羟氨苄青霉素的微观电离常数

测知酸碱性物质的微观电离常数, 对全面深入地了解该物质的化学行为及生物活性均很重要, 本文报道了用电位滴定法和分光光度法, 测求羟氨苄青霉素在20℃时的微观电离常数.     

盐酸美西律的两点滴定法和沉淀电位滴定法测定

利用过滤和不过滤两种方式配制盐酸美西律试液,分别采用两点滴定法和沉淀电位滴定法测定了盐酸美西律片的含量.结果表明,基于两种测定方法的测定结果均处于《药典》规定的范围之内;与《药典》规定的紫外分光光度法测定结果相比,相对偏差均小于2%.而采用过滤方法配制试液的测定结果与采用不过滤方法配制试液的测定结果之间的偏差约为1%.     

钝感炸药DNP和NTO的酸性解离常数的测定方法研究

采用滴定法、半中和法、p H法、电导率法、紫外分光光度法5种方法,测定了3,4-二硝基吡唑(DNP)和3-硝基-1,2,4-三唑-5-酮(NTO)两种钝感炸药的酸性解离常数p Ka,并对不同方法所测的结果进行比较和讨论。结果表明,滴定法、半中和法、紫外分光光度法3种方法适合DNP类物质的p Ka测定,实验结果基本一致,与文献值的相对误差RE5%;滴定法、p H法更适合NTO类物质的p Ka测定,实验结果基本一致,与文献值的相对误差RE4%。DNP的p Ka大于NTO的p Ka,即DNP比NTO的酸性弱,对设备等的腐蚀作用较小,更适宜用作熔铸炸药载体。根据这5种酸性解离常数测定方法的优缺点,讨论了测定不同性质物质的p Ka时可选用的方法。     

三种方法联合测试硝酸-氢氟酸-醋酸混酸组成

提出了测定硝酸-氢氟酸-醋酸体系各酸的方法。采用紫外分光光度法、沉淀法分别测试硝酸和氢氟酸含量,电位滴定法测定总酸含量,减去硝酸和氢氟酸得到醋酸含量。分光光度法测试硝酸相对标准偏差(RSD)在0.20%左右,沉淀法测试氢氟酸RSD不大于0.81%,该法测试醋酸RSD在0.40%左右,并进行了样品加入回收和空白加入回收验证。     

偶氮氯膦-mA(CPA mA)离解作用的研究

本文用pH电位法和分光光度法研究了偶氮氯膦-mA的六级离解作用,测定了其逐级电离常数,计算了离解过程的热力学参数△G°、△H°、△S°,同时与对硝基偶氮氯膦的离解常数进行了比较,其结果与量子化学计算基本相符。     

应用最小二乘法于壳聚糖测定的数据处理

应用紫外分光光度法和旋光法分别测定了壳聚糖的含量.在建立壳聚糖浓度与吸光度(紫外分光光度法)及壳聚糖浓度与旋光度(旋光法)之间的线性方程中,采用最小二乘法(LS法)对相关数据进行了处理.试验结果所示:用LS法所得上述两种测定方法的拟合曲线得出的测定结果,与常规方法所得曲线相比,具有更高的精密度和准确度.再者,两种测定方法的拟合曲线相比较,紫外分光光度法的曲线具有更高的精密度.     

双等色点光度法测定姜黄素-铁(Ⅱ)的稳定常数及试验方法改进

采用双等色点光度法测定姜黄素-铁(Ⅱ)络合物的稳定常数并对试验方法进行了改进。采用两种紫外-可见分光光度法设计试验方案,考察了姜黄素的光谱特性,获得姜黄素与铁(Ⅱ)的络合物吸收光谱中两个等色点,姜黄素-铁(Ⅱ)络合物的稳定常数为1.48×1011(pH 6.50),改进后试验方法的稳定常数为1.49×1011。     

顺二氨二水合铂(Ⅱ)离子与半胱氨酸等的络合反应——电位法及分光光度法研究

用电位滴定法及分光光度法研究了顺二氨二水合铂(Ⅱ)离子与半胱氨酸、蛋氨酸及谷胱甘肽的络合反应.用电位滴定法测定[(NH_3)_2PtA](A 为氨基酸)型混合配体络合物的形成常数β,测得 A 为半胱氨酸及蛋氨酸时,1gβ分别为7.55及8.70.按(?)=0.5处 pA 计算谷胱甘肽络合物的最可能1gβ为9.00.用 Job 分光光度法测得结果与之符合.据此讨论了络合物的可能结构.在所有情况中,硫可能是优先配位原子.     

