Simultaneous spectrophotometric determination of La, Ho, Mn5-Br-PADAP complexes using multivariate calibration with partial least-squares (PLS) data evaluation

A simple and fast analytical pocedure is proposed for the simultaneous spec trophotometric determination of lanthanum, holmium and manganese in synthet ic ceramics, (La(0.8-x) Ho-x Sr-0.2 MnO3), by using the partial least-squar es (PLS) method. As chromogenic agent 5-Br-PADAP [2-(5-bromo-2-pyridylazo)- 5-diethylaminophenol was used, which form colored complexes with the three elements studied. To avoid metal hydrolysis, a mixture of ethanol and Trito n X-100 at pH 9.5 was used for all experiments. A set of 17 calibration sol utions measured throughout the 400-700 nm wavelength range was used in the calibration step. The concentration range for Mn(II) was 1-12 x 10(-6) mol L-1, while the range for the rare earth elements La(III) and Ho(III) was 2- 8 x 10(-6) mol L-1. In order to demonstrate the applicability of the propos ed method, a set of artificial samples containing the three analytes in var iable proportions was prepared and analyzed. The analytical results obtaine d were quite acceptable with relative errors not greater than 7% in most ca ses.