Membrane desolvator

Flow-injection (FI) on-line analyte preconcentration and matrix removal techniques greatly enhance the performance of atomic spectrometry [348], By using USN with membrane desolvation (MDS) as the interface, FI sorbent extraction can be directly coupled with ICP-MS for the analysis of organic solutions [349]. 

A frequently used micronebulizer with heated spray chamber and membrane desolvator is the Aridus from CETAC Technologies, Ohama, NE. The experimental setup of the Aridus II microconcentric nebulizer is shown in Figure 5.16. 

Figure 5.17 Setup of ultrasonic nebulizer with membrane desolvator (USN 6OOOAT, CETAC Technologies, Ohama). (Reproduced by permission of CETAC Technologies.)...

Figure 6.19 Schematic setup of IA-ICP-MS with solution based calibration using microconcentric or ultrasonic nebulizer with membrane desolvator. (j. S. Becker et ai, Int. /. Mass Spectrom. 237, 13 (2004), reprinted by permission of Elsevier.)...

V.V-dicthyl-V -bcnzoy I thiourea (DEBT). The palladium complex formed was eluted with methanol and introduced into an ICP-SFMS via microconcentric nebulization with membrane desolvation. Isotope dilution analysis was employed for quantification purposes.80... 

ICP-MS is a multi-element technique suitable for the analysis of liquid samples, which provides higher selectivity and detection power and LoDs lower than other multi-element techniques, such as ICP-AES. These characteristics make ICP-MS an excellent tool for the detailed characterization of the elemental composition of beverages. In this context, ICP-MS was the technique selected for the determination of 31 trace elements in wine at concentrations ranging from 0.1 to 0.5 ng ml-1 [82]. Samples were diluted 1 + 1 and it was investigated whether a matrix effect derived from the presence of ethanol could be overcome by using a microconcentric nebulizer with membrane desolvation. The authors compared their results with those obtained using a conventional Meinhard nebulizer and concluded that the matrix effect observed could only be minimized by using an internal standard with the Meinhard nebulizer, but not with the other one. 

A method for the accurate online ultratrace analysis of palladium in environmental samples (road dust and contaminated soil samples) by ICP-MS after separation of interferent cations by cation exchange chromatography was introduced by Hann and co-workers. ° Palladium was selectively adsorbed online onto a Cjg microcolumn which had been reversibly loaded with a complexing agent A,Al-diethyl-Al -benzoylthiourea (DEBT). The palladium complex formed was eluted with methanol and introduced into an ICP-SFMS via microconcentric nebulization with membrane desolvation. Isotope dilution analysis was employed for quantification purposes. ... 

Figure 8.1. (A) CETAC ultrasonic nebulizers U-5000AT+ (1-15) and U-6000AT+ (1-19). 1 — transducer, 2 — aerosol chamber stand, 3 — aerosol chamber, 4 — sample/rlse adapter, 5 — U-tube, 6 — heat cords, 7 — glassware module, 8 — transducer radio frequency (RF) cable, 9 — sample inlet tubing, 10 — electronics module, 11 — auxiliary rinse port, 12 — operate switch, 13 — fast pump switch, 14 — heater controller (nebulizer), 15—cooler controller (nebulizer), 16 — heater controller (desolvator), 17 — flow meter, 18 — flow control and 19 — membrane desolvator controller. (B) Detailed scheme of the U-6000AT+ glassware module. (Reproduced with permission of CETAC Technologies.)...

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. 

Figure 2.14 Schematic diagram of Cetac Ultrasonic UT5000 and UT6000 complete with the membrane desolvator. (Reproduced with kind permission from CETAC Laboratories)...

The membrane desolvator is very effective in reducing the solvent loading further when used in conjunction with the ultrasonic nebuliser. This will allow a range of solvents to be used for ICP-AES that would otherwise quench the plasma by almost totally removing the solvent from the sample and only allowing the dried particles containing the elements of interest to enter the source. 

Fig. 52. Aerosol drying by using a single tube NafionR membrane desolvation stage. (Reprinted with permission from Ref. [148].)...

The addition of oxygen was found to be helpful when nebulizing effluents from HPLC containing organic eluents such as acetonitrile. This was useful when using ICP-MS for on-line detection in speciation as well as in trace-matrix separations. Here, however, it is useful to use desolvation, even in the case of low consumption, high efficiency nebulizers, such as the HEN or DIHEN. This can be done efficiently with membrane desolvation using Nafion membranes [148]. 

In this paper, an accurate method for determining the concentration of manganese and other metals in gasoline and diesel fuel by ICP without the use of chilled spray chamber, direct injection nebulizer, ultrasonic nebulizer with micro-porous membrane desolvator, thermostated condenser, or emulsification is discussed. 

Apart from high resolution mode, which is not able to eliminate all those interferences, further possibihties to overcome these interferences are mathematical correction procedures, which can be applied to rectify results, but they have to be specifically modeled for each sample matrix (Krachler et al. 1998 Barbante et al. 2001 Carol et al. 2001) and are prone to errors due to the relatively high abundance of interferents. By employing membrane desolvation for the reduction of oxide formation, spectral interferences can be significantiy reduced, but in case of road dust mathematical correction stiU had to be applied to compensate for Sr interference (KoUensberger et al. 2000). To further minimize the risk of interferences, pretreatment routines have to be employed, entaihng additional risks of analyte losses. 

A typical layout of an ultrasonic nebulization and membrane desolvation system is shown in Fig. 4. 

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]. 

Botto, R.l. and Zhu, J.J. (1994) Use of an ultrasonic nebulizer with membrane desolvation for analysis of volatile solvents by inductively[Pg.70]

Kahen, K., Jorabchi, K, and Montaser, A. (2006) Desolvation-induced nonlinearity in the analysis of bromine using an ultrasonic nebulizer with membrane desolvation and inductively coupled plasma mass spectrometry. 

Minnich, M.G. and Houk, R.S. (1998) Comparison of cryogenic and membrane desolvation for attenuation of oxide, hydride and hydroxide ions and ions containing chlorine in inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom., 13, 167-174. 

Kwok, K., Carr, J.E., Webster, G.K., and Carnahan, J.W., (2006) Determination of active pharmaceutical ingredients by heteroatom selective detection using inductively coupled plasma mass spectrometry with ultrasonic nebulization and membrane desolvation sample introduction. j4ppi. Spectrosc., 60, 80-85. 

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