A multicommuted system has been developed for lead (Pb) isolation, pre-concentration and determination using an atomic fluorescence spectrometer as the detector. The lab-on-valve (LOV) technique allows automatic separation and pre-concentration of lead by means of solid phase extraction. The Pb resin was conditioned with nitric acid (1 mol L À1 ) and the analyte was eluted with 1.3 mol L À1 glycine solution. Chemical and flow variables affecting the extraction/pre-concentration of Pb 2+ were investigated by a multivariate approach. First, screening of the independent variables and their interactions was carried out by a two level full factorial design (2 k ). Then, a face centered central composite design was performed in order to find the optimal values of the significant variables. Because a wide range of sample volumes can be loaded on the microcolumn (1-100 mL), a mass calibration curve was obtained in order to quantify Pb in sample batches with a wide variability in lead concentration. Under optimal conditions, the limit of detection and the quantification limit were 0.004 and 0.014 ng of Pb 2+ , respectively. The linear response range was 0.014-20 ng of Pb 2+ . The repeatability, expressed as relative standard deviation (RSD), is 2.4% for 4 mg L À1 Pb 2+ (n ¼ 10). A small amount (0.6 g) of Pb resin is enough to fill the microcolumn of the LOV device. The durability of the resin reached 154 injections. The injection frequency permitted between a sample frequency of 1-10 h À1 depending on the sample pre-concentration volume. This method was validated using certified reference materials such as SRM-1400 (bone ash), SRM-2976 (mussel tissue) and BCR-610 (groundwater), and the results obtained showed good agreement with the certified values. The proposed LOV system was successfully applied to different samples of environmental and biological interest (water, fish and human teeth) with satisfactory recoveries, between 90-110%. The proposed system has some advantages such as minimization of sample handling, sensitivity, good precision, reduction of reagent volumes, high durability of the column and the versatility achieved by a variety of managed sample volumes.

A new automated, sensitive, and fast system for the simultaneous online isolation and preconcentration of lead and strontium by sorption on a microcolumn packed with Sr-resin using an inductively coupled plasma mass spectrometry (ICP-MS) detector was developed, hyphenating lab-on-valve (LOV) and multisyringe flow injection analysis (MSFIA). Pb and Sr are directly retained on the sorbent column and eluted with a solution of 0.05 mol L–1 ammonium oxalate. The detection limits achieved were 0.04 ng for lead and 0.03 ng for strontium. Mass calibration curves were used since the proposed system allows the use of different sample volumes for preconcentration. Mass linear working ranges were between 0.13 and 50 ng and 0.1 and 50 ng for lead and strontium, respectively. The repeatability of the method, expressed as RSD, was 2.1% and 2.7% for Pb and Sr, respectively. Environmental samples such as rainwater and airborne particulate (PM10) filters as well as a certified reference material SLRS-4 (river water) were satisfactorily analyzed obtaining recoveries between 90 and 110% for both elements. The main features of the LOV-MSFIA-ICP-MS system proposed are the capability to renew solid phase extraction at will in a fully automated way, the remarkable stability of the column which can be reused up to 160 times, and the potential to perform isotopic analysis.

Lead hydride or plumbane (PbH 4 ) generation was optimised by exploiting a simple flow-injection method coupled to atomic fluorescence spectrometry (HG-AFS), and allowing ultra-trace lead determination. Plumbane was generated through two methods: (1) 5% (v/v) H 2 O 2 was employed as oxidant with 1.5% (m/v) KBH 4 as a reducing agent and 1.5% (v/v) HCl solution; (2) with 1.5% (m/v) K 3 [Fe(CN) 6 ] as an oxidant/sensitiser, 1% (m/v) KBH 4 as a reducing agent and 1.5% (v/v) HCl. Variables such as reagent concentrations, flow rates and sample and reagent volumes were tested and critically compared. The best results were obtained with potassium ferricyanide K 3 [Fe(CN) 6 ], achieving a detection limit of 0.03 μg Pb L −1 and a relative standard deviation (RSD) of 1.1%. The selected method was validated by analysis of certified reference materials such as SRM-2976 (mussel tissue) and BCR-610 (groundwater), with good agreement with the certified values. The developed methodology was successfully applied to different environmental sample matrices, such as rain water, tap water, ground water, spring water and drinking water, and biological samples, i.e., human blood, plasma and serum.

Lead and chromium contamination represents one of the most serious problems in the aquatic environments. The aim of this work was to develop and validate an accurate, sensitivity, and rapid method for the simultaneous determination of Pb and Cr at trace levels in tissues and fat of marine organisms such as turtle (Chelonia mydas), shark (Rhizoprionodon terraenovae), and dolphin (Tursiops truncatus), utilizing the total reflection X-Ray fluorescence (TXRF) spectroscopy. Working solutions were prepared in 10 mL of a solution 0.005 mol·L−1 EDTA and 1 mol·L−1 HNO3. In order to correct possible instrument drifts, 20 μg·L−1 of gallium was used as internal standard (IS). The results showed that TXRF method was linear over the concentration ranges of 5.242–100 μg·L−1 for Pb and 2.363–100 μg·L−1 for Cr. Limits of detection (LOD) achieved were 1.573 and 0.709 μg·L−1 for Pb and Cr, respectively, while limits of quantification achieved were 5.242 μg·L−1 for Pb and 2.363 μg·L−1 for Cr. The validated method was accurate and precise enough for determination of these heavy metals in samples of marine organisms as indicated by acceptable values of recovery between 90–101%. In addition, a certified reference material (BCR-279, sea lettuce) and a Centrum tablet were satisfactory analyzed, and the T-test for comparison of means revealed that there were no significant differences at the 95% confidence level between the values obtained with the proposed TXRF method and the certificated values. The repeatability of the method, expressed as relative standard deviation (RSD), was 5.1% and 4%, for Pb and Cr, respectively. In addition, other features of the developed method were a low sample volume of 10 μL, and the sample frequency achieved was 20 h−1.