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PubMed1996

NMR Study of Phase Transitions in Pure Water and Binary H(2)O/HNO(3) Films Adsorbed on Surface of Pyrogenic Silica.

Pyrogenic silica (aerosil) was employed as host within which the phase transitions in the adsorbed pure water and binary H(2)O/HNO(3) films have been studied with NMR spectroscopy. The median freezing temperature and freezing temperature region were shown to be highly sensitive both to the average thickness of the adsorbed films and to the amount of adsorbed nitric acid. The molar concentration of nitric acid in the adsorbed films was found to be very small, on the order of 10(-3)-10(-2) (M/liter). The concentration was found to be greater in the layers adjacent to the surface of silica and sharply decreases with distance from the surface. The difference between the median freezing temperatures for adsorbed pure water and for the binary system was found to be about 9 K for films of equal thickness. This is about 150 times greater than the difference between the freezing temperatures of bulk pure water and a solution with the same concentration of nitric acid.

Journal Article↗
PubMed1984

Double-blind study of variables influencing the clinical effect of Solcoderm.

Double-blind clinical studies of pairs of lesions were initiated to evaluate several components of Solcoderm treatment. The superiority of Solcoderm over plain nitric acid was as evident with plastic as with wooden applicators. A mixture of oxalic and nitric acid had effects similar to Solcoderm, while acetic and nitric acid was similar in effect to plain nitric acid.

Acetates↗
PubMed2001

Mechanisms of nitric oxide release from nitrovasodilators in aqueous solution: reaction of the nitroprusside ion ([Fe(CN)5NO]2-) with L-ascorbic acid.

Nitric Oxide (NO) is a very diverse endogenous molecule and is responsible for a number of mammalian physiological activities. Sodium nitroprusside (SNP) is a long known hypotensive agent due to its ability to produce NO in situ. In this study, we have carried out a detailed investigation on the kinetics and mechanism of the decomposition of SNP by L-ascorbic acid to afford NO in aqueous medium. Spectrophotometric and electrochemical methods were employed in these studies. Experiments were performed under an argon atmosphere and reaction rates were strongly pH dependent and increases with pH. NO release increases up to about pH 7 after which it decreases at higher pHs. The two ionized forms of ascorbate present in aqueous solution reduce SNP in the order A2->>HA->>H2A (H2A=L-ascorbic acid) to release NO. The outer-sphere reduction of SNP by ascorbate involved three clear stages with NO being released in the last stage. Our kinetic results also show catalysis by group 1 alkali metal ions to increase down the group from Li+ to Cs+. A detail study presented here, strongly illustrate the possibility of the biological antioxidant, L-ascorbic acid, to play a vital role in the in situ metabolism of nitrosocompounds such as SNP to produce NO.

Journal Article↗
PubMed2005

Matrix effects during phosphorus determination with quadrupole inductively coupled plasma mass spectrometry.

A quadrupole inductively coupled plasma mass spectrometer was evaluated for use in the detection of phosphorus. The influences of nitric acid and methanol (simulating the composition of a sample solution after nitric acid digestion) on phosphorus determination were studied using two different measuring methods at different plasma conditions: detection of phosphorus ions at m/z 31 and detection of phosphorus oxide ions at m/z 47. The existence of polyatomic interferences at m/z 31 and 47 was explored. Nitric acid and methanol are shown to be the sources of polyatomic ions and therefore cause poorer detection limits. Better detection limits were achieved in such matrices when phosphorus was detected as 31P+. The presence of methanol improves the system sensitivity towards phosphorus sevenfold; however, this positive effect is hindered by the high background signal due to carbon-based polyatomic ions. For samples with an organic matrix an appropriate mineralization procedure should be applied (high excess of nitric acid and high temperature) to quantitatively oxidize organic compounds to carbon dioxide, which is easily removed from the sample, in order to achieve correct results.

Carbon Dioxide↗
PubMed2005

Nitration and photonitration of naphthalene in aqueous systems.

