Determination of nitrate in lettuce by ion chromatography after microwave water extraction

Lettuce is worldwide known as the most important vegetable. In this context, most farmers are searching new techniques for best quality products including hydropony. However, nitrate is of great concern, since it has a negative impact on human metabolism. The main objective of the present work was to evaluate the nitrate content of lettuce produced by conventional and hydroponic systems. The determination was conducted by ion chromatography and a new method of extraction was tested using microwave oven digestion. The results indicated that nitrate level produced in the conventional system was lower than in the hydroponic system.

MSPD procedure combined with GC-MS for the determination of procymidone, bifenthrin, malathion and pirimicarb in honey

A method based on matrix solid-phase dispersion and gas chromatography-mass spectrometry to determine procymidone, malathion, bifenthrin and pirimicarb in honey is described. The best results were obtained using 1.0 g of honey, 1.0 g of silica-gel as dispersant sorbent and acetonitrile as eluting solvent. The method was validated by fortified honey samples at three concentration levels (0.2, 0.5 to 1.0 mg kg-1). Average recoveries (n=7) ranged from 54 to 84%, with relative standard deviations between 3.7 and 8.5%. Detection and quantification limits attained by the developed method ranged from 0.02 to 0.08 mg kg-1 and 0.07 to 0.25 mg kg-1 for the honey, respectively.

Adsorção de arsênio(V) pelo compósito magnético hidrotalcita: óxido de ferro

In this work, hydrotalcite, a layered double hydroxide, had its adsorption and ion exchange properties combined with the magnetic properties of iron oxide to produce a magnetic adsorbent, HT-Fe. The removal of As(V) by a HT-Fe adsorbent was evaluated under various conditions. The Kinetic process was well described by a pseudo-second order rate model. The maximum adsorption capacity, calculated with the Langmuir model showed to be dependent on pH, reaching values of 24.09, 10.19 and 7.44 mg g-1, respectively, for pH values of 4.0, 7.0 and 9.0. The inhibition by competition of anions is dependent on the type of ionic species.

Ion pair-dispersive liquid-liquid microextraction of trace amount of rhodium ion in water and road dust samples prior to flame atomic absorption spectrometry determination

A simple ion pair-dispersive liquid-liquid microextraction method was proposed for preconcentration trace amounts of rhodium. An ion association complex of RhCl4- and tetradecyldimetylbenzylamonium was extracted into cholorobenzene. The volume and the type of extractive and dispersive solvents, the extraction time and the pH of the aqueous solutions were optimized. The calibration curve was linear in the range of 0.6-500 ng mL-1 of rhodium. The limit of detection was 0.10 ng mL-1 in initial solution and preconcentration factor was 40. The proposed method was successfully applied to the extraction and determination of rhodium in road dust and water samples.

Combined experimental powder X-ray diffraction and DFT data to obtain the lowest energy molecular conformation of friedelin

Friedelin molecular conformers were obtained by Density Functional Theory (DFT) and by ab initio structure determination from powder X-ray diffraction. Their conformers with the five rings in chair-chair-chair-boat-boat, and with all rings in chair, are energy degenerated in gas-phase according to DFT results. The powder diffraction data reveals that rings A, B and C of friedelin are in chair, and rings D and E in boat-boat, conformation. The high correlation values among powder diffraction data, DFT and reported single-crystal data indicate that the use of conventional X-ray diffractometer can be applied in routine laboratory analysis in the absence of a single-crystal diffractometer.

Remoção de cromo (VI) de soluções aquosas utilizando o compósito magnético calcinado hidrotalcita-óxido de ferro: estudo cinético e de equilíbrio termodinâmico

In this work, hydrotalcite, a layered double hydroxide, had its ion exchange properties combined with the magnetic properties of iron oxide to produce a magnetic adsorbent, HT-Fe 500. These magnetic composites can be used as adsorbents for anionic contaminants in water and subsequently removed from the medium by a simple magnetic process. Removal of chromium (VI) from aqueous solutions using HT-Fe 500 was achieved using batch adsorption experiments. The adsorption capacity, calculated with the Langmuir-Freundlich model showed to be dependent on temperature, reaching values of 25.93 and 48.31 mg g-1, respectively, for temperatures of 25 and 30 ºC.

Preparative separation and purification of bufadienolides from ChanSu by high-speed counter-current chromatography combined with preparative HPLC

Eight bufadienolides were successfully isolated and purified from ChanSu by high-speed counter-current chromatography (HSCCC) combined with preparative HPLC (prep-HPLC). First, a stepwise elution mode of HSCCC with the solvent system composed of petroleum ether - ethyl acetate - methanol - water (4:6:4:6, 4:6:5:5, v/v) was employed and four bufadienolides, two partially purified fractions were obtained from 200 mg of crude extract. The partially purified fractions III and VI were then further separated by prep-HPLC, respectively, and another four bufadienolides were recovered. Their structures were confirmed by ESI-MS and ¹H-NMR spectra.

Synthesis, characterization and application of ion imprinted poly(vinylimidazole) for zinc ion extraction/preconcentration with faas determination

In this paper, we describe the synthesis of an ion imprinted polymer (IIP) by homogeneous polymerization and its use in solid-phase to extract and preconcentrate zinc ions. Under optimal conditions (pH 5.0, preconcentration flow rate of 12.0 mL min-1, and eluted with 1.0 mol L-1 HNO3) this procedure allows the determination of zinc with an enrichment factor of 10.2, and with limits of detection and quantification of 1.5 and 5.0 µg L-1, respectively. The accuracy of our results was confirmed by analysis of tap water and certified reference materials: NIST 1570a (Spinach leaves) and NIST 1515 (Apple leaves).

