Phase-detection method

This section presents an overview of the cold-trap pre-concentration gas phase detection method for the determination of mercury in seawater. A more thorough and complete discussion of the analytical details (e.g., cleaning procedures, reagent preparation, analytical manipulations) can be found in Fitzgerald et al (21). 

High detection sensitivity is frequently needed in biochemical research pertaining to amino acid metabolism. While the gas-phase detection methods are generally known for sensitivity, there are large differences in the capabilities of various... 

Supercritical Fluid Chromatography. The origin of SFC with packed columns goes back over two decades (17-26). The recent interest in SFC has been due in large part to the limitations in both chromatographic efficiency and detection methods with HPLC. The introduction of fused silica capillary columns with nonextractable stationary phases for SFC (O and the potential compatibility with gas phase detection methods (13) has served to further increase the attention given these methods. 

In order to test the accuracy of the SCSI-MS technique, the masses of the calcium isotopes " a+ and " a+ were measured with reference to the mass of the Ca ion one of the isotopes was trapped together with a Ca ion and the COM resonance frequency was determined by the phase-detection method (see Ref. [3]). As a reference, the COM frequency for two " Ca ions was determined also by the phase-detection method. The experimental oscillation frequencies from a series of measurements... 

SI. no. Compound. D,L-mixture Rf Mobile phase Detection method... 

Figueroa, J. F., Barbieri, E. (1991). Increased measurement range via frequency division in ultrasonic phase detection methods. Acoustic, 73, 47-49. 

One advantage of the photon counting teclmique over the phase-shift method is that any non-exponential decay is readily seen and studied. It is possible to detect non-exponential decay in the phase-shift method too by making measurements as a fiinction of tlie modulation frequency, but it is more cumbersome. 

SERS has also been applied as a sensitive, molecule-specific detection method in chromatography, e.g. thin layer, liquid, and gas chromatography. SERS-active colloids were deposited on the thin layer plates or mixed continuously with the liquid mobile phases. After adsorption of the analytes, characteristic spectra of the fractions were obtained and enabled unambiguous identification of very small amounts of substance. 

Other detection methods are based on optical transmittance [228-231], Alcohol sulfates have been determined by spectrophotometric titration with barium chloride in aqueous acetone at pH 3 and an indicator [232] or by titration with Septonex (carbethoxypentadecyltrimethylammonium bromide) and neutral red as indicator at pH 8.2-8.4 and 540 nm [233]. In a modified two-phase back-titration method, the anionic surfactant solution is treated with hyamine solution, methylene blue, and chloroform and then titrated with standard sodium dodecyl sulfate. The chloroform passing through a porous PTFE membrane is circulated through a spectrometer and the surfactant is analyzed by determining the absorbance at 655 nm [234]. The use of a stirred titration vessel combined with spectrophotometric measurement has also been suggested [235]. Alternative endpoint detections are based on physical methods, such as stalag-mometry [236] and nonfaradaic potentiometry [237]. 

Separation and detection methods There exists an array of methods for the separation of the Sb species, ranging from liquid-liquid extraction to the formation of complexes with immobilized reagents, followed by HPLC or reversed phase chromatography, and eletroanalytical methods. Detection is based on spectrophotometric measurement, AAS, ICP-OES and ICP-MS. 

Experimental probes of Born-Oppenheimer breakdown under conditions where large amplitude vibrational motion can occur are now becoming available. One approach to this problem is to compare theoretical predictions and experimental observations for reactive properties that are sensitive to the Born-Oppenheimer potential energy surface. Particularly useful for this endeavor are recombinative desorption and Eley-Rideal reactions. In both cases, gas-phase reaction products may be probed by modern state-specific detection methods, providing detailed characterization of the product reaction dynamics. Theoretical predictions based on Born-Oppenheimer potential energy surfaces should be capable of reproducing experiment. Observed deviations between experiment and theory may be attributed to Born-Oppenheimer breakdown. 

---