Sensitivity detection system

In fact, this phenomenon has been used as the basis of a very sensitive detecting system. An example of the temperature profile of an adsorbent as a peak passes over it is shown in figure 2. Unfortunately, it was found almost impossible to produce a true simulation of the concentration profile of the peak from the temperature profile and interest in the detector declined. 

Both methods obtain the necessary sensitivity by modulating the electrode potential between two values which define two distinct states of the electrode surface thus the chemistry to be observed is directly modulated and may be detected with great sensitivity by an appropriate form of synchronous detection. In the case of EMIRS, the modulation frequency is made sufficiently high compared to the wavelength scanning rate to enable a phase sensitive detection system to be used whereas, for SNIFTIRS, the electrode potential is held for a sufficient period at each potential to accumulate data from several interferometric scans and, after an adequate number, the two sets of data are ratioed. 

The simplest fluorescence measurement is that of intensity of emission, and most on-line detectors are restricted to this capability. Fluorescence, however, has been used to measure a number of molecular properties. Shifts in the fluorescence spectrum may indicate changes in the hydrophobicity of the fluorophore environment. The lifetime of a fluorescent state is often related to the mobility of the fluorophore. If a polarized light source is used, the emitted light may retain some degree of polarization. If the molecular rotation is far faster than the lifetime of the excited state, all polarization will be lost. If rotation is slow, however, some polarization may be retained. The polarization can be related to the rate of macromolecular tumbling, which, in turn, is related to the molecular size. Time-resolved and polarized fluorescence detectors require special excitation systems and highly sensitive detection systems and have not been commonly adapted for on-line use. 

The detection of the migrating sample boundary in CE can be accomplished by UV, fluorescent, electrochemical, radiochemical, conductivity, and mass spectrometry (MS) means. The use of high-sensitivity detection systems is always a key issue in CE applications. The sensitivity of HPCE detectors may be at least 2 to 3 orders of magnitude better than that of HPLC detectors. Since the detection cell volume is very small, the concentration sensitivity... 

In conjunction with molecular weight sensitive detection systems, SEC can be used for determining various molecular weight parameters, such as molecular size, conformation and branching, as a function of MW. Furthermore, by interfacing SEC with spectrometry, polymer compositional heterogeneity can be determined. 

Limited detector choice (need for extremely sensitive detection systems)... 

Helium MIP-MS is also a very sensitive detection system for organotin compounds, such as tetraethyltin (TET), tetrabutyltin (TBT), triethyltin bromide (TET-Br), tripropyltin chloride (TPT-C1), tributyltin chloride (TBT-C1), and others, separated by CGC [213]. Detection limits at sub-pg levels were achieved, and linear dynamic ranges of at least three orders of magnitude were obtained. 

The chiral amines (55) were first derivatized by conventional reaction with fluorescene-isothio-cyanate (57) leading to fluorescein-active compounds (58) (Equation (9)) that enable a sensitive detection system, specifically laser-induced fluorescence detection (LIF), to be used.90 Although... 

In order to study the identity and nature of the intermediate, Aylmer-K.elly et al. (1973) employed modulated specular reflectance spectroscopy. They studied the reduction reaction at a lead cathode in both aqueous and non-aqueous electrolytes. A phase-sensitive detection system was employed by the authors, locked-in to the frequency of the potential modulation. The potential was modulated at 30 Hz between the reference potential of — 1.0 V vs. Ag/AgCl and a more cathodic limit. 

Figure 7.21 Dendrimers that are fluorescently labeled as well as biotinylated create enhanced detection reagents for use in (strept)avidin-biotin-based assays. Large complexes containing multiple fluorescent dendrimers can bind to antigens and form a highly sensitive detection system that exceeds the detection capability of fluorescently labeled antibodies.

The presence of biotin labels on an antibody molecule provides multiple sites for the binding of avidin or streptavidin. If the biotin binding protein is in turn labeled with an enzyme, fluoro-phore, etc., then a very sensitive detection system is created. The potential for more than one labeled (strept)avidin to become attached to each antibody through multiple biotinylation sites provides an increase in detectability over antibodies directly labeled with a detectable tag. 

Stears, R.L., Getts, R.C., and Gullans, S.R. (2000) A novel, sensitive detection system for high-density microarrays using dendrimer technology. Physiol. Genomics 3, 93-99. 

Since the magnetic moments are smaller, now we have a smaller susceptibility and therefore much smaller signal, requiring more sensitive detection systems. These are resonance or SQUID (see Section 14.5) techniques. Thermal response time are shorter, since pure metals can be used with good thermal conductivity and fast spin-lattice relaxation. The parameter to be measured is the nuclear susceptibility ... 

Another antibody-based method is immunoligand assay (ILA) technology. The Threshold system (Molecular Devices, Sunnyvale, CA) shortens assay development and assay turnaround time.11 It adapts a sensitive detection system originally... 

Fluorescence excitation techniques provide a more sensitive detection system in which fluorescent X-ray photons (a fraction of the ionized absorbing atoms relax by emission of a fluorescent X-ray photon) are counted as the photon energy is scanned. The signal generated is proportional to the absorption coefficient, p, of the absorbing atom. 

All detection systems can be employed following HER and noticeable improvement of most antigen detection will be observed. However, we recommend using sensitive detection systems, such as streptavidin-biotin-peroxidase methods when antigen density is low. 

LaBrie, S., Protein analysis in an array format using a novel, highly sensitive detection system. Presentation, International Business Communication, Drug Discovery Technologies, Session FI, Boston, MA, 2001. 

Assortment of Sensitive Detecting Systems. GC detectors (see Chapter 5) are relatively simple, highly sensitive, and possess rapid response. 

In common with all other sensitive detection systems, maintenance of the label enzyme in its active state is important. The precautions detailed in Notes 1—3 should be observed to maximize the sensitivity achieved. Reagents for enhanced chemiluminescence can be prepared in the laboratory or ure available commercially (see Note 4). The purity of the substrate solution is important in achieving maximum sensitivity. Therefore, the precautions detailed in Notes 5-7 should be followed if preparing substrate solutions. The free base form of lummoi undergoes rearrangement ro a mixture of luminol and a series of contaminants. Therefore, luminol should be purified by recrystaliistation as the sodium salt before use (see Note 8). 

Immunohistochemistry of multiple antigens in monolayer cell cultures during the same experimental conditions is also important in cell biology. Advanced techniques for antibody production combined with sensitive detection systems have facilitated the localization of... 

The main advantage of OT CEC is that separation efficiency can be doubled using this type of column. The trade-off is that the OT columns can easily be overloaded and therefore require a sensitive detection system. The small diameter of these columns precludes the use of UV detection, and fluorometric detection or mass spectrometry (MS) needs to be used. The use of fused silica capillaries with a bubble cell at the detection window has been reported as an alternative to employ UV detection. This features limit, to a certain extent, the range of practical applications of OT CEC. 

The requirements that the radicals are formed and trapped in isolated sites results in low radical concentrations and hence the total concentration of non-radical products is also small. Most samples contain 100-200 ppm of products but in some instances product concentrations as low as 10 ppm have to be determined. Such low concentrations necessitate the use of sensitive detection systems and the meticulous elimination of contaminants from all the gases used in the g.l.c. analysis. The compounds used as radical somrces and as matrices must also be extremely pure and to this end preparative g.l.c. has been used to piudfy the compounds. Mixtures of materials immiscible at room temperatme... 

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