The nitration of naphthalene was studied in aqueous solution to gain insight into the processes leading to the nitration of aromatic compounds in atmospheric hydrometeors. Reactants used were nitric acid, nitrogen dioxide and peroxynitrous acid in the dark, nitrate, and nitrite/nitrous acid under illumination. Naphthalene nitration can lead to two possible isomers, 1- and 2-nitronaphthalene. The former nitrocompound preferentially forms upon electrophilic processes and in the presence of nitrogen dioxide. Electrophilic nitration of naphthalene takes place in the presence of concentrated nitric acid, but nitration with nitric acid and oxidants (charge-transfer nitration) occurs under much milder conditions than with nitric acid alone. Charge-transfer nitration may have some environmental significance in particular cases, e.g. in acidic aerosols in the presence of HNO3 and oxidants. Nitrogen dioxide is thought to have a role in PAH nitration in the Antarctic particulate matter. In previous papers we have found that nitration induced by peroxynitrous acid, HOONO, can follow two pathways, the former electrophilic (leading for instance to the formation of nitrophenols from phenol) and the latter probably involving HOONO itself (accounting for the formation of nitrobenzene from benzene). In the case of naphthalene and HOONO the electrophilic pathway mainly leads to 1-nitronaphthalene, while the other one preferentially yields 2-nitronaphthalene. The nitration of naphthalene in the presence of nitrite/nitrous acid under irradiation leads to both nitroisomers in similar ratios, and the process is not inhibited by hydroxyl scavengers. This excludes nitrogen dioxide as reactive species for nitration and marks a difference with phenol photonitration and a similarity with the behavior of benzene under comparable conditions. Nitrite photochemistry (and nitrite-induced photonitration as well) is expected to be relevant in fog and cloudwater in polluted areas. An important difference with the gas-phase nitration is that the radicals OH and NO3 are unlikely to play a relevant role in the nitration of naphthalene in aqueous solution.

Benzene↗
PubMed2001

Vicinal nitrohydroxyeicosatrienoic acids: vasodilator lipids formed by reaction of nitrogen dioxide with arachidonic acid.

Nitric oxide (NO)-derived species could potentially react with arachidonic acid to generate novel vasoactive metabolites. We studied the reaction of arachidonic acid with nitrogen dioxide (NO2), a free radical that originates from NO oxidation. The reaction mixture contained lipid products that relaxed endothelium-removed bovine coronary arteries. Relaxation to the lipid mixture was inhibited approximately 20% by indomethacin and approximately 70% by a soluble guanylate cyclase (sGC) inhibitor (ODQ). Thus, novel lipid products, which activate sGC presumably through a mechanism involving NO, appeared to have contributed to the observed vasorelaxation. Lipids that eluted at 9 to 12 min during high-performance liquid chromatography fractionation accounted for about one-half of the vasodilator activity in the reaction mixture, which was inhibited by ODQ. Lipid products in fractions 9 to 12 were identified by electrospray tandem mass spectrometry to be eight isomers having molecular weight of 367 and a fragmentation pattern indicative of arachidonic acid derivatives containing nitro and hydroxy groups and consistent with the structures of vicinal nitrohydroxyeicosatrienoic acids. These lipids spontaneously released NO (183 +/- 12 nmol NO/15 min/micromol) as detected by head space/chemiluminescence analysis. Mild alkaline hydrolysis of total lipids extracted from bovine cardiac muscle followed by isotopic dilution gas chromatography/mass spectrometry analysis detected basal levels of nitrohydroxyeicosatrienoic acids (6.8 +/- 2.6 ng/g tissue; n = 4). Thus, the oxidation product of NO, NO2, reacts with arachidonic acid to generate biologically active vicinal nitrohydroxyeicosatrienoic acids, which may be important endogenous mediators of vascular relaxation and sGC activation.

8,11,14-Eicosatrienoic Acid↗
PubMed2006

Processes influencing secondary aerosol formation in the San Joaquin Valley during winter.

