José Lima

Multicommutation in flow analysis. Part 1. Binary sampling: concepts, instrumentation and spectrophotometric determination of iron in plant digests

Abstract A novel strategy to handle sample and reagent introduction in continuous flow systems is proposed. Basic features such as the effect of flow cell volume, analytical pathlength and peristaltic pump pulsation on the precision of measurement were studied. The manifold was based on a set of three-way solenoid valves controlled by a microcomputer using software written in QuickBASIC. It could also control the rotation speed of the peristaltic pump. By sampling slugs of sample and reagent solutions synchronized with pulsation of the peristaltic pump, aliquots with volumes as low as 2 μl could be sampled with a relative standard deviation

Novel resveratrol nanodelivery systems based on lipid nanoparticles to enhance its oral bioavailability

Video abstract Video

In vitro scavenging capacity of annatto seed extracts against reactive oxygen and nitrogen species.

Bixa orellana L. (annatto), from Bixaceae family, is a native plant of tropical America, which accumulates several carotenoids (including bixin and norbixin), terpenoids, tocotrienols and flavonoids with potential antioxidant activity. In the present study, the in vitro scavenging capacity of annatto seed extracts against reactive oxygen species (ROS) and reactive nitrogen species (RNS) was evaluated and compared to the bixin standard. Annatto extracts were obtained using solvents with different polarities and their phenolic compounds and bixin levels were determined by high performance liquid chromatography coupled to diode array detector. All annatto extracts were able to scavenge all the reactive species tested at the low μg/mL range, with the exception of superoxide radical. The ethanol:ethyl acetate and ethyl acetate extracts of annatto seeds, which presented the highest levels of hypolaetin and bixin, respectively, were the extracts with the highest antioxidant capacity, although bixin standard presented the lowest IC(50) values.

Sample preparation in sequential injection analysis. Spectrophotometric determination of total phosphorus in food samples

Abstract A sequential injection (SI) procedure involving in-line sample preparation is proposed. A natural suspension or a slurry is transported together with nitric acid towards a home-made digestion bomb placed inside a microwave oven for subsequent digestion. The sample zone is stopped inside the oven and, after digestion, directed in reverse flow towards a holding coil and then towards detection. This is a good strategy because the SI system is versatile; the formed air bubbles are efficiently disposed of, thus avoiding the need for a debubbling unit, and the digestion bomb acts also as a mixing device promoting easy homogenization regardless of the number of required reagents. As application, the spectrophotometric determination of total phosphorus in foodstuffs based on the molybdenum blue method was selected. The proposed system is very robust and yields reproducible measurements, (r.s.d. usually −1 P–PO 4 . Results are in agreement with a conventional spectrophotometric procedure involving manual sample digestion.

Development of a tubular periodate electrode for flow-injection determination of glycerol

Periodate electrodes without inner reference solution based on tetraoctylammonium periodate plus solvent mediator (dibutyl phthalate or 2-nitrophenyl octylether) were constructed. Linear dynamic range, practical detection limit, slope, stability, selectivity coefficients, pH dependence, response time and lifetime were evaluated. A tubular version was further developed and coupled to a flow-injection system for glycerol determination in samples relevant to the industrial production of soaps, detergents and similar. The method involves glycerol oxidation by periodate with potentiometric evaluation of its consumption. The influence of oxidizing agent concentration (10(-5)-10(-2)M NalO(4)), ionic strength (0.0-1.0M Na(2)SO(4)) and mean resident time were investigated and the feasibility of using a single-fine manifold was discussed. The proposed system handles about 40 samples/hr, is very stable and suitable to industrial control. Results within the 1000 and 5000 mg/l range glycerol are precise (r.s.d. <0.005) and in fair agreement with conventional procedures. Baseline drift or noise is not observed and a thermostat water bath is not required. A noteworthy feature is the almost linear relationship between glycerol concentration and recorded peak height which is a consequence of combined effects of reaction kinetics and electrode Nernstian response.

