María S. Jiménez

Detection, characterization and quantification of inorganic engineered nanomaterials: A review of techniques and methodological approaches for the analysis of complex samples

The increasing demand of analytical information related to inorganic engineered nanomaterials requires the adaptation of existing techniques and methods, or the development of new ones. The challenge for the analytical sciences has been to consider the nanoparticles as a new sort of analytes, involving both chemical (composition, mass and number concentration) and physical information (e.g. size, shape, aggregation). Moreover, information about the species derived from the nanoparticles themselves and their transformations must also be supplied. Whereas techniques commonly used for nanoparticle characterization, such as light scattering techniques, show serious limitations when applied to complex samples, other well-established techniques, like electron microscopy and atomic spectrometry, can provide useful information in most cases. Furthermore, separation techniques, including flow field flow fractionation, capillary electrophoresis and hydrodynamic chromatography, are moving to the nano domain, mostly hyphenated to inductively coupled plasma mass spectrometry as element specific detector. Emerging techniques based on the detection of single nanoparticles by using ICP-MS, but also coulometry, are in their way to gain a position. Chemical sensors selective to nanoparticles are in their early stages, but they are very promising considering their portability and simplicity. Although the field is in continuous evolution, at this moment it is moving from proofs-of-concept in simple matrices to methods dealing with matrices of higher complexity and relevant analyte concentrations. To achieve this goal, sample preparation methods are essential to manage such complex situations. Apart from size fractionation methods, matrix digestion, extraction and concentration methods capable of preserving the nature of the nanoparticles are being developed. This review presents and discusses the state-of-the-art analytical techniques and sample preparation methods suitable for dealing with complex samples. Single- and multi-method approaches applied to solve the nanometrological challenges posed by a variety of stakeholders are also presented.

Semiquantitative simultaneous determination of metals in olive oil using direct emulsion nebulization

A simple method for the semiquantitative determination of several metals in olive oil by ICP-MS is described. The formation of olive oil emulsions, as a simplified sample preparation procedure is demonstrated. Optimization of the chemical conditions for the formation and stabilization of olive oil emulsions is reported: pH, emulsifiers, stirring (mechanical and ultrasonic mode) time, reagents and sample volumes. The semiquantitative determination of Ba, Cd, Co, Cr, Cu, Mn, Ni, Tl, Pb, U, V and Zn was carried out by ICP-MS with direct introduction of the emulsions into the plasma after optimization of the instrumental parameters (power, pump flow, nebulizer gas flow, use of auxiliary oxygen flow). Results from spike and recovery experiments at levels of 100 and 200 ng mL –1 are 93-115% and detection limits based on 3 times standard deviation of the blank (10 replicates) are 0.25-50 ng g –1 in the olive oil.

Speciation of methyl- and inorganic mercury in biological tissues using ethylation and gas chromatography with furnace atomization plasma emission spectrometric detection

A sensitive and interference-free method for the quantification of inorganic and methylmercury species in biological tissues is presented using purge-and-trap injection–GC–AES. Samples were solubilized with tetramethylammonium hydroxide and the ionic species were purged from aqueous solution after ethylation with sodium tetraethylborate. The species were preconcentrated on Tenax-TA and thermally desorbed onto an isothermal (90 °C) GC column packed with 15% OV-3 on Chromasorb W. The separated species were eluted in He to a FAPES source for detection by AES at 253.6 nm. Absolute detection limits of 1 and 7 pg for inorganic and methylmercury, respectively, can be obtained, corresponding to concentration LODs of 0.2 and 1.4 ng g -1 , respectively, in solid tissue samples. Precision of determination is better than 10% RSD. The accuracy of the technique was validated by the analysis of National Research Council of Canada CRMs DORM-2, DOLT-2 and TORT-2, certified for mercury species content.

