摘要:

Thermospray aerosols are generated by forcing a liquid sample through a capillary tube that is heated to partially vaporize the solvent, resulting in a blast of vapor that converts the remaining liquid to droplets. The droplet size character of thermospray aerosols can be electrically varied by changing the temperature and degree of solvent vaporization of the liquid stream. The primary droplets produced by thermospray under optimal conditions are smaller on average then those produced by pneumatic nebulizers, particularly of the types used for inductively coupled plasmas (ICPs). Solvent vaporization is enhanced for smaller particles and higher temperatures, with both aspects leading to faster size reduction due to solvent evaporation than would occur with pneumatic sample introduction at room temperature. As smaller droplets are more efficiently transported through sample introduction systems, the use of thermospray aerosol generation provides higher analyte transport, higher sensitivity, and lower LODs than pneumatic sample introduction with most atomic spectrometric detectors. Factors that affect the extent of improvement are the operating temperature of the thermospray vaporizer, the temperature of the spray chamber, the presence or absence of a desolvation system, the diameter of the capillary, and the liquid sample flow rate. The absence of desolvation results in degradation of excitation conditions within ICPs, and in smaller improvements in analytical peformance with ICP atomic emission spectrometry (ICP-AES). Smaller capillary exit diameters provide better performance. Specific LOD improvements with thermospray sample introduction compared to pneumatic sample introduction vary, but typically are a factor of 15 to 25 times lower when desolvation is used with thermospray, and when both systems operate at comparable flow rates. Matrix effects are generally higher with thermospray sample introduction than with pneumatic sample introduction, but are comparable to those reported for ultrasonic nebulization. Thermospray systems have been shown to provide LODs an order of magnitude lower than that obtained with pneumatic sample introduction, even in the presence of high dissolved solids, such as 3000 μg/ml Ca. Thermospray capillaries as small as 25 to 50 μm can operate effectively at optimal conditions with high dissolved solids content samples, without problems of capillary clogging.

ISSN:1040-8347    

DOI:10.1080/10408349208050851

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Recent spectroscopic applications of laser-induced plasmas are reviewed. Virtually all substances are susceptible to breakdown when illuminated by a sufficiently intense laser beam. In a plasma, matter breaks apart into atoms, ions, and electrons, producing a visible flash and an audible popping sound due to the acoustical shock wave generated by the sudden, high-velocity expansion of matter outward from the plasma volume. Useful information about the elemental composition of the target material can be obtained from analysis of the emissions emanating from the plasma volume. Among the applications currently being tested in many laboratories are studies of particulate as well as gaseous pollutants in air, toxic substances present in flowing wastewater, elemental content of alloys, composition of iron ores and coal samples, contaminants on the surface of microcircuit boards, and the contents of fluid inclusions in geological samples. The beauty of laser-induced plasma spectroscopy is sample accessibility.

ISSN:1040-8347    

DOI:10.1080/10408349208050852

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Membrane electrodes are relatively simple electrochemical devices that can be used for the direct measurement of ions, gases, and biomolecules in complex samples. Selectivity for one species over another is determined by the nature and chemical composition of the membranes and associated reaction layers used to fabricate the devices. All membrane electrode probes employ at least one ion-selective membrane as the ultimate transduction element. This indicator membrane serves as an additional component of a classic two-electrode galvanic cell. The potential developed at the membrane/sample interface is directly or indirectly related to the activity or concentration of analyte in the sample. Because cell potentials are detected under essentially zero-current conditions, analytical measurements with these probes are generally not subject to the mass transfer and electron transfer kinetic limitations that often plague voltammetric or amperometric techniques.

ISSN:1040-8347    

DOI:10.1080/10408349208050853

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Luminescence spectroscopy provides a unique set of tools for the study of micellar systems. Variations in emission and excitation spectra of fluorescent probes may be used to assess the onset of micellization, while fluorescence lifetime, anisotropy, sensitization, and quenching measurements have made it possible to determine important micellar characteristics. Thus, critical micelle concentrations; micellar aggregation numbers; shapes, sizes, and structures of micelles; and micellar microviscosities have been determined. Work has been carried out with both normal and reverse micelles, and the influence of various solution-borne species on these aggregates has been evaluated through fluorescence and phosphorescence measurements.

ISSN:1040-8347    

DOI:10.1080/10408349208050854

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:1040-8347    

DOI:10.1080/10408349208050850

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor