Universal calibration for metal determination in fuels and biofuels by inductively coupled plasma atomic emission spectrometry based on segmented flow injection and a 350 °C heated chamber

Abstract

The benefits of using a 350 °C heated single pass spray chamber following a segmented flow injection methodology were demonstrated for the analysis of petroleum products through inductively coupled plasma atomic emission spectrometry (ICP-OES). The present work shows that a small sample volume (i.e., 5 μl or less) can be precisely injected into the system following a manual procedure. Two different sample introduction systems were employed: a Cyclonic spray chamber and a single pass spray chamber (a modified version of the Torch Integrated Sample Introduction System, TISIS) equipped with a heating brass hollow cylinder. First the effect of temperature on the peak shape and sensitivity has been studied for a set of nineteen different organic products (gasoline, superethanol, diesel and biodiesel diluted in xylene). The results have proved that the higher the chamber walls temperature, the higher the sensitivity. As a result limits of detection decreased below 7 μg l⁻¹ for elements such as manganese, vanadium and silicon. Furthermore, memory effects were less severe as the temperature raised. Another benefit of increasing the TISIS chamber walls temperature is that matrix effects became less pronounced as compared to a Cyclonic chamber. Thus, at 350 °C non-spectral interferences are eliminated likely because the analyte transport efficiency to the plasma is close to 100% irrespective of the sample analyzed. This has two important consequences: (i) it is possible to obtain a calibration line by merely modifying the injected solution volume and (ii) a single xylene based solution can be used as a universal standard. The developed procedure was applied to the analysis of nineteen spiked petroleum derivatives with recoveries for manganese, silicon, vanadium and copper in the range 95–106%.