Detection sensitivity enhancement

Another method, cross-correlation chromatography, was also reported for detection sensitivity enhancement (see Figure 7.12). Multiple injections were performed in a continuous but random sequence. A single point detection output was recorded. This output was correlated with the injection profile. This correlation enhanced the detection sensitivity due to the multiplex advantage [705]. 

Precolumn derivatization is the generally accepted approach for the determination of amino acids, because it offers significant advantages increased detection sensitivity, enhanced selectivity, enhanced resolution, and limited needs for sophisticated instrumentation (in contrast with postcolumn derivatization techniques). 

Detection Sensitivity Enhancement 3.2.7 Isotopic Enrichment and High Magnetic Field... 

As femtomolar detection of analytes become more routine, the goal is to achieve attomolar (10 molar) analyte detection, corresponding to the detection of thousands of molecules. Detection sensitivity is enhanced if the noise ia the analytical system can be reduced. System noise consists of two types, extrinsic and intrinsic. Intrinsic aoise, which represents a fundamental limitation linked to the probabiHty of finding the analyte species within the excitation and observation regions of the iastmment, cannot be eliminated. However, extrinsic aoise, which stems from light scatteriag and/or transient electronic sources, can be alleviated. 

The reaction of ort/io-phthalaldehyde and a thiol compound with an amino acid to form an isoindole derivative can be used to enhance the detection sensitivity for the normally only weakly UV-detectable amino acid compounds, and to introduce an... 

In analytical LC there are two primary reasons why chemical derivatization of the sample constituents would be necessary, and they are 1) to enhance the separation and 2) to increase the sensitivity of detection. Under certain circumstances, derivatization can also be used to reduce peak asymmetry, i.e. to reduce tailing, or to improve the stability of labile components so that they do not re-arrange or decompose during the chromatographic process. However, sensitivity enhancement is the most common goal of derivatization. For example, aliphatic alcohols that contain no UV chromaphore can be reacted with benzoyl chloride to form a benzoic ester. 

The sensitivity enhancement in the INEPT experiment is particularly marked when nuclei of low magnetogyric ratios are being detected. A comparison of the signal intensities obtained by polarization transfer against those obtained by full NOE for various nuclei is presented in Table 2.1. 

In TLC the detection process is static (sepaurations achieved in space rather than time) and free from time constraints, or from interference by the mobile phase, which is removed between the development and detection process. Freedom from time constraints permits the utilization of any variety of techniques to enhance detection sensitivity, which if the methods are nondestructive, nay be applied sequentially. Thus, the detection process in TLC is nore flexible and variable than for HPLC. For optical detection the minimum detectable quantities are similar for both technlqpies with, perhaps, a slight advantage for HPLC. Direct comparisons are difficult because of the differences in detection variables and how these are optimized. Detection in TLC, however, is generally limited to optical detection without the equivalent of refractive... 

The main implications of the new remote detection methodology are the sensitivity enhancement, which can be several orders of magnitude in certain applications, the option to study flow transiently with time-of-flight techniques and the broadening of the application range of NMR and MRI to samples that were previously... 

The amount of information, which can be extracted from a spectrum, depends essentially on the attainable spectral or time resolution and on the detection sensitivity that can be achieved. Derivative spectra can be used to enhance differences among spectra, to resolve overlapping bands in qualitative analysis and, most importantly, to reduce the effects of interference from scattering, matrix, or other absorbing compounds in quantitative analysis. Chemometric techniques make powerful tools for processing the vast amounts of information produced by spectroscopic techniques, as a result of which the performance is significantly... 

Cross-polarisation (CP) in the rotating frame has been introduced as a means of transferring polarisation between different nuclear species in solids [168], and has become of central importance for obtaining spectra of rare spins with low gyromagnetic ratios such as 13C, since a significant sensitivity enhancement may be achieved. Cross-polarisation can be used either for direct observation of low-sensitivity nuclei or for indirect detection of such nuclear species via high-sensitivity nuclei such as protons [169]. 

Sensitivity impacts upon the limit of detection and resolution of the device, making it a key performance parameter. Recently, several strategies have been developed in order to provide sensitivity enhancements for optical sensor platforms based on both optical absorption and fluorescence phenomena. These strategies are the result of rigorous theoretical analyses of the relevant systems and, combined with polymer processing technology and planar fabrication protocols, provide a viable route for the development of low-cost, efficient optical sensor platforms. 

DNA probes have been covalently immobilized onto the distal end of the optical fiber bundle in the construction of a novel CL DNA bisensor [101]. Hybridization of HRP-labeled complementary nucleotides to the immobilized probes was detected by enhanced CL. This approach was specific, sensitive, and available for diagnostic application with a detection limit of 0.1 ppm. 

Two methods of further enhancing detection sensitivity rely on the use of multiple resonators or multiple fiber modes. The first will just be mentioned briefly, because although it is absorption based it uses a frequency shift. When two microresonators have resonances that are coincident in frequency, and the second resonator is brought near to the first resonator, which is in contact with the coupling fiber, the... 

The enhanced evanescent field, as confirmed by the coupling enhancement results noted above, has been shown to significantly enhance detection sensitivity in preliminary experiments using dye in water solution at 800 nm. In addition, a... 

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