Sensitive determination of nitric oxide in some rat tissues using polymer monolith microextraction coupled to high-performance liquid chromatography with fluorescence detection

A simple, sensitive, selective, and low-cost method is proposed for rapidly determining nitric oxide (NO) in some rat tissues. Polymer monolith microextraction (PMME) using a poly(methacrylic acid–ethylene glycol dimethacrylate) (MAA-EGDMA) monolithic column was combined with derivatization of NO using 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s-indacene (TMDABODIPY), and this was used to analyze the derivatives of NO by high-performance liquid chromatography (HPLC) with fluorescence detection at λ _ex/λ _em = 498/507 nm. The baseline separation of TMDABODIPY and its NO derivative is performed under simple conditions in which a C₁₈ column is used and eluted with 50 mmol L⁻¹ ethanolamine and methanol. The conditions for the extraction of NO derivatives were optimized. The limit of detection of NO was 2 × 10⁻¹² mol L⁻¹ (S/N = 3). The linearity range of the method was 9 × 10⁻¹¹−4.5 × 10⁻⁸ mol L⁻¹. The interday and intraday relative standard deviations were less than 5%. The proposed method was successfully applied to the determination of NO levels in some rat tissue samples including heart, kidney, and liver with recoveries varying from 87.1 to 95.2%.     

Effectiveness of nitric oxide ozonation

Attempts to develop new technologies of NO _x (NO + NO₂) emission reduction are still carried out all around the world. One of the relatively new approaches is the application of ozone injection into the exhaust gas stream followed by the absorption process. Ozone is used to transform NO _x to higher nitrogen oxides which yield nitric acid with better effectiveness. The main objective of this paper was to study the influence of mole ratio (MR) O₃/NO used in the ozonation process of NO _x on the effectiveness of NO _x oxidation to higher oxides. The ozonation process was carried out in a flow reactor for concentrations of nitric oxide in the range of 1.5 × 10⁻⁵−7.7 × 10⁻⁵ mol dm⁻³ and varying O₃/NO mole ratios. Measurements were conducted with the use of a FTIR spectrometer. The results obtained prove that for MR higher than 1, the oxidation effectiveness of nitric oxides generally reaches 95 %, whereas for MR higher than 2, oxidation of NO _x to higher nitrogen oxides is completed.     

Electrocatalytic oxidation of nitric oxide at nano-TiO2/Nafion composite film modified glassy carbon electrode

A novel nanocrystalline TiO₂ (nano-TiO₂) and Nafion composite film modified glassy carbon electrode has been developed for the determination of nitric oxide (NO) radical in an aqueous solution. This modified electrode can be employed as a NO sensor with a low detection limit, fast response, high sensitivity and selectivity. Two apparent anodic peaks were observed at 0.67 and 0.95 V at the nano-TiO₂ modified glassy carbon electrode by differential pulse voltammetry (DPV). After further modification with a thin film of Nafion, which was capable of preventing some anionic interference such as nitrite and ascorbic acid, only one peak appeared and the peak current enhanced greatly. The chronocoulometric experimental results showed NO was oxidized by one-electron transfer reaction at the composite film modified electrode. The amperometric responses increased linearly with the concentrations of NO ranging from 3.6×10⁻⁷ mol/L to 5.4×10⁻⁵ mol/L. The detection limit was estimated to be 5.4×10⁻⁸ mol/L. In this sensor system, the modification film provides complete selectivity for NO over nitrite anions (NO₂⁻).     

An Ni(chitin)2 modified nitric oxide microsensor

The development of a simple, sensitive, selective, and stable amperometric nitric oxide microsensor is described. It is based on Ni(chitin)₂ mediators immobilized on a platinum, Nafion modified electrode. The detection of NO is based on the Ni(chitin)₂ catalysis of NO oxidation at an anodic potential of +0.74 V (vs. SCE). The catalytic peak current is linear for a NO concentration in the range of 8.5 × 10^–8 mol/L to 1.5 × 10^–5 mol/L, with a correlation coefficient of 0.9992. The detection limit of the microsensor is 5.0 × 10^–8 mol/L. It is suitable for the direct measurement of NO in biological systems. Received: 5 February 1999 / Revised: 15 June 1999 / Accepted: 17 June 1999     

Direct detection of nitric oxide in human blood serum by use of 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)difluoroboradiaza-s-indacene with HPLC

