Synthesis of highly fluorescent carbon dots from lemon and onion juices for determination of riboflavin in multivitamin/mineral supplements.

In this work, lemon and onion biomasses commonly found in street markets are for the first time used to develop a facile, fast and low-cost one-step microwave-assisted carbonization method for synthesis of highly fluorescent carbon dots (CDs). The structure and optical properties of CDs were investigated by TEM, XRD, XRF, UV-Vis, FTIR, and fluorescence spectroscopy. CDs displayed satisfactory optical proprieties, a high quantum yield of 23.6%, and excellent water solubility, and the particle size was 4.23-8.22 nm with an average diameter of 6.15 nm. An efficient fluorescent resonance energy transfer (FRET) between the CDs and riboflavin was achieved with CDs acting as donor and riboflavin as acceptor. A linear relationship between FRET and the riboflavin concentration from 0.10 to 3.0 µg/mL was observed, allowing the development of an accurate and fast analytical method to determine this vitamin in multivitamin/mineral supplements. Despite the potential interferences in these supplements, CDs were selective for riboflavin under optimized conditions. A paired t-test at a 95% confidence level indicated no statistically significant difference between the proposed and the reference methods. Recovery test presented values ranged from 96.0% to 101.4%. The limit of detection and relative standard deviation were estimated at 1.0 ng/mL and <2.6% (n = 3), respectively. CDs were successfully synthesized in a domestic microwave oven (1450 W, 6 min), presenting satisfactory parameters when compared with results of other studies reported in the literature, suggesting that the proposed method is a potentially useful method for the synthesis of CDs and determination of riboflavin.

A robotic magnetic nanoparticle solid phase extraction system coupled to flow-batch analyzer and GFAAS for determination of trace cadmium in edible oils without external pretreatment.

A lab-made magnetic-mechanical robotic (MMR) system coupled to a flow-batch analyzer (FBA) for magnetic nanoparticles solid phase extraction (MSPE) is presented. As an illustrative application, an NMR-FBA couple was connected to a graphite furnace atomic absorption spectrometer (GFAAS) for quantification of trace cadmium in edible oils. Factors affecting MSPE, such as the amount of adsorbent, the type, concentration and volume of the eluent and elution time were studied. Under the optimized experimental conditions, the interferents studied did not reveal a significant change in the analytical response, indicating that proposed method is selective. The sampling rate, characteristic mass, working linear range, limits of detection (LOD), and sensitivity were 10h-1, 0.18pg, 0.05-1.0µgkg-1, 0.006µgL-1, and 0.4197, respectively. An enrichment factor of 9 was achieved using a 2.5mL oil sample. In order to evaluate the accuracy, a certified reference material was analyzed by the proposed and a reference method. The values obtained were compared with the one provided from the manufacturer and no statistically significant differences were observed among three values at a confidence level of 95% using paired t-test. In addition, the precision intra-day and inter day of the proposed method and the robustness were assessed and again no statistically significant differences were observed at a confidence level of 95%. The use of a microcolumn to immobilize the MNPs is not needed with the proposed MMR-FBA-GFAAS system, thus avoiding the well-known problem of non-uniform packing of the MNPs presented in previous flow-based automatic methods. Despite a high organic load of edible oils, the method developed is simple, robust and presents satisfactory analytical features when compared with others that have been reported in the literature, suggesting that it is a potentially useful alternative to determine trace analytes in viscous matrices without external pretreatment.

A micro-flow-batch analyzer with solenoid micro-pumps for the photometric determination of iodate in table salt.

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<1.5% (n=3), respectively. The accuracy was assessed through recovery test (97.6-103.5%) and independent analysis by a conventional titrimetric method. Comparing this technique with the conventional method, no statistically significant differences were observed when applying the paired t-test at a 95% confidence level. The proposed microsystem using solenoid micro-pumps presented satisfactory robustness and high sampling rate (170 h(-1)), with a low reagents consumption and a low cost to build the device. The proposed microsystem is a new alternative for automatic determination of iodate in table salt, comparing satisfactory to the recently flow system.

Photometric determination of phosphorus in mineralized biodiesel using a micro-flow-batch analyzer with solenoid micro-pumps.

A method for the determination of phosphorus in mineralized biodiesel using a micro-flow-batch analyzer (µFBA) with solenoid micro-pumps was proposed. The samples were mineralized using an ashing procedure at 550 °C followed by dissolution of the residue. The determination of phosphorus was performed by employing the well-known molybdenum blue method. The measures of the absorbance were performed at 850 nm using an InfraRed LED integrated into the µFBA. Comparing with the reference method, no statistically significant differences were observed when applying the paired t-test at a 95% confidence level. Recovery study shows results between 97.9% and 105.8%. The proposed microsystem using solenoid micro-pumps presented satisfactory robustness and high sampling rate (190 h(-1)), with satisfactory reproducibility (relative standard deviation <4.5%, n=3), low reagents consumption (32 µL per analysis) and cost to build the device. Moreover, µFBA presents limit of detection (0.014 mg Kg(-1)), precision and accuracy compatible with the biodiesel regulations that establish a maximum concentration of 10 mg Kg(-1) (Brazil, USA, EU), suggesting that it is a good alternative for the determination of phosphorus in biodiesel.

