Montserrat Hidalgo

Application of laser-induced breakdown spectroscopy technique to hair tissue mineral analysis

The concentration of the main minerals present in human hair is measured on several subjects by Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) and compared with the results obtained through a commercial analytical laboratory. The possibility of using CF-LIBS for mineral analysis in hair is discussed, as well as its feasibility for the fast and inexpensive determination of the occurrence of heavy-metal poisoning in hair.

Effect of Laser-Induced Crater Depth in Laser-Induced Breakdown Spectroscopy Emission Features:

The influence of crater depth on plasma properties and laser-induced breakdown spectroscopy (LIBS) emission has been evaluated. Laser-induced plasmas were generated at the surface and at the bottom of different craters in a copper sample. Plasmas produced at the sample surface and at the bottom of the craters were spatially and temporally resolved. LIBS emission, temperature, and electronic number density of the plasmas were evaluated. It is shown that the confinement effect produced by the craters enhances the LIBS signal from the laser-induced plasmas.

Dispersive liquid-liquid microextraction for metals enrichment: A useful strategy for improving sensitivity of laser-induced breakdown spectroscopy in liquid samples analysis

A rapid and efficient Dispersive Liquid-Liquid Microextraction (DLLME) followed by Laser-Induced Breakdown Spectroscopy detection (LIBS) was evaluated for simultaneous determination of Cr, Cu, Mn, Ni and Zn in water samples. Metals in the samples were extracted with tetrachloromethane as pyrrolidinedithiocarbamate (APDC) complexes, using vortex agitation to achieve dispersion of the extractant solvent. Several DLLME experimental factors affecting extraction efficiency were optimized with a multivariate approach. Under optimum DLLME conditions, DLLME-LIBS method was found to be of about 4.0-5.5 times more sensitive than LIBS, achieving limits of detection of about 3.7-5.6 times lower. To assess accuracy of the proposed DLLME-LIBS procedure, a certified reference material of estuarine water was analyzed.

Temporal and spatial evolution of a laser-induced plasma from a steel target.

The space and time evolution of a laser-induced plasma from a steel target has been studied using optical time-of-flight and shadowgraphic techniques. The results, obtained for two distinct laser energy regimes, allow us to individuate two different regions in the plume, one characterized by air and continuum emissions produced by the shock wave ionization and the other characterized by emissions from ablated material. Moreover, it was shown that a sufficiently high laser fluence and short delay time of acquisition are needed to avoid inhomogeneous effects in the plasma, as required in analytical applications such as laser-induced breakdown spectroscopy.

Compensation for matrix effects on ICP-OES by on-line calibration methods using a new multi-nebulizer based on Flow Blurring® technology

In this work, on-line calibration methods were applied for compensation for matrix effects in Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) using three novel multiple sample introduction systems based on Flow Blurring® technology. The methods were compared with conventional calibration methods, using a Conikal nebulizer and a cyclonic spray chamber (i.e., Standard Sample Introduction (SSI) system). Experiments were carried out with synthetic samples containing different matrices. The total liquid flow through the multinebulizers was 400 μL min−1 whereas in the SSI system it was 1000 μL min−1. One type of calibration method tested was external calibration. By using this calibration method, the mean of absolute values corresponding to the relative error values of different multiple sample introduction systems and all the matrices was 14% and uncertainty was 0.6%. When on-line internal standard calibration was used, the mean relative error value dropped to 3% and uncertainty was 0.6%. With on-line standard addition calibration, relative error values went down to 2%. However, uncertainty values increased to 2% in all cases. With all the calibration methodologies, the accuracy and uncertainty of the obtained results were very similar for both standard and multiple sample introduction systems. The main difference was a significant reduction in resource consumption (i.e., samples, reagents and time) when multinebulization systems were used. Sensitivity, precision and limits of detection were evaluated for the different Flow Blurring® based systems and SSI system. For most of the emission lines evaluated, all the Flow Blurring® based systems gave higher precision values and lower limits of detection than SSI system. A certified reference material (Estuarine Water, LGC6016), without prior sample treatment (i.e., dilution), was analyzed using external calibration with the SSI system and on-line standard addition calibration with Flow Blurring® based systems. The certified reference material analysis gave relative error values ranging between +20% and −30% for the SSI system, and between +4% and −2% for Flow Blurring® based systems.

