Flame solvent vapor entering

These factors make it necessary to reduce the amount of solvent vapor entering the flame to as low a level as possible and to make any droplets or particulates entering the flame as small and of as uniform a droplet size as possible. Desolvation chambers are designed to optimize these factors so as to maintain a near-constant efficiency of ionization and to flatten out fluctuations in droplet size from the nebulizer. Droplets of less than 10 pm in diameter are preferred. For flow rates of less than about 10 pl/min issuing from micro- or nanobore liquid chromatography columns, a desolvation chamber is unlikely to be needed. 

Open Flames or Hot Surfaces No degreaser should be installed near open flames or near high-temperature surfaces (above 750°F [399°C]). Welding and heat treatment operations and space heaters should not be located in proximity to solvent degreasing equipment. When these operations are in the same general area as solvent degreasing equipment, precautions should be taken, such as enclosures and local ventilation to ensure that no traces of solvent vapors enter these areas. 

The vent gas from the process enters the bottom of the mineral oil absorber. The mineral oil absorber is a tall, small-diameter packed column. Cold mineral oil cascades down through the column, absorbing solvent vapor from the vent gas as the vent gas rises up through the packing. When the vent gas exits the mineral absorber, it generally contains less than 10-g solvent per cubed meter of air. The vent gas is pulled from the mineral oil absorber via a spark-proof suction fan and is discharged to the atmosphere through a flame arrestor. 

For use in ICP/MS, an aerosol of analyte solution is produced in a nebulizer by mechanically breaking the solution into a spray of droplets and solvent vapor. This spray is swept along to the plasma flame by a flow of argon gas. The droplets have a range of diameters, depending on the type of nebulizer used. Frequently, before entering the torch, the aerosol first passes through a spray... 

To measure an atomic absorption signal, the analyte must be converted from dissolved ions in aqueous solution to reduced gas phase free atoms. The overall process is outlined in Fig. 6.16. As described earlier, the sample solution, containing the analyte as dissolved ions, is aspirated through the nebulizer. The solution is converted into a fine mist or aerosol, with the analyte still dissolved as ions. When the aerosol droplets enter the flame, the solvent (water, in this case) is evaporated. We say that the sample is desolvated . The sample is now in the form of tiny solid particles. The heat of the flame can melt (liquefy) the particles and then vaporize the particles. Finally the heat from the flame (and the combustion chemistry in the flame) must break the bonds between the analyte metal and its anion, and produce free M° atoms. This entire process must occur very rapidly, before the analyte is carried out of the observation zone of the flame. After free atoms are formed, several things can happen. The free atoms can absorb the incident radiation this is the process we want. The free atoms can... 

As the sample solution, in which the analyte element is in the form of a dissolved salt (for example, KCl(s) = K (aq) + Cl (aq)), enters the flame at a temperature of 2000 to 3000 K, the atomization process is considered to occur as follows (i) First the solvent rapidly evaporates and a solid aerosol will be formed (K (aq) + Cl (aq) = KCl(s)) (ii) Then the solid particles melt and vaporize (KCl(s) = KCl(g)). The vaporization is fast, provided the melting and boiling points of the analyte compound are well below the temperature of the flame (iii) The vapour consists of separate molecules or molecule aggregates which tend to decompose into individual atoms (KCl(g) = K(g) + Cl(g)) (iv) Individual atoms may absorb energy by collision and become excited or ionized (K(g) K (g) or K(g)... 

The solution containing the elements of concern is converted into small droplets by a nebulization (step 1 to 2) process. The small droplets enter the flame and the solvent is evaporated to produce small, dry particles. This is followed by vaporization of the dry particles and their subsequent dissociation into atoms. The atoms are excited by the flame, usually to low lying energy states, followed by emission of the excitation energy as spectral lines. 

---