Determination of silicon, phosphorus, iron and aluminum in biodiesel by multicommutated stepwise injection analysis with сlassical least squares method

Recently suggested multicommutated stepwise injection analysis (MCSWIA) coupled with classical least squares method (CLS) has been developed for silicon, phosphorus, iron and aluminum determination in biodiesel samples after a microwave digestion. This method allows to carry out four color-forming reactions simultaneously: aluminum (III) and iron (III) with chromazurol S and phosphate and silicate ions with ammonium molybdate, in two mixing chambers which are commutated into MCSWIA manifold. The concentrations of analytes were determined by two data matrixes using CLS method. Each of experimental calibration matrixes for CLS were designed with 10 calibration set solutions of 1–10 mg kg−1 for aluminum and 2–20 mg kg−1 for iron, silicon and phosphorus. The appropriate experimental conditions for microwave digestion and automated MCSWIA spectrophotometric determination of analytes were investigated. Recovery tests show results between 98% and 107% for all type of biodiesel samples. The limits of detection (LOD) obtained using the MCSWIA-CLS system were 0.3 mg kg−1 for aluminum and 0.6 mg kg−1 for iron, silicon and phosphorus. The proposed method was successfully applied for the determination of analytes in different type of biodiesel. The analytical results obtained by MCSWIA-CLS were compared with the results obtained by reference methods.