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排序方式: 共有334条查询结果,搜索用时 15 毫秒
31.
In this paper, a new highly sensitive potentiometric pH electrode is proposed based on the solid-state PbO2 film electrodeposited on carbon ceramic electrode (CCE). Two different crystal structures of PbO2, α and β were examined and the similar results were obtained. Moreover, the experimental results obtained for the proposed
pH sensor and a conventional glass pH electrode were in good agreement. The electromotive force (emf) signal between the pH-sensitive
PbO2-coated CCE and SCE reference electrode was linear over the pH range of 1.5–12.5. Near-Nernstian slopes of −64.82 and −57.85 mV/pH
unit were obtained for α- and β-PbO2 electrodes, respectively. The interferences of some mono-valence and multi-valence ions on potentiometric response of the
sensor were studied. The proposed pH sensor displayed high ion selectivity with respect to K+, Na+, Ca2+, and Li+, with log values around −12 and has a working lifetime of about 30 days. Key parameters important for the pH sensor performance, including
kind of PbO2 film, selectivity, response time, stability, and reproducibility, have been characterized. The proposed electrode showed
a good efficiency for direct pH-metry after calibration and pH-metric titrations without calibration step. The response time
was about 1 s in acidic medium and less than 30 s in alkaline solutions. The pH values of complex matrix samples such as fruit
juices measured by the proposed sensor and a conventional glass pH electrode were in good agreement. 相似文献
32.
Diisopropyltetrahydroquinoxalinedione derivatives are synthesized from the reaction of various catechols with N,N′-diisopropylethylenediamine. Both chemical and electrochemical methods give the same products. While the chemical synthesis is faster, the electrochemical synthesis provides higher yields. 相似文献
33.
Elnaz Iranmanesh Moslem Jahani Azizollah Nezhadali Maliheh Mojarrab 《Journal of separation science》2020,43(6):1164-1172
This paper describes the synthesis of a molecularly imprinted polymer by chemical oxidation of pyrrole as the functional monomer, and at the presence of guaifenesin as the template. The prepared polymer was used as adsorbent in molecularly imprinted solid‐phase extraction followed by spectrophotometric determination. Different parameters in the solid‐phase extraction including sample pH, adsorbent weight, washing solution, and elution solvent were studied to determine optimum conditions for isolation and enrichment of guaifenesin. The results showed guaifenesin was quantitatively adsorbed on the molecularly imprinted polymer at pH 6.0 and completely eluted with an ethanol–water solution (50% v/v). An enrichment factor of four with satisfactory recoveries (87.0–95.0%) was obtained. The solid‐phase extraction columns could be used for up to six consecutive elution‐loading cycles without significant decreases in the analyte recoveries. The method had a dynamic range of 3.0 × 10?6–1.5 × 10?4 mol/L with a limit of detection and limit of quantification of 1.4×10?6 and 4.5×10?6 mol/L, respectively. The proposed procedure was used for the extraction and determination of guaifenesin in different pharmaceutical formulations, with satisfying results being achieved. 相似文献
34.
Zohreh Habibi Peyman Salehi Maryam Yousefi Yahya Hejazi Ahmad Laleh Valiollah Mozaffarian Shiva Masoudi Abdolhossein Rustaiyan 《Chemistry of Natural Compounds》2006,42(6):689-692
The hydrodistilled oils from the aerial parts of Ferula latisecta and Mozaffariania insignis, which is endemic to Iran, were analyzed by GC and GC/MS. (Z)-Ocimenone (32.4%), (E)-ocimenone (20.3%), and cis-pinocarvone (11.4%) were the main components among the 22 constituents characterized in the oil of F. latisecta, representing 87.7% of the total components detected. Twenty-five compounds were identified in the oil of M. insignis, representing 99.0% of the total oil, with octyl acetate (41.1%), β-pinene (30.3%), and α-pinene (23.9%) as the main constituents. The essential oils were examined for their potential antimicrobial activities.
Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 561–563, November–December, 2006. 相似文献
35.
36.
Photodegradation of several thiols and thiones including 2-pyrimidinethiol, thiazolidine-2-thione, imidazolidine-2-thione, 1,2,4- triazole 3-thiol and 2,5-dimercapto- 1,3,4-thiadiazole have been studied in aerated aqueous solution using zinc oxide under irradiation with 400W high pressure mercury lamp. Rate constants span the range from 2.44 x 10(-2) min x (-1) to 1.76 x 10(-1) min x (-1). The slower degradation rate of 2-imidazoline 2-thione could be related to oxidation potential of the corresponding ring. The Langmuir-Hinshelwood (L-H) rate constant k(r) and adsorption constant, (KA) for all five thiols and thiones are reported. 相似文献
37.
<正>A novel calix[4]arene derivative 2 with amino functional groups at the lower rim was first prepared via introduction of nitro functional groups and amination of the dinitro derivative of calix[4]arene.The optically active monomers were synthesized by dehydration of L-leucine(and L-isoleucine) and 3,3',4,4'-benzophenonetetracarboxylic- 3,3',4,4'-dianhydride(3) followed by reaction with thionyl chloride to form 5a and 5b.Two methods,polymerization under microwave irradiation and solution polymerization in CH_2Cl_2/TEA,were then employed to carry out the condensation polymerization of 2 with the optically active monomers 5a and 5b,respectively.The polymerization conditions affected the kind of resulting polymers,poly(amide-imide)s(PAIs) 6a and 6b and poly(ester-imide)s(PEIs) 6a' and 6b' were obtained selectively in good yields and moderate inherent viscosities.Sorption-extraction experiments were carried out using cram picrate extraction method and verified good binding ability of the resulting calixarene-based polymers towards silver,alkali metal and toxic heavy metal cations.Also thermogravimetric analysis indicated that the resulting PAIs and PEIs were thermally stable. 相似文献
38.
39.
Beheshti A Clegg W Khorramdin R Nobakht V Russo L 《Dalton transactions (Cambridge, England : 2003)》2011,40(12):2815-2821
Reaction of (NH(4))(2)[MO(2)S(2)] (M = Mo or W) with KI, CuCl and 1,3-diazepane-2-thione (Diap) in acetone affords air- and moisture-stable mixed-metal cluster compounds [MOS(3)(CuDiap)(3)]I (1 and 2). Attempts to produce [WS(4)Ag(2)(Mim(Ph))(4)] (Mim(Ph) = 2-mercapto-1-phenylimidazole) led to the unexpected polymeric compound [Ag(5)I(5)(Mim(Ph))(4)](n) (4), subsequently obtained from a rational direct reaction between AgI and Mim(Ph) in chloroform. The complexes have been characterized by IR, (1)H and (13)C NMR spectroscopy, and single-crystal diffraction. 1 and 2 have crystallographic threefold rotation symmetry, with an incomplete distorted cube MS(3)Cu(3) core bearing terminal oxo and Diap ligands on M and Cu, respectively. The cube vertex opposite M is empty, giving an overall +1 cationic cluster and a separate I(-) anion too distant from the three Cu atoms to be considered as covalently bonded and resulting in discrete ion pairs in the crystal structures. This arrangement is different from previously reported related OMS(3)(CuL)(3)X complexes (L = monodentate ligand, X = halide), in which X, when present, is directly bonded to one, two or three Cu atoms. 4 has a one-dimensional polymeric chain structure in which silver displays five different approximately tetrahedral coordination environments, iodide ions serve as μ(2), μ(3) and μ(4) bridges, and the thione ligands are each either terminal or bridging. This unusually complex structure for a relatively simple chemical formula represents only the fifth example of a complex (AgI)(n)L(m) in which L is a neutral S-donor ligand, and the five structures display a wide range of individual features. In all three of the new structures, N-H···S and/or N-H···I hydrogen bonds are found. 相似文献
40.