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.