Performance of different preconcentration columns used in sequential injection analysis and inductively coupled plasma-mass spectrometry for multielemental determination in seawater☆

Abstract A simple, versatile and economical method of sequential injection analysis and inductively coupled plasma-mass spectrometry with matrix removal in two different ion-exchange resins for the determination of Al, As, Co, Cu, Mn, Mo, Ni, Pb and V is reported. The resins used, both of which contain the iminodiacetic acid functional group, were Chelex 100 and Metpac CC-1. With both resins, a matrix removal step (alkaline and alkaline-earth metals) with ammonium acetate is required before elution of the analytes with 2 M HNO 3 . The procedure was validated by analyzing CASS-3 seawater reference material and good agreement was found with the certified values. Precision ( n =8) for the nine elements was in the range 0.8–4.9% for the Chelex 100 column and the recoveries ranged from 87.4 to 107.9%, except for Cu (78.7%) and Pb (74.9%), owing to the formation of hydroxides. For the Metpac CC-1 column, precision for the nine elements was in the range 1.2–7.1% and the recoveries between 91.7 and 109.3%, except for Al (127.2%), Co (118.5%) and Ni (127.5%) due to contamination problems.

Metal-protein binding losses in proteomic studies by PAGE-LA-ICP-MS

Some experiments to study the influence of electrophoresis conditions and subsequent LA-ICP-MS (laser ablation-inductively coupled plasma mass spectrometry) determination of two metal-binding proteins with different metal-protein affinities (superoxide dismutase, containing Cu and Zn, and alcohol dehydrogenase, containing Zn) are performed. In metal-binding proteins with weak metal-protein affinities, metal losses can happen during electrophoretic separation. It has been demonstrated that the detection of these metals bound to the proteins depends, not only on the nature of the electrophoretic process (naturing or non-denaturing) and post-separation gel treatment, but also on the trailing ion chosen and current applied in the electrophoretic method used. Non-denaturing methods are preferred to denaturing ones in the case of alcohol dehydrogenase being BN-PAGE (Blue Native-Polyacrylamide Gel Electrophoresis) with the use of Tricine as trailing ion the most recommended method. The concentration obtained for Zn in ADH applying BN-PAGE-LA-ICP-MS was 2.6+/-0.30 mg g(-1) very close to the one obtained for ADH solution by ICP-MS (3+/-0.23 mg g(1)). For superoxide dismutase either denaturing or non-denaturing electrophoresis conditions can be used, but a denaturing method based on the use of Tricine as trailing ion is recommended to preserve metals-protein binding when the use of non-denaturing conditions must be avoided. The found concentration for Cu and Zn in SOD after applying SDS-Tris-Tricine-PAGE-LA-ICP-MS was 2.5+/-0.33 and 2.4+/-0.37 mg g(-1) respectively, more or less close (especially for Cu) to the one obtained in SOD solution by ICP-MS (3+/-0.21 and 3.7+/-0.32 mg g(-1) for Cu and Zn). We observe that as higher current is applied the possibility of metal-protein binding losses is higher. In all cases staining of the gel prior to LA-ICP-MS is not recommended.

Preconcentration and atomic absorption determination of iron by sequential injection analysis

A sequential injection analysis (SIA) assembly for the atomic absorption determination of Fe(III) in natural waters is proposed. Iron is preconcentrated on a microcolumn packed with a chelating resin (Chelex 100) that is inserted in the manifold. The sample is passed through the column and the iron retained by the resin is subsequently eluted with 2 M HNO(3). The proposed SIA system affords automatic preconcentration, elution, detection of Fe(III), data acquisition and treatment. When 9 ml of iron solution containing 0.4 or 1 mg l(-1) was passed through the resin, the retention efficiency was 93.1 +/- 0.6 and 7.4 +/- 3.0% respectively, and when 27 ml of iron solution of 0.2 mg l(-1) was preconcentrated, the retention was 8.4 +/- 2.9%. The detection limits thus achieved is 12 mug l(-1) when 9 ml of sample are preconcentrated and 6 mug l(-1) for 27 ml.

Multi-element analysis of compost by laser ablation-inductively coupled plasma mass spectrometry

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been applied to multi-element determination in compost samples. Since compost is a heterogeneous mixture of organic and inorganic materials, the influence of sample heterogeneity on the accuracy and precision of analysis was investigated. Several parameters related to the following were studied: laser (energy, laser-beam diameter, preablation. rastering speed, carrier-gas flow rate), sample preparation (use of compacted pellets, grinding time, particle size, sample amount, length of hydraulic press treatment, position of line scan), and the ICP-MS system (quantitative versus semiquantitative analysis, matrix-matched standards and liquid standards calibration). The main causes of imprecision in sample preparation were determined to be particle size and grinding time. The effect of sample heterogeneity on precision was also evaluated by using different test samples (pellets). For Ni, Zn and Pb, the greatest contribution to the total relative standard deviation (R.S.D.) was related to analyte determination. For Mn and Cu, sample heterogeneity and analyte determination contributed equally to the total R.S.D., whereas for Cr, Co, Cd and Hg sample heterogeneity accounted for most of the total R.S.D. A comparison of semiquantitative and quantitative analysis modes showed that better precision and very good agreement with certified reference material was obtained with the latter, but semiquantitative analysis could be a practical alternative. Although accuracy of results was improved with matrix-matched standards calibration the use of standard addition calibration with aqueous standards could be another possibility.