Air quality data collected in the California Regional PM10/ PM(2.5) Air Quality Study (CRPAQS) are analyzed to qualitatively assess the processes affecting secondary aerosol formation in the San Joaquin Valley (SJV). This region experiences some of the highest fine particulate matter (PM(2.5)) mass concentrations in California (< or = 188 microg/m3 24-hr average), and secondary aerosol components (as a group) frequently constitute over half of the fine aerosol mass in winter. The analyses are based on 15 days of high-frequency filter and canister measurements and several months of wintertime continuous gas and aerosol measurements. The phase-partitioning of nitrogen oxide (NO(x))-related nitrogen species and carbonaceous species shows that concentrations of gaseous precursor species are far more abundant than measured secondary aerosol nitrate or estimated secondary organic aerosols. Comparisons of ammonia and nitric acid concentrations indicate that ammonium nitrate formation is limited by the availability of nitric acid rather than ammonia. Time-resolved aerosol nitrate data collected at the surface and on a 90-m tower suggest that both the daytime and nighttime nitric acid formation pathways are active, and entrainment of aerosol nitrate formed aloft at night may explain the spatial homogeneity of nitrate in the SJV. NO(x) and volatile organic compound (VOC) emissions plus background O3 levels are expected to determine NO(x) oxidation and nitric acid production rates, which currently control the ammonium nitrate levels in the SJV. Secondary organic aerosol formation is significant in winter, especially in the Fresno urban area. Formation of secondary organic aerosol is more likely limited by the rate of VOC oxidation than the availability of VOC precursors in winter.

Aerosols↗
PubMedDate not supplied

[Clinical-epidemiological characteristics in caustics ingestion patients in the Hipólito Unanue National Hospital].

UNLABELLED: The ingestion of caustic substances represents a serious problem, often with devastating consequences on the esophagus and the stomach. OBJECTIVES: 1) Determine the main caustic substance ingested and the lesions on the esophageal-gastric mucose. 2) Find out the clinical-epidemiological characteristics of these patients in our hospital. RESULTS: 45 inpatients at the Hipólito Unanue National Hospital were evaluated between 1996 and 2001, 29 female patients (64.4%) and 16 male patients (35.6%) with an average age of 28 years in a range between 15 and 60 years. The caustic substances ingested were: bleach, 30 patients (66.7%), muriatic acid (hydrochloric acid) 13 patients (28.9%), nitric acid and caustic soda, one patient each (2.2%). Among the women: 24 patients ingested bleach (82.7%) 4 patients, muriatic acid (13.7%) and one patient, caustic soda (3.4%). Among the men: 9 patients took muriatic acid (56.3%) 6 patients, bleach (37.5%) 1 patient, nitric acid (6.25%); 29 patients ingested the caustic substances in pure form (64.4%) and 16 patients diluted with other substances: water, soft or alcoholic drinks, oatmeal (35.5%). The time passed between the ingestion and medical attention was of 104 minutes, with a range of 15 to 360 minutes. The average of total ingested solution was 73 ml., ranging between 10 ml and 170 ml. The reason for the ingestion was a conflict with their spouse, 24 patients (53.4%) family conflict, 13 patients (28.9%) accident, 4 patients (8.9%) psychiatric problems, 3 patients (6.7%) and a monetary factor, 1 patient (2.2%). The signs and symptoms when admitted into the hospital were: abdominal pain, 31 patients (68.9%) nausea, 22 patients (48.9%) vomit, 21 patients (46.7%) mouth cavity pain, 19 patients (42.2%) dysphagia, 14 patients (31.1%) sialorrhea, 14 patients (31.1%) odynophagia, 13 patients (15.6%) sensory disorder, 7 patients (15.6%) dysphonia, 3 patients (6.7%) and cephalea, 1 patient (2.2%). Oral compromise was: normal in 11 patients (24.4%) congestion in 23 patients (51.1%) and erosions in 11 patients (24.1%). Endoscopic lesions found were: grade 0 in 6 patients (13.3%) grade 1 in 21 patients (46.7%) Grade 2A in 7 patients (15.6%) Grade 3B in 2 patients (4.4%). CONCLUSIONS: Adolescents and young adults are the age groups which most suffer of this pathology. Bleach is the most ingested caustic substance (66.7%). Women have a higher risk of ingesting a caustic substance (64.4%). Caustic substances are mostly ingested pure (64.4%). Conjugal conflicts are the main reason for caustic ingestion. Clinical symptoms vary, with abdominal pain being the main discomfort among these patients. Oropharyngeal congestion is the most frequent finding. Esophageal-gastric mucose edema and hyperemia (Zargar 1) are the endoscopic lesions mostly found.

