Polarization selective detection

Fig. 2 Measurement of the Cs hyperfine splitting, (a) Polarization selective detection with Ne buffer gas at 70.3 hPa.

For measurement of atomic coherence see also "Polarization Selective Detection of Hyperfine Quantum-Beats in Cs", by H. Lehmitz and H. Harde, this symposi+im... 

The method takes advantage of an excite and probe technique with polarization selective detection. A circularly polarized pxnnp pulse of ps duration generates a coherent superposition of atomic substates. The coherence induces an optical anisotropy in the atomic sample, which oscillates exactly with the splitting frequency of the respective substates. 

Raman peaks tend to be sharp and bunched close together, so spectral resolution is also an important factor to be taken into account when designing or acquiring a Raman spectrometer. Raman modes intensities and polarization properties are often dependent of the polarization state of the excitation source, sample orientation, temperature and crystallinity. For that reason, setups which allow for the selection of the polarization state of the excitation source, for sample conditioning and orientation and are capable of polarization selective detection, are common, as they enable a more complete characterization of the sample by Raman spectroscopy. 

Its principles include polar extraction with acetone-water (2 1, v/v), homogeneous partitioning of the target molecules into an organic solvent, GPC cleanup on Bio-Beads, fractionation by adsorption column chromatography on silica gel (Si02) deactivated with 1.5% water and finally GC with various selective detection methods (NPD, BCD, FPD). 

In recent years, also the number of articles concerning HILIC stationary phases has enormously increased, especially as regards the hydrophilic interactions that resolve some important problems separation and resolution of less retained compound in reversed phase chromatography. With this novel stationary phase, where the silica surface is covered with cross-linked diol groups to increase polar selectivity in hydrophilic conditions, is possible obviate to the use of normal phase with high water content. This allows facilitating the interfacing with sensible and selective detection instruments, such as mass spectrometer with ESI source. The HILIC stationary phase was often chosen to interface the mass spectrometry detector, because it would be... 

Zhang X, Talley JW, Boggess B, Ding G, Birdsell D (2008) Fast selective detection of polar brominated disinfection byproducts in drinking water using precursor ion scans. Environ Sci Technol 42(17) 6598-6603... 

Levenson, M. D., and Eesley, G. L. 1979. Polarization selective optical heterodyne detection for dramatically improved sensitivity in laser spectroscopy. Appl. Phys. 19 1-17. Librizzi, R, Viapianni, C., Abbruzzetti, S., and Cordone, L. 2002. Residual water modulates the dynamics of the protein and of the external matrix in trehalose-coated MbCO An infrared and flash-photolysis study. J. Chem. Phys. 116 1193-1200. 

The mammalian liver through its tremendous metabolic flexibility disposes of many toxic substances, including those released from hazardous waste sites, in very few common, polar forms. In a sense we hope to exploit this capability to convert pollutants to polar, involatile forms amenable to direct TSP LC/MS determination. The development of improved means for separation, selective detection and identification of metabolic conjugates in biological fluids has applications in the dosimetry of many toxic substances. Such techniques may be useful in screening exposures to a multitude of compounds simultaneously. 

Since its introduction in the 1960s, SFC has experienced several ups and downs in its development. Either a gas or a Uquid above its critical temperature and pressure is used as the mobile phase for SFC. In most cases, COj is used because of its favorable critical parameters (i.e., a critical temperature of 31 °C and a critical pressure of 7.3 MPa). Moreover, CO2 is cheap, nontoxic, and nonflammable. A high-pressure pump delivers the mobile phase through either a packed (pSFC) or capillary column (cSFC) to the detector. The mobile phase is maintained under supercritical or subcritical conditions via an electronic controlled variable restrictor that is positioned after detection (pSFC) or via a fixed restrictor positioned before a gas-phase detector (cSFC). The retention characteristics of the analytes are influenced by the properties of the stationary phase and by the polarity, selectivity, and density of the CO2 mobile phase. The density is controlled by variation of the temperature and pressure of the supercritical medium. Furthermore, the elution of very polar compounds under high densities can be achieved with a precolumn addition of polar modifiers such as methanol. Nowadays, pSFC formats use the same injector and column configurations as LC methods. Consequently, pSFC formats are considered to be more useful for routine operation than cSFC. The most remarkable... 

Details on the methods used (extraction, clean-up, separation) are given in the certification report [26]. Extraction was either carried out ultrasonically or by Soxhlet using organic solvent, e.g. hexane, acetone, n-pentane, dichloromethane. Clean-up was performed e.g. by treatment with concentrated H2SO4 followed by desulphurisation, column chromatography with e.g. activated alumina, silica etc. Capillary gas chromatography was used, identifying the CB compounds on the basis of their relative retention times and, in case of mass selective detection, on the basis of their ion masses. In all cases, at least two columns of different polarity have been used for quantification. For each CB, the participant selected the best suited column. 

HPLC advantages Amenable to thermally labile, nonvolatile, and polar components Rapid and automated analysis of complex samples Precise and quantitative (with spectral confirmation possible) Quantitative recovery (good sample preparation technique) Sensitive and selective detection (UV, FL, MS) Can tolerate injections of large volumes of aqueous samples (0.5-1 mL)... 

Rotational recurrences may be detected in polarization selected spontaneous fluorescence (provided the photodetector has a sufficiently fast response) or by a variety of sub-nanosecond pump/probe schemes (Felker and Zewail, 1987 Felker, 1992 Hartland, et al. 1992 Joireman, et al.. 1992 Smith, et al., 2003a,b). 

The Gasbadge and OVM 3500 samplers were applied in a study of 230 homes in western Germany (Krause et al., 1987). The exposure period for both types of badge was 2 weeks, and 57 VOCs were determined. GC analyses were conducted with two fused silica capillary columns of different polarity, and detection was by simultaneous FID/ECD. During the course of the study the commercial manufacture of the Gasbadge monitor was discontinued. Table 1.5-2 shows results of a selection of the compounds monitored that includes compounds with both significant outdoor sources such as benzene from motor vehicle exhausts and indoor sources such as solvents containing undecane. 

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