Sensitivity of the detection system

Figure 3. Total emission and phosphorescence spectrum of MBC (II) at —190°C, corrected for the sensitivity of the detecting system (%).

The process of chemically modifying the test molecules before the separation procedure is known as preparing derivatives or pre-column derivatization. In liquid chromatography this is done to permit the test molecules to be more easily detected after separation and to increase the sensitivity of the detection system and less frequently to alter the separation process. 

Quantitative spectrographic analyses for trace elements in high-temperature ash samples of coal have been reported by Abemethy et ah (1), Zubovic et ah (2,3,4,5), Rao (6), and Hunter and Headlee (7). We felt that it was desirable to develop additional analysis methods, especially for the direct-reading spectrometric technique, in which small changes of some matrix constituents might cause relatively large variations in results because of the increased sensitivity of the detection system. A... 

Separation of the enantiomers of pantoprazole sodium was described by Kuhn et al [14]. Bovine serum albumin (BSA) was used as the chiral selector, and different experimental parameters were investigated to obtain good resolution between the enantiomers. Increasing the concentration of BSA improved the chiral resolution, but the sensitivity of the detection system was lowered. Using a buffer system having a pH around 7.4 and addition of 1-propanol caused an enhancement to the peak shape and the resolution. This method is suitable for routine analysis. 

G is the correction factor and allows one to take into account the differences in sensitivity of the detection system in the two polarizing directions /w and Ivh. The G factor can be... 

The chemiluminescence spectrum obtained from the reaction of ozone with methyl mercaptan at a pressure of 0.2 torr is shown in Figure 5. Reaction of hydrogen sulfide with dimethylsulfide with ozone give identical spectra consisting of a broad structureless band centered at approximately 370 nm (uncorrected for spectral sensitivity of the detection system). We have recently shown that this emission is identical to the fluorescence spectrum of sulfur dioxide (16). Since ozone oxidizes hydrogen sulfide to sulfur dioxide and water in the gas phase 17, 18), this result is not surprising. 

In order to obtain true emission and excitation spectra it is uaially necessary to apply conections for variations in excitation intentity and the wavelength sensitivity of the detection system. The correction needed may be calculated by comparing the instmment response for a standard compound of known corrected ectral characteristics with that of the sample under study, although q)ectrofluorimeters have been described which fully electronically compensate for intensity and wavelength response of the system Comparison of the area under the corrected emission spectrum with that of various standard fluorescence compounds allows the quantum yield of the luminescence process to be calculated ... 

The best results concerning the separation techniques are achieved by using capillary electrophoresis 310 in this case, the problem is the sensitivity of the detecting system, which is unconnected with the sensitivity of the separation technique. 

For TRXRD measurements to be meaningful, special attention must be devoted to the questions posed, to the manner in which the experiments designed to answer these questions are performed, and to the proper choice of materials and complete documentation of experimental protocols and results. As an example, in the case of a T-jump experiment, documentation should include direction, rate and magnitude of the jump, initial and final temperatures, and the thermal history of the sample. Ideally, in-sample temperature should be recorded at or close to the interrogating X-ray beam throughout the course of the transition. The manner in which the characteristic transition time is determined must be adequately described and, where possible, an estimate made of the number of molecules transforming per unit of time and volume. A measure of the sensitivity of the detection system to the presence of intermediates or minor and disordered phases would enormously benefit data evaluation. 

Preparation of specimens. The mixture to be separated is applied to the paper as a solution. The solution should be 0.5% of which 10 pi are applied to the paper. The precise amount and concentration will depend on the complexity of the sample mixture and the sensitivity of the detection system. The nature of the solvent is immaterial, as long as it will evaporate completely without leaving a residue, and without attacking the paper. Solid samples, such as oils, or biological cell or tissue material, are macerated with the solvent, or submitted to some standard extraction procedure, such as Soxhlet. Many important samples, such as urine or other biological fluids, are already in an aqueous medium. In other cases water is used as the solvent when the substances are soluble in it. 

By using a field stop in front of the detector, light from outside the focus can be suppressed. This can be useful to suppress fluorescence of the cuvette walls, fluorescence of dye moleeules bound to the cuvette walls, or distortions by scattering or reabsorption. Confocal detection can also be used to reduce the daylight-sensitivity of the detection system. 

NECEEM-based quantitative affinity analysis is simple, fast, and accurate. The limit of detection is defined by the sensitivity of the detection system used. Eor best systems utilizing laser-induced fluorescence detection, the mass limit of detection can be as low as 1000 molecules and the concentration limit of detection can reach picomolar. 

The donor contribution in the acceptor channel (crosstalk) should be as low as possible the impact of this contribution on a bioassay is not obvious to anticipate starting from a lanthanide complex emission spectrum, since many instmmental factors, such as the filter settings (bandpass width), have to be considered. The intensity distribution between the emission lines is critical, particularly for europium complexes, with a strong impact of the ligand structure and symmetry (for terbium complexes, this impact is reduced). Care must be exercised in comparing published emission spectra, since many of the published spectra are not corrected for the photomultiplicator sensitivity (which falls off rapidly between 650 and 800 nm even using a red PMT ). The consequence is that the 690-nm ( Dq p4) band seems much smaller than its true value. Some articles do indeed show spectra corrected for the sensitivity of the detection system (which contains contributions from the PMT, but also from the monochromators and optics). Whenever such corrections have been applied, this is usually indicated in the experimental section of the article. 

Fluorescence anisotropy can also be calculated by the quotient between the fluorescence intensities obtained at the four different combinations of the excitation and emission polarizer positions, as shown by Equation (12.3), Iw and Ihh account for the fluorescence intensity obtained with both polarizers at the vertical and horizontal position, respectively. Ihv corresponds to the fluorescence emission obtained with excitation polarizer horizontally and emission polarizer vertically oriented. In contrast, lyn corresponds to the fluorescence emission obtained with excitation polarizer verticahy and emission polarizer horizontally oriented. The G factor (Equation 12.4) is a parameter that accounts for the sensitivity of the detection system for verticahy and horizontally polarized lights [3]. 

---