Noise nebulizer

Finally, periodic cleaning of the burner head and nebulizer is needed to ensure minimal noise level due to impurities in the flame. Scraping the slot in the burner head with a sharp knife or razor blade to remove carbon deposits and removing the burner head for the purpose of cleaning it in an ultrasonic cleaner bath are two commonplace maintenance chores. The nebulizer should be dismantled, inspected, and cleaned periodically to remove impurities that may be collected there. 

Greenfield ef. ai.l l) observed a reduction of signal intensity that correlates with sample intake effects from the modified solution viscosity and/or surface tension of mineral acids. This, coupled with peristaltic pumping of solutions into the nebulizer, considerably reduces physical interferences. Increased salt concentration also has an effect on solution physical properties. In the experience of these authors, the high levels of salt in the matrix also increases the noise from the nebulizer system. This degradation of nebulizer performance, which is not necessarily accompanied by a proportional reduction in sensitivity, is the cause of the observed deterioration of detection limits in real samples as opposed to ideal solutions. 

The solution to be nebulized is usually pumped to the nebulizer using a peristaltic pump, unlike for FAAS, where the solution uptake is by free aspiration. The solution is pumped through polymeric tubing [usually poly(vinyl chloride)] and also connecting tubing (usually Teflon) to the nebulizer. Both of these materials can be manufactured to a high degree of purity, hence contamination is minimized. The solution is pumped at a rate of 1 -2 ml min, which is much slower than the 5-10 ml min uptake rate for FAAS. This tends to favour the formation of fewer but smaller droplets, which results in less noise but a lower overall sample transport efficiency. 

Volatile components of the aerosol produced by the nebulizer are evaporated in the drift tube to produce nonvolatile particles in a dispersed mixture of carrier gas and solvent vapors. Ideally, the temperature in the drift tube should be high enough to ensure the complete evaporation of solvents, yet not so high as to be able to volatilize the analytes. If solvent removal is incomplete, detector noise will increase. When extremely large... 

Fig. 9. Noise power spectra for ICP-OES using a Fassel-type torch, (a) 0-500 Hz and (b) 0-24 Hz sample 10000 pg/mLAI solution power 1.8 kW, outer gas 18 L/min Ar nebulizer pressure 3 bar Ar sample uptake rate 1 mL/min. (Reprinted with permission from Ref. [37].)...

Fig. 13. Noise power spectra in ICP-MS for ArO+ (56 dalton). Meinhard nebulizer, power 1350 W, outer gas 14 L/min, intermediate gas 1.4 L/min, nebulizer gas 1.0 L/min, sample uptake rate 1.05 mL/min, doubly distilled water. (Reprinted with permission from Ref. [41].)...

Provided both the source (primary source and/or atom reservoir, nebulizer, etc.) as well as the detector contribute to the noise, the signal-to-noise ratio (S/N) in the case of a Poisson distribution for all types of noise is then given by ... 

The noise comprises contributions from the nebulizer as well as from the flame. However, detector noise limitations can also occur. The last can be minimized by operating the hollow cathode lamp at a sufficiently high current. 

As the sample introduction into the plasma is very stable, RSDs in ICP-AES are about 1% and the limiting noise is proportional to this, including flicker noise and nebulizer noise. 

A considerable portion of the noise originates from the nebulizer and the noise level can generally be decreased by cooling the spray chamber. The latter is shown to decrease the white noise somewhat as well as some 1/f contributions and also the standard deviations for the blanks [41]. This leads directly to an improvement in the detection limits. 

Van Borm W. A. and Broekaert J. A. C. (1990) Noise characteristics in inductively coupled plasma optical emission spectrometry using slurry nebulization and direct powder introduction techniques, Anal Chem 62 2527-2532. 

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