Although the research described in this article was funded wholly or in part by the United States Environmental Protection Agency, through its cooperative agreement program, it has not been subjected to the Agency's peer and policy review and, therefore, does not necessarily reflect the views of the Agency, and no official endorsement should be inferred.
Data as in Figure 11 exchange reaction at a membrane permeable to the exchanging ions, Rg in fact represents the sum of two resistances in series, one related to the kinetics of the ion exchange reaction and the second representing the mobility of the counter ions in the membrane. Where the glass membrane is coated by a surface-hydrolyzed film, the equivalent circuit has, in addition to that described above, a series Warburg diffusional impedance shunted by a resistance. It is, perhaps, surprising that under an applied electric field the counter ions show any diffusion at all as they are the major charge carrier present in solution. The large resistance in parallel with the Warburg impedance is interpreted as representing the effects of electromigration through 'pores' in the surface film.The results of the current step measurements of potentialtime curves are compatible with the equivalent circuit model obtained by impedance measurements. In the absence of a
which cause deviations from Beer's law.In this study, only one emission in the visible region was available. The use of lasers in light absorption studies is at present limited because of comparatively few emission lines. Recently, more transitions have been reported in the visible light region with a He-Ne gas laser (3). Other gas laser systems have been studied or suggested which demonstrate many transitions in the UV, ultraviolet, visible, infrared, and far infrared (2,4,5,7,8,10). These developments increase potential applications in the spectro-chemical field.Work is currently in progress in this laboratory in which more complex systems are being studied to determine how other causes of nonlinearity in calibration curves are effected by a laser light source.In addition, other dye systems have been selected whose absorption maxima are significantly different from the 632.8 µ transition of the He-Ne laser. From these studies, some estimate of the applicability of the laser-spectrophotometer combination can be made in respect to off-peak measurements of these kinds.
As analytical methodology improves and instrumental methods allow, or often require, the use of smaller and smaller analytical test portions, the error in the sampling operations becomes increasingly significant. Also, heterogeneity of trace components can introduce major sampling problems. Sampling errors cannot be controlled by use of blanks, standards, or reference samples and so are best treated independently.
Sampling errors may be classified as determinate or indeterminate. We consider here a statistical approach to the question of variance of sampling of particulate matter, as distinct from the variance of analysis, with special emphasis on problems in trace analysis. In addition, the related topic of preparation of reference samples for trace measurements is considered.
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