Use of a Carbon Paste Electrode Modified with Spinel‐Type Manganese Oxide as a Potentiometric Sensor for Lithium Ions in Flow Injection Analysis

A potentiometric sensor constructed from a mixture of 25% (m/m) spinel‐type manganese oxide (lambda‐MnO₂), 50% (m/m) graphite powder and 25% (m/m) mineral oil is used for the determination of lithium ions in a flow injection analysis system. Experimental parameters, such as pH of the carrier solution, flow rate, injection sample volume, and selectivity for Li⁺ against other alkali and alkaline‐earth ions and the response time of this sensor were investigated. The sensor response to lithium ions was linear in the concentration range 8.6×10^?5–1.0×10^?2 mol L^?1 with a slope 78.9±0.3 mV dec^?1 over a wide pH range 7–10 (Tris buffer), without interference of other alkali and alkaline‐earth metals. For a flow rate of 5.0 mL min^?1 and a injection sample volume of 408.6 μL, the relative standard deviation for repeated injections of a 5.0×10^?4 mol L^?1 lithium ions was 0.3%.     

Nafion-PAN optical chemical sensor: optimization by FIA

A copper-sensitive optical chemical sensor (optrode) is described. The optrode is based on a Nafion membrane and an immobilized organic ligand coupled with a flow injection (FI) system. The FI system includes a flow-through removable measuring cell and a simple spectrophotometer. Owing to the miniature size of the system and the efficient use of optical fibers, this optrode is well suited for monitoring environmental water samples. The success of the described optrode system depends on the effectiveness of the FI reagent delivery system. Optimum contact time with the membrane (as determined by the reagent flow rates) and the injected sample volume are critical. Environmental water samples were analyzed for copper content using the optimized optrode system. To validate the optrode's performance, the same water samples were analyzed using the atomic absorption spectrophotometer.     

Chemical sensors (review)

The capabilities and development prospects of chemical sensors as a new area in analytical chemistry and instrument engineering are discussed. Problems of terminology, principles of operation, basic characteristics, and also applications of chemical sensors and sensor analyzers made from them are discussed.From the materials of a report given at a joint scientific session of the departments of the physicochemistry and technology of inorganic materials and of general and technical chemistry.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow 117975. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 487–493, March, 1992.     

Immobilization of glucose oxidase with the blend of regenerated silk fibroin and poly(vinyl alcohol) and its application to a 1,1′- dimethylferrocene-mediating glucose sensor

The structure and properties of the blend of regenerated silk fibroin (RSF) and poly(vinyl alcohol) (PVA) were investigated. The two polymers in the blend are in the state of phase segregation. Infrared (IR) spectra indicate that the RSF in the blend maintains its intrinsic properties, thus, ethanol treatment can transfer silk I structure of RSF to silk II structure. The water absorption property and mechanical property of the blend are improved in comparison with those of RSF. The blend maintains the major merit of RSF, that is, it can immobilize glucose oxidase on the basis of the conformational transition from silk I structure to silk II structure. The properties of the immobilized enzyme are examined. Moreover, the second generation of glucose sensor based on the immobilized enzyme is fabricated and it has a variety of advantages including easy maintenance of enzyme, simplicity of construction, fast response time and high stability.     

The surface and materials science of tin oxide

The study of tin oxide is motivated by its applications as a solid state gas sensor material, oxidation catalyst, and transparent conductor. This review describes the physical and chemical properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are also incorporated in order to provide connecting points between surface science studies with the broader field of materials science of tin oxide. The key for understanding many aspects of SnO₂ surface properties is the dual valency of Sn. The dual valency facilitates a reversible transformation of the surface composition from stoichiometric surfaces with Sn⁴⁺ surface cations into a reduced surface with Sn²⁺ surface cations depending on the oxygen chemical potential of the system. Reduction of the surface modifies the surface electronic structure by formation of Sn 5s derived surface states that lie deep within the band gap and also cause a lowering of the work function. The gas sensing mechanism appears, however, only to be indirectly influenced by the surface composition of SnO₂. Critical for triggering a gas response are not the lattice oxygen concentration but chemisorbed (or ionosorbed) oxygen and other molecules with a net electric charge. Band bending induced by charged molecules cause the increase or decrease in surface conductivity responsible for the gas response signal. In most applications tin oxide is modified by additives to either increase the charge carrier concentration by donor atoms, or to increase the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by which additives modify the gas sensing and catalytic properties of SnO₂ are discussed and the few surface science studies of doped SnO₂ are reviewed. Epitaxial SnO₂ films may facilitate the surface science studies of doped films in the future. To this end film growth on titania, alumina, and Pt(1 1 1) is reviewed. Thin films on alumina also make promising test systems for probing gas sensing behavior. Molecular adsorption and reaction studies on SnO₂ surfaces have been hampered by the challenges of preparing well-characterized surfaces. Nevertheless some experimental and theoretical studies have been performed and are reviewed. Of particular interest in these studies was the influence of the surface composition on its chemical properties. Finally, the variety of recently synthesized tin oxide nanoscopic materials is summarized.     

