Determination of Ca, K, Mg, Na, sulfate, phosphate, formate, acetate, propionate, and glycerol in biodiesel by capillary electrophoresis with capacitively coupled contactless conductivity detection

In this work, a new method employing capillary electrophoresis (CE) for the determination of several species in biodiesel is introduced. The concentrations of inorganic species (Na(+), K(+), Ca(2+), Mg(2+), SO(4)(2-), and PO(4)(3-)) and glycerol are of interest to the regulatory authorities due to their ability to form undesirable compounds in engines. Additionally, other species of low molecular weight (e.g., acetate, formate, and propionate) are of interest because they contribute towards increasing the acidity. These species are formed by the degradation of biodiesel and cause damage to engines and the environment. The cation separation was performed in background electrolyte (BCE) composed of 30 mmol L(-1) of 2-(N-morpholino)ethanesulfonic acid (MES)/L-histidine (His), pH 6. The separation of anionic species was carried out in similar BCE with 0.2 mmol L(-1) cetyltrimethylammonium bromide (CTAB) added. For glycerol, a neutral species, its oxidation with periodate was employed. This well-known reaction is specific to polyols and generates iodate. The amount of iodate produced by the reaction was determined by CE. The separation was carried out in approximately I min using BCE composed of 30 mmol L(-1) acetic acid, pH 3. The analytical parameters evaluated were: linearity (r>0.99), the RSD values for area and migration time were <3.4% and 0.9%, respectively, and recovery was in the range of 89 to 107%. (C) 2011 Elsevier B.V. All rights reserved.