top of the MC. Rigorous luminosity and time control were required to acquire accurate and precise data from digital images taken during the reaction. An algorithm based on RGB norm vectors (∥νRGB∥) with gamma correction was developed for absorbance calculations. The proposed method was applied to sulfite quantification in five different vinegar samples (apple cider, distilled, lemon, and white and red wine), with iodometric titration as a comparative method. The estimated LOD was 0.04 mg L−1, with a linear range of from 0.13 to 32.7 mg L−1, recoveries were in the range 94–107%, and the sample throughput was 43 h−1 at a reaction time of 30 s. Both the proposed and reference methods were statistically compared using a paired t-test at a confidence level of 95% and the maximum standard deviation was 1.6 and 1.7 mg L−1, respectively. All of the results reported here confirm the proposed method's potential to be a very rapid, low-cost and trustworthy tool, applicable for the quality control of sulfite in a wide variety of vinegar. The low levels of reagent consumption and waste generation in the proposed method qualify the analytical procedure as environmentally friendly and in alignment with green chemistry guidelines.

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

This work proposes a simple, rapid and low-cost method for the determination of total furanic aldehyde (TFA, sum of furfural and hydroxymethylfurfural) compounds in Brazilian cachaca samples, based on liquid–liquid extraction followed by UV-vis spectrophotometry. For this, 5.0 mL of chloroform and the sample are mixed and the mixture is then stirred for 2 minutes to form an emulsion, which rests for 1 minute to complete the phase separation. An aliquot of the decanted chloroform phase is then analyzed in a quartz cell (10 mm optical path) for absorbance at 279 nm. Effects of solvent, pH, temperature, possible interferences and fraction extracted were investigated. This method is not only sensitive and accurate, with an LOQ of 0.0203 mg 100 mL−1 and recoveries in the range 101–109%, but also simple and rapid (15 h−1). The new method for TFA compounds can be a potential reference method in routine safety testing for Brazilian cachaca samples or other beverages.

In this study, a micro-flow-batch analyzer (μFBA) using an in-line cadmium reduction microcolumn for the photometric determination of nitrate and nitrite in dairy samples is described. The method is based on the Griess-Llosvay reaction and measuring of the absorbance at 540 nm using a green LED integrated into the μFBA built in the urethane-acrylate resin. Initially, the nitrite content of the dairy sample is analyzed in the mixing chamber, while the nitrate is reduced to nitrite in cadmium sponge microcolumn coupled to the microsystem. Nitrate content was calculated from the difference between nitrate plus nitrite (expressed as nitrite) and nitrite content. The analytical curve for nitrate and nitrite was linear in the work range of 10.0–100.0 μg L−1 with a correlation coefficient of 0.992 and 0.998, respectively. The limit of detection and relative standard deviation were estimated at 0.39 μg L−1 and

This paper presents a theoretical study using density functional theory (DFT) to investigate the bonding between carbon monoxide (CO) molecules and type FeN4 macrocycle complexes of iron to form FeN4–CO adducts. In order to understand how different macrocycle ligands affect this interaction, CO molecules were bound to the following complexes: iron–porphyrin (FeP), iron–tetraaza[14]annulene (FeTAA), iron–tetramethyl-tetraaza[14]annulene (FeTMTAA), iron–dibenzotetraaza[14]annulene (FeDBTAA), and iron–tetramethyl-dibenzotetraaza[14]annulenes (FeTMDBTAA1, FeTMDBTAA2). The best description of the systems investigated was provided by the Lanl2TZ(f)/6-31G⁎ basis set, which was therefore used throughout the work. Analysis of the factors influencing the CO bonding process showed that different macrocycle ligands produced adducts that were different in terms of CO bond length, total CO fragment charge, CO vibrational frequency, and CO bond order. The activity of the interaction between CO and the iron-complex was inversely proportional to the energy gap between the HOMO of the FeN4 complex and the LUMO of CO. Finally, a greater degree of back-bonding was characterized by increased occupancy of the px and py orbitals of the O atom of the CO fragment, confirming that the TAAs were more active than porphyrin, in the ascending order: FeP

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.

