Application of simplified complementary tristimulus colorimetry to chemical kinetics in solution-I: analysis of reaction mixtures and determination of first- or pseudo first-order rate constants

A graphical method is described which allows estimation of the number of reacting light-absorbing species from the plots of complementary colour points which are obtained with the use of simplified complementary tristimulus colorimetry (SCTS method) from absorption spectra of a series of kinetics solutions. It is shown that the mole function of the reactant or the product at any time can be calculated from the complementary colour points, so that the rate constant can also be determined. The present method has some advantages over the common approach to the determination or reaction rates in presence of a colour impurity.     

Determination of plutonium oxidation states in dilute nitric acid by complementary tristimulus colorimetry

The preparation of reference standards for use in complementary tristimulus colorimetry for plutonium is described. Plutonium(III) and (VI) are prepared by hydrazine reduction and silver(II) oxidation, respectively, of plutonium(IV). Plutonium(V) is prepared by reduction of plutonium(VI) with ascorbic or sulphurous acid. A method for computerizing tristimulus colorimetry is presented, and the technique is extended to three dimensions ("quadristimulus colorimetry").     

Microionization constants of sulphonamides

The macroionization constants and thermodynamic parameters of twelve commercial sulphonamides were determined by potentiometric titration at 15 degrees , 25 degrees and 35 degrees and by spectrophotometry at 25 degrees , in aqueous solution of ionic strength 0.1 (NaClO(4)). The microionization constants and the tautomeric constants (concentration ratios of zwitterion to uncharged or neutral species) were obtained according to the Edsall method combined with complementary tristimulus colorimetry. By utilizing the microionization constants, the species distribution as a function of pH were calculated for the three kinds of sulphonamides.     

A tristimulus colorimetric study of the acid–base properties of 6,7-dihydroxybenzopyrylium chlorides in solutions

The acid–base equilibria of 6,7-dihydroxybenzopyrylium chloride derivatives in solutions are studied by tristimulus colorimetry. The ionization constants of their functional groups are determined. Possible schemes of the equilibria and the distribution diagrams of the ion-molecular forms of the reagents are proposed depending on the pH of the medium. It is shown that tristimulus colorimetry can be used to determine the protonation and hydroxylation constants of the dyes. The relation between these constants and the charges on the oxygen atoms and 2-C atoms of the benzopyrylium ring is established.     

Tristimulus colorimetric and spectrophotometric study of the state of 4-hydroxystyryl dyes in aqueous solutions

Acid-base properties of 4-hydroxystyryl dyes in aqueous solution have been studied by means of chemical tristimulus colorimetry and spectrophotometry. Ionization and hydroxylation constants of the dyes have been determined using chromaticity functions of specific and CIE color difference. It has been shown that aggregation processes in the solution of 4-hydroxystyryl dyes can be observed by means of tristimulus colorimetry. A scheme of acid-base transformations of the studied dyes in the solution has been suggested, and selected spectrophotometric parameters of the equilibrium ionic and molecular forms have been determined.     

数码比色法测定环境及生物样品中的氰化物浓度

在传统氰化物检测方法的基础上,提出了一种新的方法—数码比色法。在一定条件下,苦味酸与氰化物生成黄色化合物,用数码相机对显色溶液拍照,通过数码比色,进行灰度处理,照片的三原色值与氰化物的浓度成线性关系,可以直接分析出其氰化物的浓度。对唾液样品测定,其回收率为98.18%,对照品测定的相对标准偏差RSD为1.5%。研究结果表明,数码比色法具有准确度和精密度都比较理想,方便快速、环境友好等特点。     

Microscopic acid dissociation constants of 3,4-dihydroxyphenylpropionic acid and related compounds, and 3,4-dihydroxyphenylalanine (DOPA)

The dissociation constants of 3,4-dihydroxyphenylpropionic acid and related compounds and of DOPA were determined by potentiometric titration and complementary tristimulus colorimetry at 25 degrees and mu = 0.1 (NaClO(4)) in aqueous solution. The thermodynamic parameters were calculated from the values of the dissociation constants at various temperatures. The dissociation constants and corresponding thermodynamic parameters for the first phenol group of the catechols showed almost the same values as those of the phenol derivatives. In the dissociation of the second phenol group of the catechols, formation of an intramolecular hydrogen bond was indicated. The microscopic acid dissociation constants of 3,4-dihydroxyphenylacetic acid and 3,4-dihydroxyphenylpropionic acid were calculated by two different methods. In the physiological pH-region (pH 7.2-7.4), 3,4-hydroxyphenylpropionic acid is present in the carboxylate form, and the two possible monophenolate anions are present to the extent of about 45% and 40%, respectively, at pH 11.0. The twelve micro-constants for the eight chemical species from DOPA were similarly evaluated.     

