On-line preparation of microsamples prior to CE

An experimental setup is presented here for the automated analysis of microsamples, based on the on-line coupling of a capillary SPE module and a CE unit using a two-position six-port valve, an open-closed valve to isolate electrically the sample preparation from the CE unit and a "T" interface. A C18 trapping microcolumn (dimensions 2.5 cm x 100 microm id x 360 microm od) was used for the SPE step. The utility of the proposed experimental setup was demonstrated by applying it to the determination of quinolone antibiotics in serum microsamples, which was efficiently carried out in less than 20 min (4 min for protein denaturation and 15 min for analytes preconcentration and CE-UV separation-determination). A complete optimization study was performed for preconcentration and cleanup of quinolones, the coupling of sample preparation module to the CE unit and electrophoretic separation of quinolones. A preconcentration factor of 10.4 was achieved. The volume injected with the proposed method was 125 nL versus 160 nL introduced by hydrodynamic injection. The volume required for the analysis was 2 microL, which makes the proposed experimental setup very useful for the analysis of microsamples in fields of current interest such as metabolomics or proteomics.     

Determination of naturally radioactive elements in construction materials by means of gammaspectroscopy,track registration techniques and neutron activation analysis

Five types of Cuban concretes and their main components (mineral aggregates and cements) were analyzed for uranium, thorium, radium, potassium and radon (²²⁰Rn,²²²Rn) using -spectroscopy, track registration methods and neutron activation analysis. Comparative evaluation of different concretes, aggregates and two types of cements concerning their natural radioactivity is presented.     

Upgrade of recommended nuclear cross section data base for production of therapeutic radionuclides

Journal of Radioanalytical and Nuclear Chemistry - The IAEA Nuclear Data Section has coordinated several actions to setup and improve a database for recommended cross sections and nuclear decay...     

Far-infrared giant dipole resonances in neutral quantum dots

A resonance behaviour of the far-infrared absorption probability at a frequency N^1/4 is predicted for clusters of N electron–hole pairs (2N110) confined in disk-shaped quantum dots. For radially symmetric dots, the absorption is dominated by a giant dipole resonance, which accounts for more than 98% of the energy-weighted photoabsorption sum rule.     

Continuous flow system for lead determination by faas in spirituous beverages with solid phase extraction and on-line copper removal

A continuous flow system for the determination of lead in home made spirituous beverages was developed. The determination was based on the formation of a neutral chelate of the element with ammonium pyrrolidine dithiocarbamate, its adsorption onto a minicolumn packed with sodium faujasite type Y synthetic zeolite, followed by elution with methyl isobutyl ketone and determination by flame atomic absorption spectrometry. Ethanol and copper interfere strongly in the determination and therefore, must be separated prior to the analysis. Copper is removed by precipitation with rubeanic acid, while ethanol is eliminated by rotaevaporation. Sample solutions containing Pb²⁺ in the concentration range from 5 to 120 μg l⁻¹ at pH 2.5 could be analyzed, by using a preconcentration time of 3 min. Preconcentration factors from 80 to 140 were achieved for a sample volume of 6 ml and the detection limit varied from 1.4 to 3.5 μg l⁻¹, depending on the matrix composition. The relative standard deviations for 60 μg l⁻¹ Pb was 3.2% (n = 10) and the recovery of spikes (20, 40, 60 and 80 μg l⁻¹) added to the samples was estimated within 92–105% range, suggesting that lead can be quantitatively determined in such samples. Determining lead in several samples by an alternative technique further checked the accuracy. Finally, the concentrations of Pb²⁺ determined in 28 samples of Venezuelan spirituous beverages were in 12.6–370.0 μg l⁻¹ range, depending on the fermenting material based on different mixtures of agave, raw sugar cane and white sugar.     

Higher Landau levels contribution to the energy of interacting electrons in a quantum dot

Properly regularized second-order degenerate perturbation theory is applied to compute the contribution of higher Landau levels to the low-energy spectrum of interacting electrons in a disk-shaped quantum dot. At “filling factor” near , this contribution proves to be larger than energy differences between states with different spin polarizations. After checking convergence of the method in small systems, we show results for a 12-electron quantum dot, a system which is hardly tractable by means of exact diagonalization techniques.     

