Multivariate optimization and validation studies in on-line pre-concentration system for lead determination in drinking water and saline waste from oil refinery

The present paper proposes an on-line pre-concentration procedure for lead determination in drinking water and saline waste from oil refinery by flame atomic absorption spectrometry (FAAS). It is based on the sorption of lead (II) ions in a minicolumn of polyurethane foam loaded with 4-(2-pyridylazo)-resorcinol (PAR) reagent. The optimization step was performed using Doehlert matrix involving the variables: sampling flow rate (SR), buffer concentration (BC), pH and eluent concentration (EC). The validation process was performed considering the parameters: linearity and other characteristics of the calibration curve, analytical features of on-line system, precision, robustness, effect of other ions in the pre-concentration system and accuracy. Using the established experimental conditions, the procedure allows lead determination with detection limit (3delta/S) of 0.4 mug l(-1), quantification limit (10delta/S) of 1.4 mug l(-1), and a precision, calculated as relative standard deviation (RSD) of 5.7 (n=8) and 2.1% (n=8) for lead concentration of 5 and 50 mug l(-1), respectively. The pre-concentration factor (PF) considering the ratio among the slopes of the analytical curves with and without pre-concentration is 51. The achieved recovery for lead determination in presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The accuracy was confirmed by analysis of the standard reference material NIST 1640 Trace elements in natural water. The sorption process was characterized by the Langmuir isotherm. The method was applied for lead determination in drinking water collected in Salvador City, Brazil and in saline effluent samples from oil refinery. The lead content for 16 samples of drinking water analyzed varied from 0.77 to 6.98 mug l(-1). (C) 2004 Elsevier B.V. All rights reserved.