No description available.

Nearshore and estuarine environments play a vital role in the cycling of carbon, but the effects of ocean acidification in estuarine waters have not been studied as extensively as in the open ocean. One reason for this is the limitation of pH measurement capabilities in low-salinity waters. Typically, pH in these environments has been measured using potentiometric methods that are subject to uncertainties on the order of 0.01. Spectrophotometric methods for measuring pHT offer precision and accuracy superior to those of potentiometric methods. However, previous characterizations for purified sulfonephthalein indicators, used for marine spectrophotometric measurements, are not applicable to estuarine salinities. Some estuarine datasets using unpurified indicators exist, but the presence of dye impurities affects the accuracy of these characterizations. Colorimetric impurities are known to interfere with absorbance measurements and can cause errors in pH on the order of 0.02. In this work, a mathematical model has been developed to correct spectrophotometric pHT determined with unpurified m-Cresol Purple (mCP), the indicator used most widely for these measurements. The model accounts for absorbances of colorimetric impurities that interfere with absorbance by mCP. This corrective approach brings measurements made using unpurified mCP in synthetic solutions of 0.7 M NaCl into better agreement with those made using purified mCP: within ±0.004 pH units for all six indicators tested at pHT ≤ 8.0. The model is useful for both (a) research groups currently using unpurified mCP to measure pHT, and (b) retrospective correction of historic pHT datasets collected using unpurified mCP. The correction requires only that a small sample of the unpurified mCP is saved for a single-point test at high pHT (~12), and that historic absorbance measurements are archived for subsequent correction. The principles of the corrective model were applied to an historic calibration of the mCP dissociation constant (KI) at 0 ≤ S ≤ 40 and T = 298.15 K using unpurified indicator. After correction of absorbances for dye impurities, recalculation of KI was performed, and the recalculated values were combined with mCP KI data for freshwater and seawater. The combined dataset was then refitted as a function of S and T. The resulting model is representative of mCP behavior across 0 ≤ S ≤ 40 and 278.15 ≤ T ≤ 308.15 K and produces p(KIe2) values that are within ±0.004 of p(KIe2) values from previously published purified mCP calibrations. This refitting approach was also applied to pHT determinations made with Thymol Blue (TB) and Cresol Red (CR), two sulfonephthalein indicators that have been previously used in waters outside the indicating range of mCP. The models, which were of the same form as the estuarine p(KIe2) model for mCP, performed approximately as well as the mCP model: with the exception of one high-salinity, high-temperature TB datum, all residuals were within ±0.0043 of the previously published TB and CR calibrations. Finally, an internal consistency analysis was performed using carbon chemistry data collected during two recent coastal ocean acidification research cruises. For pHT measurements performed during both cruises, purified mCP was used, and corresponding measurements of total alkalinity (TA) and dissolved inorganic carbon (DIC) were conducted. Both cruises included excursions into the Columbia River, where low salinities prevent usage of the marine p(KIe2) model for purified mCP. The Columbia River samples provided the opportunity to evaluate the internal consistency of pHT measurements made in low-salinity waters using the refitted estuarine p(KIe2) model. Although internal consistency agreement in the estuarine range is poor compared to marine measurements, pHT calculated using the new estuarine model compared well with pHT calculated using the previously published estuarine mCP model. The poor internal consistency in the estuarine range, even when making state-of-the-art pH measurements, points toward the need for a more robust characterization of the carbonic acid dissociation constants in the estuarine salinity range. This characterization should take into account the contributions of organic acids to total alkalinity in nearshore waters.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1963. / Includes bibliographical references (p. 71-74).

No description available.