In this study a flow-batch analyzer (FBA) was utilized and its feasibility was demonstrated for the determination of Fe(III) in edible and lubricating oils without external pretreatment. The FBA method uses the reaction of this ion with thiocyanate in organic medium. The formed red complex was monitored by employing a light emitting diode (LED, λmax = 520 nm) and a phototransistor linked to the mixing chamber by optical fibers. All standard solutions were prepared in-line and all analytical processes were carried out by simply changing the operational parameters in FBA control software. Comparing with the reference method, no statistically significant differences were observed when applying the paired t-test at a 95% confidence level. The relative standard deviation, analytical frequency and limit of detection were estimated for both viscous matrices (edible and lubricating oils) at

In this work, a micro-flow-batch analyzer (µFBA) using webcam for spectrophotometric determination of ortho-phosphate and aluminium(III) in tap water is proposed. PO43- and Al3+ determinations were performed by employing molybdenum blue and quecertin methods, respectively. In order to build linear analytical curves, a mathematical model was used on the basis of the RGB (red, green and blue) values. Working ranges were from 25 to 500 µg L-1 for both analytes with estimated limits of detection, relative standard deviation (RSD, n = 5) and sampling rate of 0.82 µg L-1, < 0.8% and 160 h-1 for PO43-, and 0.93 µg L-1, < 1.1% and 160 h-1 for Al(III). Comparing with the reference methods, no statistically significant differences were observed when applying the paired t-test at a 95% confidence level. Recovery study shows results between 98.1 and 102.8%. The proposed µFBA presented satisfactory portability, robustness, flexibility, low-cost device and reduced chemicals consumption.

In this study, a micro-flow-batch analyzer (μFBA) with solenoid micro-pumps for the photometric determination of iodate in table salt is described. The method is based on the reaction of iodate with iodide to form molecular iodine followed by the reaction with N,N-diethyl-p-phenylenediamine (DPD). The analytical signal was measured at 520 nm using a green LED integrated into the μFBA built in the urethane-acrylate resin. The analytical curve for iodate was linear in the range of 0.01-10.0 mg L(-1) with a correlation coefficient of 0.997. The limit of detection and relative standard deviation were estimated at 0.004 mg L(-1) and

An automatic method for kinetics independent spectrometric analysis is proposed in this study. It uses a non-linear calibration model that explores concentration gradients generated by a flow-batch analyser (FBA) for the samples, dye, and the single standard solution. The procedure for obtaining the gradients of the dye and standard solution is performed once at the beginning of analysis. The same procedure is applied thereafter for each sample. For illustration, the proposed automatic methodology was applied to determine total protein and albumin in blood serum by using the Biuret and Bromocresol Green (BCG) methods. The measurements were made by using a laboratory-made photometer based on a red and green bicolour LED (Light-Emitting Diode) and a phototransistor, coupled to a "Z" form flow cell. The sample throughput was about 50 h(-1) for albumin and 60 h(-1) for total protein, consuming about 7 microL of sample, 2.6 mL of BCG and 1.2 mL of biuret reagents for each determination. Applying the paired t-test for results from the proposed analyser and the reference method, no statistic differences at 95% confidence level were found. The absolute standard deviation was usually smaller than 0.2 g dL(-1). The proposed method is valuable for the determination of total protein and albumin; and can also be used in other determinations where kinetic effects may or may not exist.

The study proposes a low cost and very simple quantitative spot test technique for determination of soluble tannin in green tea samples using a portable diffuse reflectometer. The lab-made instrument was made of polytetrafluoroethylene (PTFE), using a light emitting diode (LED) for its light source, and a phototransistor as the detector. The proposed method measured diffuse reflectance from a complex formed by reaction between soluble tannin and ferrous tartrate in a buffered medium at pH 6.8. The spot test is a reliable and advantageous alternative technique because it uses fewer chemicals than the reference method. The study obtained good limits of detection (0.11 mg L−1), and precision (RSD = 0.9%), and at a 95% confidence level (paired t-test) no statistically significant difference between the results of either method was found.