Adolescent↗
PubMed2000

Mercury determination with ICP-MS: signal suppression by acids.

When mercury is quantified by ICP-MS under routine conditions (external calibration) in reference materials, which require mineralization with nitric acid, the experimental concentrations are almost always unacceptably low in comparison to certified values. Sorption of mercury on the Teflon surfaces of the digestion vessels, changes in the viscosity of the aspirated solutions, in the efficiency of the nebulization, in the aerosol transport, and memory effects cannot be responsible for the low results. The intensity of a mercury signal is strongly dependent on the concentration of nitric acid (and other mineral acids) in the measured solutions. Correct results for mercury in the SRM GBW-90101 (Chinese human hair; 2.16+/-0.21 mg Hg/kg certified) can only be obtained, when the solutions, with which the external calibration curves were established, have exactly the same nitric acid concentration as the aspirated digests (2.03+/-0.01 mg Hg/kg; n = 5), when mercury is determined by the standard addition method (2.10+/-0.01 mg Hg/kg; n = 5), or when the experimental mercury concentration obtained at a nitric acid concentration in the digest, different from the concentration in the external calibration solutions, is corrected mathematically based on a pre-established function [Hg2+] = f [HNO3]. The concentrations found by this mathematically based correction 2.04+/-0.01 mg Hg/kg (n = 5) is in good agreement with the values obtained by acid matched calibration or by the standard addition method. For practical work with large numbers of samples the mathematical correction appears to be the method of choice. For occasional mercury determinations, the standard addition method seems to be the most practicable.

China↗
PubMed1999

Surface characterization of implant materials c.p. Ti, Ti-6Al-7Nb and Ti-6Al-4V with different pretreatments.

The biocompatibility of commercially pure titanium and its alloys is closely related to their surface properties, with both the composition of the protecting oxide film and the surface topography playing an important role. Surfaces of commercially pure titanium and of the two alloys Ti-6Al-7Nb and Ti-6Al-4V (wt %) have been investigated following three different pretreatments: polishing, nitric acid passivation and pickling in nitric acid-hydrogen fluoride. Nitric acid treatment is found to substantially reduce the concentration of surface contaminants present after polishing. The natural 4-6 nm thick oxide layer on commercially pure titanium is composed of titanium oxide in different oxidation states (TiO2, Ti2O3 and TiO), while for the alloys, aluminium and niobium or vanadium are additionally present in oxidized form (Al2O3, Nb2O5 or V-oxides). The concentrations of the alloying elements at the surface are shown to be strongly dependent on the pretreatment process. While pickling increases the surface roughness of both commercially pure titanium and the alloys, different mechanisms appear to be involved. In the case of commercially pure titanium, the dissolution rate depends on grain orientation, whereas in the case of the two alloys, selective alpha-phase dissolution and enrichment of the beta-phase appears to occur.

Journal Article↗
PubMed1999

Synergistic effects of oxidative environments and mechanical stress on in vitro stability of polyetherurethanes and polycarbonateurethanes.