Speciation of chromium by dispersive liquid–liquid microextraction followed by laser-induced breakdown spectrometry detection (DLLME–LIBS)

In this study, an analytical methodology based on a combination of dispersive liquid–liquid microextraction with laser-induced breakdown spectrometry was evaluated for simultaneous pre-concentration, speciation and detection of Cr. The microextraction procedure was based on the injection of appropriated quantities of 1-undecanol and ethanol into a sample solution containing the complexes formed between Cr(VI) and diethyldithiocarbamate (DDTC). The main experimental factors affecting the complexation and the extraction of metal (pH, DDTC concentration, extractant and volume of disperser solvents) were optimized using a multivariate analysis consisting of two steps: a Plackett–Burman design followed by a Circumscribed Central Composite Design (CCCD). Under optimum microextraction conditions, the analytical figures of merit of the proposed methodology were assessed. The method was finally applied to the analysis of a certified reference material hard drinking water (ERM® CA011a), yielding results in good agreement with the certified value.

The determination of V and Mo by dispersive liquid-liquid microextraction (DLLME) combined with laser-induced breakdown spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) is a promising analytical technique with well-known advantages and limitations. However, despite its growing popularity, this technique has been applied mainly to solid samples and there have been a smaller number of studies devoted to liquid samples. This lack of studies is mainly due to experimental difficulties in the analysis of liquid matrices. Sensitivity can be improved and matrix effects minimized in the LIBS analysis of aqueous samples by using a dispersive liquid–liquid microextraction (DLLME) procedure followed by drying the extract on a suitable surface prior to laser irradiation. The combination of DLLME-LIBS is fast, easy to use, and inexpensive. The small volume of the final extract is sufficient for LIBS analysis, and the procedure generates little waste. It is likely that this combination could be automated during future work. The limits of detection (LOD) and quantification (LOQ) achieved using the proposed method were 30 and 70 μg L−1 for Mo and 5 and 20 μg L−1 for V, respectively. Using this method, we analyzed samples of pharmaceutical, multimineral formulation, soil, mineral water and a reference material NCS ZC 85005 (Beef Liver). In the latter, the concentration of V was below the LOQ, and the recovery of Mo was 103%.

Analysis of biodiesel and oil samples by on-line calibration using a Flow Blurring® multinebulizer in ICP OES without oxygen addition

A new multinebulizer, based on Flow Blurring® technology (FBMN), is evaluated for a simple, fast and direct analysis of organic samples in Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES). Organic samples are analyzed by on-line standard addition calibration using aqueous calibration standards. A Standard Sample Introduction (SSI) system (i.e., MicroMist® commercial nebulizer (MM) and a spray chamber) is used for comparison using a conventional standard addition with organic calibration standards. Both systems are coupled to the same cyclonic-type spray chamber and organic samples are nebulized at the same flow rate (100 μL min−1). Aerosol characterization revealed that when using the FBMN, practically all the organic primary aerosol volume is contained in droplets smaller than 33 μm, whereas when using the MM nebulizer, it is contained in droplets smaller than 114 μm. The on-line standard addition calibration was tested with diluted oil samples, providing results as accurate as those obtained with the reference system, with percent relative error values ranging from −5% to 4% for the reference system, and slightly lower, from −3% to 3% for the FBMN-based system. Figures of merit estimation shows that sensitivity, precision and limits of detection are better in the on-line calibration analysis than in the conventional one. In particular, long-term stability studies reveal that the addition of water in the on-line standard addition calibration significantly contributes to carbon compounds combustion, and therefore eliminates spectral interferences from carbon compounds and avoids carbon deposits in ICP components. After 2 hours of continuous organic sample introduction, the RSD (%) values ranged between 1.5% and 2% with the FBMN-based system and between 10% and 13% with the SSI system. Accuracy and uncertainty of the proposed on-line calibration was also evaluated in the analysis of various organic samples (i.e., biodiesel certified material and real diesel samples). In the analysis of certified reference material, the relative error values were found to be in the range from −4% to +4% for the SSI system and from −4% to +1.0% for the FBMN-based system. Recovery values of real samples of 5% biodiesel in diesel were, in all cases, close to 100%.

