Atmospheric desorption

El = electron ionization Cl = chemical ionization ES = electrospray APCI = atmospheric-pressure chemical ionization MALDI = matrix-assisted laser desorption ionization PT = plasma torch (isotope ratios) TI = thermal (surface) ionization (isotope ratios). 

VACUUM RADIATING DESORPTION AND INFRARED SPECTROMETRY (VRDIR) FOR CONTINUOUS MONITORING OF SUSPENDED PARTICULATE ORGANIC MATTERS IN ATMOSPHERE... 

Wetness of a metal surface The lime of wetness of the metal surface is an exceedingly complex, composite variable. It determines the duration of the electrochemical corrosion process. Firstly it involves a consideration of all the means by which an electrolyte solution can form in contact with the metal surface. Secondly, the conditions under which this solution is stable with respect to the ambient atmosphere must be considered, and finally the rate of evaporation of the solution when atmospheric conditions change to make its existence unstable. Attempts have been made to measure directly the time of wetness , but these have tended to use metals forming non-bulky corrosion products (see Section 20.1). The literature is very sparse on the r61e of insoluble corrosion products in extending the time of wetness, but considerable differences in moisture desorption rates are found for rusted steels of slightly differing alloy content, e.g. mild steel and Cor-Ten. 

The ionic current intensity corresponding to the peak at 169 amu was analyzed under isothermal and polythermal conditions [383]. It was found that in a gaseous atmosphere, the intensity changes are in correlation with the CO content and in negative correlation with the C02 content. The presence of CO in vacuum systems equipped with heating elements is usually related to thermo-cycling and desorption of CO by nickel atoms [386]. Based on the above, the presence of NbF4+ ions in mass spectra is most probably related to the niobium reduction process, which can be represented as follows ... 

As already noted the strength of chemisorptive bonds can be varied in situ via electrochemical promotion. This is the essence of the NEMCA effect. Following initial studies of oxygen chemisorption on Ag at atmospheric pressure, using isothermal titration, which showed that negative potentials causes up to a six-fold decrease in the rate of 02 desorption,11 temperature programmed desorption (TPD) was first used to investigate NEMCA.29... 

Models of chemical reactions of trace pollutants in groundwater must be based on experimental analysis of the kinetics of possible pollutant interactions with earth materials, much the same as smog chamber studies considered atmospheric photochemistry. Fundamental research could determine the surface chemistry of soil components and processes such as adsorption and desorption, pore diffusion, and biodegradation of contaminants. Hydrodynamic pollutant transport models should be upgraded to take into account chemical reactions at surfaces. 

Advantages and disadvantages of thermal desorption are listed in Table 9.3. (Charcoal badges are also available which require no pump these are termed passive samplers .) Instruments are also available to give direct readout of atmospheric levels of pollutant. 

After treatment, the gases are evacuated either diieetly to the outside atmosphere or through a speeial exhaust system. Filtered, sterile air is then admitted either for a repeat of the vaeuum/air cycle or for air purging until the ehamber is opened. In this w, safe removal of the ethylene oxide is achieved ledueing the toxie hazard to the operator. Sterilized artieles are removed directly from the ehamber and arranged for desorption. 

This study presents kinetic data obtained with a microreactor set-up both at atmospheric pressure and at high pressures up to 50 bar as a function of temperature and of the partial pressures from which power-law expressions and apparent activation energies are derived. An additional microreactor set-up equipped with a calibrated mass spectrometer was used for the isotopic exchange reaction (DER) N2 + N2 = 2 N2 and the transient kinetic experiments. The transient experiments comprised the temperature-programmed desorption (TPD) of N2 and H2. Furthermore, the interaction of N2 with Ru surfaces was monitored by means of temperature-programmed adsorption (TPA) using a dilute mixture of N2 in He. The kinetic data set is intended to serve as basis for a detailed microkinetic analysis of NH3 synthesis kinetics [10] following the concepts by Dumesic et al. [11]. 

PFE is based on the adjustment of known extraction conditions of traditional solvent extraction to higher temperatures and pressures. The main reasons for enhanced extraction performance at elevated temperature and pressure are (i) solubility and mass transfer effects and (ii) disruption of surface equilibria [487]. In PFE, a certain minimum pressure is required to maintain the extraction solvent in the liquid state at a temperature above the atmospheric boiling point. High pressure elevates the boiling point of the solvent and also enhances penetration of the solvent into the sample matrix. This accelerates the desorption of analytes from the sample surface and their dissolution into the solvent. The final result is improved extraction efficiency along with short extraction time and low solvent requirements. While pressures well above the values required to keep the extraction solvent from boiling should be used, no influence on the ASE extraction efficiency is noticeable by variations from 100 to 300 bar [122]. 

Fast atom bombardment (FAB) Plasma desorption (PD) Liquid secondary-ion mass spectrometry (LSIMS) Thermospray (TSP)/plasmaspray (PSP) Electrohydrodynamic ionisation (EHI) Multiphoton ionisation (MPI) Atmospheric pressure chemical ionisation (APCI) Electrospray ionisation (ESI) Ion spray (ISP) Matrix-assisted laser desorption/ionisation (MALDI) Atmospheric pressure photoionisation (APPI) Triple quadrupole (QQQ) Four sector (EBEB) Hybrid (EBQQ) Hybrid (EB-ToF, Q-ToF) Tandem ToF-ToF Photomultiplier... 

PD, LDI, MALDI, etc.) and laser desorption. Recent developments in LC-MS, mainly atmospheric ionisation and off-axis spraying, have made the technique as reliable, versatile and easy to use as capillary GC-MS. 

The effect of oxidizing atmospheres on the reduction of NO over rhodium surfaces has been investigated by kinetic and IR characterization studies with NO + CO + 02 mixtures on Rh(lll) [63], Similar kinetics was observed in the absence of oxygen in the gas phase, and the same adsorbed species were detected on the surface as well. This result contrasts with that from the molecular beam work [44], where 02 inhibits the reaction, perhaps because of the different relative adsorption probabilities of the three gas-phase species in the two types of experiments. On the other hand, it was also determined that the consumption of 02 is rate limited by the NO + CO adsorption-desorption... 

A different picture was obtained in the case of the reference Pt—BaAy-A Oj (1/20/100 w/w) sample (Figure 6.12). In the case of the TPD experiment performed after NO, adsorption at 350°C, the decomposition of stored NO, species was observed only above 350°C. Evolution of NO and 02 was observed in this case, along with minor quantities of N02 [25,28,33,35], Complete desorption of NO, was attained already slightly below 600°C. As in the case of the binary Ba/y-Al203 sample, the data hence indicate that nitrates formed upon N0/02 adsorption at 350°C followed by He purge at the same temperature, did not appreciably decompose below the adsorption temperature during the TPD run under inert atmosphere. 

Then the reduction of stored NO with hydrogen was addressed. The stability/reactivity of the NO adsorbed species was analysed under different atmospheres (inert and reducing) both at constant temperature and under temperature programming. The bulk of data pointed out that in the absence of significant thermal effects in the catalyst bed, the reduction of stored nitrates occurs through a Pt-catalysed surface reaction that does not involve the thermal desorption of the stored nitrates as a preliminary step. A specific role of a Pt-Ba interaction was suggested, which plays a role in the NO storage phase as well. 

Moyor, S. C. Marzilli, L. A. Woods, A. S. Laiko, V. V. Doroshenko, V. M. Cotter, R. J. Atmospheric pressure matrix-assisted laser desorption/ionization (AP MALDI) on a quadrupole ion trap mass spectrometer. Int. I. Mass Spectrom. 2003, 226,133-150. 

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