Influence of solution composition on the results of flame-photometric analysis as a function of solution introduction rate

Abstract

In using flame photometry, the reliability of the analysis is governed to a considerable extent by the influence of sample composition on the analytic results. The relative role of various factors depends on the composition of the solution to be analyzed and the specific analytic conditions. However, the dominant role is often played by effects associated with the variation in atomic concentration in the flame caused by displacement of the ionization equilibrium ("ionization" effects) and formation in the solution (or during its vaporization) of compounds of the element to be determined with other solution components, these having low volatility or low dissociabflity ("chemical" factors). Ionization effects are known to be reduced in low-temperature flames (T ~ 2000~ while high-temperature flames are best employed to reduce chemical effects [i]. We investigated the feasibility of reducing the chemical effects in a low-temperature flame by increasing the completeness of aerosol vaporization. This cab be expected to reduce both the ionization effects and certain chemical effects associated with formation of comparatively volatile, unstable compounds. These include, for example, effects due to excess nitric, sulfuric, hydrochloric, or acetic acid in the solution, these being the acids most frequently employed in analytic practice. At the same time, it is obvious that this method cannot eliminate chemical effects associated with formation of low-volatility (of the AI203 type) or low-dissociabili ty compounds. Complete aerosol-drop vaporization in a low-temperature flame can be achieved by reducing the solution-drop size during vaporization and by increasing the time for which the aerosol particles remain in the flame. Production of a fine aerosol with a solution-drop diameter of about I0 ~ is possible with a sufficiently high dispersing-gas flow speed (300-350 m/sec) [2, 3]. The time for which the aerosol particles remain in the flame zone being photometered is usually very short (NI0 -4 see). Only the chlorides of most metals have time to undergo vaporization within this period, while sulfates and nitrates are usually not completely vaporized [3]. In order to increase the time for which the particles remain in the flame, it is necessary to reduce the flow speed of the gas mixture. This obviously reduees the rate at which the solution is introduced into the flame that corresponds to maximum line intensity. Our investigations were conducted in an apparatus that permitted emission flame-photometri