Simple method for the determination of Cu and Fe by electrothermal atomic absorption spectrometry in biodiesel treated with tetramethylammonium hydroxide

A simple analytical procedure for the determination of Cu and Fe in biodiesel samples by electrothermal atomic absorption spectrometry is proposed. An aliquot of the sample is simply mixed with tetramethylammonium hydroxide (TMAH) and heated to 90 °C for 5 min. Pyrolysis and atomization temperatures were optimized through pyrolysis and atomization curves. The high pyrolysis temperature adopted, of 1000 °C, certainly helped minimizing potential interferences. Even though, calibration should be carried out with aqueous standard solutions in the presence of the TMAH. The detection limits (3 s, n = 10), in the sample, were quite low 15 ng g⁻¹ and 24 ng g⁻¹ for Cu and Fe, respectively. Seven biodiesel samples, produced from different raw materials, including vegetable seed, frying oil and animal fat were analyzed. Accuracy was validated by applying the recovery test to two samples, enriching the samples with two concentration levels (recoveries from 105% to 120%). The precision, expressed by the relative standard deviation was less than 3% for Cu and less than 7% for Fe. Copper could be quantified in two and Fe in three of the seven samples. The biodiesel sample from fodder turnip was especially rich in the analytes in comparison to the other samples.