A New Look at Calcium Flame Interferences
A detailed study of the effects of PO4 −3, SO4 −2, AlCl3, and Al(NO3)3 on the flame-spectroscopic behavior of Ca led to some clarification concerning the origin and nature of these common interferences. By utilizing atomic absorption and emission as well as molecular and ion- emission measurements, the relative concentrations of the following Ca species in the flame could be studied: Ca*, Ca°, Ca+, and CaOH—CaO*. Data indicated that the depressive effects of the interfering substances were similar on each Ca species studied. Thus the mechanism by which these interferences originate cannot be due to shifts in the equilibria of the reactions of CaCl2 in the flame. Results also showed that the Al interference was not due to a gas phase reaction between CaO and Al2O3 to form CaAl2O4 or some similar Ca aluminate. The AlCl3 interference on Ca was eliminated in the nitrous oxide flame, but that due to Al(NO3)3 was not. Therefore in the nitrous oxide flame it was possible to determine effects of Ca and Al excitation as well as the effects of Al on Ca excitation. The association of Ca ions with PO4 −3 and SO4 −2 in solutions to form probably CaSO4 and Ca3(PO4)2 would be consistent with our results. The effects of AI salts would appear to be due to the occlusion of CaCI2 in matrices of AICI3 and AI(N03)3.
KeywordsRelative Signal Intensity Fuel Flow Rate Relative Emission Intensity Common Interference Burner Head
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