Automated solid-phase extraction for concentration and clean-up of female steroid hormones prior to liquid chromatography-electrospray ionization-tandem mass spectrometry: an approach to lipidomics

A method for determination of free and glucuronide-conjugated female steroid hormones in urine at the pgmL(-1) level is here presented. For this purpose, a dual approach with or without beta-glucuronidase hydrolysis has been developed to succeed in this analysis. The target analytes were two progestogens - progesterone and pregnenolone - and three endogenous estrogens - estradiol, estriol and estrone. Separation and detection were carried out by liquid chromatography electrospray ionization and tandem mass spectrometry (LC-ESI-MS-MS) with a triple quadrupole (qQq) mass detector. The determination step was optimized by multiple reaction monitoring for highly selective identification and sensitive quantification of female hormones in a complex sample such as human urine. As these compounds are present in urine at very low concentration (ngmL(-1) level), a preconcentration and clean-up step by solid-phase extraction was automatically carried out prior to the chromatographic step in order to improve the sensitivity of the method. This sample pretreatment was performed using a lab-on-valve (LOV) manifold which provided preconcentration factors ranging from 59.1 to 72.3 for 10mL urine. The detection and quantification limits were in the ranges 1.8-18pg and 6-61pg on-column, respectively, with precision values from 1.93 to 10.99%, expressed as relative standard deviation. These results enable to conclude the suitability of the LOV-LC-qQq approach for determination of the lipidomic profiling of the main female steroid hormones in a difficult matrix as human urine. The method can be potentially applied to the clinical and other metabolomic areas.     

Ultrasonic enhancement of leaching and in situ derivatization of haloacetic acids in vegetable foods prior to gas chromatography-electron capture detection

With a new oxidant for post-column chemical derivation, a novel approach was developed for the determination of Malachite Green (MG) and Leucomalachite Green (LMG) in fish by high-performance liquid chromatography (HPLC). A C(8) column was used for separation, and elution was performed with a pH 2.5 phosphate buffer (0.02molL(-1)) containing 40% acetonitrile. When the eluate was combined with 3.0x10(-4)molL(-1) iodine solution, LMG was converted to MG and detected at 618nm after post-column derivatization. The recoveries of MG and LMG were ranged from 67.3% to 73.9% and 84.7% to 92.1%, respectively, which were obtained by measuring the amount of MG and LMG in the samples with solvent calibration curve. The decision limit (CCalpha) and the detection capability (CCbeta) obtained for MG and LMG were in the range of 0.10-0.17 and 0.13-0.23mugkg(-1) in grass carp, shrimp and shellfish. This method appeared suitable for the control of MG and LMG residues in aquatic products.     

Ultrasound-assisted extraction and silylation prior to gas chromatography-mass spectrometry for the characterization of the triterpenic fraction in olive leaves

One of the most important fractions of bioactive compounds isolated from plants is that formed by triterpenic compounds, which have proved to be anti-bacterial, antifungal, anti-inflammatory, cytotoxic and anti-tumour. A method for leaching and determination of the main triterpenic compounds (oleanolic acid, ursolic acid, uvaol, erythrodiol) in olive leaves is here presented. Quantitative leaching was obtained with ethanol as leachant and ultrasonic assistance for 20 min, a very short time as compared to conventional procedures by maceration, which usually requires at least 5 h. After isolation, an aliquot of the ethanolic leachate was silylated to derivatize the analytes prior to gas chromatography-mass spectrometry analysis. Silylation reaction was also assisted with ultrasound in order to accelerate the derivatization step, which only required 5 min--a dramatic shortening in comparison to conventional silylation of terpenic compounds with derivatization times ranging from 30 min to 3 h. The proposed method has demonstrated to be useful for isolation and characterization of the triterpenic fraction in plants; the capability of ultrasound to assist sample preparation (acceleration of leaching and derivatization) has also been proved.     

Ultrasound in analytical chemistry

Ultrasound is a type of energy which can help analytical chemists in almost all their laboratory tasks, from cleaning to detection. A generic view of the different steps which can be assisted by ultrasound is given here. These steps include preliminary operations usually not considered in most analytical methods (e.g. cleaning, degassing, and atomization), sample preparation being the main area of application. In sample preparation ultrasound is used to assist solid-sample treatment (e.g. digestion, leaching, slurry formation) and liquid-sample preparation (e.g. liquid–liquid extraction, emulsification, homogenization) or to promote heterogeneous sample treatment (e.g. filtration, aggregation, dissolution of solids, crystallization, precipitation, defoaming, degassing). Detection techniques based on use of ultrasonic radiation, the principles on which they are based, responses, and the quantities measured are also discussed.