Luz O. Leal

Determination of lead by atomic fluorescence spectrometry using an automated extraction/pre-concentration flow system

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−1) and the analyte was eluted with 1.3 mol L−1 glycine solution. Chemical and flow variables affecting the extraction/pre-concentration of Pb2+ 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 (2k). 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 Pb2+, respectively. The linear response range was 0.014–20 ng of Pb2+. The repeatability, expressed as relative standard deviation (RSD), is 2.4% for 4 μg L−1 Pb2+ (n = 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−1 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.

3D printed device including disk-based solid-phase extraction for the automated speciation of iron using the multisyringe flow injection analysis technique

The development of advanced manufacturing techniques is crucial for the design of novel analytical tools with unprecedented features. Advanced manufacturing, also known as 3D printing, has been explored for the first time to fabricate modular devices with integrated features for disk-based automated solid-phase extraction (SPE). A modular device integrating analyte oxidation, disk-based SPE and analyte complexation has been fabricated using stereolithographic 3D printing. The 3D printed device is directly connected to flow-based analytical instrumentation, replacing typical flow networks based on discrete elements. As proof of concept, the 3D printed device was implemented in a multisyringe flow injection analysis (MSFIA) system, and applied to the fully automated speciation, SPE and spectrophotometric quantification of Fe in water samples. The obtained limit of detection for total Fe determination was 7ng, with a dynamic linear range from 22ng to 2400ng Fe (3mL sample). An intra-day RSD of 4% (n = 12) and an inter-day RSD of 4.3% (n = 5, 3mL sample, different day with a different disk), were obtained. Incorporation of integrated 3D printed devices with automated flow-based techniques showed improved sensitivity (85% increase on the measured peak height for the determination of total Fe) in comparison with analogous flow manifolds built from conventional tubing and connectors. Our work represents a step forward towards the improved reproducibility in the fabrication of manifolds for flow-based automated methods of analysis, which is especially relevant in the implementation of interlaboratory analysis.

Automatic flow analysis method to determine traces of Mn2+ in sea and drinking waters by a kinetic catalytic process using LWCC-spectrophotometric detection

A new automatic kinetic catalytic method has been developed for the measurement of Mn(2+) in drinking and seawater samples. The method is based on the catalytic effect of Mn(2+) on the oxidation of tiron by hydrogen peroxide in presence of Pb(2+) as an activator. The optimum conditions were obtained at pH 10 with 0.019 mol L(-1) 22 bipyridyl, 0.005 mol L(-1) tiron and 0.38 mol L(-1) hydrogen peroxide. Flow system is based on multisyringe flow injection analysis (MSFIA) coupled with a lab-on-valve (LOV) device exploiting on line spectrophotometric detection by a Liquid Waveguide Capillary Cell (LWCC), 1m optical length and performed at 445 nm. Under the optimized conditions by a multivariate approach, the method allowed the measurement of Mn(2+) in a range of 0.03-35 µg L(-1) with a detection limit of 0.010 µg L(-1), attaining a repeatability of 1.4% RSD. The method was satisfactorily applied to the determination of Mn(2+) in environmental water samples. The reliability of method was also verified by determining the manganese content of the certified standard reference seawater sample, CASS-4.

3D printed device for the automated preconcentration and determination of chromium (VI)

