Spray chamber effect

The ICP-AES and ICP-MS techniques may also suffer from matrix effects, such as spray chamber effects caused by the different viscosity of the samples and the calibration standards. The careful choice of internal standards can reduce this problem. The effects caused by high amounts of easily ionized elements may be solved by internal standardization or by the use of matrix-matched calibration curves. An additional specific problem with ICP-AES is the risk of spectral overlaps. 

Dry-Throwaway Processes. Dry-throwaway systems were the precursor of processes that removed SO2 iu the ductwork, eg, the BCZ and IDS processes. Here, however, the device is a spray chamber similar to the wet scmbbers such as the three modules of the Colstrip iastallation (Fig. 12). Into the upper portion of the chamber a slurry or clear solution containing sorbent is sprayed. Water evaporates from the droplets, the sorbent reacts with SO2 both before and after drying, and the dry product is removed ia a downstream baghouse or ESP (72). Unfortunately, dry scmbbiag is much less efficient than wet scmbbiag and lime, iastead of the much less expensive limestone, is required to remove SO2 effectively. Consequentiy, a search has been conducted for more reactive sorbents (72—75). 

Cyclonic spray chambers greatly reduce matrix effects. 

Liquid absorbents. If the partial pressure of the water in the gas is greater than the equilibrium partial pressure at the surface of a liquid, condensation will take place as a result of contact between the gas and liquid. Thus, water vapour is frequently removed from a gas by bringing it into contact with concentrated sulphuric acid, phosphoric acid, or glycerol. Concentrated solutions of salts, such as calcium chloride, are also effective. The process may be carried out either in a packed column or in a spray chamber. Regeneration of the liquid is an essential part of the process, and this is usually effected by evaporation. 

The effect of pre-evaporation on ion distributions in ICP-MS was studied by Lui and Beauchemin.24 The connecting tube (2 or 5 mm i.d., 11cm long) between the spray chamber... 

In ICP-MS mostly liquids are analyzed. The aqueous solution is nebulized using an effective pneumatic nebulizer (e.g., Meinhard or MicroMist nebulizer with cyclonic spray chamber, ultrasonic nebulizer (USN), microconcentric nebulizer with desolvator (e.g., Aridus or APEX), the latter for the introduction of small volumes of solution)3 as described in Section 5.1.6. 

The APEX system (Element Scientific Inc., Omaha) as an improved Aridus nebulizer was introduced for ICP-MS in 2004 for more effective solution introduction at flow rates from 20-400 p,lmin-1.88 In this solution introduction system (see Figure 5.15), a microflow PFA nebulizer is combined with a heated cyclonic spray chamber followed by cooling of the nebulized aerosol in a condenser loop and using a multipass condenser cooled by a Peltier element. The APEX solution introduction system results in a significant increase of sensitivity (by a factor of ten in comparison to a standard nebulizer spray chamber arrangement) and a decreasing polyatomic formation rate.89... 

Rivas, C., Ebdon, L. and Hill, S.J. (1996) Effect of different spray chambers on the determination of organotin compounds by high-performance liquid chromatography inductively coupled plasma spectrometry.J. Anal. At. Spectrom., 11, 1147-1150. 

If there is a considerable difference in concentration between samples or standards that are analyzed in sequence, a memory effect may occur. This effect is caused by sample deposition on the cones and in the spray chamber it also depends on which type of nebulizer is being used. The washout time between samples must be long enough to bring the system down to a blank value. 

The sample is typically pumped at a rate of 0.4 to 1.0 mL/min to a nebulizer that produces an aerosol with a range of drop sizes from submicrometer to 40 x in diameter [4,5]. Recently, nebulizers with small dead volumes that can be used with sample uptake rates as low as 10 xL/min have been introduced. The aerosol is modified as it passes through a spray chamber. Most aerosol drops that are too large to be vaporized effectively in the plasma (>20 xm diameter) are eliminated in the spray chamber. The spray chamber also limits the total amount of solvent liquid aerosol and vapor that enters the plasma. The aerosol exiting the spray chamber enters the hot, atmospheric pressure plasma gas (typically argon). 

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. 

Figure 7 Effect of nebulizer gas flow rate and sample uptake rate on primary and tertiary aerosol drop size distributions. A Meinhard TR-30 nebulizer was used with a double-pass spray chamber, (a) Primary aerosol produced by nebulizer as a function of nebulizer gas flow rate for a 1-mL/min sample uptake rate, (b) Tertiary aerosol exiting spray chamber as a function of nebulizer gas flow rate, (c) Primary aerosol as a function of sample uptake rate at a nebulizer gas flow rate of 0.8 L/min. (d) Tertiary aerosol exiting spray chamber as a function of sample uptake rate. (From Ref. 18.)...

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. 

A recent study [103] described the use of a HEN nebulizer with a conical spray chamber to improve sample transport for low flows in CE (Fig. 10.18). A stainless steel tee was used with the capillary threaded through the collinear ends of the tee. A makeup buffer, termed a sheath electrolyte, was also introduced through the lower arm of the tee. The effect of sheath electrolyte flow on the laminar ow (flow in the direction of the detector) was investigated, and it was found that improved peak resolution was possible by increasing the sheath electrolyte... 

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