Desolvation systems condensers

Mixed Gas Plasmas. Water loading can be reduced by a desolvation system (condenser or membrane separator) only if the vast majority of the water can be removed. One way to eliminate the introduction of water into the plasma during measurement of the analyte signals is with electrothermal vaporization, laser ablation, or other direct solid sampling techniques. Mixed gas plasmas,... 

The combination of the ultrasonic nebulizer, heated spray chamber and condenser/desolvator leads to improvements in detection limits by a factor of about 10 compared to that of a pneumatic nebulizer without a desolvation system. This is the main reason ultrasonic nebulizers are used despite their higher cost (approximately U.S. 15,000 in 1998). 

Desolvation systems can provide three potential advantages for ICP-MS higher analyte transport efficiencies, reduced molecular oxide ion signals, and reduced solvent loading of the plasma. Two different approaches have been used for desolvation in ICP-MS. The heated spray chamber/condenser combination has been discussed it is the most commonly used system. The extent of evaporation of the solvent from the aerosol and cooling to reduce vapor loading varies from system to system. The second approach is the use of a membrane separator to remove solvent vapor before it enters the ICP. 

Spray chambers can be cooled via a water jacket or Peltier cooling to reduce the amount of solvent vapor introduced into the ICP [31, 32). A further reduction in the amount of solvent introduced can be realized via a desolvation system. Traditionally, such a desolvation system consisted of a sequence of a heated and a cooled tube. In the heated tube, the solvent is vaporized, after which it condenses on the inner wall of the cooled tube and is thus removed. Nowadays, desolvation systems equipped with a membrane desolvator are often used [33, 34). These basically consist of a tube manufactured from a semipermeable porous material, around which heated Ar gas is flowing in the opposite direction to the sample aerosol flow. The solvent is vaporized, and the gaseous solvent molecules leave the central tube via the pores and are carried off by the heated Ar flow. Desolvation of the sample aerosol can lead to an 10-fold increase in signal intensity. For rather volatile analyte elements, (partial) analyte loss needs to be taken into account [35]. 

To optimize the applicability of the electrothermal vaporization technique, the most critical requirement is the design of the sample transport mechanism. The sample must be fully vaporized without any decomposition, after desolvation and matrix degradation, and transferred into the plasma. Condensation on the vessel walls or tubing must be avoided and the flow must be slow enough for elements to be atomized efficiently in the plasma itself. A commercial electrothermal vaporizer should provide flexibility and allow the necessary sample pretreatment to introduce a clean sample into the plasma. Several commercial systems are now available, primarily for the newer technique of inductively coupled plasma mass spectroscopy. These are often extremely expensive, so home built or cheaper systems may initially seem attractive. However, the cost of any software and hardware interfacing to couple to the existing instrument should not be underestimated. 

Such is the added capability and widespread use of these nebulizers across all application areas that manufacturers are developing application-specific integrated systems that include the spray chamber and a choice of different desolvation techniques to reduce the amount of solvent aerosol entering the plasma. Depending on the types of samples being analyzed, some of these systems include a low-flow nebulizer, Peltier-cooled spray chambers, heated spray chambers, Peltier-cooled condensers, and membrane desolvation technology. Some of the commercially available equipment include the following ... 

Microflow nebulizer with heated spray chamber and Peltier-cooled condenser An example of this design is the Apex inlet system from ESI. This unit includes a microflow nebulizer, heated cyclonic spray chamber (up to 140°C), and a Peltier multipass condenser/cooler (down to -5°C). A number of different spray chamber and nebulizer options and materials are available, depending on the application requirements. Also, the system is available with Teflon or Nafion microporous membrane desolvation, depending on the types of samples being analyzed. Figure 17.12 shows a schematic of the Apex sample inlet system with the ctoss-Aow nebulizer. 

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