O para-cresol (4-metilfenol) e as guanidinas são compostos envolvidos em uma série de processos bioquímicos e fisiológicos. Em condições normais esses compostos são eliminados do organismo pelos rins. Entretanto, em pacientes com doença renal crônica (DRC), esses compostos acumulam nos fluidos biológicos e tecidos, e são de difícil remoção, gerando alta taxa de mortalidade em pacientes humanos hemodialisados. Cromatografia gasosa (GC) e cromatografia líquida de alta eficiência (HPLC) são as técnicas analíticas mais utilizadas para a separação e quantificação de p-cresol e guanidinas. A derivatização pré ou pós-coluna geralmente é empregada para aumentar a volatilidade, absorbância ou fluorescência desses compostos, permitindo a detecção e quantificação. A ninidrina é um dos reagentes mais utilizados para a derivatização das guandinas pois apresenta alta sensibilidade, solubilidade em água e o procedimento aplicado para a derivatização é simples, permitindo a automação do sistema de preparo de amostras quando necessário. Embora haja vários estudos sobre a concentração e os efeitos desses compostos no sangue de pacientes humanos com DRC, a concentração de p-cresol e das guanidinas no sangue de cães com DRC e os efeitos associados a tais compostos foram pouco estudados. Assim, são necessários estudos similares aos realizados em humanos, para o desenvolvimento de novas estratégias de tratamento veterinário para cães. Para isso, é importante o desenvolvimento de uma metodologia analítica para a quantificação desses compostos no sangue de cães. Nesse trabalho desenvolveu-se, validou-se e aplicou-se um método para análise de p-cresol e guanidinas em plasma de cães urêmicos com detecção por fluorescência. A reação de derivatização das guanidinas com a ninidrina foi revisada, caracterizada por espectrometria de massas (MS) e otimizada utilizando planejamento fatorial. Foi analisado um total de 63 amostras de plasma de cães incluindo grupo controle e urêmico. A concentração média de guanidina, metilguanidina e p-cresol livre determinada foi maior no grupo urêmico do que no grupo controle, a exemplo do que ocorre em humanos, sugerindo um comportamento metabólico similar desses compostos em cães. O método desenvolvido possibilitou as análises, sendo relativamente simples, evitando um preparo de amostras complexo. Por sua vez, a otimização por planejamento fatorial da reação de derivatizacão com ninidrina resultou em ganhos na área dos picos cromatográficos que chegaram a 1000%. / Para-cresol (4-methylphenol) and guanidino compounds are involved in a series of biochemical and physiological cycles. Under ordinary conditions, these compounds are excreted from the body by healthy kidneys. However, in uremic patients, the concentration of these compounds is highly increased in biological fluids and tissues and is of hard removal, increasing the mortality rate in dialysis patients. Gas chromatography (GC) and high performance liquid chromatography (HPLC) are the most used techniques for separation and quantification of p-cresol and guanidino compounds. For the guanidines determination, derivatizing reactions are usually employed to enhance the absorbance, fluorescence or volatility of these compounds, allowing the quantification. Ninhydrin is one of the most used reagents for derivatization because it shows high sensitivity and presents water solubility. The procedure employed for the derivatization reaction is simple, allowing the automation of sample preparation system, when it is required. There are few studies quantifying the concentration of guanidino compounds and p-cresol in blood of uremic dogs, therefore, a better understanding of the role of these compounds in the metabolism of dogs are needed. For this reason, it is important to develop an analytical method for the quantification of these compounds in dog\'s blood. The development of a method for simultaneous determination of these compounds, which is not reported in the literature, can improve the analytical productivity, decreasing the time spent with sample preparation and analysis. Here, a method based in reversed-phase HPLC for simultaneous quantification of guanidino compounds and free p-cresol in plasma of uremic dogs with fluorescence detection was developed, validated and applied. For this purpose, the ninhydrin derivatization reaction was reviewed, characterized by mass spectrometry (MS) and optimized using central composite design (CCD). A total of 63 samples of dog plasma, including healthy and uremic groups, were analyzed. The mean concentration of guanidine, methylguanidine and free p-cresol determined by the validated method, for the uremic group, were higher than the healthy group, alike usual for humans, suggesting a similar metabolic behavior of these compounds in dogs. The obtained method is relatively simple avoiding complex sample preparation and the experimentally designed optimization of the ninhydrin reaction by CCD yielded a gain of area as high as 1000% for the chromatographic peaks.

