Application of high-energy polarised-beam energy dispersive X-ray fluorescence spectrometry to cadmium determination in saline solutions.

In the present work, the analytical performance of a methodology based on a preconcentration using activated thin layers followed by high-energy polarised beam energy-dispersive XRF spectrometry (HE-P-EDXRF) for the determination of trace amounts of Cd in saline solutions is presented. Linear calibration curves were obtained over the range 5–8000 μg L−1 of Cd. When comparing the developed method to the direct analysis of Cd in sea water, the detection limits were improved by several orders of magnitude, with values of 2.25 μg L−1 (Al2O3 target) and 0.075 μg L−1 (CsI target), respectively. The accuracy was checked by analyzing spiked natural sea water at Cd concentrations of 20, 100 and 600 μg L−1 and results were compared to those obtained with anodic stripping voltametry and no significant differences at the 95% confidence level were found. The method has a good reproducibility over the investigated period of time and the precision of the method was better than 10%.This research has been developed in the framework of the Spanish National Research Programme (Projects: CGL2004- 05963-C04/HID and CGL2007-66861-C4).Peer reviewe

Improved instrumental sensitivity for Cd determination in aqueous solutions by using WDXRF, Rh-target tube, instrumentation

This work was aimed at improving the instrumental sensitivity and detection limits for Cd determination in liquid samples by using conventional Wavelength Dispersive X-ray Fluorescence (WDXRF) instrumentation equipped with Rh-anode X-ray sources. The fact that the background is drastically reduced when using activated membranes as a preconcentration tool to collect Cd from liquid samples permits an improvement of the sensitivity compared with the direct analysis of liquid samples. Instrumental WDXRF parameters, as well as the study of Cd-K and Cd-L series spectral lines, were evaluated to select the best conditions for Cd quantitation. The Cd-Lα spectral line was found to be the best choice in terms of sensitivity and repeatability. The calculated detection limit when this spectral line was used to carry out the measurements was 0.17 mg L− 1 Cd, which is suitable for Cd determination in most liquid samples involved in environmental studies.This research has been undertaken in the framework of the Spanish National Research Program (Project ref. CGL2007-66861-C4).Peer reviewe

Analytical capabilities of laboratory, benchtop and handheld X-ray fluorescence systems for detection of metals in aqueous samples pre-concentrated with solid-phase extraction disks

We aimed to achieve improved instrumental sensitivity and detection limits for the analysis of several elements (Cu, Ni, Zn, Pb and Cd) in aqueous samples with energy dispersive X-ray fluorescence spectrometry (EDXRF). The metals were pre-concentrated from aqueous solutions using commercially available organic-based solid-phase extraction (SPE) disks functionalized with iminodiacetate groups. These thin-layer organic materials provide an ideal support for XRF analysis. The elements were collected on the SPE extraction disks using a simple filtration procedure (starting with 1 L of aqueous sample) that allows direct XRF measurements to be performed in the field (in situ). We evaluated the analytical possibilities and drawbacks of using this pre-concentration procedure in combination with the following XRF configurations: a handheld unit, a benchtop EDXRF system and a high-energy polarized-beam EDXRF instrument (HE-P-EDXRF). Using the HE-P-EDXRF system, the detection limits for all metals were more than one order of magnitude lower than those attained using handheld and benchtop EDXRF instrumentation. For the detection of metal concentrations higher than ~ 20 μg/L, however, handheld or benchtop systems remain a very good option due to their extreme simplicity of operation and low-cost, compact design. We demonstrate the application of these methodologies, using the three equipment systems, to the analysis of trace concentrations of metals in different types of aqueous samples, including tap water and waste water. © 2011 Elsevier B.V.This work was supported by the Spanish “Consolider Ingenio 2010” Program (Project ref. CSD2006-00044) and the Spanish National Research Programs (Project ref. CGL2007-66861-C4 and CGL2010-22168-C03-01).Peer Reviewe

X-ray fluorescence trace metal analysis of environmental liquid samples after membrane preconcentration.

The data reporter highlights that the use of XRF spectrometry, in particular HE-P-EDXRF, in combination with membrane preconcentration is a promising alternative for metal analysis at low ugL-1 levels in complex environmental liquid.This study was financed by the Spanish National Research Programme (projects CGL2004-05963-C04/HID and CGL2007-66861-C04).Peer reviewe

Polymer inclusion membrane to access Zn speciation: Comparison with root uptake

Metal speciation studies can be performed with a new technique based on a functionalized membrane. The estimation of not only the total amount of metal, but also the metal available to living organisms is very important. In this context, we have investigated the use of a polymer inclusion membrane (PIM) in a new tool for the determination of free metal ion concentration. In order to check the usefulness of PIM devices in metal speciation studies and metal availability to potato plants (Solanum tuberosum), Zn has been chosen as a case study. The PIM designed for Zn transport uses polyvinyl chloride (PVC) as polymer and di-(2-ethylhexyl) phosphoric acid (D2EHPA) as carrier, with 0.01M nitric acid in the receiving solution. The stability of the PIM has been demonstrated and good linearity of PIM-device fluxes (JPIM) with free metal concentration was observed for total metal concentrations ranging from 3 µM up to 70 µM. The presence of different ligands, such as ethylenediaminetetraacetic acid (EDTA), humic acid (HA) and citrate, greatly influences the measured JPIM because the formation of metal complexes in the donor phase decreases the free Zn concentration in the sample. Good correlation has been found when comparing PIM fluxes and metal accumulation in potato plants roots in the presence of EDTA. But, the root uptake did not change when adding citrate and HA to the hydroponic medium, so the uptake does not always follows the Free Ion Activity Model (FIAM). These ligands might induce physiological changes in the roots and enhance metal uptake

Method for the Determination of Pd-Catalyst Residues in Active Pharmaceutical Ingredients by Means of High-Energy Polarized-Beam Energy Dispersive X-Ray Fluorescence

In medicinal chemistry, Pd is perhaps the most-widely utilized precious metal, as catalyst in reactions which represent key transformations toward the synthesis of new active pharmaceutical ingredients (APIs). The disadvantage of this metal-catalyzed chemistry is that expensive and toxic metal residues are invariably left bound to the desired product. Thus, stringent regulatory guidelines exist for the amount of residual Pd that a drug candidate is allowed to contain. In this work, a rapid and simple method for the determination of Pd in API samples by high-energy polarized-beam energy dispersive X-ray fluorescence spectrometry has been developed and validated according to the specification limits of current legislation (10 mg kg−1 Pd) and the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH guidelines). Sample and calibration standards preparation includes a first step of homogenization and then, in a second step, the pressing of the powdered material into pellets without any chemical treatment. The use of several synthetic calibration standards made of cellulose to simulate the API matrix appears to be an effective means to obtain reliable calibration curves with a good spread of data points over the working range. With the use of the best measuring conditions, the limit of detection (0.11 mg kg−1 Pd) as well as the limit of quantitation (0.37 mg kg−1 Pd) achieved meet rigorous requirements. The repeatability of the XRF measurement appeared to be less than 2%, while the precision of the whole method was around 7%. Trueness was evaluated by analyzing spiked API samples at the level of the specification limit and calculating the recovery factor, which was better than 95%. To study the applicability of the developed methodology for the intended purpose, three batches of the studied API were analyzed for their Pd content, and the attained results were comparable to those obtained by the daily routine method (acid digestion plus atomic spectroscopy) used in most pharmaceutical laboratories.This work was supported by the Spanish National Research Programme (Project CGL2007-66861-C4).Peer reviewe