A 3D printed device for the fully automated disk-based solid-phase extraction (SPE) of Cr (VI) from water samples has been fabricated. The compatibility of the use of organic solvents for analyte elution with 3D printed flow devices based on polymers fabricated using stereolithographu200by has been evaluated. The developed methodology comprises the complexation of Cr (VI) with 1, 5-diphenylcarbazide (DPC) in acidic medium and the subsequent retention of the complex in a SBD-RPS disk contained within the 3D printed device. A multisyringe flow injection analysis system with online spectrophotometric detection has been used for the automation of the method. The fabricated 3D printed device integrates the different components of the flow analysis manifold, including connectors and mixers, being a powerful approach towards the reproducible construction of highly integrated flow-based manifolds. The extracted Cr (VI)-DPC complex is eluted with a mixture of methanol- sulfuric acid and quantified at 540u202fnm. The effect on the analytical signal and the optimization of variables were evaluated using multivariate and univariate techniques. A detection limit of 1u202fng Cr (VI) and a linear working range of 3.2-600u202fng Cr (VI) were obtained using a sample volume of 2u202fml. The intra-day and inter-day RSDs were 4.8% (10u202fµgu202fL-1, nu202f=u202f12) and 3.4% (nu202f=u202f5, different day with a different disk), respectively. The applicability of the fabricated 3D printed device has been proved by the determination of Cr (VI) in groundwater, surface water and leachates.

Determination of lead in complex sample matrices by atomic fluorescence spectrometry: optimisation of online hydride generation

Lead hydride or plumbane (PbH4) 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) H2O2 was employed as oxidant with 1.5% (m/v) KBH4 as a reducing agent and 1.5% (v/v) HCl solution; (2) with 1.5% (m/v) K3[Fe(CN)6] as an oxidant/sensitiser, 1% (m/v) KBH4 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 K3[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.

MSFIA-LOV system for (226)Ra isolation and pre-concentration from water samples previous radiometric detection.

An automatic system based on multisyringe flow injection analysis (MSFIA) and lab-on-valve (LOV) flow techniques for separation and pre-concentration of (226)Ra from drinking and natural water samples has been developed. The analytical protocol combines two different procedures: the Ra adsorption on MnO2 and the BaSO4 co-precipitation, achieving more selectivity especially in water samples with low radium levels. Radium is adsorbed on MnO2 deposited on macroporous of bead cellulose. Then, it is eluted with hydroxylamine to transform insoluble MnO2 to soluble Mn(II) thus freeing Ra, which is then coprecipitated with BaSO4. The (226)Ra can be directly detected in off-line mode using a low background proportional counter (LBPC) or through a liquid scintillation counter (LSC), after performing an on-line coprecipitate dissolution. Thus, the versatility of the proposed system allows the selection of the radiometric detection technique depending on the detector availability or the required response efficiency (sample number vs. response time and limit of detection). The MSFIA-LOV system improves the precision (1.7% RSD), and the extraction frequency (up to 3xa0h(-1)). Besides, it has been satisfactorily applied to different types of water matrices (tap, mineral, well and sea water). The (226)Ra minimum detectable activities (LSC: 0.004xa0Bqxa0L(-1); LBPC: 0.02xa0Bqxa0L(-1)) attained by this system allow to reach the guidance values proposed by the relevant international agencies e.g. WHO, EPA and EC.

Multivariate optimisation of a rapid and simple automated method for bismuth determination in well water samples exploiting long path length spectrophotometry

ABSTRACT An automated spectrophotometric system is proposed for the determination of bismuth in well water samples, using multi-syringe flow injection analysis (MSFIA) and exploiting a liquid waveguide capillary cell (LWCC). This method is based on the colorimetric reaction of bismuth and methylthymol blue (MTB) in the presence of polyvinylpyrrolidone (PVP) in acid medium (0.1 mol L−1 HNO3). The Bi(III)–MTB complex was measured at 600 nm. The method was optimised by multivariate techniques. Some figures of merit of the proposed system are worth being highlighted, such as its wide linear working range (between 4.9 and 600 μg L−1), its low detection limit (1.5 μg L−1 of bismuth) and its high intra-day precision and inter-day precision (0.7% (n = 12) and 1.4% (n = 5), respectively, both expressed as RSD). Moreover, a high injection frequency of 30 h−1 is achieved, as the proposed analyser is a powerful tool for fast Bi(III) determination. The method developed was successfully validated by analysing reference samples (pharmaceutical samples) by comparing the results with those obtained by ICP-OES and it was satisfactorily applied to well water samples. Besides, the present system is miniaturised allowing in situ measurements in control processes and field analysis.