O para-cresol (4-metilfenol) e as guanidinas são compostos envolvidos em uma série de processos bioquímicos e fisiológicos. Em condições normais esses compostos são eliminados do organismo pelos rins. Entretanto, em pacientes com doença renal crônica (DRC), esses compostos acumulam nos fluidos biológicos e tecidos, e são de difícil remoção, gerando alta taxa de mortalidade em pacientes humanos hemodialisados. Cromatografia gasosa (GC) e cromatografia líquida de alta eficiência (HPLC) são as técnicas analíticas mais utilizadas para a separação e quantificação de p-cresol e guanidinas. A derivatização pré ou pós-coluna geralmente é empregada para aumentar a volatilidade, absorbância ou fluorescência desses compostos, permitindo a detecção e quantificação. A ninidrina é um dos reagentes mais utilizados para a derivatização das guandinas pois apresenta alta sensibilidade, solubilidade em água e o procedimento aplicado para a derivatização é simples, permitindo a automação do sistema de preparo de amostras quando necessário. Embora haja vários estudos sobre a concentração e os efeitos desses compostos no sangue de pacientes humanos com DRC, a concentração de p-cresol e das guanidinas no sangue de cães com DRC e os efeitos associados a tais compostos foram pouco estudados. Assim, são necessários estudos similares aos realizados em humanos, para o desenvolvimento de novas estratégias de tratamento veterinário para cães. Para isso, é importante o desenvolvimento de uma metodologia analítica para a quantificação desses compostos no sangue de cães. Nesse trabalho desenvolveu-se, validou-se e aplicou-se um método para análise de p-cresol e guanidinas em plasma de cães urêmicos com detecção por fluorescência. A reação de derivatização das guanidinas com a ninidrina foi revisada, caracterizada por espectrometria de massas (MS) e otimizada utilizando planejamento fatorial. Foi analisado um total de 63 amostras de plasma de cães incluindo grupo controle e urêmico. A concentração média de guanidina, metilguanidina e p-cresol livre determinada foi maior no grupo urêmico do que no grupo controle, a exemplo do que ocorre em humanos, sugerindo um comportamento metabólico similar desses compostos em cães. O método desenvolvido possibilitou as análises, sendo relativamente simples, evitando um preparo de amostras complexo. Por sua vez, a otimização por planejamento fatorial da reação de derivatizacão com ninidrina resultou em ganhos na área dos picos cromatográficos que chegaram a 1000%. / Para-cresol (4-methylphenol) and guanidino compounds are involved in a series of biochemical and physiological cycles. Under ordinary conditions, these compounds are excreted from the body by healthy kidneys. However, in uremic patients, the concentration of these compounds is highly increased in biological fluids and tissues and is of hard removal, increasing the mortality rate in dialysis patients. Gas chromatography (GC) and high performance liquid chromatography (HPLC) are the most used techniques for separation and quantification of p-cresol and guanidino compounds. For the guanidines determination, derivatizing reactions are usually employed to enhance the absorbance, fluorescence or volatility of these compounds, allowing the quantification. Ninhydrin is one of the most used reagents for derivatization because it shows high sensitivity and presents water solubility. The procedure employed for the derivatization reaction is simple, allowing the automation of sample preparation system, when it is required. There are few studies quantifying the concentration of guanidino compounds and p-cresol in blood of uremic dogs, therefore, a better understanding of the role of these compounds in the metabolism of dogs are needed. For this reason, it is important to develop an analytical method for the quantification of these compounds in dog\'s blood. The development of a method for simultaneous determination of these compounds, which is not reported in the literature, can improve the analytical productivity, decreasing the time spent with sample preparation and analysis. Here, a method based in reversed-phase HPLC for simultaneous quantification of guanidino compounds and free p-cresol in plasma of uremic dogs with fluorescence detection was developed, validated and applied. For this purpose, the ninhydrin derivatization reaction was reviewed, characterized by mass spectrometry (MS) and optimized using central composite design (CCD). A total of 63 samples of dog plasma, including healthy and uremic groups, were analyzed. The mean concentration of guanidine, methylguanidine and free p-cresol determined by the validated method, for the uremic group, were higher than the healthy group, alike usual for humans, suggesting a similar metabolic behavior of these compounds in dogs. The obtained method is relatively simple avoiding complex sample preparation and the experimentally designed optimization of the ninhydrin reaction by CCD yielded a gain of area as high as 1000% for the chromatographic peaks.

This work provides improved procedures for spectrophotometric carbon system measurements. Indicator dyes used for routine spectrophotometric pH measurements in seawater suffer from impurity issues, which introduce vendor-specific systematic errors in pH determinations. The magnitude of these errors for several vendors was investigated for meta Cresol Purple (mCP) and Cresol Red (CR). Flash chromatography procedures were developed to obtain purified mCP and CR on a bulk scale in order to supply the oceanographic research community with the indicators. Easy access to the purified indicators ensures global intercomparability of spectrophotometric pH determinations. Internal consistency of marine inorganic carbon system measurements was studied using datasets obtained on two large coastal ocean acidification research cruises. In both cases, purified mCP was used to obtain the pH measurements, thereby improving accuracy relative to previous studies in which measurements were obtained with unrefined mCP. Based on this internal consistency study, recommendations are made for selecting the parameter pairs used for saturation state calculations. Direct spectrophotometric methods for measuring carbonate ion concentrations in seawater were improved by (a) using a higher concentration of lead as the carbonate indicator and (b) altering the carbonate computational algorithm based on high quality field data. Measurements of DIC and pH (using purified mCP) were used to calculate carbonate ion concentrations for comparison with spectrophotometrically measured carbonate ion concentrations (i.e., via spectrophotometric measurements of Pb(II) spectra in the ultraviolet). Minor changes in the computational algorithm substantially improved agreement between measured and calculated carbonate ion concentrations.

