Nebuliser, adjustment

For a given ICP-OES instrument, the intensity of an analyte line is a complex function of several factors. Some adjustable parameters that affect the ICP source are the radiofrequency power coupled into the plasma (usually about 1 kW), the gas flow rates, the observation height in the lateral-viewing mode and the solution uptake rate of the nebuliser. Many of these factors interact in a complex fashion and their combined effects are different for dissimilar spectral lines. The selection of an appropriate combination of these factors is of critical importance in ICP-OES. This issue will be addressed in Chapter 2, where experimental designs and optimisation procedures will be discussed. Many examples related to ICP and other atomic spectrometric techniques will be presented. 

In the premix or laminar flow system the sample aerosol, oxidant and fuel are mixed in an inert chamber such that the larger droplets of sample are broken up or drained off before entering the flame. In this way a quieter and more stable flame is produced which is supported on a, typically, 10 cm path-length burner head. Because only the fine mist and evaporated sample reaches the flame an even burning takes place. This produces better atomisation and reduces interferences. If the nebuliser is adjustable, and most will... 

As a result, their intensity can be adjusted by modifying either the applied electrospray voltage or the position of the CE capillary outlet. Prior to starting a sequence, analyses have to be performed to ensure that these electric currents remain stable, otherwise, the capillary position has to be slightly adjusted to achieve good quantitative results, furthermore, the capillary current monitoring can be a diagnostic tool of the chiral selector s entrance into the nebulisation chamber. 

A burner head, typically with a single slot (10 x 0.2 cm), is aligned along the axis of the optical beam from the radiation source. The nebuliser/burner assembly is mounted on a platform which provides for positional adjustment in both the vertical and horizontal planes. The optimal height of the optical beam above the burner slot varies with each analyte element (and somewhat with the sample composition) is established experimentally for each standard solution. An impressive graphic presentation of the spatial distribution of analyte atoms of sodium, calcium, or molybdenum in an air/C2H2 flame (under identical operating conditions) has been presented by Rann and Hambly Anal. Chem. 37, 880, 1965). 

Medicine solutions for nebulisation may contain several additives such as co-solvents, solubilising and stabilising agents, antimicrobial preservatives, salts and pH-regulators to adjust the acidity and tonicity of the solution. Additives may contribute to the osmotic value. Both high and low osmotic values can produce cough and bronchoconstriction... 

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