Standard dilution analysis (SDA) as a powerful tool for elemental determination in biodiesel by inductively coupled plasma optical emission spectrometry (ICP OES)

Abstract

Introducing organic solvents into inductively coupled plasma (ICP) source spectrometers increases maintenance costs and affects the reliability of the results due to matrix effects. To minimize these issues, standard dilution analysis (SDA) has emerged as a calibration strategy to overcome matrix effects, minimize time consumption, and reduce reagents' consumption and waste generation compared to traditional calibration methods. Calibration by SDA combines the standard addition (SA) and internal standardization (IS) methods by employing two analytical solutions: one consisting of 50% of sample + 50% of analytical standards and internal standard 1 (solution 1) and the other consisting of 50% of sample + 50% of blank solution and internal standard 2 (solution 2). By applying a second internal standard, all the data collected over time can be used for the analytical curve created when solution 2 is poured into solution 1. Thus, the SDA method was compared with the SA and IS methods for the determination of Ca, K, Mg, Na, P, Si, and S by inductively coupled plasma optical emission spectrometry in nine biodiesel samples 5-fold diluted in xylene. Limits of detection and quantification found for SDA were statistically similar to those of SA and IS, ranging from 0.02 mg kg⁻¹ (Mg) to 3.7 mg kg⁻¹ (K). The results obtained by SDA had good precision (RSD < 5%) and accuracy (recoveries from 90 to 115%). Long-term signal stability and lower economic and environmental impacts make SDA with 2 ISs an exciting resource for elemental determination in biodiesel and oil samples diluted in xylene in a simpler and faster method that compensates for instrumental drifting and matrix effects.