The in vitro structural stability of polyetherurethanes (PEUs) and polycarbonateurethanes (PCUs and PCUUs) was examined under strong oxidative conditions (0.5N HNO3, pH 0.3; and NaClO, 4% Cl2 available, pH approximately 13) and in the presence of a constant strain state. Solvent-cast dog-bone shaped specimens were strained at 100% uniaxial elongation over extension devices and completely immersed in the oxidative solutions at 50 degrees C for 15 days. Unstrained polyurethane (PU) samples were treated in the same way for comparison. The modification of the PU molecular structure was determined by DSC, GPC, ATR-FTIR, static contact angle, and surface roughness analyses. The incubation in nitric acid and sodium hypochlorite brought about a greater degradation of samples tested under the applied strain with the exception of PEU treated with nitric acid. PEU was the most affected material, showing bulk deterioration in NaClO and significant modifications in nitric acid, with the appearance of new IR bands, which were assigned to oxidation products. A higher phase separation between soft and hard domains occurred in PCUs upon incubation in nitric acid, the treatment with NaClO gave rise to new bands in the IR spectra, denoting the presence of oxidation products at the surface. The surface roughness greatly increased in strained PCUs with SEM evidence of deep cracks and holes or ragged and stretched fractures perpendicular to the direction of stress. PCUU underwent complex chemical modifications with a marked decrease of N-H and urea IR absorptions and showed a lower degradation than PEU and PCUs under mechanical constraint. From these results, sodium hypochlorite appears to be able to create an ESC-like degradation for PUs that are resistant to other aggressive chemical environments.

Microscopy, Electron, Scanning↗
PubMed1999

Removal of Formaldehyde by Activated Carbons Containing Amino Groups.

Formaldehyde has been used for disinfection and antisepsis in hospitals due to its bactericidal action, but it is toxic to humans. Hence, we developed adsorbates for the removal of formaldehyde. The adsorbate was prepared by the amination of an activated carbon surface. The removal efficiency and the adsorption mechanism of formaldehyde onto the aminated activated carbon were studied. The concentrated sulfuric acid and nitric acid treatment introduced nitro groups onto the surface of the activated carbon. The nitro groups were reduced by the reaction of powdered iron and hydrochloric acid to the amino groups. The amount of formaldehyde adsorbed onto the activated carbon increased with the amination of the activated carbon because of the increasing interaction between the surface of the activated carbon and the formaldehyde. Copyright 1999 Academic Press.

Journal Article↗
PubMed1986

Effects of various agents on staining of the maturation pattern at the surface of rat incisor enamel.

In the maturation zone, two types of ameloblasts are arranged as bands across the rat incisor; these corresponded with a staining pattern at the surface which reflected the alternating pattern of ruffle-ended and smooth-ended ameloblasts. PAS stain showed bands and stripes similar to those following glyoxal bis(2-hydroxyanil) (GBHA) staining; these stains visualize the organic (PAS) and inorganic (GBHA) components of the maturation pattern. To further elucidate the nature of these bands, dissected rat incisors were treated with various agents prior to staining with GBHA or PAS. Guanidine for 2 h at room temperature showed no maturation pattern when stained with GBHA, as did teeth treated with EDTA and a bisophosphonate (HEBP). Hydrochloric acid and nitric acid removed the layer of outer enamel and incisors did not stain with GBHA, suggesting that the staining is a surface-related phenomenon. As staining was abolished by either the removal of mineral (EDTA) or protein (guanidine), the concurrent localization of non-crystal-bound calcium by GBHA staining, and of glycoprotein by PAS staining, indicates that calcium is associated with glycoprotein at the surface of the enamel.

Ameloblasts↗
PubMed1985

Effects of methyl linoleate hydroperoxide and hydrogen peroxide on N-nitrosation of dimethylamine.

The effects of methyl linoleate hydroperoxide and hydrogen peroxide on the N-nitrosation of dimethylamine were investigated. Hydrogen peroxide inhibited the formation of N-nitrosodimethylamine by the reaction of dimethylamine and nitrite in citrate buffer (pH 3-5). The inhibitory effect was due to the loss of available nitrite by quantitative conversion into nitrate. The formation of N-nitrosodimethylamine from the reaction of dimethylamine and nitrous acid in chloroform was effectively inhibited by methyl linoleate hydroperoxide. The inhibitory effect of the hydroperoxide was much greater than that of methyl linoleate. The loss of nitrous acid from the reaction mixture was due to the conversion of nitrous acid into nitric acid and the formation of two adducts, both of which contained nitrogen and had peroxide and carbonyl or carbonyl-liberating functions. It is suggested that unsaturated fatty acids and lipid hydroperoxides are effective inhibitors of nitrosamine formation.

