Solvent vapors

In many applications of mass spectrometry, it is necessary to obtain a mass spectrum from a sample dissolved in a solvent. The solution cannot be passed directly into the mass spectrometer because, in the high vacuum, the rapidly vaporizing solvent would entail a large pressure increase, causing the instrument to shut down. 

Before WW1 neutralized TNT was further purified by crystn from solvents such as mixts of ale and benz. This method added to production cost and increased the fire and expln hazard due to the presence of flammable vapors. Solvent crystn of TNT is no longer used... 

Since APCI is a chemical ionization, it needs a gas. Indeed, a nebulising gas (generally nitrogen) is introduced into the source. The gas molecules are ionized by a corona discharge (analogous to the fdament used in Cl) thus forming the primary ions, mainly composed of N2+" and N4+". In turn, the latter ionize the vaporized solvent molecules by... 

With the thermospray interface (Figure 4.38(a)), the mobile phase, usually containing an ammonium ethanoate buffer, is passed through a heated probe (350-400°C) into an evacuated source chamber where it forms a supersonically expanding mist of electrically charged droplets. The liquid evaporates to leave charged solid particles which then release molecular ions such as MH+ and, VI by an ammonia chemical ionization (Cl) process. The analyte ions are skimmed off into the mass spectrometer whilst the vaporized solvent is pumped away. An electron beam is also employed to enhance the production of ions by Cl. 

Tested vapor Solvent polarity ET (kcal moh1) Relative solvent polarity TN Refractive index... 

Electrothermal vaporization has many appHcations relating to ICP analysis the abihty to vaporize solvents and to handle small soHd or viscous samples are particularly important. In addition, the measurement of the isotopic ratios of lead in various ores provides a unique identification of the ore and its source. Now that commercial systems are available, the technique will undoubtedly become popular. These techniques seem to have found favour, particularly in Japan. 

Splitless injection is used when the sample is dilute and cannot be introduced into the GC system with stream splitting. In practice, the column temperature is set 10° to 30°C below the boiling point of the solvent at the time of injection. When sample is introduced into the injector inlet, vaporized solvent together with the FAME condense at the beginning of the column along with the carrier gas flow. The condensed solvent plus the stationary phase of the column forms a diluted stationary phase that traps the FAME in it. After the initial sample introduction period, the column temperature is raised to normal operating conditions, and chromatographic separation starts from there. 

Aerosol Generator. The atomizer shown in Figure 7 was designed to produce aerosols of certain organic materials that are soluble only in easily vaporized solvents such as isopropanol or toluene. Difficulties were encountered when using other nebulizers because of continual concentration of the solution resulting from evaporation of the solvent, making it impossible to predict or control the test air concentration and the particle size. 

Generally, the evaporated mobile phase acts as the ionizing gas and reactant ions are produced from the effect of a corona discharge on the nebulized solvent. Typically, the corona discharge forms by electron ionization primary ions such as N2 + or 02 +. Then, these ions collide with vaporized solvent molecules to form secondary reactant gas ions. 

Moisture Loss. When the containers are inappropriately closed, part of the vaporized solvent is released and the concentration and potency of the active component may be increased [6],... 

We consider in this section the eqnilibrinm of a pnre solid (species 1) with a binary vapor mixhire containing species 1 and a second species (species 2), assnmed insolnble in the solid phase. Since it is nsnally the major constitnent of the vapor phase, species 2 is conventionally called the solvent species. Hence species 1 is the solnte species, and its mole fraction yi in the vapor phase is its solubility in the solvent. The goal is to develop a procedure for computing yi as a function of T and P for vapor solvents. 

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