To study the relationship between amounts of nitric oxide (NO) in blood and the development of ischemic cardio-cerebrovascular diseases, trace NO in human blood serum has, for the first time, been determined by use of a 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)difluoroboradiaza-s-indacene (TMDABODIPY)-based HPLC method. The proposed method is simple, rapid, and efficient, owing to its high sensitivity and good selectivity for NO. TMDABODIPY and its NO derivative are separated to baseline in 4 min, with simple separation conditions, on a C₁₈ column eluted with 50 mmol L⁻¹ ethanolamine in methanol. The derivative is detected by fluorescence at an emission wavelength of 507 nm with excitation at 498 nm. The response is a linear function of concentration in the range 0.8–800 nmol L⁻¹ NO. The detection limit can reach 2×10⁻¹¹ mol L⁻¹ (signal-to-noise ratio=3). The method has been used to detect NO in the serum of patients with five kinds of ischemic cardio-cerebrovascular disease and two diseases closely connected with ischemic cardio-cerebrovascular diseases. Recoveries of NO from spiked serum samples were between 96.58 and 105.71% and concentrations of NO observed in real samples were at 10⁻⁷ mol L⁻¹ levels. Our studies indicate that the proposed TMDABODIPY-based HPLC technique can be developed into a sensitive and new method for clinical assay and pathology research.     

Solubility of neptunium oxide in the KURT (KAERI Underground Research Tunnel) groundwater

The solubilities of NpO₂(s) in the KURT (KAERI Underground Research Tunnel) granitic groundwater with low ionic strength were measured experimentally and calculated by a geochemical code. Then these results were compared with each other as well as with foreign results. The concentrations of neptunium were measured as 6·10⁻⁸−2·10⁻⁸ mol/L at a pH = 9.5–11.1 and Eh = −0.2 V, and less than 5·10⁻⁹ mol/L at a pH = 11.8–13.0 and Eh = −0.3–0.44 V. The dominant aqueous species were presumed as Np(OH)_x(CO₃)_y ^4−x−2y complexes and Np(OH)₄(aq) at pH = 9.5–13 under the Eh<−0.2 V reducing condition.     

Oil Production Towards Biofuel from Autotrophic Microalgae Semicontinuous Cultivations Monitorized by Flow Cytometry

Two microalgae species (Scenedesmus obliquus and Neochloris oleoabundans) were cultivated in closed sleeve photobioreactors in order to select the best oil producer for further large-scale open raceway pond cultivations, aiming at biofuel production. Scenedesmus obliquus reached a higher maximum biomass concentration (1.41 g l⁻¹) with a lower lipid content (12.8% w/w), as compared to N. oleoabundans [maximum biomass concentration of 0.92 g l⁻¹ with 16.5% (w/w) lipid content]. Both microalgae showed adequate fatty acid composition and iodine values as substitutes for diesel fuel. Based on these results, N. oleoabundans was selected for further open raceway pond cultivations. Under these conditions, N. oleoabundans reached a maximum biomass concentration of 2.8 g l⁻¹ with 11% (w/w) of lipid content. A high correlation between the Nile Red fluorescence intensity measured by flow cytometry and total lipid content assayed by the traditional gravimetric lipid analysis was found for both microalgae, making this method a suitable and quick technique for the screening of microalgae strains for lipid production and optimization of biofuel production bioprocesses. Medium growth optimization for enhancement of microalgal oil production is now in progress.     

Determination of dopamine in rat striatum by microdialysis and high-performance liquid chromatography with electrochemical detection on a functionalized multi-wall carbon nanotube electrode

High performance liquid chromatography coupled with microdialysis sampling and electrochemical detection (HPLC–ECD) has been used to determine dopamine (DA). In the HPLC–ECD a multi-wall carbon nanotube electrode chemically modified with carboxyl groups (MWNT-COOH CME) was used as the working electrode for determination of DA. The results indicated that the MWNT-COOH CME enabled efficient electrocatalytic oxidation of DA with relatively high sensitivity and stability and long life. Peak currents for dopamine were linearly dependent on concentration in the range 5.0×10⁻⁹ to 5.0×10⁻⁵ mol L⁻¹ and the calculated detection limit (S/N=3) was 2.5×10⁻⁹ mol L⁻¹. The method had been successfully used to measure dopamine in rat striatal microdialysate. To study the physiological effect of nitric oxide (NO) on striatal release of DA, 0.5 mmol L⁻¹ sodium nitroprusside (SNP) was a continuously perfused into rat striatum. This resulted in a 46% increase in DA basal level.     