Analysis of waste electrical and electronic equipment (WEEE) using laser induced breakdown spectroscopy (LIBS) and multivariate analysis

This study shows the application of laser induced breakdown spectroscopy (LIBS) for waste electrical and electronic equipment (WEEE) investigation. Several emission spectra were obtained for 7 different mobiles from 4 different manufacturers. Using the emission spectra of the black components it was possible to see some differences among the manufacturers and some emission lines from organic elements and molecules (N, O, CN and C2) led to the highest contribution for this differentiation. Some polymeric internal parts in contact with the inner pieces of the mobiles and covered with a special paint presented a strong emission signal for Cr. The white pieces presented mainly Al, Ba and Ti in their composition. Finally, this study developed a procedure for LIBS emission spectra using chemometric strategies and suitable information can be obtained for identification of manufacturer and counterfeit products. In addition, the results obtained can improve the classification for establishing recycling strategies of e-waste.

Flow focusing pneumatic nebulizer in comparison with several micronebulizers in inductively coupled plasma atomic emission spectrometry

A new pneumatic concentric nebulizer (flow focusing pneumatic nebulizer, FFPN) is characterized and compared with five commercially available pneumatic micronebulizers (high efficiency nebulizer (HEN), PFA-micronebulizer (PFA), MicroMist (MM), Ari Mist (AM) and Mira Mist (MiM)) operated in conjunction with the same cyclonic spray chamber. Primary and tertiary aerosols, transport magnitudes (solvent and analyte transport rates) and analytical figures of merit obtained using inductively coupled plasma atomic emission spectroscopy are measured. Under all the conditions studied, all the primary aerosols produced by FFPN are contained in droplets smaller than 15 μm. Primary and tertiary aerosols produced by FFPN show very similar characteristics. This is the result of the small filtering action of the cyclonic spray chamber used when the FFPN is used. Under all the conditions studied, the FFPN produces a finer and narrower primary aerosol than the commercial pneumatic micronebulizers. At a solution uptake rate of 0.2 mL min−1 and a nebulizing gas flow rate of 0.7 L min−1 the median diameter (D50) values of the primary aerosols are 21.71 μm, 31.75 μm, 16.84 μm, 13.13 μm, 4.92 μm and 3.25 μm with the PFA, MM, AM, MiM, HEN and FFPN, respectively. The tertiary aerosols do not show a substantial difference, the D50 values, under the same operating conditions stated above, being 3.90 μm, 3.91 μm, 4.38 μm, 4.07 μm, 2.95 μm and 3.59 μm for the PFA, MM, AM, MiM, HEN and FFPN, respectively. For example, under the above experimental conditions, nearly 30%, 20%, 44%, 51%, 100% and 100% of primary aerosol volume is contained in droplets having sizes smaller than the cut-off diameter of the spray chamber used (20 μm) for the PFA, MM, AM, MiM, HEN and FFPN, respectively. However, the tertiary aerosol volume contained on droplets smaller than 9 μm ranges between 85%–99%. This is a clear consequence of the strong filtering action of the spray chamber when used with the PFA, MM, AM and MiM nebulizers. Solvent and analyte transport rate values obtained with the FFPN are the highest, the analyte transport rate values being 6.4 μg min−1, 7.0 μg min−1, 5.1 μg min−1, 5.9 μg min−1, 10.1 μg min−1 and 15.8 μg min−1 for the PFA, MM, AM, MiM, HEN and FFPN, respectively. In general, working under the same liquid and gas flow rates, sensitivities, precision and limits of detection obtained with the FFPN are similar to those obtained with HEN and better than for PFA, MM, AM and MiM nebulizers.