Sample introduction ultrasonic nebulizers

Montaser A, Tan H, lishi II, Nam SFI, CaiM (1991) Argon inductively coupled plasma mass spectrometry with thermospray, ultrasonic, and pneumatic nebulization. Anal Chem 63 2660-2665 Montaser A, Minnich MG, Liu FI, Gustavsson AGT, Browner RF (1998) Fundamental aspects of sample introduction in ICP spectrometry. In Inductively Coupled Plasma Mass Spectrometry. Montaser A (ed), Wiley-VCH, New York, p 335-420... 

Figure 5.1 Main parts of an inductively coupled plasma mass spectrometer sample introduction systems (left column), e.g., Meinhard or MicroMist nebulizer with cyclonic spray chamber, ultrasonic nebulizer, microconcentric nebulizer and laser ablation system (all from CETAC Technologies), ion source (middle column) and several types of mass spectrometers, (a) Agilent 7500 from Agilent, (b) Platform from CV Instruments, or (c) Element from Thermo Fisher Scientific. (Parts of this figure were reproduced with permission from CETAC Technologies, Agilent, CV Instruments and Thermo Tisher Scientific, respectively.)...

Calibration and quantification procedures are easier in LA-ICP-MS compared to other solid-state mass spectrometric techniques because the laser ablation and the ICP ion source operate at normal pressure and the laser ablation of solid samples and ionization of analytes are separated in space and time. Therefore the advantage of solution calibration in ICP-MS can be applied in this solid-state analytical technique. The introduction of solution based calibration, which is only possible in LA-ICP-MS, was an innovative step in the development of this sensitive mass spectrometric technique. A number of different calibration approaches using aqueous standard solutions in the dual gas flow technique have been discussed by various authors.74 75 In the dual gas flow injection technique , the nebulized standard solution and the laser ablated sample material are mixed in the -piece and the two gas flows from the nebulizer (e.g. ultrasonic nebulizer) and laser ablation chamber are added. Using solution based calibration with the addition of a standard solution, Leach et alP determined minor elements in steel reference materials with a relative accuracy of a few %. In comparison to the so-called dual gas flow technique proposed in the literature, where the argon flow rates through the nebulizer and ablation cell add up to 11 min-1 (e.g. 0.451 min-1 and... 

Figure 3. Emission spectra obtained from an induction coupled plasma with an ultrasonic nebulizer (for sample introduction). Aim spectrometer, JACO model with a diffraction grating blazed at 250 nm, and a slit width of 20 pm, was used. The spectral resolution was 10.3 nm/500 channels = 0.0206 nm/channel. (a) Emission spectrum of a 1 pg/l bertjlium, 1% HNOj solution, (b) Emission spectrum of a 1% HN03 blank solution, (c) Difference spectrum obtained by subtracting spectrum (b) from (a). Spectra were obtained after an on-target integration for 8 sec.

There are several drawbacks to ultrasonic nebulizer/desolvation systems. Precision is typically somewhat poorer (1% to 3% relative standard deviation) than for pneumatic nebulizers (0.5% to 1.0% relative standard deviation) and washout times are often longer (60 to 90 sec compared to 20 to 30 sec for a pneumatic nebulizer/spray chamber without desolvation). Furthermore, chemical matrix effects are dependent on the amount of concomitant species that enter the ICP per second. Therefore, use of any sample introduction device that increases the amount of sample entering the plasma per second also naturally leads to more severe matrix effects when the sample contains high concentrations of concomitant species. 

Impurities in photoresists have also been measured by ICP-MS [383,384]. Ultrasonic nebulization and electrothermal vaporization sample introduction approaches have been used. 

Analyzer Q = quadrupole, CC = collision cell, DRC = dynamic reaction cell, MC = multicollector, SF = sector field. Analytical details CV = cold vapor, ETV = electro-thermal vaporization, FI = flow injection, HG = hydride generation, ID = isotope dilution, LA = laser ablation, UN = ultrasonic nebulization. Sample introduction in liquid or slurry (si) form. 

Solid foods in powder form can be analyzed directly by means of LA- or ETV-ICP-MS to eliminate time-consuming sample dissolution procedures (see Table 8.2). However, this requires the preparation of homogeneous powdered samples and the subsequent analytical determination is not as straightforward as the one based on liquid sample introduction. Another way to perform direct analysis of solid foods is to grind and suspend them into slurries. The viability of slurry nebulization relies on the ability to prepare samples of fine particle size in a reproducible manner and on the adoption of suitable (e.g., high-solids) nebulizers. Otherwise, slurries can be analyzed by ETV-ICP-MS resorting to the ultrasonic slurry sampling technique [72-74]. 

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... 

The most common introduction of the samples in this source consists of a pneumatic nebulizer which is driven by the same flow of argon which carries the resulting droplets in the plasma. An ultrasonic nebulizer and heated desolvation tube are also used because they allow a better droplet size distribution which increases the load of sample into the plasma. Generally, the sample solutions are continuously introduced in the nebulizer at the rate of about 1 ml min-1 with the help of a peristaltic pump. However, this is not acceptable with small-sample solutions. Therefore an alternative method using the flow injection technique is employed to introduce a small sample of about 100 pi. The sample solution is injected into a reference blank flow so that the sample is transported in the nebulizer and a transitory signal is observed. 

M.B. Denton, J.M. Freeiin and T.R. Smith, Ultrasonic, Babington and Thermospray Nebulization, in J. Sneddon (Ed.), Sample Introduction in Atomic Spectroscopy, Elsevier, Amsterdam, 1988. 

The specific design of the various sample introduction devices or spray probes depends to a large extent on the technique applied, i.e., ESI, APCI, or other. With respect to ESI, systems have been described for conventional pure ESI, pneumatically-assisted ESI or ionspray, ultrasonically-assisted ESI, thermally-assisted ESI, and micro- and nano-ESI (Ch. 5.5). The heated-nebulizer system (Ch. 5.6.2) is used in APCI and atmospheric-pressure photoionization (APPI). 

Ultrasonic nebulization This has been applied since the early work on ICP-AES [151], Both nebulizer types where the sample liquid flows over the nebulizer transducer crystal and types where the ultrasonic radiation (at 1 MHz frequency) is focussed through a membrane on the standing sample solution have been used. When applying aerosol desolvation the power of detection of ICP-AES can be improved by a factor of 10 by using ultrasonic nebulization. This specifically applies to elements such as As, Cd and Pb, which are of environmental interest. However, because of the limitations discussed in Section 3.2, the approach is of particular use in the case of dilute analytes such as in water analysis [150]. Additional fine detailed development, however, is regularly carried out, as with ICP-AES the process is crucial for elements such as Cd, As and Pb for which threshold values in fresh water samples can just still be measured reliably with this type of sample introduction. Such a development is the microultrasonic nebulizer (pUSN) operated with argon carrier gas, as described by Tarr et al. [410]. 

Ultrasonic Nebulizer Ames Laboratory construction (44) 1.4 MHz, water cooled desolvation, 2.6 ml/min sample introduction rate. 

The application of a peristaltic pump in the sample introduction system in case of the ultrasonic nebulizes is necessary in each case. 

---