Flow injection spectrofluorimetric determination of cystine and cysteine

A relatively simple and sensitive procedure with spectrofluorimetric detection was developed for the determination of cystine and cysteine by flow injection system with sequential determination. This method is based on the reduction of Tl(III) with cysteine in acidic media, producing a fluorescence reagent, TlCl3(2-) (λex = 227 nm, λem = 419 nm). Before injection, the sample solution was divided into two streams. The first stream was treated with Cd reduction column and then joined with the carrier to react with Tl(III) at pH 5.0 and then passed through a 100 cm reaction coil to the flow cell of the spectrofluorimeter, where the fluorescence intensity was measured (λex = 227 nm, λem = 419 nm). This signal is related to cystine and cysteine concentrations. The second stream of sample solution was injected directly into the carrier stream to react with the reagents and then passed through the reaction coil and detector for measuring the fluorescence intensity. The signal in this step is related only to cysteine. Thus, the cystine content was determined directly from difference of the two signals. Cystine and cysteine can be determined in the range of 0.10 to 5.50 µmol L-1 and 0.20 to 8.0 µmol L-1, respectively, at a rate of 20 samples per hour. The limit of detection (3s/k) was 0.10 µmol L-1 for both analytes. The relative standard deviations for ten replicates determination of 4.0 and 3.5 µmol L-1 cystine or cysteine were 1.1% and 1.8%, respectively. The influence of potential interfering substances was studied. The proposed method was successfully applied to the sequential determination of both analytes in pharmaceutical samples

Study on the interaction between morin-bi(III) complex and DNA with the use of methylene blue dye as a fluorophor probe

Based on our investigation, although both morin-Bi(III) complex and morin can bind to DNA, the nature of the binding was found to be different for each of them. In the presence and absence of the DNA, the morin-Bi(III) complex shows different spectral characteristics which agree with those observed for other intercalators. In this work, the interaction of morin-Bi(III) complex with calf thymus DNA was investigated with the use of methylene blue (MB) dye as a spectral probe and application of UV-Vis spectrophotometry, fluorescence spectroscopy and cyclic voltammetry. The 2:1 morin-Bi(III) complex ratio was calculated by UV-Vis spectroscopy (mole ratio method). The fluorescence signal of Bi(III)-morin complex is increased with DNA addition whereas the fluorescence signal of Morin is decreased with DNA addition. The fluorescence signal of the DNA-complex is quenched by addition of MB which confirms the displacement of the complex with MB. Cyclic voltammetry studies confirm the intercalation reaction. The results showed that only morin-Bi(III) complex can intercalate into the double helix of the DNA. The apparent binding constant of morin-Bi(III) complex with DNA is found to be 2.8 × 10(4) L mol-1, while morin binds in a non-intercalation mode

Thionine-functionalized graphene oxide nanosheet as an efficient electrocatalyst for NADH oxidation and H2O2 reduction

Thionine-functionalized graphene oxide (Th-GO) has been successfully prepared for use as an efficient electrocatalyst in the electrochemical detection of hydrogen peroxide and nicotinamide adenine dinucleotide (NADH), and subsequently characterized by FT-IR spectroscopy, X-ray diffraction, transmission and scanning electron microscopy, and electrochemical methods. Electrochemical studies reveal that the carbon paste electrode modified with Th-GO decreases the working potentials to 0.24 V and 0.00 V towards oxidation of NADH and reduction of H2O2, respectively. Two linear ranges of 2.0–200 µmol L–1 and 200–500 µmol L–1 and a detection limit of 0.43 µmol L–1 have been obtained for NADH analysis. These quantitative data for H2O2 determination are 2.0–3500 µmol L–1 and 1.3 µmol L–1 respectively. Th-GO/CPE shows satisfactory results in terms of repeatability, reproducibility, and selectivity towards NADH and H2O2 analysis in both buffer and real sample

A new and sensitive reaction rate method for spectrophotometric determination of trace amounts of thiourea in different water samples based on an induction period

BACKGROUNDAgrilus bigutattus (Fabricius) is a forest pest of increasing importance in the United Kingdom. The larvae damage weakened native oaks and are thought to contribute to premature tree death. Suspected links with acute oak decline (AOD) are not yet confirmed, but AOD-predisposed trees appear to become more susceptible to A. biguttatus attack. Thus, management may be necessary for control of this insect. To explore the possibility of monitoring beetle populations by baited traps, the host tree volatiles regulating A. biguttatus-oak interactions were studied. RESULTSBiologically active volatile organic compounds in dynamic headspace extracts of oak foliage and bark were identified initially by coupled gas chromatography-electroantennography (GC-EAG) and GC-mass spectrometry (GC-MS), and the structures were confirmed by GC coinjection with authentic compounds. Of two synthetic blends of these compounds comprising the active leaf volatiles, the simpler one containing three components evoked strongly positive behavioural responses in four-arm olfactometer tests with virgin females and males, although fresh leaf material was more efficient than the blend. The other blend, comprising a five-component mixture made up of bark volatiles, proved to be as behaviourally active for gravid females as bark tissue. CONCLUSIONSThese initial results on A. biguttatus chemical ecology reveal aspects of the role of attractive tree volatiles in the host-finding of beetles and underpin the development of semiochemically based surveillance strategies for this forest insect. (c) 2015 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry

pSESYNTH project: Community mobilization for a multi-disciplinary paleo database of the Global South

How to enhance paleoscientific research, collaboration and application in the Global South? The INQUA-funded multi-year pSESYNTH project envisions the first multi-disciplinary Holocene paleo database through a collaborative vision for past human-environmental systems in the Global South, and their future sustainability

Polyurethane composite adsorbent using solid phase extraction method for preconcentration of metal ion from aqueous solution

Polyurethane composite adsorbent polymeric material was prepared and investigated for selected solid-phase extraction for metal ions, prior to its determination by inductively coupled plasma optical emission spectrometry. The surface characterisation was done using Fourier transform infrared spectroscopy. The separation and preconcentration conditions of the analytes investigated includes influence of pH, sample loading flow rate, elution flow rate, type and concentration of eluents. The optimum pH for the highest efficient recoveries for all metal ions, which ranged from 70 to 85 %, is pH 7. The metal ions were quantitatively eluted with 5 mL of 2 mol/L HNO3. Common coexisting ions did not interfere with the separation. The percentage recovery of the metal ions ranged between 70 and 89 %, while the results for the limit of detection and limit of quantification ranged from 0.249 to 0.256 and 0.831 to 0.855, respectively. The experimental tests showed good preconcentration results of trace levels of metal ions using synthesised polyurethane polymer adsorbent composite