Sensitivity enhancement factor

Element Atomization temperature <°C) Sensitivity Pyrolytically- Ta-foil lined coated furnace furnace (PCF) (TaF) Sensitivity enhancement factor (PCF/TaF) at 2600°C... 

As a quantitative measure of the far-held performance, two quantities may be introduced. First of all, sensitivity enhancement factor (SEF), a ratio of resonance angle shift due to target analyte binding on a nanowire-based biosensor to that of a conventional SPR structure using a thin gold him with equal thickness, is defined as... 

FI preconcentration system compared to one without preconcentration. For example, the response of a flame AAS detector may be influenced by a change in the solution introduction rate (cf. Sec, 2.4,2, equation 2.1). These effects should be differentiated from enrichment effects in order to obtain a valid evaluation of the preconcentration performance. This may be realized by separately determining the enhancement factor under similar operational conditions but without preconcentration. In this book the two factors will be differentiated whenever possible, otherwise the total enhancement factor, expressed as will be used instead of EF. Fang ei al.[10] have shown that when sensitivity enhancement factors exist, other than an increase in concentration of the analyte in solution, the enhancement effects will be multiplicative on EF. Provided that different factors have independent enhancement mechanisms, the total enhancement factor Nt, will be the product of the individual enhancement factors, N, and... 

When other sensitivity enhancement factors with independent mechanisms are taken into consideration, it follows from equations 1.5 and 1.12 that ... 

Rossini el al. have reported the first application of DNP-enhanced solid-state NMR spectroscopy to metal-organic frameworks (MOF) materials." The experiments are demonstrated on the N-functionalized MOF compound (In)-MIL-68-NH2 (1), on a partially functionalized variant of 1 with a terephthalate aminoterephthalate ratio of 80 20 (2), and on a 10% pro-line-functionalized derivative of 1, (In)-MIL-68-NH-Pro (3). Despite the fact that the pore size of the MOFs are much smaller (ca. 1.6 nm) than that of the mesoporous materials previously investigated by DNP surface-enhanced solid-state NMR (ca. 6 nm), it has been shown that significant effective sensitivity enhancement factors can be obtained for H- C CPMAS experiments on these MOF materials. These factors are discussed with respect to the presence or not of the bulky proline ligand, which prevents the radical from entering into the pores. The authors show in addition that the reduction in experimental time provided by the DNP technology (of the order of 10- to 30-fold) allows the fast acquisition of two-dimensional H- C correlation spectra and of H- N CPMAS NMR spectra at natural abundance. 

This same sensitivity can, however, be misleading. Even minor radical routes to a particular reaction product could give rise to intense polarized n.m.r. signals which could obscure the normal monotonic increase of the signal due to product formed by a non-radical route. This problem can be overcome in some cases by estimation of the spectral enhancement factor. Again, it is not possible to justify a firm, threshold value, but as a useful rule of thumb when enhancements fall below about 100 then the possibility of an important alternative non-radical route to the same product should be carefully investigated. 

Matched filter The multiplication of the free induction decay with a sensitivity enhancement function that matches exactly the decay of the raw signal. This results in enhancement of resolution, but broadens the Lorentzian line by a factor of 2 and a Gaussian line by a factor of 2.5. 

Solid-Fluid Equilibria The solubility of the solid is very sensitive to pressure and temperature in compressible regions, where the solvent s density and solubility parameter are highly variable. In contrast, plots of the log of the solubility versus density at constant temperature often exhibit fairly simple linear behavior (Fig. 20-19). To understand the role of solute-solvent interactions on sofubilities and selectivities, it is instructive to define an enhancement factor E as the actual solubihty divided by the solubility in an ideal gas, so that E = ysP/Pf, where P is the vapor pressure. The solubilities in CO2 are governed primarily by vapor pressures, a property of the solid... 

LC-IR using surface-enhanced IR absorption spectroscopy (SEIRAS) was recently designed in order to develop a highly sensitive and rapid analysis method for polymer additives [506]. The method, which consists of spraying the LC eluents on to a metal film of Ag on a BaF2 substrate, allows an enhancement factor of about 90. 

The 13C NMR sensitivity can sometimes be a problem, but for the kind of samples studied here the effective concentration of monomer units is several molar which does not place excessive demands on present Fourier transform NMR spectrometers. In addition to the sensitivity of the chemical shift to structure (9), the relaxation of protonated carbons is dominated by dipole-dipole interaction with the attached proton (9). The dependence of the relaxation parameters T, or spin-lattice, and Tor spin-spin, on isotropic motional correlation time for a C-H unit is shown schematically in Figure 1. The T1 can be determined by standard pulse techniques (9), while the linewidth at half-height is often related to the T2. Another parameter which is related to the correlation time is the nuclear Overhauser enhancement factor, q. The value of this factor for 13C coupled to protons, varies from about 2 at short correlation times to 0.1 at long correlation... 

Finally, Yamada and Suzuki made a comparative study of the use of DDAB, HTAB, STAC, and CEDAB to improve the sensitivity and selectivity of the determination of ultratraces of Cu(II) by means of the CL reaction of 1,10-phenanthroline with hydrogen peroxide and sodium hydroxide, used as detection in a flow injection system [46]. Of the four cited surfactants it was found that CEDAB causes the greatest enhancement of the chemiluminescent signal (Fig. 12) (an enhancement factor of 140 with respect to the absence of surfactant). 

The signal enhancement due to this approach can, in principle, be as high as 105-fold - that is, equal to the reciprocal Boltzmann factor however, the experimentally achievable enhancement factors typically range between 10 and 103. Thanks to this increase in sensitivity, the PHIP phenomenon, therefore, provides for a powerful tool to investigate the fate of the dihydrogen, the catalysts, and of the substrates during hydrogenation reactions. 

For the Z-cell, a special interface is constructed for the detection to take place in the length of the capillary instead of the diameter. Two different lengths of capillary with tapered ends on one side are connected with the interface. This takes some experience, so it is important to test putting the set together by different analysts, both experienced and inexperienced. The device is only useful if you have sufficient separation between the analytes of interest, since a longer plug is in the detection window. Consequently, if the analyte bands are simultaneously in the detection window, resolution is no longer observed. A sensitivity enhancement of a factor 10 is possible. 

Micromolar quantities of RNS are generated primarily by nitric oxide synthase 2 (NOS2), an enzyme that is up-regulated during colon-cancer progression. As discussed below, deoxycholate (DOC), a hydrophobic secondary bile acid, activates the redox-sensitive transcription factor NF-kB, resulting in increased levels of NOS2 and enhanced S-nitrosylation of proteins. Additional sources of bile-acid-induced ROS and RNS are also likely. ... 

In requiring less measuring time and producing higher sensitivity in comparison to CW, PFT NMR follows the Fellgett principle [26, 27] The signal noise of any spectroscopic experiment increases if simultaneous multichannel excitation is applied. In the PFT technique, rf pulses simulate multichannel transmitters. If m transmitters stimulate simultaneously, the enhancement factor relative to one channel excitation (m = 1) is the square root of m (eq. (2.17), [26, 27]). 

In summary, NOE sensitivity enhancements are attained in heteronuclear NMDR when the nucleus with low y is observed while the nucleus with high y is decoupled. On the other hand, negligible enhancement of H NMR sensitivity can be expected from H 13C) experiments, the enhancement factor being only >jiH(13C) = 0.216 [34]. 

---