High pressure nebulization

In atmospheric pressure chemical ionization (APCI) ion-molecule reactions occurring at atmospheric pressure are employed to generate the ions, i.e., it represents a high-pressure version of conventional chemical ionization (Cl, Chap. 7). The Cl plasma is maintained by a corona discharge between a needle and the spray chamber serving as the counter electrode. The ions are transferred into the mass analyzer by use of the same type of vacuum interface as employed in ESI. Therefore, ESI ion sources can easily be switched to APCI instead of an ESI sprayer, a unit comprising a heated pneumatic nebulizer and the spray chamber with the needle electrode are put in front of the orifice, while the atmospheric pressure-to-vacuum interface remains unchanged. [48,138]... 

Kwon JY, Moini M. 2001. Analysis of underivatized amino acid mixtures using high performance liquid chromatogra-phy/dual oscillating nebulizer atmospheric pressure micro-wave induced plasma ionization-mass spectrometry. J Am Soc Mass Spectrom 12 117. 

Arnoldsson and Kaufman optimized the response of the ELSD with a full factorial design evaluating the influence of evaporator temperature and air inlet pressure (70). As indicated in Fig. 10, the optimum conditions for both peak height and low baseline were achieved at high drift tube temperature and low-to-moderate nebulizer air pressure. The conditions chosen were 96°C and 1.6 bar. 

The second type of direct injection nebulizer, called the direct injection high-efficiency nebulizer (DIHEN), is a specific type of the Meinhard HEN [38] that is inserted into the ICP torch in place of the center, injector tube. The main advantage of the DIHEN compared to the Cetac DEN is that a high-pressure pump is not needed to deliver sample to the nebulizer. An unusually low nebulizer gas flow rate (0.25 L/min) and high ICP power (1.5 kW) were found to provide optimal ICP-MS sensitivity when DIHEN is used [38]. 

The speciation of Cr (III) and Cr (VI) has been performed by Jakubowski et al. [22] with IPC-ICP-MS and hydraulic high-pressure nebulization. A mobile phase of 25% methanol, ammonium acetate, and an ion-pair reagent (tetrabuty-lammonium acetate) was used. Oxygen addition was used to reduce carbon interferences from the high organic content in the mobile phase, along with desolvation. 

Several cfPcicnt sample introduction systems have been conceived to achieve higher precision, accuracy, and sensitivity, such as thermospray nebulization (TN) [95], ETV [88, 99], and hydraulic high pressure nebulization. The use of desolva-tation devices, for example, ultrasonic nebulization (UN), in combination with... 

E. Puskel, Z. Mester, P. Fodor, Determination of selenoamino acids by high-performance liquid chromatography-hydraulic high pressure nebulization-atomic fluorescence spectrometry, J. Anal. Atom. Spectrom., 14 (1999), 973-976. 

Commercial yeast-based supplements Hot water extraction IP HPLC-ICP-MS with hexapole collision and reaction cell, hydraulic high pressure nebulizer... 

A flame atomizer contains a pneumatic nebulizer, which converts the sample solution into a mist, or aerosol, that is then fed into a burner. The same type of nebulizers that are used with ICPs are used with flame atomizers. The concentric nebulizer is the most popular. In most atomizers, the high-pressure gas is the oxidant, and the aerosol containing oxidant is subsequently mixed with the fuel. 

Fig. 49. Particle size distributions of pneumatic nebulizers for ICP. MAK, high-pressure cross-flow nebulizer CGN, concentric glass nebulizer JAB, Jarrell—Ash Babington nebulizer JAC, Jarrell—.Ash fixed cross-flow nebulizer (Reprinted with permission from Ref. [139].)...

Apart from pneumatic nebulization through gas entrainment other types of pneumatic nebulization have been realized. In so-called jet-impact nebulization, use is made of the impact of a high pressure jet of liquid on a surface [142],... 

In addition, for speciation coupling of flow injection analysis and column chromatography with flame AAS and also a direct coupling of HPLC with flame AAS, as is possible with high-pressure nebulization, are most powerful. Here the Cr line in the visible region can be used, which makes the application of diode laser atomic absorption spectrometry possible [325]. This has been shown recently by the example of the determination of methylcyclopentadienyl manganese tricarbonyl. 

Maximum dissolved solids nebulizers [111] are usually cross-flow nebulizers operated at a high pressure. They are often made from PTFE, including the capillaries, and thus can be used for work with HF containing solutions. In this case a nebulization chamber made of PTFE and an ICP torch with an internal tube made of AI2O3 ceramics or BN should be used. 

It should be kept in mind that both thermospray nebulization and high-pressure nebulization [143] successfully allow the analyte introduction efficiency to be increased and thus also the power of detection, however, again only when aerosol desolvation is applied. They are especially interesting for speciation by on-line coupling of ICP-AES and HPLC, as shown later. 

Gas and liquid chromatography Coupled with ICP-AES these are useful approaches for speciation work, as shown by the early work of Cox et al. [418] for Crm/Crvl speciation, where AI2O3 filled columns and elution with acids and NaOH were used. Anion exchangers could also be used. New impetus has arisen from the interfacing of thermospray and high-pressure nebulization to ICP-AES. ICP-AES remains of interest for the element-specific detection in the speciation of silicon compounds and is a good alternative to ICP-MS, where considerable spectral interferences hamper the power of detection that can be obtained. 

---