Practical detection limit

This is equivalent to toxin level in a shellfish of 48 yg/mg per 100 gr of shellfish meat. Since, for the toxin and its associated assay protocol there appears to be a unique response it is possible to obtain an estimate of the median ED50 from one set of injections, provided that the dose is not too far from the ED50 value. For STX this represents a practical limit of detection of about 20 yg/100 g of meat. 

The advantages offered by interferometric detection are compromised by practical limitations related to phase noise and loss of phase qnality due to scattering. We will briefly discnss these issues in Section V. 

As in traditional methods that use univariate calibrations, the description of a method of analysis that uses multivariate calibration must also include the corresponding estimated figures of merit, including accuracy (trueness and precision), selectivity, sensitivity, linearity, limit of detection (LOD), limit of quantification (LOQ) and robustness. In this chapter, only the most common figures of merit are described. For a more extensive review, see [55]. Also, for a practical calculation of figures of merit in an atomic spectroscopic application, see [12]. 

Liquid chromatography with electrochemical detection (LCEC) is in widespread use for the trace determination of easily oxidizable and reducible organic compounds. Detection limits at the 0.1-pmol level have been achieved for a number of oxidizable compounds. Due to problems with dissolved oxygen and electrode stability, the practical limit of detection for easily reducible substances is currently about 10-fold less favorable. As with all detectors, such statements of the minimum detectable quantity must be considered only with the proverbial grain of salt. Detector performance varies widely with the analyte and the chromatographic conditions. For example, the use of 100- m-diameter flow systems can bring attomole detection limits within reach, but today this is not a practical reality. 

The resolution of the column provides much of the selectivity in LCEC therefore, the practical limitations of amperometry are circumvented to a large extent. Nevertheless, amperometry is more often than not used to improve the selectivity of an LC method. Compounds that oxidize or reduce at low potentials can be detected with great selectivity. 

Although theoretical techniques for the characterization of resonance states advanced, the experimental search for reactive resonances has proven to be a much more difficult task [32-34], The extremely short lifetime of reactive resonances makes the direct observation of these species very challenging. In some reactions, transition state spectroscopy can be employed to study resonances through "half-collision experiments," where even very short-lived resonances may be detected as peaks in a Franck-Condon spectrum [35-38]. Neumark and coworkers [39] were able to assign peaks in the [IHI] photodetachment spectrum to resonance states for the neutral I+HI reaction. Unfortunately, transition state spectroscopy is not always feasible due to the absence of an appropriate Franck-Condon transition or due to practical limitations in the required level of energetic resolution. The direct study of reactive resonances in a full collision experiment, such as with a molecular beam apparatus, is the traditional and more usual environment to work. Unfortunately, observing resonance behavior in such experiments has proven to be exceedingly difficult. The heart of the problem is not a... 

Because photomultiplier tubes can only detect events which occur on or near the surface of the scintillator column exposed to the tubes, the greater the surface to volume ratio, the more efficiently events will be detected. The literature contains a number of suggestions in which the simple U-tube is modified into coils and spirals which present larger surfaces per unit of volume to the photomultiplier tubes (3j. While this does increase sensitivity, a practical limit to minimum required sensitivity is set in most metabolism studies by the fact that we must separate enough compound to carry through identification studies. Since we have the option of selecting the specific activity of our original l c-compound, we have found the U-tubes described entirely adequate. 

The analysis of the HMBC in the region of the carbonyl carbons is hampered by the lack of digital resolution along the FI axis. Recall that the HMBC experiment is proton detected giving good resolution in the proton or F2 dimension. The only way to improve resolution along the FI axis is to increase the number of FIDs in the experiment, which has serious practical limitations. The lines drawn in the insets help clarify the correlations. 

Fig. 3. The theoretical increase in receptivity (abundance X sensitivity) obtainable by isotope enrichment and inverse ]H detection of13C, 15N and 195Pt. In practice, inverse 1H- 195Pt detection is limited by the broad linewidths of the 195Pt satellites.

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