Chromatography, Thin Layer↗
PubMed2004

Thermal reactive hazards of HMX with contaminants.

In the past, many unexpected runaway accidents occurred in manufacturing processes, involving volatile chemical and explosive storage and transportation. Incompatible product reactions of high explosives must be carefully considered using loss prevention strategies for thermal hazards risk analysis. High explosive reactions vary via environmental changes, contact materials, or process situations, such as onset temperature and shifts in reaction type when high explosives are in contact with contaminants. Therefore, the manufacture and handling of high explosives require the utmost in safety and loss prevention. HMX (cyclotetramethyene tetranitramine) is one kind of high explosive widely used around the world which is stable with high detonation strength properties. In this study, the influences of contaminants on HMX are investigated. The studied contaminants include ferrous chloride tetrahydrate, ferric chloride hexahydrate, acetone solution, acetic acid, and nitric acid. DSC thermal curves and incompatible reaction kinetic evaluations were preformed using iron, chlorine and acid. Organic acetone solution has lesser effects on HMX. Hopefully, this study will lead to improved thermal hazards risk analysis and reduce accidents.

Accidents, Occupational↗
PubMed2006

Factorial experimental design for recovering heavy metals from sludge with ion-exchange resin.

Wastewaters containing heavy metals are usually treated by chemical precipitation method in Taiwan. This method can remove heavy metals form wastewaters efficiently, but the resultant heavy metal sludge is classified as hazardous solid waste and becomes another environmental problem. If we can remove heavy metals from sludge, it becomes non-hazardous waste and the treatment cost can be greatly reduced. This study aims at using ion-exchange resin to remove heavy metals such as copper, zinc, cadmium, and chromium from sludge generated by a PCB manufacturing plant. Factorial experimental design methodology was used to study the heavy metal removal efficiency. The total metal concentrations in the sludge, resin, and solution phases were measured respectively after 30 min reaction with varying leaching agents (citric acid and nitric acid); ion-exchange resins (Amberlite IRC-718 and IR-120), and temperatures (50 and 70 degrees C). The experimental results and statistical analysis show that a stronger leaching acid and a higher temperature both favor lower heavy metal residues in the sludge. Two-factors and even three-factor interaction effects on the heavy metal sorption in the resin phase are not negligible. The ion-exchange resin plays an important role in the sludge extraction or metal recovery. Empirical regression models were also obtained and used to predict the heavy metal profiles with satisfactory results.

Analysis of Variance↗
PubMed2004

Stable isotope-enriched selenite and selenate tracers for human metabolic studies: a fast and accurate method for their preparation from elemental selenium and their identification and quantification using hydride generation atomic absorption spectrometry.

Stable isotope tracers are safe and nutritionally relevant tools for the investigation of mineral metabolism in man. Increased research into the functional role of selenium has resulted in a need for well-characterised, isotopically enriched solutions of the element in order to determine the nutritional relevance of selenium fortification of foods. A simple method for the conversion of isotopically enriched elemental selenium (2.5-10 mg) into selenite and selenate, and their accurate characterisation and quantification is described. Analysis of selenite and selenate tracers using continuous-flow hydride generation-atomic absorption spectrometry technique was based on the specificity of the selenium hydride reaction and allowed their precise (RSD<2.5%) and accurate determination in aqueous solutions. The detection and determination limits were at 0.13 and 0.36 microg Se/l, respectively. Isotopically enriched elemental selenium was converted into selenite and selenate by a nitric acid and a combined nitric acid/hydrogen peroxide oxidation, respectively. The conversion was quantitative (>95%) and specific for both inorganic selenocompounds. Selenite and selenate labels were stable in 0.1 mol/l nitric acid for at least 18 months, i.e. making them ideally suitable for use in long-term metabolic studies. An overview of data relating to the absorption and retention of selenium by humans obtained using the two, well-characterised, tracers is presented and indicates that selenite and selenate are equally well retained in adult men and infants, despite differences in their absorption and urinary excretion characteristics.

Humans↗