Nitric oxide measurement in biological and pharmaceutical samples by an electrochemical sensor

A nitric oxide (NO) electrochemical sensor was developed via one-step construction of gold nanoparticles (GNPs)–chitosan (CS) nanocomposite sensing film on a glassy carbon electrode (GCE) surface. This method is very simple and convenient. The GNPs–CS film which is controllable and stable exhibits catalytic activity to NO oxidation. The anodic peak potential significantly shifted negatively compared with that at bare GCE. The high sensitivity and good stability of developed method have been coupled to a wide linear range from 3.60 × 10⁻⁸ to 4.32 × 10⁻⁵ M for the quantitative analysis of NO. The detection limit of 7.20 nM is much lower than the vast majority of reported methods. This NO sensor has been successfully applied to NO measurement in biological and pharmaceutical samples. Real-time amperometric data show that the addition of L-arginine (L-Arg) can cause a slow release of NO from a whole rat kidney with a maximum concentration of ca. 150 nM. The concentration of NO monitoring from the drug sample was calculated to be ca. 1.60 μM.     

Hemoglobin-stabilized tetranitrosyl binuclear iron complex with pyridine-2-yl in aqueous solutions

The tetranitrosyl iron complex with pyridine-2-yl [Fe₂(SC₅H₄N)₂(NO)₄] (1) has higher NO-donating activity in 3% aqueous solutions of DMSO (pH 7.0, 25 °C) than the organic NO donor, viz., adduct of NO with diethylenetriamine (NO-adduct). The NO concentration was determined by the spectrophotometric method based on the formation of an NO complex with hemoglobin (Hb). The apparent first-order rate constants of the studied reactions are (6.15±0.6)·10⁻¹ s⁻¹ and (0.8±0.08)·10⁻¹ s⁻¹ for complex 1 and the NO-adduct, respectively, at an Hb concentration of 2·10⁻¹ mol L⁻¹ and the ratio [NO donor]/[Hb] = 10. The effect of Hb and [NO donor]/[Hb] ratio on the rate of NO generation from a solution of complex 1 was studied. For a fourfold decrease in the concentration of complex 1 the reaction rate constant decreases to 0.5·10⁻⁴ s⁻¹, whereas the fourfold increase in the Hb concentration results in the stabilization of complex 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 732–736, April, 2007.     

A Novel Enhancing Flow-Injection Chemiluminescence Method for the Determination of Glutathione Using the Reaction of Luminol with Hydrogen Peroxide

 A rapid flow-injection method with chemiluminescence (CL) detection is described for the determination of glutathione (GSH). The method is based on the CL reaction of luminol and hydrogen peroxide. GSH can greatly enhance the chemiluminescence intensity in 0.1 mol/L borax–sodium hydroxide buffer solution (pH = 9.7). The maximum CL intensity was directly proportional to the concentration of GSH in the range 3.0 × 10⁻⁷–2.0 × 10⁻⁵ mol/L, and the detection limit was 6.8 × 10⁻⁸ mol/L. The relative standard deviation was 3.4% for 5.0 × 10⁻⁶ mol/L of GSH (n = 11). Received October 23, 2001; accepted June 18, 2002     

The influence of serum fatty acid binding proteins on arachidonic acid uptake by macrophages

The role of serum fatty acid binding proteins (FABPs) in arachidonic acid (AA) uptake by murine peritoneal macrophages has been studied. The kinetics of [³H]arachidonic acid uptake by the cells was investigated over a wide range of AA concentration (10⁻¹⁰–10⁻⁵ M). It was shown that these putative fatty acid transporters dramatically change the uptake processes. In the presence of FABPs, the time-course curves of AA uptake exhibited two distinct periods: one with a rapid AA uptake during the first hour with an equilibrium in 1–2.5 h and another with an equilibrium reached in 20 h, whereas in the absence of FABPs the uptake curves were smooth without kinks and with the equilibrium reached in 10 h. In addition, it was shown that the amount of incorporated AA was linearly dependent on the concentration of AA over the range of 10⁻¹⁰–10⁻⁶ M in the presence of serum FABPs and 10⁻¹⁰–10⁻⁷ M in their absence. We assume that the changes in the character of AA uptake by macrophages in the presence of FABP soccur due to the interaction of FABPs with the cell plasma membrane.     

