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1.
Published thermodynamic data measured in aqueous mixtures of sodium or potassium dihydrogen phosphate with hydrogen phosphate
and chloride at 25°C were used to test recently developed methods for calculation of the pH of phosphate buffer solutions.
Equations for ionic activity coefficients are used in these methods. It is shown that all data used in the tests up to an
ionic strength of about 0.5 mol-kg-1 can be accurately predicted by the two methods recommended. In one of these methods, equations of the Hückel type are used
for ionic activity coefficients and in the other equations of the Pitzer type. Several sets of phosphate buffer solutions
are recommended,e.g., for calibrations of glass electrode cells. In the recommended sets, the pH of the buffer solutions can be calculated either
by the Hückel or Pitzer method, and the pH predictions of these methods agree in most cases within 0.005 at least up to ionic
strengths of about 0.2 mol-kg-1. The pH values of the two primary pH standards endorsed by IUPAC based on aqueous mixtures of KH2PO4 and Na2HPO4,i.e., pH values of 6.865 and 7.413, can also be accurately predicted by the equations recommended in this study. 相似文献
2.
Ammonia, isobutane and methane chemical ionization mass spectra have been measured for some substituted cis-1,3-cyclopentane dicarboxylic acids and their derivatives. The relative proton affinities of the different functional groups determine the protonation site in the molecule and thereby greatly affect the fragmentation. Intramolecular catalysis clearly facilitates the elimination of water in cases where functional groups can interact with each other. 相似文献
3.
ICP-MS is used as an element selective detector for chromium species in aquatic samples using a coupled columm system consisting of a cation guard column and an anion column. The effects of large concentrations of disturbing ions, like NO(3)(-), Cl(-), CO(3)(2-) and SO(4)(2-), are discussed and the comparison with the use of different chromium isotopes for data acquisition is given. Quite low concentrations such as 100 mg/l of CO(3)(2-), 10 mg/l Cl(-) and even 5 mg/l SO(4)(2-) can cause an overestimation of chromium if not properly resolved1995 / Accepted: 24 October 1995 相似文献
4.
Pentti Laukkanen 《Fresenius' Journal of Analytical Chemistry》1994,349(8-9):693-695
Anodic stripping voltammetry can be used for the determination of g/l concentrations of lead in gasoline. A gasoline sample is extracted with iodine monochloride reagent solution. An aliquot of the aqueous phase is pipetted into the measuring cell of the voltammeter. The ease of this method makes it a good alternative to atomic absorption spectrophotometry. 相似文献
5.
Kalevi Pihlaja Pentti Oksman Gza Stjer Gbor Bernth 《Journal of mass spectrometry : JMS》1990,25(2):115-118
A mass spectrometric identification and differentiation of pyrimidin-4(3H)- and -4(1H)-ones was carried out. N-Substitution at position 1 or 3 made the distinction of the two sets of compounds very easy because of their characteristic fragmentation pathways. Most interesting were the spectra of the N-unsubstituted derivatives, which illustrated a predominance of the two possible NH tautomers in relation to the 4-hydroxy structure. 相似文献
6.
Pekka Juusola Pentti Minkkinen Lasse Leino Jarmo K. Laihia 《Monatshefte für Chemie / Chemical Monthly》2007,138(10):951-965
Summary. (E)- and (Z)-Urocanic acids are endogenous chemicals in the normal mammalian skin. The first and the second thermodynamic dissociation
constants (pK
a1 and pK
a2) of urocanic acid isomers were determined using UV spectrophotometry in aqueous solutions. The values with standard deviation
(pK
a1 = 3.43 ± 0.12 and pK
a2 = 5.80 ± 0.04) and (pK
a1 = 2.7 ± 0.3 and pK
a2 = 6.65 ± 0.04) were obtained to (E)- and (Z)-urocanic acids, respectively. The second dissociations were studied also by potentiometric titration in aqueous sodium chloride
solutions up to the isotonic salt concentration (0.154 mol dm−3), and the second thermodynamic dissociation constants as well as activity parameters for both isomers were determined at
temperature 25°C and for (E)-urocanic acid also at 37°C. The obtained pK
a2 values were close to those found by UV spectrophotometry. The equations for the calculation of the second stoichiometric
dissociation constants of urocanic acid isomers on molality and molarity scale in aqueous sodium chloride solutions were derived.
The obtained pK
a1 and pK
a2 values for (Z)-urocanic acid appear to be essentially lower than some previously reported values in literature.
An erratum to this article is available at . 相似文献
7.
Pirjo Vainiotalo Pentti J. Mlknen Anto Vainiotalo 《Journal of mass spectrometry : JMS》1989,24(6):415-420
The electron impact induced fragmentations of 24 tetrahydropyrane ethers of different types of alcohols were studied by exact mass measurement and metastable ion analysis. The most characteristic features of the spectra were associated with the tetrahydropyrane ring, As the size of the molecule increased, the fragmentations with respect to exocyclic oxygen became more important allowing differentiation among the isomeric aliphatic alcohols. Under isobutane chemical ionization, loss of neutral alcohol from [M + H]+ leading to the formation of a tetrahydropyranium ion was dominant for aliphatic alcohol derivatives, whereas loss of 2-hydroxy tetrahydropyrane giving rise to an alkyl ion was dominant for bicyclic alcohol derivatives. Under ammonia chemical ionization, nucleophilic substitution reactions were always most important. 相似文献
8.
Matti Varpula Pentti Kiilholma Pekka Klemi Markku Komu 《Magnetic resonance imaging》1994,12(8):1139-1145
The purpose of this investigation was to analyze the normal anatomy and leiomyomas of the uterus with an ultra low field (0.02 T) magnetic resonance imaging (MRI) device. MR imaging was performed on 18 uteri, 11 of which were imaged both preoperatively (in vivo) and as an operative specimen (in vitro), 6 only as an operative specimen, and 1 only preoperatively. All uteri were examined histologically after imaging. The junctional zone was much better delineated in vivo than in vitro, indicating that its appearance on MR is partly due to blood flow. No structures contributing to its visibility in vitro could be demonstrated histologically. Twenty leiomyomas (size range 7–79 mm) in 12 uteri were found with MRI. They were slightly better discerned in vivo than in vitro. The leiomyomas, having no degenerative changes, had a signal intensity which was the same or lower than that of the myometrium. On images obtained in vitro the signal intensity of these leiomyomas relative to that of myometrium correlated directly with their muscular content (R = 0.74, p = .002). The authors conclude that the junctional zone is a sum of physiological and structural factors, the latter being responsible for its in vitro delineation. MR imaging of the uterus in vitro did not give more information than MR imaging in vivo. All leiomyomas larger than 10 mm could be detected, indicating that MR imaging at 0.02 T is an accurate method for the imaging of the uterine leiomyomas. 相似文献
9.
10.
Let h(x) be a polynomial with real coefficients. We introduce h(x)-Fibonacci polynomials that generalize both Catalan’s Fibonacci polynomials and Byrd’s Fibonacci polynomials and also the k-Fibonacci numbers, and we provide properties for these h(x)-Fibonacci polynomials. We also introduce h(x)-Lucas polynomials that generalize the Lucas polynomials and present properties of these polynomials. In the last section we introduce the matrix Qh(x) that generalizes the Q-matrix whose powers generate the Fibonacci numbers. 相似文献