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91.
The development of all-solid-state potentiometric ion selective electrodes for monitoring of ascorbic acid, by using a screen-printed compatible solid contact is described. The applied methodology is based on the use of PVC membrane modified with some firstly-tested ionophores (triphenyltin(IV)chloride, triphenyltin(IV)hydroxide and palmitoyl-l-ascorbic acid) and a novel one synthesized in our laboratory (dibutyltin(IV) diascorbate). Synthesis protocol and some preliminary identification studies are given. A conductive graphite-based polymer thick film ink was used as an internal solid contact between the graphite electrode and the PVC membrane. The presence and the nature of the solid contact (plain or doped with lanthanum 2,6-dichlorophenolindophenol (DCPI)) seem to enhance the analytical performance of the electrodes in terms of sensitivity, dynamic range, and response time. The analytical performance of the constructed electrodes was evaluated with potentiometry, constant-current chronopotentiometry and electrochemical impedance spectroscopy (EIS). The interference effect of various compounds was also tested. The potential response of the optimized Ph3SnCl-based electrode was linear against ascorbic acid concentration range 0.005-5.0 mM. The applicability of the proposed sensors in real samples was also tested. The detection limit was 0.002 mM ascorbic acid (50 mM phosphate, pH 5 in 50 mM KCl). The slope of the electrodes was super-Nernstian and pH dependent, indicating a mechanism involving a combination of charge transfer and ion exchange processes. Fabrication of screen-printed ascorbate ISEs has also been demonstrated. 相似文献
92.
Romero S. Bustamante P. Escalera B. Cirri M. Mura P. 《Journal of Thermal Analysis and Calorimetry》2004,77(2):541-554
Differential scanning calorimetry (DSC), supported by hot stage microscopy, IR spectroscopy and X-ray powder diffractometry,
was used to investigate the characteristics of the solid phases of mefenamic, niflumic, and flufenamic acids and of paracetamol,
before and after equilibration with saturated solutions in different solvents. Mixtures of Lewis base (dioxane and ethyl acetate)
and amphiprotic solvents (ethanol and water) were prepared for evaluating the influence of both nature and polarity of the
solvents. Solid-state analysis performed on the original samples (commercial products) made it possible to establish that
paracetamol, mefenamic acid and flufenamic acid were in their respective Form I. No polymorphic modifications are known for
niflumic acid. Paracetamol, niflumic and mefenamic acids did not show any change after equilibration with the various solvents
or solvent mixtures, regardless of their different chemical nature. In contrast, DSC, IR and X-ray analyses revealed the partial
recrystallization of flufenamic acid into its polymorphic Form III in solid phases at equilibrium with ethanol, ethyl acetate
and their blends, as well as in dioxane-water mixtures containing 30 to 100% dioxane and in ethanol-water mixtures with a
water content less than 50%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
93.
C. Auguet J. L. Seguin F. Martorell F. Moll V. Torra J. Lerchner 《Journal of Thermal Analysis and Calorimetry》2006,86(2):521-529
Micro-calorimetric
devices using Si-based sensors are very useful for the study of gas–solid
reactions, in which very low mass of reactants are necessary. But in fact
the consequence of using flat detectors is an increase of the uncertainty
in the measured energy. In this work a calorimetric gas sensor based on Xensor
chip is analysed studying the local x–y
contributions of dissipation to the sensitivity related to the value in the
centre. We study also the effects of the gas-flow on the sensitivity, comparing
the results obtained with two Xensor type chips. Finally we carry out a deeper
analysis of the x–y effects on the
calorimetric detector for dissipations in the reactant shell extremely close
to the detector surface to visualize the link between the power density distribution
and the output signal. 相似文献
94.
Brunsveld L Watzke A Durek T Alexandrov K Goody RS Waldmann H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2756-2772
Prenylated proteins with non-native functionalities are generally very difficult to obtain by recombinant or enzymatic means. The semisynthesis of preparative amounts of prenylated Rab guanosine triphosphatases (GTPases) from recombinant proteins and synthetic prenylated peptides depends largely on the availability of functionalised prenylated peptides corresponding to the proteins' native structure or modifications thereof. Here, we describe and compare solution-phase and solid-phase strategies for the generation of peptides corresponding to the prenylated C terminus of Rab7 GTPase. The solid-phase with utilisation of a hydrazide linker emerges as the more favourable approach. It allows a fast and practical synthesis of pure peptides and gives a high degree of flexibility in their modification. To facilitate the analysis of semisynthetic proteins, the synthesised peptides were equipped with a fluorescent group. Using the described approach, we introduced fluorophores at several different positions of the Rab7 C terminus. The position of the incorporated fluorescent groups in the peptides did not influence the protein-ligation reaction, as the generated peptides could be ligated onto thioester-tagged Rab7. However, it was found that the positioning of the fluorescent group had an influence on the functionality of the Rab7 proteins; analysis of the interaction of the semisynthetic Rab7 proteins with REP (Rab escort protein) and GDI (guanosine diphosphate dissociation inhibitor) molecules revealed that modification of the peptide side chains or of the C-terminal isoprenoid did not significantly interfere with complex formation. However, functionalisation of the C terminus was found to have an adverse effect on complex formation and stability, possibly reflecting low structural flexibility of the Rab GDI/REP molecules in the vicinity of the lipid-binding site. 相似文献
95.