平痛新离子选择电极的研制及应用

盐酸平痛新是一种新型的无依赖性镇痛药物。其含量测定有紫外分光光度法、滴定法、酸性染料比色法等方法。本文以盐酸平痛新与硫氰酸铬酸形成的缔合物为电活性物制备了 PVC膜盐酸平痛新离子选择性电极 ,并用此电极对盐酸平痛新片的含量进行了测定 ,结果与紫外分光光度法相符。     

毛细管区带电泳法测定3种香豆素的离解常数

采用毛细管区带电泳法(CZE)测定瑞香苷(DN)、瑞香素(DP)和7-羟基香豆素(7-HC)的离解常数(p Ka).通过测试不同酸度条件下各香豆素的迁移时间,以香豆素在电泳中有效淌度和运行液中OH-浓度的关系,推导了毛细管区带电泳-紫外分光光度(CZE-UV)法测定3种香豆素离解常数(p Ka)的线性模型,并建立了这3种香豆素的p Ka测定方法.测得3种香豆素的p Ka值分别是7.43(7-HC)、6.91(DN)和6.86(DP).同时也采用传统方法 -紫外分光光度法对这些物质的p Ka进行测定以验证CZE的可靠性,两种测定结果相一致,说明CZE-UV法用于3种香豆素的离解常数的测定,快速、简便、结果可靠.     

Determination of dissociation constants for coordination compounds of Cr(III) and Co(III) using potentiometric and spectrophotometric methods

The acid–base properties of analogous complex ions of chromium(III) and cobalt(III) in aqueous solution have been studied. The equilibrium constants for all metal complexes were determined by using potentiometric and spectrophotometric titration methods. First, dissociation constants for the studied complexes of Cr(III) and Co(III) were determined by means of the potentiometric titration method and using the STOICHIO computer programme. Then, pH-spectrophotometric titrations were performed and the OriginPro 7.5 computer programme was used to calculate the same constants. The measurements using both methods were carried out under the same conditions of temperature, T = 298.15 K, and over the same pH range 2.00–10.00, respectively. It turned out that the two methods used enabled us to obtain acidity constants in very good agreement.     

Thermal and Potentiometric Titrations of Phytic Acid

Abstract

Values for the ionization constants and the heats of ionization of phytic acid (inositol hexaphosphate) have been determined by simultaneous potentiometric and thermal titration in a titration microcalorimeter. The potentiometric results are in substantial agreement with those found by discontinuous titration; the heat liberated from pH 10.4 to 6.8 is essentially that found using a batch microcalorimeter. Ionization of phytic acid may be generally characterized as having five groups similar to pK of phosphoric acid, two groups similar to pK2 of phosphoric acid and 4 groups similar to pK4 of pyrophosphoric acid. A single group has pK ～ 5 with ΔH_i ～ -1.1 kcal/mol.     

The acid dissociation constants of 2,3-quinoxalinedithiol

Sodium salts of 2,3-quinoxalinedithiol have been prepared and used for determination of the acid ionization constants by potentiometric titration. The fully protonated form of the reagent was used in an alternative determination of the first ionization constant by a solubility method. The constants are pK(2), == 6.84 +/- 0.04 and pK(2) = 9.95 +/- 0.03.     

Characterization of the ionization and spectral properties of mercapto-carboxylic acids Correlation with substituents and structural features

The ionization constants in aqueous solutions of meso- and dl-dimercaptosuccinic acid and of monomethyl and dimethyl meso-succinates were carefully determined by potentiometric and spectrophotometric methods as a result of the increasing interest in these molecules as heavy metal chelators. In order to explain the influence of various substituents on ionization and (13)C NMR properties, the study was extended to the related oxygen derivatives of succinic acid and to simpler ethanoic derivatives. With the Swain-Lupton dual substituent treatment it was possible to clarify the influence of substituents on both spectral and equilibrium parameters. The differences in pK due to conformation are also discussed.     

pH-switchable porphyrin receptor for binding halide ions

Main properties of 5,10,15,20-tetra(4-chlorophenyl)porphyrin in the acetonitrile-perchloric acid system were studied by the method of spectrophotometric titration at standard temperature. The protonation of nitrogen atoms of the tetrapyrrole macrocycle was shown to occur in two steps, through the formation of mono- and diprotonated forms. The corresponding ionization constants and concentration intervals were determined. The diprotonated form of porphyrin was shown to bind effectively iodide, bromide and chloride ions, the stability constants of the complexes of 1:1 and 1:2 composition were determined.     

