Fundamental detection limits

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. 

One of the fundamental performance characteristics of any analytical procedure is the Limit of Detection. Just as with the imprecision (standard deviation), with which it is intimately connected, the Detection Limit (Lp) is undefined unless there... 

Isotopes can be divided into two fundamental kinds, stable and unstable (radioactive) species. The number of stable isotopes is about 300 whilst over 1,200 unstable ones have been discovered so far. The term stable is relative, depending on the detection limits of radioactive decay times, hi the range of atomic numbers from 1 (H) to 83 (Bi), stable nuclides of all masses except 5 and 8 are known. Only 21 elements are pure elements, in the sense that they have only one stable isotope. AU other elements are mixtures of at least two isotopes. The relative abundance of different isotopes of an element may vary substantially. In copper, for example, Cu accounts for 69% and Cu for 31% of all copper nuclei. For the light elements, however, one isotope is predominant, the others being present only in trace amounts. 

As already mentioned, absorption bands in this region are overtones or combination bands of fundamental stretching bands that occur in the 3000-1700 cm1 region (Figure 12). The bonds involved are usually C—H, N—H, and —H. Because the bands are overtones or combinations, their molar absorptivities are low and detection limits are around 0.1%. 

Spontaneous Raman spectroscopy has the ability to provide clinically relevant chemical concentration measurements of multiple analytes in biofluids. Blood serum, whole blood, and urine have all been studied. The detection limit (assuming a few hundred seconds of spectral acquisition) appears, based upon fundamental noise considerations, to be around 0.1 mM for most biochemicals this places several important analytes within reach but certainly precludes... 

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 ... 

Fundamental issues relate primarily to achieving determinations of the required precision, accuracy, specificity, and detection limit. Due to development of methods for analyzing samples taken from the patient, the limitations considered at the stage of defining the problem are the number and size of samples tested, and the time needed to process and obtain analytical results. 

Quantitation. The most easily interpreted part of a quantitative residue analysis is the recording of a detector response found linear to concentration when checked by standard solutions. It has to be verified also that the response of sample and standard solution with a specific method is obtained at the same analytical position—e.g., on a gas chromatogram. The use of blanks will demonstrate the degree of infiuence of interfering materials and thus exhibit the detection limit of the recording system. However, because of the fundamental limitation of any monodetector system, only considerable knowledge of the sample will make a quantitative residue analysis reliable. 

There are many substances which would appear to be good candidates for LC-EC from a thermodynamic point of view but which do not behave well due to kinetic limitations. Johnson and co-workers at Iowa State University used some fundamental ideas about electrocatalysis to revolutionize the determination of carbohydrates, nearly intractable substances which do not readily lend themselves to ultraviolet absorption (LC-UV), fluorescence (LC-F), or traditional DC amperometry (LC-EC) [2], At the time that this work began, the EC of carbohydrates was more or less relegated to refractive index detection (LC-RI) of microgram amounts. The importance of polysaccharides and glycoproteins, as well as traditional sugars, has focused a lot of attention on pulsed electrochemical detection (FED) methodology. The detection limits are not competitive with DC amperometry of more easily oxidized substances such as phenols and aromatic amines however, they are far superior to optical detection approaches. 

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