Moisture induced solid phase degradation of l-ascorbic acid Part 1: a kinetic study using tristimulus colorimetry and a quantitative HPLC assay

l-Ascorbic acid was found to degrade in the solid phase with discoloration under the influence of moisture in proportion to the moisture content. This degradation pattern was different to that in solution and followed zero order kinetics. The exclusion of air reduced the rate of reaction suggesting the degradation may proceed via an oxidative route but no evidence was found for the presence of dehydroascorbic acid. A method was developed for the determination of dehydroascorbic acid using an automated precolumn reduction reaction with dl-dithiothreitol. The degradation was found to be zero order and activation energy was been measured at 37.57 kJ mol(-1) by high performance liquid chromotography (HPLC) assay and 33.30 kJ mol(-1) by tristimulus colorimetry, resulting in a 12.8% difference between the two methods. Tristimulus colorimetry was more sensitive to the onset of degradation than HPLC assay, but it is non-specific. The purpose of this study was to obtain kinetic data on the rate of degradation of l-ascorbic acid alone under the influence of moisture and air and to identify whether tristimulus colorimetry could be used as a rapid and non-destructive means of monitoring for the degradation of l-ascorbic acid in the solid phase. Further studies to determine the degradation pathway and to identify the degradation products are to be reported in subsequent papers.     

Some studies on the determination of indicator transition and its use in the titration of weak basic samples

In the titration of a weak basic sample, especially in the dilute solution, the transition color of the indicator is not sharp at the equivalence point. In order to avoid the indicator error, the color transition near the equivalence point must be known accurately. The color transition of an acid-base indicator can be calculated from complementary tristimulus data. To ensure accuracy, however, the chemical stoichiometric relationships about the acid-base equilibria are considered. A general expression for determination of the equivalence point is presented and factors influencing the titration are discussed.     

Sulfonephthalein dyes: Part VII. Chromogenic Reactions of Semi-Glycicethymol Blue

The chromogenic reactions of semi-glycinethymol blue have been studied spectrophotometrically and by complementary tristimulus colorimetry. The separation of the dye from a commercial product of glycinethymol blue is described. The five dissociation constants were determined; the means of the pK_a (H_iI) values for i= 5, 4, 3, etc. are —1.5, 0.3, 1.5, 7.5, and 12.7, respectively. Colour reactions with some metal ions are reported; the reaction with copper(II) is suggested for the determination of the composition of commercial samples of glycinethymol blue.     

光声光谱技术在色分析研究中的应用

现行测色法多以常规光谱为基础。通过测量样品对光的透射或反射率以及光源的能量分布,叠合色匹配函数,来寻找颜色的三刺激量,由此获取样品的色别、色饱和度和明度的信息。这些方法的共同特点是定向输入光子,并计量定向输出光子的情况。为了能将测定范围扩展到那些高反射、散射、漫射、辐射和层状样品,对一般常规光谱法是困难的。我们因此提出了光声测色法(PAC)。     

Screened indicators in anhydrous acetic acid medium: Chromatic evaluation of their transitions

Three efficient indicators consisting of Malachite Green and a screening dye for use in anhydrous acetic acid media have been designed by use of complementary tristimulus data. The transition quality can be evaluated by plotting the relative greyness of the indicator against free perchloric acid concentration. Several bases have been successfully determined titrimetrically with use of these indicators.     

Tristimulus analysis for sensors set with either positive or negative sensitivities—determination of the relative concentration of an analyte in a binary mixture

We consider the general case of a set of three sensors that show a response proportional to analyte concentration and apply tristimulus analysis to represent the set of responses as tristimulus coordinates in a two-dimensional representation. These coordinates are a signature of the analyte and can be used for analyte identification. We extend the tristimulus analysis for cases where the sensors may present either positive or negative sensitivities, a situation in which the usual tristimulus analysis has limitations. We propose a different approach, taking the coordinates where the tristimulus vector crosses the unitary radius spherical shell, taking the angular coordinates as signature of the analyte. We also consider the case of binary mixtures and derive the set of equations that can be used to determine the relative concentration of each one of the analytes in the binary mixture from the tristimulus coordinates of the mixture.     

