Surface ionization negative

Hyperthermal negative surface ionization operating principle. 

The use of an atomic emission detector (AED) coupled to a GC may provide under ideal conditions information about the empirical formula of the analyte corresponding to a GC peak. However, it was found that the AED responses of C, Cl and O of a series of phenols is related to the working condition of the AED. The elemental response of Cl is independent of molecular structure, but those of C and O are not, probably due to formation of CO in the plasma. The O response is also affected in nitrophenols, probably due to NO2 formation. A novel detector, based upon hyperthermal negative surface ionization, shows up to 100-fold higher sensitivity than that of the FID for alcohols and phenolic compounds. ... 

A detector system (SID) based on hyperthermal negative surface ionization has been used for the analysis of alkanols and phenols (Kishi et al. 1998), and was =100 times more sensitive than FID. 

Fig. 1 A cutaway view of the core portion of XSD. PSI, positive surface iouization NSI, negative surface ionization TEE, thermal electron emission."" ...

The work functions of metal surfaces show a marked dependence on the crystal planes that constitute the surface. For polycrystal metal surfaces, the experimentally determined value of the work function is an average of the work functions of all the crystal planes that are present on the surface. It is made up of the contributions from the individual crystal planes. If /a, / and tp are defined as the mean effective work functions for thermionic electron emission, positive surface ionization, and negative surface ionization, respectively, it is generally evident that /+ > /, and / =... 

Stoffels, J.J. (1982). Measurement of iodine-129 at the femtogram level by negative surface ionization mass spectrometry, Radiochem. and Radioanal. Lett. 55, 99. 

Cesium ions are also sometimes used to enhance the secondary-ion yield of negative elemental ions and that of some polymer fragments [3.6]. They are produced by surface ionization with an extraction technique similar to that of FI sources. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

The liquid metal Ion source could help dramatically In the area of+negatlve secondary Ion mass spectrometry where bombarding with Cs ions has proven very beneficial (19). This is due to the large Increase In negative ion emission from a cesiated, low work function surface. Unfortunately, the sources used to produce cesium ions are of the surface ionization type (20) which has a low brightness. If the liquid metal field emission Ion source can be developed to operate reliably with liquid cesium, then small, high-current density ion beams could be formed. Currently, however, the reactive nature of the metal makes the liquid metal field emission cesium Ion source more of a research project than a routine analytical technique. 

The latter mechanism, operating in addition to the equivalent adsorption of cations on the ionized Ti - 0 sites (cf. Eq. (7)), would account for the abnormally large negative surface charge densities, observed in solutions containing Mg " or Li ions, at pH s higher than the PZC. 

The electron affinities Ea of the main group atoms are the most precisely measured values. Recall that the Ea is the difference in energy between the most stable state of the neutral and a specific state of a negative ion. It was once believed that only one bound anion state of atoms and molecules could exist. However, multiple bound states for atomic and molecular anions have been observed. This makes it necessary to assign the experimental values to the proper state. The random uncertainties of some atomic Ea determined from photodetachment thresholds occur in parts per million. These are confirmed by photoelectron spectroscopy, surface ionization, ion pair formation, and the Born Haber cycle. Atomic electron affinities illustrate the procedure for evaluating experimental Ea. 

Fig. 18. Total cross sections Q for the production of negative ions in collisions of K, Na and Li on Br2 and Cl2, divided by the unknown energy dependent surface ionization detector efficiency / , vs. the CM-energy. The thresholds are indicated by arrows. The insets show enlargements of the thresholds. Notice the small structure at about 4eV in the Na-Cl2 cross section. The constant signal below threshold is due to the presence of dimers in the alkali beam (Baede and Los, 1971).

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