E. García-Ruiz

Amperometric cholesterol biosensors based on the electropolymerization of pyrrole and the electrocatalytic effect of Prussian-Blue layers helped with self-assembled monolayers.

Three cholesterol biosensor configurations based on the formation of a layer of Prussian-Blue (PB) on a Pt electrode for the electrocatalytic detection of the H(2)O(2) generated during the enzymatic reaction of cholesterol with cholesterol oxidase (ChOx) were constructed. The enzyme was entrapped within a polypyrrole (PPy) layer electropolymerized onto the PB film. The influence of the formation of self-assembled monolayers (SAMs) on the Pt surface on the adherence and stability of the PB layer and the formation of an outer layer of nafion (Nf) as a means of improving selectivity were both studied. A comparative study was made of the analytical properties of the biosensors corresponding to the three configurations named: Pt/PB/PPy-ChOx, Pt/SAM/PB/PPy-ChOx and Pt/SAM/PB/PPy-ChOx/Nf. The sensitivity (from 600 to 8500nAmM(-1)cm(-2)) and selectivity of the developed biosensors permitted the determination of the cholesterol content in reference and synthetic serum samples. The detection limit for the Pt/SAM/PB/PPy-ChOx/Nf biosensor was 8muM. Formation of the SAM on the electrode surface and covering with a Nf film considerably improved the stability and lifetime of the biosensor based on the catalytic effect of the PB layer (as the PB layer was retained longer on the electrode), and the Nf layer protects the enzyme from the external flowing solutions. Lifetime is up to 25 days of use. The formation of the SAM also has an effect on the charge transfer and the formation of the PB layer.

Laser ablation‐inductively coupled plasma mass spectrometry in archaeometric research

Laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) is a solid sampling technique in continuous expansion in all types of research fields in which direct multi-elemental or isotopic analysis is required. In particular, this technique shows unique characteristics that made its use recommended in many archaeometric applications, where valuable solid artifacts are often the target samples, because it offers flexibility to achieve spatially resolved information with high detection power and a wide linear range, in a fast and straightforward way, and with minimal sample damage. The current review provides a systematic survey of publications that reported the use of LA-ICPMS in an archaeological context, highlights its main capabilities and limitations and discusses the most relevant parameters that influence the performance of this technique for this type of application.

High-resolution continuum source graphite furnace atomic absorption spectrometry: Is it as good as it sounds? A critical review

AbstractThe recent arrival of high-resolution continuum source atomic absorption spectrometry represents a potential revolution in this field, in particular for direct analysis of complex samples. This review tries to illustrate the main advantages of this technology, paying particular attention to the development of direct solid sampling methods. Three solid sampling applications will be discussed, each one of them highlighting one of the main advantages of this technique. The review also intends to clarify some misconceptions on the true potential of the instrumentation that is currently commercially available, such as its performance for multielemental analysis. FigureGraphite furnace: still burning hot!

Characterization of cobalt pigments found in traditional Valencian ceramics by means of laser ablation-inductively coupled plasma mass spectrometry and portable X-ray fluorescence spectrometry

In this work, a comparison of the performances of laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) and portable X-ray fluorescence (XRF) spectrometry for the characterization of cobalt blue pigments used in the decoration of Valencian ceramics is presented. Qualitative data on the elemental composition of the blue pigments obtained using both techniques show a good agreement. Moreover, the results clearly illustrate that potters utilized different kinds of cobalt pigments in different historical periods. While both techniques seem suitable for the proposed task, they show different strengths and weaknesses. Portable X-ray fluorescence spectrometry is a cheaper and totally non-destructive technique, capable of providing fast and reliable results at the mgg(-1) level. LA-ICPMS, on the other hand, offers a much higher detection power and better spatial resolution, but its use results in some sample damage (sample consumption at the mug level), while it is a more expensive and non-portable technique.

Strategies for the improvement of an amperometric cholesterol biosensor based on electropolymerization in flow systems: use of charge-transfer mediators and platinization of the electrode

Different configurations based on an amperometric biosensor with cholesterol oxidase entrapped in a polypyrrole film have been developed with a view to improving the analytical properties of this biosensor. The alternatives considered involve the simultaneous entrapment of the enzyme and a charge-transfer mediator as well as previous platinization of the surface of the Pt electrode. Both artificial (a ferrocene derivative) and natural (flavin nucleotides) mediators were studied as constituents of the charge-transfer process between the enzyme and the electrode. The comparative study of these biosensors, which were prepared in situ in a continuous flow system, made it possible to determine the advantages and disadvantages of each configuration when applied to flow-injection determination of cholesterol.