Study of acid-base properties of morin by tristimulus colorimetry

Acid-base properties of morin in aqueous solutions have been studied by means of chemical tristimulus colorimetry, and the ionization constants have been determined. The pK values have been assigned to the corresponding functional groups, and their dissociation scheme has been suggested. Diagram of distribution of ionic and molecular forms of morin at pH 1–13 has been constructed. Spectral parameters of equilibrium acid-base forms of morin have been determined.     

Screening and specification of colour changes of nitritometric indicators

The specification of colour changes of nitritometric indicators, viz., cresyl fast violet acetate, amethyst violet, safranine O, neutral red, methylene violet, neutral violet, phenosafranine, brilliant cresyl blue and lissamine blue BF, in the titration of sulphanilamide has been carried out with the help of tristimulus colorimetry. Apart from the determination of true colour co-ordinates and complementary colour co-ordinates, the quantitative parameters specific colour discrimination (SCD), total colour difference (E*) values of CIE La^*b^*, CIE Lu^*v^* and LAB HNU colour spaces together with the standard deviation of colour matching (S) were also evaluated for all the indicators at different concentrations ratios of nitrite and sulphanilamide, for a quantitative measure of quality of colour change. The quality of colour change of many of the studied indicators is further improved by screening with appropriate inert colorants to obtain a colour transition between complementary colours through colourlessness at the equivalence point.     

Theoretical prediction of emulsion color

The perceived quality of many commercial products that are based on emulsions is determined by their color. In this article, a theory is presented to relate the color of emulsions to their composition and microstructure. First, the scattering characteristics (Qs and g) of individual droplets are calculated using Mie Theory. Second, the scattering (S) and absorption (K) coefficients of a concentrated emulsion are calculated using radiative transfer theory. Third, the reflectance spectrum (R) of the emulsion is calculated using Kubelka-Munk Theory. Finally, the tristimulus coordinates (XYZ, or L*a*b*) of the emulsion are calculated using color theory. There is excellent agreement between theoretical predictions and experimental measurements of the influence of droplet and chromophore characteristics on the tristimulus coordinates of concentrated oil-in-water emulsions.     

Evaluation of the quality of colour changes of complexometric indicators in the titration of copper (II) with EDTA by tristimulus colorimetry

The quality of colour changes of the indicators hematoxylin, 4(2-pyridylazo)resorcinol (PAR), xylenol orange, pyrocatechol violet, chromazurolS and eriochrome cyanineR in the complexometric titration of copper(II) with ethylenediaminetetraacetic acid (EDTA) were studied with the help of tristimulus colorimetry, utilising a comparative study of the parameters SCD (specific colour discrimination), CIE La^*b^* 1976 and LABHNU 1977. Hematoxylin was found to be the best indicator among those studied. A screened indicator, viz. PAR + malachite green (52), was developed to enhance the quality of colour transition at the end-point and the accuracy of the titrimetric determination.     

The brilliant blue FCF ion-molecular forms in solutions according to the spectrophotometry data

The brilliant blue FCF acid–base properties in aqueous solutions have been studied and its ionization constants have been defined by tristimulus colorimetry and spectrophotometry methods. The scheme of the acid–base dye equilibrium has been proposed and a diagram of the distribution of its ionic-molecular forms has been built. It has been established that the dominant form of the dye was the electroneutral form, which molar absorptivity (ε₆₂₅ = 0.97 × 10⁵) increases with the increase of the dielectric permittivity of the solvent. It has been shown that the replacement of polar solvents by less polar ones is causing a bathochromic shift of the maximum absorption band of the dye, the value of which is correlated with the value of the Hansen parameter. Tautomerization constants have been defined in a number of solvents and associated with the value of the Dimroth-Reichardt parameter.     

酸洗比色法在直链烷基苯生产质量控制中的应用

对于首次应用于大亚湾中微子物理实验的液体闪烁介质——直链烷基苯( LAB)的工业化生产,其最重要的质量控制指标为光衰减长度,这通常需要在实验室里利用专门仪器进行测量分析.经过对比研究,在LAB工业化生产流程的基础上,建立了相应的测试方法——酸洗比色分析方法,即使直链烷基苯和98.4％的发烟硫酸反应,在波长403 nm处...     

光度法快速分析苯乙酮酸含量的研究

研究了一种快速定量分析发酵液中苯乙酮酸的方法。在氢氧化钠溶液中,苯乙酮酸和2,4-二硝基苯肼形成一种红棕色的溶液,该溶液在458 nm处有最大吸收,据此可以快速分析混合物中苯乙酮酸的含量。该法在微生物还原苯乙酮酸生产D-扁桃酸的工艺中进行样品分析,结果表明方法简便、快速、灵敏度高,可以用于监控反应进程。