Detection limits, limitations

Lifetimes of samples and standards Lifetimes of reagents Detection limits Limits of quantitation [10]... 

The secondary DQIs are not immediately obvious to the data user not all of them are applied for data quality evaluation. Nevertheless, they are among the fundamental concepts of analytical chemistry, have a great effect on results of qualitative and quantitative analysis, and affect the outcome of the primary DQIs. The meaning and importance of the secondary DQIs are discussed in Chapter 4, which details laboratory analysis and quality control. The secondary DQIs, which include sensitivity, recovery, memory effects, method detection limit, limit of quantitation, repeatability, and reproducibility, are defined as follows ... 

LOD) quantitative detection limit limit of determination. The smallest detectable concen- tration an analytical instrument can determine at a given confi- dence level. IUPAC defines the i quantitative detection limit as Cld = ks/m, where k is 10, s is. the standard deviation of in- i strument readings taken on a j blank (a solution with zero concentration of analyte), and 1 m is the slope of a plot of in- strument response vs. concen- oration, as calculated by linear regression. J... 

Test kit producer-generated data to verify performance claims are required according to an AOAC-approved protocol, to generally include ruggedness tests, calibration curves, accuracy, precision, cross reactivity, test kit component stability, detection limit, limit of quantification and rates of false positives and false negatives. 

Detection limit (limit of detection) is the smallest quantity of an analyte that can be detected, and not necessarily determined, in a quantitative fashion. Approaches may include instrumental or non-instrumental procedures and could include those based on ... 

Out of these efforts have come a multitude of terras such as Limit of Detection, Method Detection Limit, Instrument Detection Limit, Limit of Quantitation, Criterion of Detection and a multitude of symbols such as the less than sign, RD, TR (for trace), U, M, J, T and w, and K. EPA is now proposing LTL (less than lower limit of detection) and LTC (less than criteria of detection) in computer standards. Some of the conventions come with rigid definitions for prescribed use and others come with vague definitions and allow for "analytical judgment" and flexibility. 

As with any analytical technique, detection limits limit the ability of spectrochemical methods to detect the presence of minute traces of elements. Several methods are available to produce lower detection limits and can be used, especially if information is needed concerning one or more specific elements. 

X-ray spectroscopy Analytical method by which a sample is irradiated with X-rays, characteristic radiation being emitted after scattering from the specimen. The detection limits for various elements are of the ordering cm. ... 

The sample is burned in oxygen at 1000°C. Nitrogen oxide, NO, is formed and transformed into NO2 by ozone, the NO2 thus formed being in an excited state NO. The return to the normal state of the molecule is accompanied by the emission of photons which are detected by photometry. This type of apparatus is very common today and is capable of reaching detectable limits of about 0.5 ppm. 

The detectable limits for a dispersion apparatus are a few g-g/g, and vary according to the environment around from a few pg/g for heavy elements in light matrices to a few mg/g for light elements. 

Detectable limit, p.g/g Error, A /g Flaune Furnace Detectable limit, p.g/1... 

The detectable limits are given for samples such as they are introduced into the apparatus they should be previously diluted in order to be nebulized. It thereby is useful to apply a dilution coefficient, usually at least 10. The dilution depends on the sample viscosity. 

The choice between X-ray fluorescence and the two other methods will be guided by the concentration levels and by the duration of the analytical procedure X-ray fluorescence is usually less sensitive than atomic absorption, but, at least for petroleum products, it requires less preparation after obtaining the calibration curve. Table 2.4 shows the detectable limits and accuracies of the three methods given above for the most commonly analyzed metals in petroleum products. For atomic absorption and plasma, the figures are given for analysis in an organic medium without mineralization. 

THz. Therefore, for laboratory absorption experiments, a typical FIR detector provides an estimated detection limit (NEP/source power) of 10 with a source output of 20 nW. In general, high-sensitivity bolometers... 

The advantages of SIMS are its high sensitivity (ppm detection limit for certain elements), its ability to detect hydrogen and the emission of molecular fragments which often bear tractable relationships with the parent... 

Adsorptive stripping analysis involves pre-concentration of the analyte, or a derivative of it, by adsorption onto the working electrode, followed by voltanmietric iiieasurement of the surface species. Many species with surface-active properties are measurable at Hg electrodes down to nanoniolar levels and below, with detection limits comparable to those for trace metal detemiination with ASV. 

This localization phenomenon has also been shown to be important in a case of catalysis by premicellar aggregates. In such a case [ ] premicellar aggregates of cetylpyridinium chloride (CPC) were shown to enhance tire rate of tire Fe(III) catalysed oxidation of sulphanilic acid by potassium periodate in tire presence of 1,10-phenantliroline as activator. This chemistry provides a lowering of tire detection limit for Fe(III) by seven orders of magnitude. It must also be appreciated, however, tliat such premicellar aggregates of CPC actually constitute mixed micelles of CPC and 1,10-phenantliroline tliat are smaller tlian conventional CPC micelles. 

Table 7.18 Detection Limits in ng/mL Table 7.19 Sensitive Lines of the Elements...

The detection limits in the table correspond generally to the concentration of an element required to give a net signal equal to three times the standard deviation of the noise (background) in accordance with lUPAC recommendations. Detection limits can be confusing when steady-state techniques such as flame atomic emission or absorption, and plasma atomic emission or fluorescence, which... 

The detection limits in the table correspond generally to the concentration of analyte required to give a net signal equal to three times the standard deviation of the background in accordance with lUPAC recommendations. 

Data for the several flame methods assume an acetylene-nitrous oxide flame residing on a 5- or 10-cm slot burner. The sample is nebulized into a spray chamber placed immediately ahead of the burner. Detection limits are quite dependent on instrument and operating variables, particularly the detector, the fuel and oxidant gases, the slit width, and the method used for background correction and data smoothing. 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

Designing an experimental procedure involves selecting an appropriate method of analysis based on established criteria, such as accuracy, precision, sensitivity, and detection limit the urgency with which results are needed the cost of a single analysis the number of samples to be analyzed and the amount of sample available for... 

The ability to demonstrate that two samples have different amounts of analyte is an essential part of many analyses. A method s sensitivity is a measure of its ability to establish that such differences are significant. Sensitivity is often confused with a method s detection limit. The detection limit is the smallest amount of analyte that can be determined with confidence. The detection limit, therefore, is a statistical parameter and is discussed in Chapter 4. 

The topic of detection limits is discussed at the end of this chapter. 

A method s detection limit is the smallest amount or concentration of analyte that can be detected with statistical confidence. The International Union of Pure and Applied Chemistry (lUPAC) defines the detection limit as the smallest concentration or absolute amount of analyte that has a signal significantly larger than the signal arising from a reagent blank. Mathematically, the analyte s signal at the detection limit, (Sa)dl, is... 

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