AFM-tip-induced crystallization of poly(ethylene oxide) melt droplets

The AFM-tip-induced crystallization of poly(ethylene oxide) (PEO) melt droplets was studied. The melt droplets with a height of 50–100 nm and a lateral size of 2–3 μm were obtained by melting the PEO ultra-thin films on a mica surface. For the PEO samples with average molecular weights (M _n) ranging from 1.0 × 10³ g/mol to 1.0 × 10⁴ g/mol, the lateral perturbation from the AFM tip in the hard-tapping or nanoscratch modes could not induce the growth of the flat-on lamellae. In contrast, under AFM nanoindentation mode, the tip-induced crystallization occurred when a sufficiently high vertical tip force was applied to the melt droplets of PEO with M _n ⩾ 1.0 × 10⁴ g/mol. Moreover, the experimental results indicated that the AFM-tip-induced crystallization of PEO in the nanoindentation process had molecular weight dependence. Translated from Acta Polymerica Sinica, 2006, (4): 553–556 (in Chinese)     

Nitrite formation in aerated aqueous azide solutions: A radiation chemical study

Gamma radiolysis of oxygenated 1–10 mM azide solutions was carried out at various pH values. In oxygenated 10 mM azide solutions, H₂O₂ and NO ₂ ⁻ were observed as radiolytic products while NH3 was not. The concentration of H₂O₂ reached its maximum level at a dose of 1 kGy, whereas NO ₂ ⁻ yield increased non-linearly beyond 2 kGy in this system. Both in aerated and oxygenated systems, G(NO ₂ ⁻ ) and G(H₂O₂) were found to vary with N ₃ ⁻ concentration. The yield of NO ₂ ⁻ was found to be dependent on both dose rate and pH. On pulse radiolysis, NO ₂ ⁻ was found as a radiolytic product in aerated 1 mM azide solution at pH 6.8. In this system the intermediate generated exhibits absorbance around 250 nm. The overall results obtained during the present study reveal that in presence of both reducing radical (mainly e _aq ⁻ ) and oxygen, N ₃ ⁻ produced an intermediate possibly NH₂O ₂ ^• radical, which is the prime source for NO ₂ ⁻ generation.     

Effect of pH and ionic strength on the interaction of humic acid with aluminium oxide

The effect of pH and neutral electrolyte on the interaction between humic acid/humate and γ-AlOOH (boehmite) was investigated. The quantitative characterization of surface charging for both partners was performed by means of potentiometric acid–base titration. The intrinsic equilibrium constants for surface charge formation were logK _a,1 ^int=6.7±0.2 and logK _a,2 ^int = 10.6±0.2 and the point of zero charge was 8.7±0.1 for aluminium oxide. The pH-dependent solubility and the speciation of dissolved aluminium was calculated (MINTEQA2). The fitted (FITEQL) pK values for dissociation of acidic groups of humic acid were pK ₁ = 3.7±0.1 and pK ₂ = 6.6±0.1 and the total acidity was 4.56 mmol g⁻¹. The pH range for the adsorption study was limited to between pH 5 and 10, where the amount of the aluminium species in the aqueous phase is negligible (less than 10⁻⁵ mol dm⁻³) and the complicating side equilibria can be neglected. Adsorption isotherms were determined at pH ∼ 5.5, ∼8.5 and ∼9.5, where the surface of adsorbent is positive, neutral and negative, respectively, and at 0.001, 0.1, 0.25 and 0.50 mol dm⁻³ NaNO₃. The isotherms are of the Langmuir type, except that measured at pH ∼ 5.5 in the presence of 0.25 and 0.5 mol dm⁻³ salt. The interaction between humic acid/humate and aluminium oxide is mainly a ligand-exchange reaction with humic macroions with changing conformation under the influence of the charged interface. With increasing ionic strength the surface complexation takes place with more and more compressed humic macroions. The contribution of Coulombic interaction of oppositely charged partners is significant at acidic pH. We suppose heterocoagulation of humic acid and aluminium oxide particles at pH ∼ 5.5 and higher salt content to explain the unusual increase in the apparent amount of humic acid adsorbed. Received: 20 July 1999 /Accepted in revised form: 20 October 1999     

Profile distribution of As(III) and As(V) species in soil and groundwater in Bozanta area

The profile distribution of arsenic(III) and arsenic(V) species in soil and groundwater was investigated in the samples collected in 2005 from a hand-drilled well, in the Bozanta area, Baia Mare region, Romania. The total content of arsenic in the soil was in the range of 525–672 mg kg⁻¹ exceeding 21–27 times the action trigger level for sensitive soil. 0.9–11.3 % of the total content was soluble in water, 83.0–92.6 % in 10 mol dm⁻³ HCl and 2.6–13.3 % was the residual fraction. Arsenic(V) was the dominant arsenic species in the soil in the range of 405–580 mg kg⁻¹. The distribution and mobility of arsenic species was governed by soil pH and contents of Al, Fe, and Mn. The mobility of arsenic(V) decreased with depth, while that of arsenic(III) was high at the surface and in the proximity of groundwater. The total concentration of arsenic in groundwater was (43.40 ± 1.70) μg dm⁻³, which exceeded the maximum contaminant level of 10 μg dm⁻³. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Interaction of nitric oxide with cobalt(II) phthalocyanine: kinetics, equilibria and electrocatalytic studies

