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A new lead(II) electrode has been constructed with poly(hydroxamic acid) (PHXA) as the active material and silicone rubber as the supporting material. The electrode gave near Nerstian response over the concentration range 4 × 10−5−1 × 10−2M lead(II). The detection limit of the electrode is approximately 4 × 10−6M and the electrode works well in the pH range 4.5–6.0. The response time was 50–120 sec over the whole concentration range and the electrode has a working life of at least 4 weeks. Iron(III) severely poisoned the electrode membrane. Nickel(II) and mercury(II) gave very strong interference compared to copper(II), silver(I), cobalt(II), sodium(I), potassium(I), zinc(II) and cadmium(II) which gave some or little interference. Values determined with atomic absorption (AAS) and a commercial lead(II) electrode were in good agreement with those measured with the lead(II) electrode reported here. 相似文献
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Galvani M Hamdan M Righetti PG 《Rapid communications in mass spectrometry : RCM》2000,14(20):1925-1931
Matrix-assisted laser desorption/ionisation mass spectrometry was used to monitor interaction between three proteins and two basic Immobiline chemicals (pK 10.3 and pK >12) commonly used in immobilised pH gradients (IPG). For two of the investigated proteins, the observed alkylation channels of the cysteine residues exhibited unmistakable response to their gradual denaturation following treatment with different concentrations (0-8 M) of two commonly used denaturants, urea and guanidine hydrochloride. Our assessment for protein unfolding is based on the number and relative intensity of the alkylation channels, yet the present mass spectrometry data are in good agreement with data based on optical rotatory dispersion, in which another approach was used to assess protein unfolding. Whether the present simple, fast and specific mass spectrometry method can be developed as a probe for monitoring folding/unfolding of cysteine-containing proteins can only be demonstrated by generating similar data for a larger number of proteins. 相似文献
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Galvani M Hamdan M Righetti PG Gelfi C Sebastiano R Citterio A 《Rapid communications in mass spectrometry : RCM》2001,15(3):210-216
Quaternized piperazine ((N-methyl-N-omega-iodobutyl-N'-methyl)piperazine; QPzl) is a novel compound described as an ideal coating material for the silica capillaries that are commonly used for capillary zone electrophoresis. In the course of such analysis, contact between such coatings and biomolecules may result in certain modifications of the latter. To gain specific information on such potential modifications, solutions at pH 10.0 containing both QPzl and standard proteins/peptides were incubated for various periods and examined by matrix-assisted laser desorption/ionisation mass spectrometry. The reduction of the S-S bridges, denaturation in 8 M urea, the isoelectric point of the protein and the duration of the incubation had a profound influence on the investigated reaction. Analysis in reflectron mode and post source decay identified Cys as the likely site of interaction. The implications of the present measurements for proteome analysis using capillary and gel electrophoresis are discussed. 相似文献
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In order to illustrate the class of conservative dynamical systems for which a Boltzmann entropy can be obtained under finite coarse-graining [2], we consider dynamical systems defined by the shift transformation on K
, where K is any finite set of integers. We give a class of non-Markovian invariant measures that verify the Chapman-Kolmogorov equation (equivalent to a Boltzmann entropy) for any positive stochastic matrix and that are ergodic but not weakly mixing. 相似文献
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Positive fast ion bombardment, positive chemical ionization (CI+) and positive electron impact (EI) ionization mass spectrometry were used to investigate a number of relatively large and structurally related organic molecules. Some of the major dissociation pathways observed in the CH4-CI+ mass spectra are not present under NH3-CI+ conditions, but are obtained in the collision-induced dissociation (CID) spectrum of the 50 eV MH+ molecular ion, formed in the latter reaction. The resemblance between the EI mass spectra and their fast ion bombardment counterparts, the effect of changing the energy of the bombarding Cs+ ion beam over the range 2–16 keV and the different degrees of internal excitation of ions formed in different CI reagent gases are discussed. 相似文献
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