Two manifold designs were evaluated. Water samples and wine digests in 10% nitric acid were pumped through a column containing a commercially available resin (Pb-Spec ® ), an immobilized crown ether with a cavity size selective for Pb 2+ . The column was rinsed with 2% HNO 3 and the eluent, 0.1 mol l −1 ammonium oxalate was injected via a six-port rotary valve. The eluted lead was delivered to the flame atomic absorption spectrometer at 4.0 ml min −1 . The following flow-injection (FI) parameters were optimized: sample acidity and volume, loading and elution flow rates, and eluent composition and volume.The detection limit for the water samples, estimated from the noise on the signal obtained for 250 ml of 10 g l −1 loaded at 19.1 ml min −1 was 1 g l −1 . For 50 ml of wine digest loaded at 4 ml min −1 , the value was 3 g l −1 . The roles of loading flow rate and sample volume were investigated in detail. The variation in retention efficiency with loading flow rate showed that the amount of lead retained (during a fixed loading time) increased with flow rate until the upper performance limit of the peristaltic pump was reached. The variation of detection limit with sample volume followed the expected hyperbolic relationship and showed that only small improvements in LOD were obtained for volumes greater than 50 ml. The method was evaluated through spike recovery for both water and wine. The lead contents of tap (0.24 g l −1 ), pond (0.40 g l −1 ), and river waters (not detected) were determined. The concentrations of lead in three Port wine samples ranged from not detected to 190 g l −1 . No significant matrix suppression effects were observed.

The determination of trace elements in lead by inductively coupled plasma ICP Ž.source mass spectrometry ŽMS is . not possible without the removal of a substantial proportion of the lead matrix. This was achieved by the retention of lead from a 130-l sample solution Ž100 mg l y1 lead in 2% vrv nitric acid injected into a single-line .Ž3% vrv nitric acid. flow injection manifold, on 100 mg of Pb-Spec ᮋ packed into a cylindrical column Ž6 cm =4 mm internal diameter.. The analytes, Ag, As, Bi, Cd, Cu, Sb and Sn, passed through the column and were quantified against matrix-matched standards. Only Ag showed significant retention, but could still be measured in an 8-min run. The column was rinsed by flushing with 0.1 M ammonium citrate solution. Lead was monitored by flame atomic absorption spectrometry in preliminary experiments concerning column capacity and breakthrough. Although the capacity of the material in the dynamic, flow-through mode was less than the literature value based on equilibrium studies, the lead from up to 13 successive injections was sufficiently retained to allow accurate determination of the analytes without intermediate rinsing of the column. The precision wpercentage relative standard deviation %R.S.D.Ž., ns5x of the procedure ranged from 1.7% Ž100 ng ml y1 copper to 2.8% .Ž5 ng ml y1 cadmium., and detection limits were in the range 0.2᎐10 ng ml y1 . The accuracy of the procedure was assessed by the analysis of three National Institute of Standards and Technology standard reference materials ŽSRM 2416 bullet lead, SRM 2415 battery lead, and SRM 2417 lead base alloy.. For each SRM, duplicate determinations of seven analytes were made. Of the 42 determinations, 36 fell within the confidence interval around the accepted value. Three real bullets were analyzed for seven elements by both the flow injection solid-phase extraction ICP-MS method and by aspiration of the bullet solutions Ž10 000 mg l y1 lead. directly into an ICP emission spectrometer. A linear least squares regression of these U Corresponding author. two sets of results gave a line with slope 1.01"0.04 and an intercept of y5"100 gg y1 , where the " terms are 95% confidence intervals. The column lifetime was in excess of 5 months of daily use.

The selective transport of a target metal ion across a membrane from a donor to an acceptor solution is an attractive concept for preconcentration or separation in a flow injection (FI) system. However, we found that the transport of lead across a supported liquid membrane consisting of dicyclohexano-18-crown-6 in decanol embedded in Celgard 2400 was too slow to be practical for an FI atomic spectrometry system. On the other hand, the same chemistry in an on-line, solid-phase reactor (a mini-column containing Pb-Spec resin) gave a satisfactory performance. In an attempt to understand the kinetics of the system, we have calculated the rate of transport across the membrane. As flux is proportional to concentration on the donor side -which decreases with time -we performed a series of numerical simulations involving fixed time intervals of decreasing values. These calculations show that for the sizes of membranes in a typical FI system, transport is very slow compared with the adsorption of lead by the Pb-Spec resin: it takes about 100 min for the concentration in a 0.06 mL donor solution to decrease by a factor of 1000. The time required for the same decrease in concentration for a membrane having the same surface area and ligand concentration as the Pb-Spec column was calculated as approximately 9 s.Key words: supported liquid membrane, solid-phase extraction, flow-injection, lead. Résumé :Le transport sélectif d'un ion métallique cible à travers une membrane à partir d'un donneur vers une solution accepteuse est un concept attrayant pour la préconcentration ou la séparation dans un système à injection continue (IC). Cependant, nous avons trouvé que le transport du plomb à travers une membrane liquide incrustée dans un support, cette membrane est constituée de dicyclohexano-18-couronne-6 dans le décanol incorporé dans du Celgard 2400, est trop lent pour être pratique dans un système de spectrométrie atomique à injection continue (IC). Par ailleurs la même chimie en continu dans un réacteur en phase solide (une mini colonne contenant une résine Pb-Spec), a donné une performance satisfaisante. Dans une tentative pour comprendre la cinétique du système, nous avons calculé la vitesse de transport à travers la membrane. Comme le flux est proportionnel à la concentration du côté du donneur, laquelle diminue avec le temps, nous avons réalisé une série de simulations numériques impliquant des intervalles de temps fixes de valeurs décroissantes. Ces calculs montrent que, compte tenu des dimensions des membranes dans un système typique à injection continue, le transport est très lent comparativement à l'adsorption du plomb par la résine Pb-Spec; il faut environ 100 minutes pour que la concentration dans 0,06 mL d'une solution donneuse décroisse d'un facteur de 1000. Le temps requis pour la même diminution de concentration dans le cas d'une membrane ayant la même superficie et la même concentration de ligand dans une colonne de Pb-Spec est selon les calculs approximativement de 9 s.