Studies on parameters of inductively coupled plasma spectrometer

Abstract

Analytical aspects of different adjustment of parameters of an inductively coupled plasma atomic emission spectrometer (ICP‐AES) were investigated. The ICP‐AES was a LABTAM 8440M (now called GBC) spectrometer. Since at many times, the elemental concentration of the analyte is near to the detection limit, the lowest possible detection limit has to be reached. When the signal‐to‐background ratio (SBR) is maximized, the detection limit is the smallest. This is the reason why the effects of each adjustable parameters on the signal‐to‐background ratios were investigated. Seven adjustable parameters can be analyzed in this equipment: (i) viewing height, (ii) forward power, (iii) sample gas, (iv) coolant gas, (v) auxiliary gas, (vi) flushing gas, and (vii) sample uptake flow rates. Furthermore aerosol distribution by droplet size and nebulization efficiency were also examined applying three different sample gas flow rates and four elements [iron (Fe), magnesium (Mg), manganese (Mn), and nickel (Ni)]. The alkali metals with low excitation energy [potassium (K), lithium (Li), and sodium (Na)] were detectable in higher regions of the plasma, some alkali‐earth and transition metals with medium excitation energy [calcium (Ca), srontium (Sr), and copper (Cu)] were well detectable in medium height, whereas the maximum signal‐to‐background ratios of the other elements with relatively high excitation energy [e.g. cadmium (Cd), Ni, and phosphorus (P)] reached in lower regions of the plasma. On the basis of results the compromised viewing height for all the elements is found 5 mm, the optimum sample gas flow rate 1.14 dm³ min^‐1 and the forward power 1200 W. Change of coolant and auxiliary gas flow rates has not changed the signal‐to‐background ratios significantly. Consequently the optimum argon flow rates in aspect of consumption of argon are the possible lowest flow rates, where plasma remains stable. For coolant and auxiliary gas flow rates these values are 10 dm³ min^‐1 and 0.1 dm³ min^‐1, respectively. Changing the rate of peristaltic pump (i.e. sample uptake rate) the signal‐to‐background ratios increase to 4‐ or 5‐fold of the original values, therefore the optimum sample uptake rate is considered 4 cm³min^‐1. Increase of flushing gas flow rate has not changed the signal‐to‐background ratios significantly, except in case of sulfur (S) and P, because of oxygen (O₂) absorption from the air. When analysis of S and P content is necessary, 0.13 dm³min^‐1 and 0.2 dm³ min^‐1, respectively, of flushing gas flow rate is recommended to use.