A monosegmented flow-batch system for slow reaction kinetics: spectrophotometric determination of boron in plants.

This work introduces the monosegmented flow-batch (MSFB) analysis concept. This system combines favourable characteristics of both flow-batch and the monosegmented analysers, allowing use of the flow-batch system for slow reaction kinetics without impairing sensitivity or sampling throughput. The MSFB was evaluated during spectrophotometric determination of boron in plant extracts, which is a method that involves a slow reaction between boron and azomethine-H. All calibration solutions were prepared in-line, and all analytical processes completed by simply changing the operational parameters in the MSFB control software. The limit of detection was estimated at 0.008 mg L(-1). The measurements could be performed at a rate of 120 samples per hour with satisfactory precision. The proposed MSFB was successfully applied to analyse 10 plant samples and the results are in agreement with the reference method at a 95% level of confidence.

Automatized flow-batch method for fluorescent determination of free glycerol in biodiesel samples using on-line extraction.

An automatic method, based on flow-batch (FB), for determining glycerol in biodiesel was developed. The FB systems draw upon the useful features of flow, batch and multi-commutation approaches. The standards and samples preparation, as well as, derivatization and analysis were fully automated. For that purpose, a homemade chamber was built. The proposed method is based on liquid-liquid extraction of glycerol and simultaneous oxidation with periodate, generating formaldehyde that reacts with acetylacetone. A fluorescent product of 3,5-diacetyl-1,4-dihydrolutidine was obtained. The fluorescence signal was recorded at λ(ex) =417 nm and λ(em) = 514 nm. A linear response was observed from 0.10 to 5.00 mg L(-1) glycerol, variation coefficient 1.5%, sampling rate 14 h(-1) and detection limit 0.036 mg L(-1) glycerol. The procedure was successfully applied to the analysis of biodiesel samples, and the results agreed with the reference method (ASTM D6584-07) at 95% confidence level.

Turbidimetric and photometric determination of total tannins in tea using a micro-flow-batch analyzer.

Both turbidimetric and photometric determinations of total tannins in samples of green and black tea, using a micro-flow-batch analyzer (µFBA) were studied. The miniaturized system was formed using photocurable urethane-acrylate resin and ultraviolet lithography technique. The turbidimetric method was based on the precipitation reaction of Cu (II) with tannins in acetate medium at a pH of 4.5. The photometric method was based on the complexation reaction of tannins with ferrous tartrate. The turbidimetric µFBA was able to test 200 samples per hour. The photometric µFBA allowed 300 analyses per hour, generating 136µL of residue per analysis. The paired t test, at a 95% confidence level, showed no statistically significant differences between results obtained by both methods and the reference method. The urethane-acrylate µFBA maintained satisfactory physical and chemical properties, and represents an improvement over conventional flow-batch analyzer.

Flow-batch miniaturization.

This study introduces the first micro-flow-batch analyzer (µFBA). A simple, low-cost, deep urethane-acrylate photo-resist ultraviolet-lithographic technique was used in its development. Details of the microfabrication process are presented including; the use of two superimposed photo-masks to improve the micro-channel and stop chamber border definition, as well as integration of an LED/phototransistor photometric pair, while using an open nylon-thread (fishing line) micro-mixing system for solutions homogenization. The system was used for photometric determination of Fe(II) in oral solution iron supplements employing the well-known 1,10-phenanthroline method, with instantaneously prepared micro-chamber calibration solutions. All analytical processes were accomplished by simply changing the timing parameters in the control software. It must be emphasized here that there was no outside preparation of the standard calibration solutions; the mixing was all done in-chamber/in-line, with all solutions maintained flowing while being proportioned for the measurement processes. The µFBA results were acceptable when compared to the reference method, and comparable to normal flow-batch systems. It was possible both to project and build a low-cost probe with high sample throughput (about 120 h(-1)), low relative standard deviations (about 1.1%), and reduced reagent consumption (30 times less than the reference method). The µFBA system based on urethane-acrylate presented satisfactory physical and chemical properties while keeping the flexibility, versatility, robustness, and multi-task characteristics of normal flow-batch analyzers. The µFBA system contributes to the advance of micro-analytical instrumentation, while realizing the basic principles of "Green Chemistry".