Desolvation systems heated spray chamber

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. 

In this device the liquid sample is sprayed into a heated spray chamber, where the nebulizer gas transfers the aerosol through the membrane desolvator. An argon flow removes the solvent vapour from the exterior of the membrane. If compared to conventional pneumatic nebulizers, this system enhances analyte transport efficiency and limits solvent loading to the plasma. Oxide and hydride polyatomic ion interferences are significantly reduced, improving the detection limits by an order of magnitude. 

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. 

The Thermospray jet is introduced into a spray chamber which is heated sufficiently to complete the vaporization process. Helium is added through a gas inlet in sufficient quantity to maintain the desired pressure and flow rate. The fraction of the solvent vaporized in the thermospray vaporizer and the temperature of the desolvation chamber is adjusted so that essentially all of the solvent is vaporized within the desolvation region. The Thermospray system allows very precise control of the vaporization so that all of the solvent can be vaporized while most of even slightly less volatile materials will be retained in the unvaporized particles. 

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]. 

Microflow nebulizer coupled with membrane desolvation An example of this is the Aridus system from Cetac Technologies. The aerosol from the nebulizer is either self-aspirated or pumped into a heated PEA spray chamber (up to 110°C) to maintain the sample in a vapor phase. The sample vapor then enters a heated PTFE membrane desolvation unit, where a coun-... 

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