E. Tomaszewicz 《Thermochimica Acta》2006,447(1):69-74
Reactivity in the solid state between CoWO4 and some rare-earth metal tungstates RE2WO6 (RE = Sm, Eu, Gd) was investigated by the XRD method. Two families of new isostructural cobalt and rare-earth metal tungstates, Co2RE2W3O14 and CoRE4W3O16, were synthesized. The Co2RE2W3O14 phases are formed by heating in air the CoWO4 and RE2WO6 compounds mixed at the molar ratio 2:1, while the CoRE4W3O16 phases are synthesized at the molar ratio of CoWO4/RE2WO6 equals to 1:2. The Co2RE2W3O14 phases as well as the CoRE4W3O16 compounds crystallize in the orthorhombic system. The Co2RE2W3O14 and CoRE4W3O16 compound melt above 1150 °C. A melting manner of the Co2RE2W3O14 and CoRE4W3O16 compounds was determined in an inert atmosphere. The formation of CoWO4−x phase was observed during heating in an inert atmosphere. 相似文献
96.
With frontal analysis(FA),the dependence of adsorption isotherms of insulin on the composition of mobile phase in reversed phase liquid chromatography (RPLC) has been investigated,This is also a good example to employ the stoichiometric displacement theory (SDT) for ivestigating solute adsorption in physical chemistry.Six kinds of mobile phase in RPLC were employed to study the effects on the elution curves and adsorption isotherms of insulin.the key points of this paper are:(1) the stability of insulin due to delay time after preparing,the organic solvent concentration,the kind and the concentration of ion-pairing agent in mobile phase were found to affect both elution curve and adsorption isotherm very seriously.(2)To obtain a valid and comparable result,the composition of the mobile phase employed in FA must be as same as possible to that in usual RPLC of either analytical scale or preparative purpose.(3)Langmuir Equation and the SDT were employed to imitate these obtained adsorption isotherms.The expression for solute adsorption from solution of the SDT was found to have a better elucidation to the insulin adsorption from mobile phase in RPLC. 相似文献
97.
建立了酱油中1,3-二氯-2-丙醇、2,3-二氯-1-丙醇、3-氯-1,2-丙二醇和2-氯-1,3-丙二醇的分散固相萃取-气相色谱-高分辨质谱快速筛查检测方法。样品采用乙酸乙酯提取,提取液浓缩后经N-丙基乙二胺净化,气相色谱-高分辨质谱测定,内标法定量。结果表明,该方法对于酱油中4种氯丙醇的定量限为0.5~10 μg/kg。在3个浓度水平下的加标回收率为78%~103%;相对标准偏差均不大于8.8%。该方法快速、简便、准确、灵敏,可作为酱油中4种氯丙醇的有效检测方法。 相似文献
98.
Crespi M. S. Silva A. R. Ribeiro C. A. Oliveira S. C. Santiago-Silva M. R. 《Journal of Thermal Analysis and Calorimetry》2003,72(3):1049-1056
The thermal behavior and non-isothermal kinetics of thermal decomposition of three different kinds of composting of the USR
like: stack with drilled PVC tubes (ST), revolved stack (SR) and stack with material of structure (SM), from the usine of
composing of Araraquara city, Săo Paulo state, Brazil, within a period of 132 days of composting were studied. Results from
TG, DTG and DSC curves obtained on inert atmosphere indicated that the cellulosic fraction present, despite the slow degradation
during the composting process, is thermally less stable than other substances originated from that process. Due to that behavior,
the cellulosic fraction decomposition could be kinetically evaluated through non-isothermal methods of analysis. The values
obtained were: average activation energy, Ea=248, 257 and 259 kJ mol-1 and pre- exponential factor, logA=21.4, 22.5, 22.7 min-1, to the ST, SR and SM, respectively. From Ea and logA values and DSC curves, Málek procedure could be applied, suggesting that the SB (Šesták-Berggren) kinetic model is the appropriated
one to the first thermal decomposition step.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
99.
偏钛酸型锂离子交换剂固相合成反应动力学 总被引:1,自引:1,他引:1
偏钛酸型锂离子交换剂固相合成反应动力学钟辉*郭灵虹(成都理工学院应用化学系成都610059)(四川联合大学分析测试中心成都)关键词偏钛酸锂,离子交换剂,合成,固相反应动力学1997-08-25收稿,1997-12-10修回四川省应用基础研究基金资助项... 相似文献
100.