Potentiometric determination of Nickel (II) ion using 2-hydroxy-1-naphthylidene-N-cyanoacetohydrazone as electroactive material

A potentiometric Nickel sensor was prepared using 2-hydroxy-1-naphthylidene-N-cyanoacetohydrazone as electro-active material and epoxy resin as a binding material. A membrane composed of 40% Schiff's base and 60% epoxy resin exhibited the best performance. The membrane showed excellent response in the concentration range of 0.15 ppm to 0.1 mol L- 1 Ni+2 ions with non-Nernstian slope of 22.0 mV/decade, had a rapid response time (less than 10 s), and can be used for three months without any considerable loss of potential. The sensor was useful within the pH range of 1.3 to 9.6, and was able to discriminate between Ni2+ and a large number of alkaline earth and transition metal ions. The practical utility of the sensor has been demonstrated by using it successfully as an indicator electrode in the potentiometric titration of Ni2+ with EDTA and oxalic acid.

Separation and purification of three stilbenes from the radix of Polygonum cillinerve (Nakai) Ohwl by macroporous resin column chromatography combined with high-speed counter-current chromatography

An effective method for the rapid separation and purification of three stilbenes from the radix of Polygonum cillinerve (Nakai) Ohwl by macroporous resin column chromatography combined with high-speed counter-current chromatography (HSCCC) was successfully established. In the present study, a two-phase solvent system composed of chloroform-n-butanol-methanol-water (4:1:4:2, v/v/v/v) was used for HSCCC separation. A one-step separation in 4 h from 150 mg of crude extract produced 26.3 mg of trans-resveratrol-3-O-glucoside, 42.0 mg of pieceid-2"-O-gallate, and 17.9 mg of trans-resveratrol with purities of 99.1%, 97.8%, and 99.4%, respectively, as determined by high-performance liquid chromatography (HPLC). The chemical structures of these compounds were identified by nuclear magnetic resonance (NMR) spectroscopy.

Determination of Mn2+ ion by solution scanometry as a new, simple and inexpensive method

In this research, scanometry was used as a new, simple, fast and inexpensive method for a colorimetric determination of Mn2+ ion in water samples and thermocouple wire through the use of periodate reagent in an acidic medium. The results showed the oxidization of colorless Mn2+ ion by periodate and the formation of a purplish MnO4- ion. The system had a linear range of 1.0 to 70.0 µg mL-1 Mn2+ ion with a detection limit of 0.314 µg mL-1 and a relative standard deviation of 2.77% for G color value. This method has the capability to determine low levels of Mn2+ ion in thermocouple wire and water samples.

Uses of nitrate ion sensitive electrodes

Some models of ion-selective electrodes (ISE) and other methods have been elaborated, to quantify nitrate levels in environmental samples (water, fruits, vegetables and others), using direct potentiometry

Combined electromagnetic and thermal design platform for totally enclosed induction machines

The aim of the thesis is to design a suitable thermal model that can be used as a tool for constructing the TEFC squirrel cage induction machine in addition to the electromagnetic model. A lumped-parameter thermal model is developed. The related problems and aspects of implementation are discussed in details. Losses are calculated analytically and the loss values are used in the thermal model. The sensitivity analysis is introduced to determine the most critical parameters of the model.

Voimalaitos- ja jätevesitutkimus

Tässä työssä tutkittiin Stora Enso Oyj:n Heinolan Flutingtehtaan voimalaitos- ja jätevesien seuranta-analyysimenetelmien kehittämistä. Käytössä olevia menetelmiä vertailtiin vaihtoehtoisiin uusiin menetelmiin, jotka perustuvat erotustekniikoihin ja automaatioon. Flutingtehtaalla nykyisin käytössä olevat analyysimenetelmät perustuvat suurelta osin standardimäärityksiin, joissa käytetään pääasiassa titrausta. Määritykset vievät paljon aikaa, koska titraukset toteutetaan manuaalisesti. Titrausten päätepisteet tulkitaan esim. indikaattorin värinmuutoksella ja saostamalla, joten määritysten tarkkuus vaihtelee. Kokeellisessa osassa Flutingtehtaan puhtaista voimalaitosvesistä yhdistetty sekoitenäyte analysoitiin kahdella ionikromatografilla, liekkiatomiabsorptiospektrometrillä ja kapillaarielektroforeesilla. Yksittäisiä näytteitä ei tutkittu. Lisäksi vesilaboratoriossa määritettävistä jätevesistä yhdistettiin sekoitenäyte, joka analysoitiin kapillaarielektroforeesilla. Samat sekoitenäytteet analysoitiin myös nykyisillä menetelmillä tehtaan vesilaboratoriossa. Tulokset osoittivat, että kokeellisessa osassa tutkitut menetelmät soveltuvat sekoitenäytteen perusteella hyvin vesilaboratoriossa käytössä oleviin kuukausianalyyseihin. Automaattisella näytteensyötöllä varustettuna kaikki kolme kokeellisessa osassa tutkittua menetelmää ovat yksikertaisia käyttää ja ne nopeuttavat analyysejä. Päivittäisiä titrausanalyysejä voidaan tehostaa ja nopeuttaa automaation avulla. Erotustekniikoilla esimerkiksi typpi voidaan määrittää kokonaistyppenä, mutta myös komponentteinaan eli ammoniakkina, nitraattina ja nitriittinä. Lisäksi samalla erotuksella voidaan määrittää useita alkali- ja maa-alkalimetalleja sekä raskas-metalleja toistomittauksilla. Menetelmän käyttöalue on laajempi erotustekniikoilla kuin perinteisillä liuoskemian mittauksilla. Erotustekniikoilla tunnistetaan helposti määritysten oikeellisuus detektointimahdollisuuksien monipuolisuuden vuoksi.