The coordination of nitric oxide (NO) to cobalt(II) phthalocyanine (CoPc) in dimethyl sulphoxide (DMSO) has been studied. CoPc coordinates with NO in a 1:1 ratio, forming a CoPc(NO) species. The IR band observed at 1680 cm⁻¹ is assigned to the coordinated NO. In the presence of excess NO, pseudo first order kinetics were followed. The observed rate constant, k_f, was determined to be 15.0±0.3 dm⁻³ mol⁻¹ s⁻¹ and the equilibrium constant was K=5.4±0.4×10⁴dm³ mol⁻¹. Solution or adsorbed CoPc catalyses the reduction of NO. The products of reduction include NH₃ and NH₂OH.     

Low-temperature activation of nitrogen oxide on Cu-ZSM-5 catalysts

The adsorption and activation of NO molecules on Cu-ZSM-5 catalysts with different Cu/Al and Si/Al ratios (from 0.05 to 1.4 and from 17 to 45, respectively) subjected to different pretreatment was studied by ultraviolet-visible diffuse reflectance (UV-Vis DR). It was found that the amount of chemisorbed NO and the catalyst activity in NO decomposition increased with an increase in the Cu/Al ratio to 0.35–0.40. The intensity of absorption bands at 18400 and 25600 cm⁻¹ in the UV-Vis DR spectra increased symbatically. It was hypothesized that the adsorption of NO occurs at Cu⁺ ions localized in chain copper oxide structures with the formation of mono- and dinitrosyl Cu(I) complexes, and this process is accompanied by the Cu²⁺...Cu⁺ intervalence transfer band in the region of 18400 cm⁻¹. The low-temperature activation of NO occurs through the conversion of the dinitrosyl Cu(I) complex into the π-radical anion (N₂O₂)⁻ stabilized at the Cu²⁺ ion of the chain structure, [Cu²⁺-cis-(N₂O₂)⁻], by electron transfer from the Cu⁺ ion to the cis dimer (NO)₂. This complex corresponds to the L → M charge transfer band in the region of 25600 cm⁻¹. The subsequent destruction of the complex [Cu²⁺-cis-(N₂O₂)⁻] at temperatures of 150–300°C leads to the release of N₂O and the formation of the complex [Cu²⁺O⁻], which further participates in the formation of the nitrite-nitrate complexes [Cu²⁺(NO₂)⁻], [Cu²⁺(NO)(NO₂)⁻], and [Cu²⁺(NO₃)⁻] and NO decomposition products.     

Simultaneous analysis of three catecholamines by a kinetic procedure: comparison of prediction performance of several different multivariate calibrations

A rapid kinetic method for the simultaneous determination of levodopa, dopamine, and dobutamine was examined and developed. It was based on a consecutive reaction of a reduction of Cu(II) to Cu(I) by catecholamines, followed by the complexation of Cu(I) with neocuproine to form a yellow product in an acetic acid-acetate buffer. Spectrophotometric data were recorded at 453 nm (wavelength at the yellow complex absorption maximum) for 300 s. Linear calibrations were obtained in the concentration ranges of (0.08–1.44) × 10⁻⁵ mol L⁻¹, (0.08–1.44) × 10⁻⁵ mol L⁻¹, and (0.16–1.44) × 10⁻⁵ mol L⁻¹ for levodopa, dopamine, and dobutamine, respectively. A variety of multivariate calibration models was developed for simultaneous analysis of the three analytes; while most models produced satisfactory prediction results for synthetic samples, the hybrid linear analysis method was arguably the best-performing (relative prediction error, RPET = 6.6 %). The proposed method was applied to an analysis of spiked rabbit serum samples and the results showed good agreement with the high performance liquid chromatography measurements.     

A nitric oxide biosensor based on the photovoltaic effect of nano titanium dioxide on hemoglobin

A nitric oxide biosensor based on the photovoltaic effect of nano titanium dioxide on hemoglobin was fabricated with high sensitivity, selectivity, as well as stability. The linear detection concentration range was 5.0 × 10⁻⁶–4.0 × 10⁻⁴ M. The detection limit was 1.0 × 10⁻⁶ M with a sensitivity of 8 nA/μM. The possible coexisting compounds would not interfere with the nitric oxide detection. The article is published in the original.