Detection enhancement

MS detection enhancement factor = [conventional HPLC column diameter (4.6 mm)/(nano LC column diameter in mm)]2 (14.1)... 

For a 75 /.mi ID nano LC column as an example, the MS detection enhancement factor (ion count) in comparison to a 4.6 mm column is much higher than (4.6/0.075)2 = 3761 because of the reduction in sample molecular zone dilution and because a nano LC solvent flow rate at 0.02 to 2 /iL/min can be 100% directly sprayed into the MS ion source. No post-column flow splitting is required for nano-LC-MS as that required when 1 mL/min is used in a 4.6 mm ID column. This large enhancement of MS detection and the ability to directly interface with MS presents nano LC-MS as the best tool for life science research. 

In liquid chromatography, derivatization for detection enhancement is frequently needed, since no universal, sensitive, and simple-to-operate detector exists (the preparation of UV-absorbing derivatives is essential to obtain the sensitivity required for samples in the nanogram range). Since most fatty acids do not absorb UV radiation (at least not in the wavelength ranges of most commercial UV monitors), detection of quantities in the 1-ng range can be difficult. Tag-... 

Localized surface plasmon resonance (LSPR) at the metal surface has been exploited to enhance the signal obtained from optical biochips and thereby lower the limits of detection. There are two main enhancement factors (i) an increase in the excitation of the fluorophore by localizing the optical field on the nanoparticles near the fluorophore and (ii) an increase in quantum efficiency of the fluorophore. The plasmon resonance wavelength should coincide with the fluorophore absorption band to obtain the maximum emission efficiency. Several parameters concerning the signal detection enhancement are as follows (84)... 

There exist a variety of methods to detect enhanced antibody formation and autoantibodies in humans and experimental animals following environmental exposure. In contrast, tests available for measuring the potential of chemicals or environmental factors to produce autoimmune disease or augment existing autoimmune disease are not readily available. 

PSA Prostate cancer 0-4ngmL < 1 PSA-specific receptor, sandwich detection enhanced Buffer [25]... 

Stay alert for attack warning signs. Early detection enhances survival. 

Figure 4.12. Schematic illustration of DNA conductimetric detection enhanced by reporter DNA-Au-NP conjugates [71] (reprinted with permission ofWiley],...

For SDC applications, apart from detection enhancement and the automation of the injection system, much effort is put into the development of novel stationary phases and the apphcation of gradient elutions. 

There are two other sources worth noting, although they are currently used in a very small fraction of the instruments employed. Continuum sources can be used if their intensity is sufficient to minimize noise levels and if the spectrometer has sufficient dispersion to make the spectral bandpass comparable with the absorbing line width. While feasibility has been demonstrated in research laboratories, there currently is no commercial instrument available. At the other extreme, using a very bright, stable somce with a narrow line width has produced viable absorbance readings that are two to three orders of magnitude below those available with HCLs and EDLs. The somce that provides this detection enhancement is a tunable diode laser. 

Hankemeier, Th. van derLaan, H.T.C. Vteuls, J. Vredenbregt, M.J. Visser, T. Brinkman, U.A.Th. Detectability enhancement by the use of large-volume injections in gas chromatography-cryotrapping-Fourier transform infrared spectrometry. J. Chromatogr. A, 1996, 732, 75. 

The combination of UHPLC systems with MS analyzers is an additional and important approach, since the application of deconvolution tools does not require complete resolution of the phenolic compounds, improving the capability of the system more compounds in less time. Moreover, MS/MS detection enhances spedlicity compared to single-stage MS, minimizing sample handling and allowing the reduction of running time. 

Although the use of these detection enhancement parameters may increase specificity of VT detection, the concern exists that these parameters may mistakenly inhibit therapy, or delay time to detection, for true VT. To circumvent this, ICD programs allow therapy to be delivered when a tachycardia is sustained for a programmed period of time. If a therapy is withheld because of discriminators and the rate of the tachycardia remains in a detection zone, therapy will be delivered once the programmable duration period has expired. This feature ensures delivery of therapy if a tachycardia is sustained at a high rate for a period of time, regardless of whether the device categorizes it as SVT or VT. 

Dorian P, Philippon F, Thibault B, Kimber S, Stems L, Greene M, Newman D, Gelaznikas R, Barr A. Randomized controlled study of detection enhancements versus rate-only detection to prevent inappropriate therapy in a dual-chamber implantable cardioverter-defibrillator. Heart Rhythm 2004 1 540-7. 

Antigen-primaiy monoclonal antibody complexes are recognized by a second-aiy anti-immunoglobulin antibody conjugated to a marker to provide a means of detection. Enhanced sensitivity is achieved in this signal amplification step as each primary monoclonal antibody is recognized by many molecules of the secondajy antibody. 

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