6291型热变形温度和维卡软化温度测试仪的校准及故障排除

介绍6291型热变形温度和维卡软化温度测试仪的温度校准和位移校准方法，对测试仪的一些常见故障，例如电源故障，主温度传感器故障，电加热系统控制单元故障及测试站的温度偏差较大等进行了分析，并给出了排除故障的方法。     

GaPO4 high temperature crystal microbalance demonstration up to 720°C

Quartz-homeotypic gallium (ortho-) phosphate, GaPO₄, is of special interest for resonator applications asking for temperature compensated cuts with higher electro-mechanical coupling than quartz and operational temperatures up to 970°C. The crystal microbalance technique, well known for quartz (QCM) which can be used only at moderate temperatures, can now be extended to much higher temperatures using GaPO₄ crystals, benefiting from all three advantages mentioned above. Two different experiments were done to demonstrate the advantages of a crystal microbalance based on GaPO₄. First, the GaPO₄ resonator was used for film thickness determination and compared with a commercial QCM. This experiment demonstrated that the measuring range can be extended by using GaPO₄ resonators instead of quartz. The second experiment demonstrates the possibility for thermogravimetric analysis up to 720°C by using a new concept for resonator mounting.This revised version was published online in November 2005 with corrections to the Cover Date.     

A mini-review on MXenes as versatile substrate for advanced sensors

MXenes have emerged as versatile 2D materials that are already gaining paramount attention in the areas of energy,catalyst,electromagnetic shielding,and sensors.The unique surface chemistry,graphene-like mo rphology,high hydrophilicity,metal-like conductivity with redox capability identifies MXenes,as an ideal material for surface-related applications.This short review summarizes the most recent reports that discuss the potential application of MXenes and their hybrids as a transducer material for advanced sensors.Based on the nature of transducing signals,the discussion is categorized into three sections,which include electrochemical(bio) sensors,gas sensors,and finally,electro-chemiluminescence fluorescent sensors.The review provides a concise summary of all the analytical merits obtained subsequent to the use of MXenes,followed by endeavors that have been made to accentuate the future perspective of MXenes in sensor devices.     

Formation of SnO2 Nanoparticles on External Surface of NaY Zeolite

Tin dioxide nanoparticles of 5 nm in size were prepared on NaY zeolite external surface by impregnation of SnCl2 solution and subsequent calcination at 623 K. A SnO2-NaY based chemical sensor for detecting H2 was demonstrated.     

用热聚法固定指示剂的光纤氧气传感器研究

采用热聚法将甲叉双丙烯酰胺（MBBA）聚合并共价交联在硅烷化的玻璃微珠上 ，同时将指示剂Ru（Ⅱ）-邻啡咯啉配合物物理包埋于聚合物中，研制了一种基于 荧光猝灭原理的光纤氧气传感器，采用NaHSO_3-O_2-MnSO_4体系引发MBBA水溶液热 聚合后应，通过确定NaHSO_3,MnSO_4,MBBA和Ru(phen)_3Cl_2的最佳反应浓度以及 玻璃微珠的尺寸，优化了聚合反应条件，改善了指示剂的固定效果，制备了性能较 好的传感器探头，该传感器的检测下限为5×10~(-6)(V/V)，响应时间为10s该传感 器连续工作50min,重复性标准偏差为±1%。