• Analytical Science and Technology
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• v.34 no.3
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• pp.128-133
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• 2021

During titration, several chemical reactions result in changes not only in the potential of chemicals, but also in the colors of the indicator. In a potentiometric titration, a titration curve is obtained by measuring the abrupt change in the potential at the endpoint. Generally, acid-base titration is performed by observing the color change caused by an indicator to determine the endpoint. The method of determining the endpoint by measuring the potential difference has been well established and commercialized; however, the devices that can obtain the endpoint by observing the color change are limited. Consequently, in this study, a simple and precise spectral endpoint detector was manufactured using a drop-counter comprising an infrared emitter and a phototransistor, a white light LED as the light source and photodetector, and an analog-to-digital converter (Arduino). Spectrator, a new named, showed excellent results in terms of the reproducibility of acid-base titration using thymol blue as an indicator. Herein, we present the results of the Spectrator-manufacturing process as well as the experimental results.

• Journal of Photoscience
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• v.9 no.2
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• pp.305-307
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• 2002

Spectroscopic titration of D 193N and D 193E mutants of pharaonis phoborhodopsin (ppR) were performed to evaluate the pK$_{a}$ of the Schiff base Asp 193 corresponds to Glu204 of bacteriorhodopsin (bR). The pK$_{a}$ of the Schiff base (SBH$^{+}$) of D193N was 10.1~10.0 (at XH$^{+}$) and 11.4~11.6 (at X) depending on the protonation state of a certain residue (designated by X) and independent on CI$^{[-10]}$ , while those of the wild-type and D193E were> 12. pK$_{a}$ of XH$^{+}$ were; 11.8~11.2 at the state of SB, 10.5 at SBH$^{+}$ state in the presence of CI$^{[-10]}$ , and 9.6 at SBH$^{+}$ without CI$^{[-10]}$ These imply the presence of a long-range interaction in the extracellular channel.r channel.

• Bulletin of the Korean Chemical Society
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• v.27 no.9
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• pp.1397-1400
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• 2006

A detailed spectroscopic study ($^1H$ NMR, COSY, ROESY) of complexation of venlafaxine hydrochloride (VEN) with $\beta$-cyclodextrin ($\beta$--CD) was carried out in solution. The stoichiometry of the complex was determined to be 1 : 1 and penetration of aromatic ring into $\beta$-Cyclodextrin cavity was confirmed from primary rim side, with the help of ROESY spectral data. The structure of the venlafaxine hydrochloride-$\beta$-CD complex has been proposed. The association constant was determined to be 234 $M^{-1}$.

• Analytical Science and Technology
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• v.34 no.6
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• pp.267-274
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• 2021

Acid-base titration experiments were carried out using the same sample to obtain a direct comparison of analysis results between a new titrator and conventional Spectrator (SPT) titrators. This allowed the confirmation of an endpoint both by spectroscopic detection and by conventional titrators (automatic burette (ABT) and autotitrator (ATT)). Statistical analysis was performed on the measured values (endpoints) obtained using different titrators, to assess their differences by comparison of straightness, equivalence, ANOVA, F-test, and t-test results. The coefficients of determination, confirmed by straightness, were all >0.999. Thus, the null hypothesis that there was no statistical difference could not be rejected. The Bland-Altman analysis method was used to confirm agreement with the new experimental method. No discrepancy was found in the measured values obtained using different titrators used in this study.

• Macromolecular Research
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• v.12 no.6
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• pp.586-592
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• 2004

Poly(glycidyl methacrylate)-grafted polyethylene microbeads (POPM) presenting epoxy groups were prepared by radiation-induced graft polymerization of glycidyl methacrylate on the polyethylene microbead. The obtained POPM was characterized by IR spectroscopic, X-ray photoelectrons spectroscopy (XPS), scanning electron microscope (SEM), and thermal analyses. Furthermore, the abundance of epoxy groups on the POPM was determined by titration and elemental analysis after amination. The epoxy group content was calculated to be in the range 0.29-0.34 mmol/g when using the titration method, but in the range 0.53-0.59 mmol./g when using elemental analysis (EA) after amination. The lipase was immobilized to the epoxy groups of the POPM under various experi­mental conditions, including changes to the pH and the epoxy group content. The activity of the lipase-immobilized POPM was in the range from 160 to 500 unit/mg-min. The activity of the lipase-immobilized POPM increased upon increasing the epoxy group content. The lipase-immobilized POPM was characterized additionally by SEM, elec­tron spectroscopy for chemical analysis (ESCA), and EA.

