Aerosol generation and sampling system

TABLE XIX. Comparison of the precision of the aerosol generation and sampling system with the analytical precision obtained by using the ruggedized method. 

Figure 5.21. Torch and sample aerosol generation system (QVAC 127 system). Source [510]...

The aerosol generation/sampling system which was used for this was built and characterized in a previous study (ll). The system was found to produce 90 of the particle mass in the size range of 0.1 to 10 pm. 

Table IX. Precision of combined sampling and analytical method using Fluoropore filters loaded in the aerosol generation/sampling system (N = 7)...

The role of the sample introduction system is to convert a sample into a form that can be effectively vaporized into free atoms and ions in the ICP. A peristaltic pump is typically used to deliver a constant flow or sample solution (independent of variations in solution viscosity) to the nebulizer. Several different kinds of nebulizers are available to generate the sample aerosol, and several different spray chamber designs have been used to modify the aerosol before it enters the ICP Gases can be directly introduced into the plasma, for example, after hydride generation. Solids can be introduced by using electrothermal vaporization or laser ablation. 

To analyze metals and alloys directly without dissolution, both spark ablation [349] and laser ablation [61,211] dry aerosol generation systems have been used to introduce samples into an ICP-MS. These approaches often require matrix-matched standards, although several active research groups are focusing on techniques to reduce that requirement. The amount of material ablated depends on the sample type. Fractionation of elements can also be a problem, depending on the sample, the laser fluence, the laser wavelength, and the number of laser pulses used to sample from a fixed location. Volatile elements that are segregated in the samples appear to be most prone to fractionation problems [61],... 

As a final test, three different analysts applied the method to the analysis of Cd, Co, Cr, Ni, and Pb on filter samples from the generation system. The results of this test are presented in Table XXI. Small differences (3 percent) were experienced, but the overall percent standard deviation for each metal compares well with the percent standard deviation obtained in the characterization of the aerosol generation system by analyses performed by a single operator. 

Nebulizer. For the present studies, the sample aerosol was generated with a 3-MHz ultrasonic nebulizer, as illustrated in Figure 2, and the sample aerosol was desolvated prior to its injection into the plasma. A complete description of the nebulizer and desolvation system has been given elsewhere (2). The main virtue of ultrasonic nebulizers is that their efficiency of nebulization (mass of sample injected into the plasma/ mass of sample fed to the nebulizer) is 10 to 12 times greater (2) than that of common pneumatic nebulizers which are suitable for use with... 

An inductively-coupled plasma (ICP) is an effective spectroscopic excitation source, which in combination with atomic emission spectrometry (AES) is important in inorganic elemental analysis. ICP was also considered as an ion source for MS. An ICP-MS system is a special type of atmospheric-pressure ion source, where the liquid is nebulized into an atmospheric-pressure spray chamber. The larger droplets are separated from the smaller droplets and drained to waste. The aerosol of small droplets is transported by means of argon to the torch, where the ICP is generated and sustained. The analytes are atomized, and ionization of the elements takes place. Ions are sampled through an orifice into an atmospheric-pressure-vacuum interface, similar to an atmospheric-pressure ionization system for LC-MS. LC-ICP-MS is extensively reviewed, e.g., [12]. 

Since their introduction in the 1980s thermospray systems have been shown to increase the aerosol generation efficiencies and accordingly the power of detection. In ICP-AES they have been further developed into systems where a gain in the power of detection and high accuracy can be achieved for real samples as compared with conventional pneumatic nebulization [411]. 

The mostly liquid samples are introduced into an ICP-mass spectrometer by different techniques. Each of these techniques aims to generate fine aerosol of the liquid sample to achieve efficient ionization of the sample atoms in the plasma. However, only 1-2% of the sample can find way into the plasma hence, the sample introduction system is considered as the weakest component of an ICP-MS. The introduction system works in two steps, namely, aerosol generation using nebulizer and droplet selection by the spray chamber. Most commonly, the liquid sample is pumped into the nebulizer by a peristaltic pump at a speed of 1 mL/min. When the liquid sample enters the nebulizer, it is transformed into fine aerosol under the pneumatic action of the nebulizer gas flow ( l L/min). However, some pneumatic nebulizers do not use a pump. They suck the sample through the tubing through the action of positive pressure of the nebulizer gas. 

As mentioned previously, the main function of the sample introduction system is to generate a fine aerosol of the sample. It achieves this with a nebulizer and a spray chamber. The sample is normally pumped at about 1 mL/min via a peristaltic pump into the nebulizer. A peristaltic pump is a small pump with lots of minirollers that all rotate at the same speed. The constant motion and pressure of the rollers on the pump tubing feeds the sample through to the nebulizer. The benefit of a peristaltic pump... 

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