Optical detection sensitivity

One of the reasons for high-aspect-ratio (deep-glass) etching is to increase the optical detection sensitivity. Why (2 marks)... 

The small diameters of separation capillaries provide high efficiencies in CE separations, but also cause decreased optical detection sensitivity. The concentration sensitivity is generally one or two orders of magnitude lower than that for HPLC. Unfortunately, both direct UV and indirect UV rarely exhibit detection capabilities suitable for monitoring natural concentrations of species in real-world samples, and interfacing of technologies is recommended. 

For IBSCA analysis, standard HV or, better, UHV-equipment with turbomolecular pump and a residual gas pressure of less than 10 Pa is necessary. As is apparent from Fig. 4.46, the optical detection system, which consists of transfer optics, a spectrometer, and a lateral-sensitive detector, is often combined with a quadrupole mass spectrometer for analysis of secondary sputtered particles (ions or post-ionized neutrals). 

Since the sensitizer Rose Bengal is recyclable, relatively high concentrations (5 10 M) can be used without raising cost issues and optical detection problems [21]. Under these conditions, it was shovm that molecules at any position in the micro channel have a similar photon flux. 

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... 

A number of other laser spectroscopic techniques are of interest but space does not permit their discussion. A few specialized methods of detecting laser absorption worthy of mention include multiphoton ionization/mass spectrometry (28), which is extremely sensitive as well as mass selective for gas-phase systems optically detected magnetic resonance (29) laser intracavity absorption, which can be extremely sensitive and is applicable to gases or solutions (30) thermal blooming, which is also applicable to very weak absorbances in gases or liquids (31) and... 

From a practical point of view, the optical detection of possible X—H bonds in hydrogenated samples is performed at LHeT as a better sensitivity is obtained at this temperature because the features are sharper than the ones observed at ambient. The sensitivity of Fourier Transform Spectroscopy (FTS) allows usually a normal incidence geometry of the optical beam. Two kinds of samples are generally used in the hydrogenation studies. The first are thin epitaxial layers (1 to 5 in thickness) with dopant concentrations in the 1017-102° at/cm3 range on a semi-insulating... 

Ultra-Sensitive Biochemical Optical Detection Using Distributed Feedback Nanolasers... 

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