Theory detection limits

Kirchner, C. J. Estimation of Detection Limits for Environmental Analytical Procedures, In Currie, L. A., ed. Detection in Analytical Chemistry Importance, Theory and Practice. American Chemical Society Washington, DC, 1988. 

Fast concentration and sample injection are considered with the use of a theory of vibrational relaxation. A possibility to reduce a detection limit for trinitrotoluene to 10 g/cnf in less than 1 min is shown. Such a detection limit can by obtained using selective ionization combined with ion drift spectrometry. The time of detection in this case is 1- 3 s. A detection technique based on fluorescent reinforcing polymers, when the target molecules strongly quench fluorescence, holds much promise for developing fast detectors. 

As in the case of the detection limit (Section 2.2.7), one commonly used algorithm is based on the theory that any point outside z 5 is to be regarded as an outlier if recalculation of Xmean and 5 without this questionable point confirms the decision, the outlier is to be cast out. The coefficient z is often fixed at 2.0 or 3.0 the r-function (see the two thin curves in Fig. 1.24) and other functions have also been proposed. An obvious disadvantage of these approaches is that extreme values strongly affect Sx, and that more or less symmetrical outliers cannot be detected. 

We recently synthesized several reasonably surface-active crown-ether-based ionophores. This type of ionophore in fact gave Nernstian slopes for corresponding primary ions with its ionophore of one order or less concentrations than the lowest allowable concentrations for Nernstian slopes with conventional counterpart ionophores. Furthermore, the detection limit was relatively improved with increased offset potentials due to the efficient and increased primary ion uptake into the vicinity of the membrane interface by surfactant ionophores selectively located there. These results were again well explained by the derived model essentially based on the Gouy-Chapman theory. Just like other interfacial phenomena, the surface and bulk phase of the ionophore incorporated liquid membrane may naturally be speculated to be more or less different. The SHG results presented here is one of strong evidence indicating that this is in fact true rather than speculation. 

Boumans PWJM (1991) Measuring detection limits in inductively coupled plasma emission spectrometry using the SBR-RSDB approach -I.A tutorial discussion of the theory. Spectrochim Acta 46B 431... 

This field is therefore at an exciting stage. Ion-selective electrodes have a proven track record in terms of clinical and biomedical analysis, with a well-developed theory and a solid history of fundamental research and practical applications. With novel directions in achieving extremely low detection limits and instrumental control of the ion extraction process this field has the opportunity to give rise to many new bioana-lytical measurement tools that may be truly useful in practical chemical analysis. 

In theory, the limit of detection (LOD) may be lower with indirect detection than with direct detection. Macka and Haddad describes the LOD with the equation ... 

This number, which is also called peak capacity, is inhni e n theory, but Jimiied in practice. Time considerations require that k noii exceed a certain limit, which in fact decreases when the column efficiency increases, because should not exceed a few hours except in very social circumstances. The maximum peak number is also limited by the fact that with increasing retention the width and height of the peak inpi ases dnd decreases, respectively. As a consequence of the limitations oil sample size, peaks whose maximum concentration at the column outlet is lower than the detection limits remain unnoticed. 

Under isocratic development, if the early peaks of the mixture are adequately separated, then the late peaks are often broad, and consequently, at concentrations so low that they are hardly detectable. Conversely, if the late peaks are eluted at a sufficiently low k values to improve detection limits, the early peaks become bunched together and are not resolved. This problem is obviated considerably by employing gradient elution, but if there are a large number of individual solutes present in the sample,then the same problems will arise. These difficulties are caused by the column having a limited peak capacity and it is, therefore, important to determine how to calculate peak capacity and how to control it. From the Plate Theory, the peak width at the base is given by -... 

Alternative 2 Set RMCLs at the Analytical Detection LIMIT. Because of limitations in analytical techniques, it will always be impossible to say with certainty that the substance is not present. In theory, RMCLs at zero will always be unachievable (or at least not... 

Figure 1 Observed photon luminosity vs. time during a year after the supernova explosion predicted from standard cooling theory of neutron stars. Shown are three representative nuclear models PS (dashed), FP (solid), and BPS (dot-dashed). The detection limit from Ginga is shown as a horizontal line.

Hare P. E. and St. John P. A. (1988) Detection limits for amino acids in environmental samples. In Detection in Analytical Chemistry. Importance, Theory, and Practice (ed. L. A. Currie). ACS Press, Washington, DC, pp. 275 -285. 

The calculation of the detection limit is based on the theory developed by Currie concerning the errors a and A value of 0.05 is assigned to a and P which indicates that the conclusion will be exact in 95 % of the cases. Currie indicates that in the case of a well known blank, the detection limit (in CPM) could be established as follows ... 

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