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1.
While there is a considerable interest in the food industry in determining various analytes using ion-selective electrodes (ISEs), only few reports describe their use for direct measurements in food. In this study, the suitability of glass electrodes and ionophore-based solvent polymeric ISEs for the determination of pH in Process cheese, Cheddar cheese and milk was investigated. The liquid junction potential between a 3 M KCl bridge electrolyte and diluted as well as undiluted Process cheese was found to be negligible. Reference electrodes with ceramic plug and sleeve-type junctions performed well, although precautions needed to be taken to prevent plugging at the junctions. While the protein rennet casein posed no problems in pH measurements, the extraction of neutral lipophilic compounds or hydrophobic peptides into solvent polymeric membranes was evident, resulting in some loss of selectivity for monovalent cations upon exposure to cheese. However, it was found that ISEs based on tridodecylamine (R3N) as ionophore and o-nitrophenyl octyl ether (oNPOE) as plasticizer can be used to accurately measure the pH of milk and, after desensitization of the electrodes in a cheese emulsion, of diluted Process cheese. Since pH measurements with a glass electrode showed that emulsions of cheese moderately diluted to a cheese content of 70% have the same pH as undiluted cheeses, it is possible to determine the pH in cheese with ionophore-based ISEs. R3N membranes also performed well in undiluted milk. 相似文献
2.
EPR studies of Gd3+ doped in single crystals of Nd2(SO4)3·(NH4)2SO4·8H2O (hereafter referred to as NASO) at room (RT) and liquid nitrogen (LNT) temperatures exhibit that (1) the metal aquo complex has a tetragonal symmetry with abnormally low magnitudes of crystalline field parameters at RT and (2) NASO undergoes a possible phase transition between RT and LNT. 相似文献
3.
G.C. Upreti 《Chemical physics letters》1973,18(1):120-122
EPR of Mn2+ has been studied in cobalt ammonium sulphate hexahydrate from ≈ 90°K to ≈ 373°K. The spin-hamiltonian analysis is presented. It is concluded that the coordination of water ligands around the divalent ion is almost the same as that in other Tutton salts. 相似文献
4.
The contribution of the ferroelectric soft-mode to the zero-field splitting is calculated and separated from the thermal contribution arising from the splitting due to the electron-phonon interaction. The predicted effect is compared with the measured values in Mn2+-doped NaNO2. 相似文献
5.
Three novel diterpene glycosides were isolated for the first time from the commercial extract of the leaves of Stevia rebaudiana, along with several known steviol glycosides, namely stevioside, rebaudiosides A-F, rubusoside and dulcoside A. The new compounds were identified as 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy] ent-kaur-15-en-19-oic acid, 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy]-16β-hydroxy-ent-kauran-19-oic acid and 13-methyl-16-oxo-17-nor-ent-kauran-19-oic acid-β-D-glucopyranosyl ester on the basis of extensive 2D NMR and MS spectroscopic data as well as chemical studies. 相似文献
6.
A temperature dependent EPR study of Mn2+ impurity-doped crystals of Mg(ClO4)2·6H2O has led to the detection of two critical temperatures T1 ~ 335K and T2 ~ 324K where the EPR characteristics undergo distinct changes. The monoclinic distortion of the water octahedron around the metal ion shows little temperature dependence between T1 and T2 and T2 and T3 ~ 272K, while it is found to be comparatively strongly temperature dependent above T1 and below T3, decreasing as T approaches T1 from the high temperature side and as T approaches T3 from the low temperature side. At room temperature the water-perchlorate symmetry seems to deviate slightly from the perfect P63mc symmetry proposed from previous X-ray measurements by West. Although the space symmetry group of the unit cell appears to remain unchanged at T1 and T2, the temperatures T1 and T2 are suspected to be related to structural phase transitions in this crystal. 相似文献
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8.
[reaction: see text] A facile synthesis of bisformylated calix[4]arenes via ipso substitution of p-tert-butylcalix[4]arenes through treatment with hexamethylenetetramine/trifluoroacetic acid is described. Under identical conditions, p-tert-butylcalix[4]arene tetramethyl ether 4 gives proximally substituted bisformylated derivative 4a in a pinched cone conformation. 相似文献
9.
We discuss and complement the knowledge about generalized Orlicz classes $ \tilde X_\Phi $ and Orlicz spaces X Φ obtained by replacing the space L 1 in the classical construction by an arbitrary Banach function space X. Our main aim is to focus on the task to study inequalities in such spaces. We prove a number of new inequalities and also natural generalizations of some classical ones (e.g., Minkowski’s, Hölder’s and Young’s inequalities). Moreover, a number of other basic facts for further study of inequalities and function spaces are included. 相似文献
10.
A series of new calix[4]arene(amido)mono-crown compounds have been synthesized through aminolysis of calix[4]arene esters and intramolecular cyclization of the intermediates. The title compounds were converted into their nitro and azo substituted derivatives to provide novel photoresponsive molecular receptors for transition metal ions. Single crystal X-ray analysis of calix[4]arene(ethyleneamido)mono-crown (2a) revealed that the compound is present in a cone conformation with an amido loop that caps the lower rim of calix[4]arene cavity to result in stacking along axis a and axis c to provide supramolecular aggregates in the solid state. Evaluation of synthesized macrocycles in the solution phase for recognition of transition metal cations (Cr3+, Fe2+, Co2+, Ni2+, Cu2+, Ag+, Cd2+, Pb2+, Hg+, Hg2+, Pd2+, and Pt2+) by UV-visible spectroscopy revealed that p-tert-butyl-calix[4]arene mono-(amidocrown) 1c selectively shows a blue shift at 38 nm on interaction with Hg+ ions. 相似文献