• Tribology and Lubricants
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• v.35 no.3
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• pp.151-157
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• 2019

Insulated oil degradation produces charged by-products, such as acids and hydro-peroxides, which tend to reduce the insulating properties of the oil. In this study, UV-vis spectroscopy measurement technology is developed and experimentally compared with other measurement methods, such as the titration method and IR spectroscopy, to validate its ability to monitor the degradation of electrical insulating paper. The degradation characteristics of the insulating paper are appropriately represented through various types of measurement methods, such as the Tan (delta) method, $CO_2$ gas production measurement, the titration method, and IR spectroscopy. The results are demonstrated to be well comparable to a change in the fluorescence emission ratio (FER), which is defined as the shift in fluorescence intensity in the measured wavelength range, and also to the chromatic ratio, which is defined as a color shift to longer wavelength ranges. The results also show that, by using UV-vis spectroscopy, it is possible to detect the degradation of the insulating paper. This study suggests that UV-vis spectroscopy can be applied as an alternative to high-performance liquid chromatography, which is the internationally recognized measurement technology for cellulose paper degradation. The FER detector is also verified to be useful as an effective condition-monitoring device for power transformers.

• Bulletin of the Korean Chemical Society
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• v.32 no.3
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• pp.793-799
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• 2011

We report the complexation behavior of calix[4]arenemonoquinone-triacid (CTAQ), which is an electroactive and water-soluble receptor for calcium ion. UV-visible and NMR spectroscopic studies revealed that CTAQ in aqueous media forms 1:2 as well as 1:1 (metal ion:CTAQ) stoichiometric complexes with $Ca^{2+}$, $Sr^{2+}$, and $Ba^{2+}$ ions. The nonlinear fitting of titration curves based on UV-visible absorption spectra showed that the binding constants of CTAQ for $Ca^{2+}$ ion are 4 $({\pm}2){\times}10^6\;M^{-1}$ for 1:1 and 1.4 $({\pm}0.5){\times}10^{11}\;M^{-2}$ for 1:2 complex. NMR conformational studies and the titration curves corroborate that the $Ca^{2+}$:CTAQ complex in aqueous solution is not present in the form of merely 1:1 one, being consistent with UV-visible spectrophotometric results. The Monte Carlo simulation supports the presence of a stable conformer of 1:2 complexes in which a $Ca^{2+}$ ion is interposed between two CTAQs at the global minimum. This is the first model of 1:2 stoichiometric complex of calix[4]arene and alkaline earth ions in aqueous media.

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.916-922
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• 1997

A superconducting phase La2CuO4+δ (Tc=44 K) has been prepared by electrochemical oxidation which allows the oxygen to intercalat into the La2O2 layers. According to the Cu K-edge X-ray absorption near edge structure spectroscopic analysis, the oxidized phase shows an overall spectra shift of about 0.5 eV to a higher energy region compared to the as sintered one with the occurrence of an additional peak corresponding to the transition to the |1s13dn+1L-14pσ1 > final state, indicating the oxidation of CuO2 layer. From the X-ray photoelectron spectroscopic studies, it is found that the binding energy of La 3d5/2 is significantly shifted from 834.3 eV (as sintered La2CuO4) to 833.6 eV (as electrochemically oxidized La2CuO4+δ), implying that the covalency of the (La-O) bond is decreased due to the oxygen intercalation. The O 1s spectra do not provide an evidence of the superoxide or peroxide, but the oxide (O2-) with the contaminated carbonate (CO32-) based on the peaks at 529 eV and 532 eV, respectively, which is clearly confirmed by the Auger spectroscopic analysis. Oxygen contents determined by iodometric titration (δ=0.07) and thermogravimetry (δ=0.09) show good coincidence each other, also giving an evidence for the "O2-" nature of excess oxygen. From the above results, it is concluded that "O2-" appeared as O 1s peak at 528.6 eV is responsible for superconductivity of La2CuO4+δ.

• International Journal of Safety
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• v.9 no.1
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• pp.43-46
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• 2010

In the recycle process of organic solvent, the atmospheric oxygen can cause autoxidation and product peroxide. The time-saving method to evaluate the hazards has been required. In this study, oxygen pressure monitoring experiment was proposed as a new method to evaluate autoxidative resistances of solvents. Some of organic solvents were pressurized by oxygen and kept under isothermal condition. At the same time, the pressure in the vessel tracked. Iodometrical titration, thermal analysis and spectroscopic analysis were performed to measure peroxide concentration, the heat of reaction and chemical bonding change. From the results that THF has larger oxygen consumption rate than CPME, it is considered that autoxidative resistance of THF is lower than that of CPME. This method enables to obtain results in shorter time than other methods. These experimental results were consistent with the previous research with longer test durations [1-2].

• Bulletin of the Korean Chemical Society
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• v.15 no.11
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• pp.1001-1003
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• 1994

A series of phosphodiesters of p-nitrophenyl phosphoryl derivatives were synthesized and used as a model substrate for phospholipase D (PLD). The phosphodiester substrates were synthesized from p-nitrophenyl phosphorodichloridate and corresponding alcohols with different chain lengths and polar groups. To measure the activity of PLD, either spectroscopic method for p-nitrophenol or pH-stat titration method was employed. For each substrate, effects of substrate concentration, pH, and $Ca^{2+}$ ion were examined. The kinetic parameters $V_{max}$ for the different substrates were varied depending on the chain lengths or charge of the alcohols. No calcium effect was observed in the hydrolysis of neutral and negatively charged alcohol derivatives, while positively charged choline derivative showed a strong $Ca^{2+}$ ion dependence.