Progress in the determination of metalloids and non-metals by means of high-resolution continuum source atomic or molecular absorption spectrometry. A critical review

AbstractThis work examines the new possibilities introduced with the arrival of commercially available high-resolution continuum source atomic absorption spectrometers for the determination of metalloids (B, Si, Ge, As, Se, Sb and Te) and non-metals (P, S, F, Cl, Br, I and N-based species), such as the improved potential to detect and correct for spectral overlaps and the strategies available to correct for matrix effects. In particular, and considering the increasing number of papers reporting on the use of molecular absorption spectrometry using graphite furnaces and flames as vaporizers, the work discusses in detail the advantages and limitations derived from the monitoring of molecular spectra from a practical point of view, in an attempt to guide future users of the technique. FigureHeating of a graphite furnace with platform

Evaluation of solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry and solid sampling-graphite furnace atomic absorption spectrometry for the direct determination of Cr in various materials using solution-based calibration approaches

In this work, the possibilities for the direct determination of Cr in solid samples by means of graphite furnace atomic absorption spectrometry (SS-GFAAS) and by means of electrothermal vaporization-inductively coupled plasma mass spectrometry (SS-ETV-ICPMS) have been critically evaluated and compared, the goal always being to develop simple and fast methods, only relying on the use of aqueous standards for calibration. Four reference materials of very different nature (milk powder, lobster hepatopancreas, polyethylene and sewage sludge), covering a wide Cr concentration range (from 17.7 ng g−1 to 37.2 µg g−1), were selected for the study. The diverse volatility of their matrixes, compared with that of Cr, resulted in different degrees of difficulty for both techniques. SS-GFAAS offers a better limit of detection (2 ng g−1) than SS-ETV-ICPMS (30 ng g−1), mainly due to the occurrence of C-based polyatomic interferences with the latter technique. The samples that presented the least difficulties were those for which the matrix is mainly of an organic nature and can be easily removed during the pyrolysis step, allowing a selective atomization/vaporization of the analyte. Under these circumstances, external calibration against aqueous standards was feasible for SS-GFAAS in all cases. SS-ETV-ICPMS proved to be more sensitive to matrix effects, but the use of the palladium (added for its carrier properties) signal as internal standard also allowed the use of this straightforward calibration procedure. On the other hand, the analysis of sewage sludge (containing 85% of hardly volatile inorganic compounds) represented the most complicated situation for both techniques: for SS-GFAAS, the addition of Na2CO3 to effect an in-situ microfusion of the sample during the pyrolysis step greatly helped to improve the situation, while for SS-ETV-ICPMS the single standard addition method was necessary. In all cases, a good agreement with the certified values was obtained. The precision ranged between 6 and 22% relative standard deviation, depending on the homogeneity and the sample mass used. These values could be further improved, if needed, by increasing the number of replicates per determination (usually five). Every determination required approximately 15–20 min, except when the single standard addition method was used (30–40 min). Therefore, it can be stated that both techniques show the capability of providing a direct determination of this analyte in a variety of samples, at very different concentration levels, allowing the development of fast and reliable solid sampling procedures.

Laser ablation-inductively coupled plasma-dynamic reaction cell-mass spectrometry (LA-ICP-DRC-MS) for the determination of Pt, Pd and Rh in Pb buttons obtained by fire assay of platiniferous ores

