Nikolay Kovachev

Microwave-assisted cloud point extraction of Rh, Pd and Pt with 2-mercaptobenzothiazole as preconcentration procedure prior to ICP-MS analysis of pharmaceutical products

New approaches for acceleration of cloud point extraction of Rh, Pd and Pt by microwave and ultrasound irradiation have been investigated. 2-Mercaptobenzothiazole and Triton X-100 were used as ligand and non-ionic surfactant, respectively. Microwave irradiation substantially increased the procedure efficiency. In contrast no significant effect was observed when a micellar solution was treated with ultrasound energy. The acceleration of complex formation reactions by reducing agents (KI and SnCl2) has also been studied. The use of SnCl2 was a prerequisite for quantitative extraction of Rh. Since the extraction kinetics of platinum depends on its oxidation state and presence of Pd, the addition of SnCl2 equalized the platinum extraction behavior. For the first time the whole cloud point procedure was successively accomplished in a microwave system. 10 min of irradiation were sufficient for gravimetrical phase separation and quantitative extraction of platinum group metals. As a result the procedure time was shortened by a factor of 9 in comparison to conventional hot plate cloud point extraction. The surfactant-rich phase was analyzed after dilution with 1 M HCl by continuous nebulization to ICP-MS. Quantitative recoveries and good plasma tolerance were reported. Detection limits of 1 ng.l−1 (Rh), 5 ng.l−1 (Pd), and 6 ng.l−1 (Pt) were achieved regarding a preconcentration factor of 8. The microwave-assisted cloud point extraction has been successfully applied for simultaneous determination of trace amounts of platinum group metals in pharmaceutical products (Tritace, Vivace, Laprilen and Enalapril).

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.

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%.

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.

Analysis of metals and phosphorus in biodiesel B100 from different feedstock using a Flow Blurring® multinebulizer in inductively coupled plasma-optical emission spectrometry.

A simple and fast method for determining the content of Na, K, Ca, Mg, P, and 20 heavy metals in biodiesel samples with inductively coupled plasma optical emission spectrometry (ICP OES) using a two-nozzle Flow Blurring(®) multinebulizer prototype and on-line internal standard calibration, are proposed. The biodiesel samples were produced from different feedstock such as sunflower, corn, soybean and grape seed oils, via a base catalyst transesterification. The analysis was carried out without any sample pretreatment. The standards and samples were introduced through one of the multinebulizer nozzles, while the aqueous solution containing yttrium as an internal standard was introduced through the second nozzle. Thus, the spectral interferences were compensated and the formation of carbon deposits on the ICP torch was prevented. The determination coefficients (R(2)) were greater than 0.99 for the studied analytes, in the range 0.21-14.75 mg kg(-1). Short-term and long-term precisions were estimated as relative standard deviation. These were acceptable, their values being lower than 10%. The LOQ for major components such as Ca, K, Mg, Na, and P, were within a range between 4.9 ng g(-1) for Mg (279.553 nm) and 531.1 ng g(-1) for Na (588.995 nm), and for the other 20 minor components they were within a range between 1.1 ng g(-1) for Ba (455.403 nm) and 2913.9 ng g(-1) for Pb (220.353 nm). Recovery values ranged between 95% and 106%.

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.

Microwave-assisted solid phase extraction prior to ICP-MS determination of Pd and Pt in environmental and biological samples

A sensitive and selective microwave-assisted solid phase extraction procedure coupled to inductively coupled plasma-mass spectrometry (ICP-MS) is proposed for palladium (Pd) and platinum (Pt) quantification in environmental and biological samples. Pd and Pt were quantitatively retained on commercial thioureido propyl functionalised silica gel packed inside a home-made glass microcolumn, and later eluted with 0.5% thiourea solution under microwave irradiation, followed by ICP-MS determination. The main variables affecting the procedural stages (i.e., sorption and desorption) and ICP-MS determination were optimised. The best conditions found were: (a) sorption: sample acidity, 1 M HCl; sample flow rate, 3 mL min−1; (b) desorption: microwave radiation, power 800 W; eluent concentration, 0.5% thiourea; eluent flow rate, 0.5 mL min−1; (c) ICP-MS determination: nebuliser feeding, free aspiration (0.3 mL min−1); internal standard, Rh (5 µg L−1). Analyte recoveries were higher than 90% and concentration factors up to 90 and 92 were achieved for Pd and Pt, respectively. Depending on the conditions, the methodological limits of detection were down to 0.2 ng L−1 for both analytes and repeatability, expressed as RSD%, varied between 1.3 and 11.0%. A method selectivity evaluation showed that most of the ICP-MS interferents were either quantitatively separated or more than 86% eliminated, except for Cu (elimination efficiency around 30%). Finally, the method was successfully used to determine Pd in certified reference materials (i.e. human urine and serum) and Pd and Pt in PM10 airborne particulate matter fractions.