Simultaneous determination of total iron and chromium(VI) in wastewater using a flow injection system based on the sandwich technique

A flow injection system for the simultaneous determination of total Fe and CrVI based on the sandwich technique is described. Both metals were determined spectrophotometrically at 526 nm with a single detector over the range 0.2–10 p.p.m. The sampling frequency achieved was 60 samples h–1 and the standard deviations were 0.09 and 0.08 p.p.m. for total Fe and CrVI, respectively.

Evaluation of digestion procedures for simultaneous determination of Ca, P, Mg, K and Na in biodiesel by inductively coupled plasma optical emission spectrometry

In the present work, the efficiency of two procedures for the digestion of biodiesel was investigated for the simultaneous determination of Ca, P, Mg, K and Na by axial view ICP OES. In the open system with conventional heating, concentrated nitric and sulfuric acids were added to the samples, and the addition of hydrogen peroxide completed the digestion. In the microwave-assisted closed system, complete digestion was performed using concentrated nitric acid and hydrogen peroxide. The analytical performances were evaluated through limits of quantification, precision of the overall procedures, final acidity of the digests, and residual carbon contents. The contents of residual carbon for the biodiesel samples digested were 0.358 ± 0.012% using the open system with conventional heating and 0.614 ± 0.023% using the microwave-assisted closed vessel system, demonstrating the high efficiency of both proposed procedures. The optimized microwave-assisted decomposition procedure produced the fastest, safest and most accurate analytical results with recoveries of 89.0-103.0% and deviations lower than 5% in most cases. Low limits of detection were obtained (< 0.40 µg g-1), adequate for the established limits set out in Brazilian legislation for these analytes. Three biodiesel samples produced from different oil sources were analyzed. In comparison with other procedures proposed in the literature, the developed procedure using the microwave-assisted closed system is advantageous because it neither require organic standard solutions for calibrations nor use toxic organic solvents.

Multi-site detection in flow analysis: Part 2. Monosegmented systems with relocating detectors for the spectrophotometric determination of boron in plants

Monosegmented systems with detector relocation are proposed. The sample is injected with an air plug positioned at its tailing portion in order to minimize dispersion. After the peak maximum, the detector is displaced from its original position, allowing the air phase to be discarded without flowing through it. The sample portion inside the detector is either trapped or pushed towards waste. The advantages and limitations of the approach are described, and the need for an optional washing stream is discussed. As an application, an improved system for the spectrophotometric determination of boron is plants is proposed. Four samples are simultaneously processed at a sampling frequency of 120 h−1. With a low reagent consumption (0.52 mg of Azomethine-H per determination), the system yields precise results (R.S.D. < 3%), in agreement with those given by inductively coupled plasma atomic emission spectrometry.

Sequential determination of calcium and nitrate ions in waters by potentiometric flow injection

A compact and robust flow injection system for the simultaneous determination of calcium and nitrate in waters, with sequential detection by potentiometric sensors, is described. The effects of silver ionic strength adjuster (ISA) or lead ISA carrier solutions on the response of the tubular electrodes used and on the ability of the system to control interferences were studied in detail. Under the selected experimental conditions, the response slope and lower limit of linear response were 53.4 mV per decade and 10–4.3 mol l–1 for the nitrate sensor and 31.3 mV per decade and 10–4.75 mol l–1 for the calcium sensor. The reproducibility (relative standard deviation) was better than 1% and the sample throughput was approximately 145 h–1. The results provided by the flow system were shown to be accurate, reproducible and free from interferences. The results obtained for calcium and nitrate in 23 samples with the flow injection system and with a reference method were in good agreement with each other. No significant interferences from other ions, especially chloride and hydrogencarbonate, were observed in surface waters, excluding those with a high saline content. The sequential method described was shown to be useful in routine determinations with a high sampling rate at a low cost.

Realistic simulation of a Lego Mindstorms NXT based robot

This paper describes the realistic simulation of a Lego Mindstorms NXT based robot. The presented approach does not replace the training with hardware but is an important complement, since it allows to develop robot software without accessing to the real hardware.