Optimization of the ICP OES operational parameters for determination of metals in heavy crude oil after microwave digestion

Abstract

The objective of this study was to evaluate the best operational conditions of ICP OES for Na, Ca, Mg, Sr and Fe determination in heavy oil samples (API low gravity) after acid digestion assisted by microwave. Thus, complete factorial design 24 and central composite design (CCD) were used to optimize the best conditions for the radiofrequency power, nebulization gas flow, auxiliary gas flow and sample aspiration rate. The model developed to multivariate optimization of Na presented a regression of 97.14% and the distribution of the residue, verified by the lack of fit and the pure error, proved the absence of lack of fit for the model (calculated F = 0.76 < F3.2 = 19.16 tabulated). For Ca, Mg, Sr and Fe, a univariate procedure was used to optimize the sample aspiration rate variable. Thus, this study suggests that the optimal condition for the determination of Na in the digested oil sample by ICP OES is: P = 1200 W; N = 0.69 L min-1; A = 0.6 L min-1 and T = 1.32 mL min-1, using the radial torch configuration; and for Ca, Mg, Sr and Fe: P = 1200 W, N = 0.60 L min-1, A = 0.60 L min-1 and T = 1.30 ml min-1, using the axial configuration.