Development of capillary electrophoresis methods for the separation of metal cations.

The aim of this investigation is to study the capabilities of Capillary Electrophoresis for the separation of metal cations particularly group I, group II and transition metals in liquid samples. An acac, oxalic acid and acetic acid were employed for the separation of mono and divalent cations via UV/Vis detection. However, the separation of metal cations from group I &amp; II are not possible with the buffer alone without a complexing reagents. In addition, the presence of background electrolyte such as 4-methylbenzylamine and methanol at different concentration in the buffer solution will affect the peak separations. Therefore, the optimisation of the background electrolyte was required to eanable the simultaneous separation of the metal cations. Other factors such as pH, ionic strength and viscosity were also demonstrated for the high performance of the separation of metal cations. An increases the pH buffer, the migration times of all solutes decrease due to an increase in the EOF. As the pH of buffer is increases, the metal cations becomes progressively less protonated and its apparent mobility decreases. An oxalic acid shows poor separation compared to other complexing reagent (K, Na, Ca, Mg and Cd). Good reproducibility for migration times (SD 0.03-0.29, n = 10; F-0bs < Fcrit-)* sensitive detection limits (0.1-0.5 ppm), not satisfactory working ranges (0-1 ppm, R = < 0.97), baseline separation, peak efficiencies (52,341-265,047 theoretical plates) were obtained for K, Na, Ca, Mg and Cd. The combination of 20 mmol/L acetic acid, 10 mmol/L 4-methylbenzylamine and 50% methanol (pH 3.5) was enabled a separation of 14 metals in less than 7 min. However, separation of Fe did not prove possible with this buffer. Good reproducibility for migration times (SD 0.07-0.19, n = 10; Fobs < Fcrit.), sensitive detection limits (0.12-0.94 ppm), satisfactory working ranges (1-40 ppm, R-2 = 0.9841 to 0.9977), baseline separation, peak efficiencies (204,494-609,667 theoretical plates) were obtained for Na, Ca, Mn, Co, Ni, Zn, Cr, Al, Cu and Pb. A complete separation of 8 metal cations (K, Na, Ca, Mg, Co, Ni, Cd and Pb) was achieved in less than 8.5 min using 10 mmol/L acac, 10 mmol/L 4-methylbenzylamine and 50% methanol (pH 4.0). Good reproducibility for migration times (SD 0.10-0.23, n = 10; Fobs sensitive detection limits (0.17-0.76 ppm), not satisfactory working ranges (1-25 ppm, R-2 < 0.95), baseline separation, peak efficiencies (178,163-223,749 theoretical plates) were obtained for K, Na, Ca, Mg, Co, Ni, Cd and Pb. The separation of metal cations in mineral water by CE is quite straight forward compared to ion chromatograph (IC). Lactic acid was found as an excellent complexing reagent for the separation metal cations in acid mine discharges by CE-UV/Vis detection. Good sensitivity and satisfactory working ranges (1-20 ppm, R-2= 0.9907 to 0.9928), baseline separation, peak efficiencies (114,719-774,365 theoretical plates) were obtained for K, Na, Ca, Mg, Mn and Fe. A new developed method for the separation of 13 metal cations (K, Ba, Na, Ca, Mg, Mn, Cd, Cr, Fe, Co, Ni, Zn and Cu) was achieved in less than 8.5 min using the buffer conditions of 20 mol/L lactic acid, 15 mmol/L LiOH, 10% MeOH (pH 4.3) by CE with conductivity detection. Good reproducibility for migration times (standard deviation, SD 0.03-0.23, n = 10, Fobs < Fcritt.), sensitive detection limits (0.4-2.9 ppm), satisfactory working ranges (1-100 ppm, R-2 = 0.9905 to 0.9960 except for Fe), baseline separation, peak efficiencies (311,782-770,735 theoretical plates) were obtained for K, Na, Ca, Mg, Mn and Fe in acid mine discharged. Further development need to be carried out for improving the accuracy and precision of result in quantitative analysis for CE-Conductivity detection.