The flexible substrate was fabricated by BaTi4O9 mixed with O-Cresol Novolac Epoxy, polyether imide or surface active agents. The electrical and physical characteristic measured had been finished. The dielectric property influence of substrate was changed from percentage of BaTi4O9. The dielectric constant model was used by Jayasundere and Smith equation (J. S. eq.) and Lichtenecker equation (L. eq.) The study of crystalline grain, orientation and phase transfer temperature was used by SEM, XRD, and DSC, respectively. The dielectric constant and dielectric loss tangent of the composite was measured using an HP4294A impedance analyzer. The TM mode calculated by resonate frequency of the composite was measured using an HP4156C network analyzer. The dielectric constant was obtained to TM mode at high frequency. The result was showed that dielectric constant at low frequency of BaTi4O9, OCN Epoxy and PEI are 57, 5.8 and 3.65, respectively. OCN Epoxy is better than PEI of electrical characteristic. However, OCN Epoxy is not flexible. For this reason, the PEI was focused on electrical property at high frequency. The BaTi4O9 exhibited a dielectric constant of 39 at frequency during 3~10 GHz. The dielectric constant was measured of 10 at frequency during 2~16 GHz with 70 wt% PEI composite. The dielectric constant is higher than FR-4 substrate to 6.4 of the composite. The low dielectric constant is obtaining to reduce stuffing.

No description available.

Void-free phenolic networks have been prepared by the reaction of phenolic novolac resins with various diepoxides. The stoichiometric ratio can be adjusted to achieve networks with good mechanical properties while maintaining excellent flame retardance. A series of linear, controlled molecular weight, 2,6-dimethylphenol endcapped cresol novolac resins have been synthesized and characterized. The molecular weight control was achieved by adjusting the stoichiometric ratio of cresol to 2,6-dimethylphenol and using an excess of formaldehyde. A dynamic equilibrium reaction was proposed to occur which allowed the targeted molecular weight to be obtained. A 2000 g/mol ortho-cresol novolac resin was crosslinked by a diepoxide oligomer and by an epoxidized phenolic oligomer in defined weight ratios and the structure-property relationships were investigated. The networks comprised of 60 or 70 weight percent cresol novolac exhibited improved fracture toughness, high glass transition temperatures, low water uptake, and good flame retardance. The molecular weights between crosslinks were also determined for these networks. The stress relaxation moduli were measured as a function of temperature near the glass transition temperatures. Crosslink densities as well as the ability to hydrogen bond affect the glassy moduli of these networks. Rheological measurements indicated that cresol novolac/epoxy mixtures have an increased processing window compared to phenolic novolac/epoxy mixtures. Maleimide functionalities were incorporated into cresol novolac oligomers, and these were crosslinked with bisphenol-A epoxy. The processability of oligomers containing thermally labile maleimides were limited to lower temperatures. However, sufficiently high molecular weight oligomers were necessary to obtain good network mechanical properties. Networks prepared from 1250 g/mol cresol novolac containing maleimide functionilities and epoxy exhibited good network properties and could be processed easily. Latent triphenylphosphine catalysts which are inert at processing temperatures (~140°C) but possess significant catalytic activity at cure temperatures 180-220°C were necessary for efficient composite fabrication using phenolic novolac/epoxy matrix resins. Both sequestered catalyst particles and sizings were investigated for this purpose. Phenolic novolac/epoxy mixtures containing sequestered catalysts exhibited significantly longer processing time windows than those containing free catalysts. The resins also showed accelerated reaction rates in the presence of sequestered catalysts at cure temperatures. Trihexylamine salt of a poly(amic acid) was sized onto reinforcing carbon fibers and the composite properties indicated that fast phenolic novolac/epoxy cure could be achieved in its presence. / Ph. D.