FIA titrations of phenothiazine derivatives in aqueous micellar and non-aqueous media

New methods of flow injection analysis (FIA) neutralization titrations of phenothiazine derivatives in aqueous micellar medium of a cationic surfactant using potentiometric and spectrophotometric detection were proposed; titrations with a mixing gradient chamber and high-speed titrations were compared. The FIA titration method in non-aqueous media based on an official method of determination (titration with perchloric acid in anhydrous acetic acid) was also developed. Under optimized reaction conditions and flow-through parameters, the calibration range and equations, the sensitivity, and the repeatability of all methods were found and discussed. All titrations were assayed for medicinal forms.     

pH-switched porphyrin receptor: I. Binding of iodide ions

The basic properties of 5,10,15,20-tetra(4-chlorophenyl)porphyrin in the acetonitrile-perchloric acid system at standard temperature were studied by spectrophotometric titration. The protonation of nitrogen atoms of the tetrapyrrole macrocycle was found to proceed in two steps to give mono- and diprotonated species. The corresponding ionization constants and concentration ranges were determined. Diprotonated porphyrin binds efficiently iodide ions; the stability constants of the 1: 1 and 1: 2 complexes thus formed were determined.     

Equilibrium constants and assay of benzodiazepines in acetic acid

The over-all dissociation constants, in anhydrous acetic acid, of a series of benzodiazepines have been determined. A method is described for evaluating the formation constants of the perchlorate salts. From these values simple potentiometric and visual titration methods for the assay of benzodiazepines in acetic acid are described.     

Simultaneous determination of equivalence volumes and acid dissociation constants from potentiometric titration data

New iterative methods for analysis of potentiometric titration data of (a) mixtures of weak monoprotic acids with their conjugate bases, (b) solutions of polyprotic (di- and triprotic) acids, and (c) mixtures of two diprotic acids are presented. These methods, using data exclusively resulting from the acidic region of the titration curve permits the accurate determination of the analytical concentration of one or more acids even if the titration is stopped well before the end point of the titration. For the titration of a solution containing a conjugate acid/base pair, the proposed procedure enables the extraction of the initial composition of the mixture, as well as the dissociation constant of the concerned acid. Thus, it is possible by this type of analysis to distinguish whether a weak acid has been contaminated by a strong base and define the extent of the contamination. On the other hand, for the titration of polyprotic acids, the proposed approach enables the extraction of the accurate values of the equivalence volume and the dissociation constants K(i) even when the ionization stages overlap. Finally, for the titration of a mixture of two diprotic acids the proposed procedure enables the determination of the composition of the mixture even if the sum of the concentrations of the acids is not known. This method can be used in the analysis of solutions containing two diastereoisomeric forms of a weak diprotic acid. The test of the proposed procedures by means of ideal and Monte Carlo simulated data revealed that these methods are fairly applicable even when the titration data are considerably obscured by 'noise' or contain an important systematic error. The proposed procedures were also successfully applied to experimental titration data.     

Relation between the structure and extracting power of higher tertiary amines

The effect of the composition and structure of higher tertiary amines on their efficiency in extracting nitric acid has been examined. The ionization constants of the amines in methanol have been determined by potentiometric titration. The extraction constants for nitric acid have been determined at constant ionic strength in the aqueous phase (μ=1). The dependence of these constants upon the concentrations and the degree of association of the amine salts in the organic phase has been examined. For the cases in which the role of steric factors is negligible it has been shown that at low amine salt concentrations in the organic phase there are quantitative regularities between the ionization constants of the amines in methanol, their extraction constants for nitric acid and the inductive effects of the substituents on the nitrogen atom.