As a result of the low concentration in which the platinum group metals (PGMs) Pt, Pd and Rh occur in platiniferous ores and their heterogeneous distribution over the matrix, their determination is usually preceded by analyte pre-concentration and separation of the analyte from the matrix. The Pb fire assay technique is an elegant method for this purpose, whereby the elements of interest are collected from a relatively large sample mass in a Pb button. It was the aim of this work to evaluate the capabilities of laser ablation-ICP-mass spectrometry (LA-ICP-MS) for the analysis of such Pb buttons. Matrix-matched standards were produced by spiking lead ingots with an aqueous standard solution and subsequent re-melting of these ingots to obtain homogeneous solid standards with known PGM concentrations. These standards permitted quantitative results to be obtained. In standard (vented) mode, the determination of Rh by ICP-MS was hindered by spectral overlap of the 103Rh+ signal with that of 206Pb2+. Cool plasma conditions permitted reduction of the Pb2+ signal intensity, but since analyte signal intensities decreased as well, the improvement in the limit of detection (LOD) for Rh was insufficient to make this approach fit-for-purpose. Use of NH3 as a reaction gas (at a flow rate of 0.2 Ar-equivalent mL min−1) in a dynamic reaction cell (DRC) resulted in electron transfer to Pb2+, while Rh+ showed no reactivity towards this gas. The use of chemical resolution to overcome the Rh+/Pb2+ overlap did not interfere with the determination of the other PGMs of interest. LODs achievable with this approach were <100 ng g−1 for Pt, Pd and Rh. The capability of this approach was evaluated by analysing Pb buttons produced from actual flotation concentrate samples from platiniferous ores, originating from the Merensky reef and the UG-2 reef, both located in the South-African Bushveld Igneous Complex. The accuracy attainable using LA-ICP-DRC-MS was estimated by comparison of the results thus obtained with those calculated for the lead buttons based on NiS fire assay and subsequent ICP-OES analysis of the same flotation concentrate samples. No significant differences could be established and in the majority of cases, the deviation between the LA-ICP-DRC-MS result and the corresponding reference value was <10%. The precision was typically ∼10% relative standard deviation (RSD) for Pt and Rh. For Pd, however, the precision was observed to be worse (typically ∼15% RSD), probably as a result of a more heterogeneous distribution over the Pb matrix.

Solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry for the direct determination of traces of iodine

In this work, the possibilities of electrothermal vaporization-inductively coupled plasma mass spectrometry for the direct determination of I at the ppm and sub-ppm level in solid samples have been evaluated. Five reference materials of different natures (NIST SRM 1549 and BCR CRM 150 Milk Powder, BCR CRM 129 Hay Powder, NIST SRM 1548a Typical Diet and NIST SRM 2709 San Joaquin Soil) were selected for this study.The importance of the use of pre-reduced Pd in the analysis of biological materials was demonstrated. The use of this chemical modifier results in a better stabilization of the analyte (up to 700 °C), enabling complete removal of the organic matrices without analyte losses. Moreover, for those samples for which some matrix effects were still observed (milk powder materials), the use of the Pd signal as internal standard permitted correction for these effects, allowing accurate results to be obtained. A detection limit of 8 ng g−1 and a sample throughput of 20–25 min per determination were estimated for these biological materials. The potential of the technique for inorganic samples was also evaluated with a soil material (NIST SRM 2709). For this sample, an alternative approach was developed. By taking advantage of the volatility of the analyte in the absence of any modifier and of the refractory nature of most matrix components, it was possible to selectively vaporize I at 1500 °C, ensuring the absence of significant matrix effects. A higher sample throughput of 10 min per determination (due to the faster temperature program) and a higher detection limit (30 ng g−1, due to the absence of Pd) were calculated for this material. In all cases, external calibration with aqueous standards was possible and RSD values were in the vicinity of 10%.

Comparison of the solid sampling techniques laser ablation-ICP-MS, glow discharge-MS and spark-OES for the determination of platinum group metals in Pb buttons obtained by fire assay of platiniferous ores

This work reports on the performance of a new Pb fire assay procedure for the extraction of Au, Cu, Ir, Ni, Pd, Pt, Rh and Ru from platiniferous ores, followed by the direct analysis of the Pb buttons thus obtained by means of three solid sampling techniques (spark-OES, LA-ICP-DRC-MS and GD-sector field-MS), therefore avoiding the process of cupellation. It can be concluded that this working scheme allows the reliable analysis of different ore materials, except for Ni and Ir, for which no quantitative extraction was achieved. The preparation of the Pb buttons using large masses of the ores permitted us to obtain representative and homogeneous buttons, resulting in acceptable precision values (typically RSD values ranged between 2–5% for spark-OES and GD-MS, and between 4–10% for LA-ICP-MS), while the simple composition of these buttons (≥99% Pb) enabled the preparation of matrix-matched standards for calibration. In general terms, all these techniques perform in a satisfactory way, although they showed different strengths and weaknesses. While spark-OES provides the highest sample throughput, its detection limits are not always sufficiently low for some analytes (Au, Ir, Pt). It is demonstrated that these detection limits can be further decreased by using techniques based on mass spectrometry (LA-ICP-MS and, particularly, GD-MS), although the use of an instrumental configuration capable of dealing with spectral overlap is required, namely a dynamic reaction cell pressurized with NH3 in the case of LA-quadrupole ICP-MS and a double-focusing sector field mass analyser in the case of GD-MS.