Standard dilution analysis in flow system: Sodium determination by flame atomic emission spectrometry

Standard dilution analysis (SDA) is a new calibration method that combines the principles of internal standardization and standard additions. The current work evaluated the feasibility of SDA automation using a flow-injection system (FIA). The FIA-SDA system was applied to sodium determination in biodiesel samples and certified reference materials (CRMs) by flame atomic emission spectrometry (FAES). Lithium was employed as internal standard in all determinations. The results for Na determination in five CRMs using FIA-SDA were in agreement with certified values at the 95% confidence level (t-test). For comparison purposes, Na was also determined by the traditional methods of external standard (ES), standard additions (SA) and internal standardization (IS). Recoveries showed increased accuracy following the sequence ES (181-202%) < IS (67-72%) < SA (111-126%) < FIA-SDA (94-98%). FIA-SDA provided more accurate and precise results than ES, SA and IS for Na determination in biodiesel and CRMs by FAES.