Multielement analysis of crude oil produced water by ICP OES after acid digestion assisted by microwave

Abstract

Disposing or reusing crude oil produced water is difficult because of the environmental impacts caused by the presence of high salinity and toxic components, or by the risk of obstruction on the production columns due to crust formation, which causes reduced crude oil production and huge losses to the extraction process. Thus, knowledge of the chemical composition of these waters is very important. The method proposed in this article is intended for determining trace elements (Co, Cr, Fe, Mn, Ni, Se and V) in crude oil produced water samples through inductively coupled plasma optical emission spectrometry (ICP OES) using microwave-assisted acid digestion for preparing the samples (15 g of sample and 2 mL of concentrated HNO₃). Analytical curve in 2% v/v HNO₃ was adopted as a calibration method after verifying that it is not necessary to use salinity for matrix matching. For Ni, there is no need of using internal standard, whereas for Co, Cr, Fe, Mn and V, the best results were achieved using Sc as the internal standard. For Se, the use of Y as the internal standard is recommended. The detection limits obtained were Co 0.67, Cr 1.2, Fe 2.3, Mn 0.49, Ni 1.9, Se 3.7 and V 5.5 μg L⁻¹, and the limits of quantification were Co 2.2, Cr 4.0, Fe 7.7, Mn 1.6, Ni 6.5, Se 12.4 and V 18.3 μg L⁻¹. Procedure accuracy was verified through recovery tests at two concentration levels (namely, 40 and 80 μg L⁻¹) and by the analysis of certified reference materials (SLEW-2 estuarine water and NASS-5 seawater). Good results were achieved from recovery tests. There was no significant difference (at 95% confidence) between the analyzed and certified values for the reference materials.