Comparison Between Two Sample Emulsification Procedures for the Determination of Mo, Cr, V and Ti in Diesel and Fuel Oil by ICP OES Along with Factorial Design

Abstract.

Inductively coupled plasma optical emission spectrometry (ICP OES) was used to determine Mo, Cr, V and Ti, in diesel and in used fuel oil. Samples were introduced into the ICP as emulsions to reduce interferences and allow the use of inorganic standards for quantification. A comparative study between one Triton X-100 emulsion and one detergentless emulsion was made. A 2³ factorial design was applied to elucidate and establish the relationship between three experimental variables: presence of HNO₃, amount of diesel fuel oil (between 5 and 25%) and the presence or O₂ into the Ar plasma gas flow rate. Results indicated that best performance were achieved using 10% sample (w/w) together with concentrated HNO₃ (0.5 mL) and using O₂ as auxiliary gas (0.047 L min⁻¹). The use of O₂ minimized both carbon deposits at the injector tip and plasma background. The addition of HNO₃ resulted in good correlation between inorganic standards used for calibration, and metallo-organic standards used for sample enrichment. Analyte enriched diesel and SRM 1634b were analyzed using the optimized conditions. Recoveries from 90.1 to 106.5% were achieved, with better results for detergent emulsions which enabled limits of detection at the ng g⁻¹ range for Mo, Cr, V and Ti and at smaller background.