Fresenius J Anal Chem (1994) 349:442-446 Fresenius' Journal of © Springer-Verlag 1994 Determination of lead in natural waters using flow injection with on-line preconcentration and flame AAS detection D. Rodriguez, P. Ferndndez, C. P~rez-Conde, A. Guti~rrez, C. Cdmara Departamento de Qu~mica Anal~tica, Facultad de Ciencias Quimicas de ia Universidad Complutense, E-28040 Madrid, Spain Received: 4 August 1993/Accepted: 16 November 1993 Abstract. A rapid and sensitive method has been deve- loped for the determination of lead in water samples by flame atomic absorption spectrometry using on-line preconcentration on a microcolumn packed with silica gel treated with a mixture of Aliquat 336 and nitroso-R-salt. The lead is retained at pH 5.5. The preconcentrated lead is directly eluted from the column to the nebulizer-burner system using 150 gL of 0.1 mol/L hydrochloric acid. The optimum preconcentration conditions are given and the retention efficiency achieved is higher than 80%. The en- richment factor is 37 and 100 for sample volumes of 5 and 30 mL, respectively. The limits of detection are 10.0, 6.0 and 4.0 ng/mL when 5, 10 and 30 mL of water is preconcentrated. Introduction Lead at low concentrations is a proven toxic element and a major cause of health disorders in certain “at-risk hu- mans“ [1]. Since the main sources of lead for humans are water and food, monitoring of the Pb content in drinking and surface water is of paramount importance. The concentration of most elements, including lead, in environmental samples is less than 10 ng/mL; so very sensitive techniques are needed for analysis. Flame atom- ic absorption spectrometry (FAAS) is a simple and well available ~technique, its main problem for lead determina- tion is the low sensitivity. This limitation can be overcome by the use of flow injection with a preconcentration microcolumn in a FAA system [2]. Graphite furnace AAS (GFAAS) is a suitable technique due to its high sensitivi- ty; but matrix effects are more important for this tech- nique than for FAAS, the former requiring frequently the use of matrix modifiers and standard addition to avoid Correspondence to: C. Cfimara such interferences [3]. Hydride generation AAS has been used for lead analysis since the early 1980s, but is selectiv- ity and sensitivity depend on the acid-oxidant mixture used for plumbane generation [4,5]. Moreover, preconcentration is often required to determine ultra trace levels of lead in environmental water [6]. It should be noted that flow injection preconcentra- tion techniques have also been applied to GFAAS [7,8]. It provides better performance because of the enhance- ment of sensitivity, separation of the analyte from the matrix and decrease of the risk of contamination. How- ever, the application of column preconcentration to GFAAS has been restricted by the discrete non- flow-through nature of the technique. Nevertheless, FAAS ig a technique that allows a complete automation, in a low-cost easy way, using instrumental facilities gener- ally available in analytical laboratories. For reasons men- tioned it will be desirable for lead analysis to have an al- ternative to the GFAAS methods, like the FIAAS tech- nique proposed here, for which automation was easy to implement and had adequate sensitivity. Several papers have described lead preconcentration using FIFAA. Olsen et al. preconcentrated lead (precon- centration factor 106) from sea water in a Chelex 100 [9]. Several authors have reported theoretical lead preconcen- tration factors in the 50-100 range, obtained by use of on-line microcolumns filled with 8-hydroxyquinoline chelated to resins or other polymeric supports [10,11]. Recently, preconcentration by chelating resins and other sorbents followed by electrothermal AAS (ETAAS) with direct heating of the sorbent in a graphite furnace [12,13] or by hydride generation has been coupled to on-line sys- tems [61. In this work we have established the analytical perfor- mance of an FIFAAS system using a chelating micro- column packed with silica gel solid support treated with a mixture of Aliquat 336 and nitroso-R-salt sorbent [14]. This inorganic support avoids the undesirable swelling of resins [15] which is a major drawback of that type of col- umns. In addition, a series of water samples have been analysed for their lead content by method proposed. 443 Experimental Reagents Standard lead(II) solutions were prepared daily by appro- priate dilution of a stock lead solution (1000 rag/L) ti- trated with EDTA. 0.10 mol/L Acetic-actate buffer (pH 5.0-5.5). 0.10 mol/L Malic-malate buffer (pH 5.0-5.5). 0.063-0.2mm Silica gel (Fluka) purified by the Przeszlakowski procedure [15]. Aliquat 336 (Aldrich-Chemie), methyltricaprylam- monium chloride, containing 93.3 07o (w/w) of quaternary alkylammonium chloride was freed from iron by shaking a 0.1 mol/L solution in chloroform with successive po。