Some pitfalls in PAGE-LA-ICP-MS for quantitative elemental speciation of dissolved organic matter and metalomics

An experimental approach to evaluate the capabilities and limitations of polyacrylamide gel electrophoresis (PAGE) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for quantitative elemental speciation is presented. Two metalloproteins (superoxide dismutase, containing Cu and Zn, and thyroglobulin, containing I) with high binding affinity for metals, and metal-dissolved organic matter (DOM) complexes (from a compost leachate sample) which show different types of metal binding are studied. Iodine can be quantitatively detected in thyroglobulin after PAGE-LA-ICP-MS using either sodium dodecyl sulfate (SDS) PAGE or native PAGE. However, detection of Cu and Zn in superoxide dismutase after PAGE-LA-ICP-MS depends on the conditions of the PAGE method because possible metal losses can occur (either with SDS-PAGE or with native PAGE). The use of PAGE-LA-ICP-MS to study the contribution of DOM to the mobilization of metals from environmental samples is possible, but it depends also on the PAGE separation conditions owing to disequilibrium effects of metal-DOM complexes.

Characterization of metal–humic acid complexes by polyacrylamide gel electrophoresis–laser ablation-inductively coupled plasma mass spectrometry

A new speciation methodology based on the use of 1D-PAGE (one dimensional-polyacrylamide gel electrophoresis), IEF (isoelectric focusing electrophoresis) and 2D-PAGE (two dimensional-polyacrylamide gel electrophoresis) as separation techniques and LA-ICP-MS (laser ablation-inductively coupled plasma mass spectrometry) as detection system have been applied to study the distribution of metal-humic acids (metal-HA) complexes in environmental samples. The use of 1D-Tris borate method using low current (10 mA) and Tris borate as trailing ion previous to LA-ICP-MS measurements, allowed to obtain the distribution of metals-HA complexes from a compost sample maintaining metals-HA complexes stability. It was observed that metals were associated with the smallest HA size fraction (around 3 kDa), validating results obtained by high performance size-exclusion chromatography (HP-SEC), cross-flow field flow fractionation (FIFFF) and ultrafiltration. IEF-LA-ICP-MS profiles indicated that there are two main regions: (A) with 35. The biggest metals-HA signals are obtained in A region (low pIs) corresponding to low molecular weight (MW) compounds which are predominant in our compost sample indicating a low stabilization of organic matter is low. These results are coincident with 1D-Tris borate PAGE-LA-ICP-MS results. The use of 2D-PAGE method followed by LA-ICP-MS confirmed the results obtained by 1D and IEF as PAGE methods and added information about humic acid molecular size distribution.

Tandem Preconcentration of Cobalt by On-line Ion Exchange and Gas Phase Chelates Generated by Merging-zones Flow Injection Analysis With Electrothermal Atomic Absorption Spectrometric Determination

An automated combined method of on-line preconcentration of Co on Amberlite IR-120 resin was developed followed by the generation of volatile cobalt chelates (diethyldithiocarbamate and acetylacetonate) which are then vaporized with a thermospray device to obtain a second preconcentration stage with decomposition of the gas phase generated on the surface of a pre-heated graphite platform with subsequent determination by ETAAS. The use of a by-pass valve between the thermospray device and the graphite chamber makes it possible to overcome the classical problems caused by condensation of the eluates. The sensitivity (0.0044 A s) achieved by the proposed tandem preconcentration–ETAAS method is 0.8 and 1.1 ng l–1 with a detection limit (3σ) of 2 and 3 ng l–1 for cobalt diethyldithiocarbamate and cobalt acetylacetonate, respectively. The method was evaluated against unpolluted certified reference natural waters and satisfactory results were obtained.