Miguel Ángel Aguirre

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.

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.

Development and characterization of a Flow Focusing multi nebulization system for sample introduction in ICP-based spectrometric techniques

In this work, a new multiple nebulizer for liquid sample introduction in ICP-based spectrometers was developed and characterized on ICP-AES. The association of the Flow Focusing multiple nebulizer (FFMN) and a dedicated spray chamber was called Flow Focusing multi nebulization system (FFMNS). The nebulizer incorporates four nebulization nozzles with independent liquid feeding and a common gas inlet. Four different spray chambers were constructed and evaluated and the geometry of the best performing one was optimized. The FFNMS was characterized at 0.6–0.9 L min−1 nebulizing gas flow and 0.04–0.6 mL min−1 total liquid sample flow. Drop size and velocity distributions of primary and tertiary aerosols were studied together with total solvent and analyte transport rates. The system was characterized on ICP-AES in both axial and radial view modes and compared to a standard sample introduction system consisting in a concentric nebulizer and a cyclonyc spray chamber using model solutions and certified reference materials (CRM). In terms of sensitivity and LOD, the FFMNS showed a similar behavior to the reference system at half of the liquid sample uptake (0.5 mL min−1 for FFMNS vs. 1 mL min−1 for the standard system). The CRM (hard drinking water) analysis recovery results are ranged between 89%–106% for FFMNS, and between 78%–102% for the reference system. Finally, the FFMNS was applied to an “in chamber” standard addition analysis of synthetic samples and CRM (estuarine water). The results of the CRM analysis showed better recoveries with respect to the external calibration for Cd, Mn and Ni, and similar results for Cu and Pb.

Hyphenation of single-drop microextraction with laser-induced breakdown spectrometry for trace analysis in liquid samples: a viability study

In this work, an analytical methodology based on single drop microextraction (SDME) followed by Laser-Induced Breakdown Spectrometry (LIBS) has been tested for trace metal determination in liquid samples. By this method, analytes in the samples were extracted into a small volume of toluene as ammonium pyrrolidinedithiocarbamate (APDC) chelates. After that, the analyte-enriched toluene was dried on a solid substrate and, finally, the resulting solid residue was analyzed by LIBS. Analyte extraction by the SDME procedure was optimized for the first time by using a multivariate optimization approach. Under optimum SDME conditions, analytical figures of merit of the proposed SDME-LIBS methodology were compared to those of the direct LIBS analysis method (i.e., without the SDME procedure). An estuarine water certified reference material was analyzed for method trueness evaluation. The results obtained in this study indicate that SDME-LIBS methodology leads to a sensitivity increase of about 2.0–2.6 times the ones obtained by LIBS. Detection limits of SDME-LIBS decrease according to the obtained sensitivity improvement, reaching values in the range 21–301 μg kg−1 for the analytes tested. The measurement repeatability was similar in both SDME-LIBS (13–20% RSD) and LIBS (16–20% RSD) methodologies, mainly limited by the LIBS experimental setup used in this work for LIBS analysis of liquid samples. The SDME-LIBS analysis of the certified reference material led to recovery values in the range of 96% to 112%.

Correction of matrix effects for As and Se in ICP OES using a Flow Blurring® multiple nebulizer

A new and efficient multiple nebulizer based on Flow Blurring® hydrodynamics (FBMN) has been employed for elemental analysis. The aerosol generated by the FBMN has been characterized and compared with a conventional pneumatic nebulizer (MicroMist®, MM). Both nebulizers have been operated with the same cyclonic spray chamber for comparison. At a solution flow rate of 300 μL min−1 and a nebulizer gas flow rate of 0.60 L min−1 the aerosol produced by the FBMN is formed by droplets smaller than 53 μm, and the Sauter mean diameter (D3,2) and the median diameter (D50) of the primary aerosols are 16.3 and 16.8 μm, and 20.4 and 23.3 μm with the FBMN and MM, respectively. The sample introduction system based on the FBMN successfully corrects matrix effects in As and Se determination by inductively coupled plasma optical emission spectrometry. The FBMN makes feasible the implementation of an on-line internal standard (I.S.) strategy by mixing the I.S. solution with analytical reference solutions or a sample solution directly in the spray chamber. It has been demonstrated that the combination of FBMN and In as an internal standard leads to better accuracy for determining As in a lake sediment.

Vortex-assisted dispersive liquid–liquid microextraction for the determination of molybdenum in plants by inductively coupled plasma optical emission spectrometry

A new procedure for determining trace concentrations of Mo in plants combining dispersive liquid–liquid microextraction and inductively coupled plasma optical emission spectrometry is proposed here. An automated discrete sample introduction system using a Flow Blurring® multiple nebulizer (FBMN) and a solenoid valve were used to insert an organic rich phase into the plasma. The experimental conditions for the microextraction procedure were: 0.5% m v−1 of 8-hydroxyquinoline, pH 3.6 and 50 μL of 1-undecanol as the extractant. A limit of detection of the instrument of 0.20 μg L−1, a limit of detection of the procedure of 17 μg kg−1 and an enhancement factor of 246 were obtained employing the developed procedure. Three certified reference materials were used to check the accuracy and no significant differences were found at the 95% confidence level between certified and determined values. The developed procedure was also successfully applied to the determination of Mo in three different varieties of sugar cane leaves samples.