Tatjana Vasiljević

Determination of multiple pharmaceutical classes in surface and ground waters by liquid chromatography-ion trap-tandem mass spectrometry.

This paper describes development, optimization and application of analytical method for determination and reliable confirmation of nineteen pharmaceuticals from different therapeutic classes (antibiotics--beta-lactams, cephalosporines, sulfonamides, macrolides and tetracyclines; benzodiazepines; antiepileptics and analgoantipyretics) in surface and ground waters at ng l(-1) levels. Water samples were prepared using solid-phase extraction and extracts were analyzed by liquid chromatography-ion trap-tandem mass spectrometry with electrospray ionization in both positive and negative ionization mode. The efficiency of ten different SPE cartridges to extract diverse compounds from water was tested. The pH-value of the water sample, the volume of elution solvent and the sample volume were optimized. Matrix effect, especially pronounced for cephalexin and metamizole, was eliminated using matrix-matched standards. It was determined that extraction should be performed at pH approximately 7.5, i.e. without pH adjustment, and at pH 3, depending on the analyte. Azithromycin, doxycycline and acetylsalicylic acid must be extracted in acidic environment, whereas extraction of paracetamol, ampicillin, erythromycin and metamizole should be performed without pH adjustment. Repeatability of the method was generally lower than 20%. The estimated limits of detection were in the range from 0.15 to 12.46 ng l(-1). The method was applied to 26 water samples for monitoring of selected drug residues. Results revealed the presence of carbamazepine (80% of water samples), azithromycin (23%), as well as trimethoprim and paracetamol (both 15%). The most striking was the false positive signal of diclofenac in every analyzed water sample. Confirmation of the positive results was performed by repeated injection of the positive sample extracts using confirmatory method with additional transitions.

Determination of pesticides in surface and ground waters by liquid chromatography-electrospray-tandem mass spectrometry.

The sensitive multiresidual analytical method for simultaneous analysis of 14 most commonly used agricultural pesticides in Serbia was developed and optimized. The selected insecticides, fungicides and herbicides belong to seven chemical classes (organophosphates, neonicotinoids, carbamates, diacylhydrazines, benzimidazoles, triazines and phenylureas). The method was based on solid-phase extraction followed by liquid chromatography-tandem mass spectrometry. The following parameters that may affect the SPE procedure efficiency were optimized: the sorbent type in combination with different elution solvents, the sample pH and the sample volume. For each pesticide, MS(n) analysis was performed and distinctive ions and transitions were selected for identification and quantification, as well as for confirmation purposes. External matrix-matched calibration method was used to eliminate variable matrix effect and ensure precise quantification. Good recoveries (72-129%), and low limits of detection (0.4-5.5 ng L(-1)) and quantification (1.1-18.2 ng L(-1)) were achieved for all selected pesticides. The developed and optimized method was successfully applied in the analysis of several river waters, as well as ground waters in Serbia, influenced by agriculture. The most frequently detected pesticide was carbendazim. Dimethoate, carbofuran and propazine were also found in the investigated samples.

Monomer elution from nanohybrid and ormocer-based composites cured with different light sources

OBJECTIVES To study monomer elution from four resin-based composites (RBCs) cured with different light sources. METHODS Twenty-eight premolars were randomly allocated to four groups. Standardized cavities were prepared and restored with a nanohybrid (Filtek Supreme XT or Tetric EvoCeram), an ormocer (Admira) or a microhybrid RBC (Filtek Z250) which served as control. Buccal restorations were cured with a halogen and oral restorations with an LED light-curing unit. Elution of diurethane dimethacrylate (UDMA), Bisphenol A diglycidylether methacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) was analyzed using high-performance liquid chromatography (HPLC) 1h to 28 days post-immersion in 75% ethanol. Data were analyzed using multivariate and repeated measures analysis of variance (α = 0.05). RESULTS The greatest elution of UDMA and BisGMA occurred from Tetric EvoCeram and the least from Filtek Z250 (p < 0.05). LED and halogen light-curing units gave similar results for all RBCs (p > 0.05) except Tetric EvoCeram which showed greater elution for the LED unit (p < 0.05). TEGDMA was below the limit of quantification. HEMA eluted in similar concentrations from Filtek Supreme and Tetric EvoCeram (p > 0.05). SIGNIFICANCE The two nanohybrid RBCs eluted more cross-linking monomers than the ormocer and the control microhybrid RBC. Continuous elution over 28 days indicates that RBCs act as a chronic source of monomers in clinical conditions. Light source may affect monomer elution since differences were found for one out of four RBCs. Mathematical models for elution kinetics of UDMA and BisGMA indicated two elution mechanisms.

Optimization of artificial neural network for retention modeling in high-performance liquid chromatography

An artificial neural network (ANN) model for the prediction of retention times in high-performance liquid chromatography (HPLC) was developed and optimized. A three-layer feed-forward ANN has been used to model retention behavior of nine phenols as a function of mobile phase composition (methanol-acetic acid mobile phase). The number of hidden layer nodes, number of iteration steps and the number of experimental data points used for training set were optimized. By using a relatively small amount of experimental data (25 experimental data points in the training set), a very accurate prediction of the retention (percentage normalized differences between the predicted and the experimental data less than 0.6%) was obtained. It was shown that the prediction ability of ANN model linearly decreased with the reduction of number of experiments for the training data set. The results obtained demonstrate that ANN offers a straightforward way for retention modeling in isocratic HPLC separation of a complex mixture of compounds widely different in pK(a) and logK(ow) values.

Determination of carbendazim residues in fruit juices by liquid chromatography-tandem mass spectrometry

In this paper a rapid optimized method for routine analysis of carbendazim residues in fruit juices is reported. The procedure is based on matrix solid-phase dispersion (MSPD) with diatomaceous earth and analysis of the extract by liquid chromatography-tandem mass spectrometry, with electrospray ionization (LC–ESI-MS/MS). In the method optimization, finding of the optimal pH for the extraction of carbendazim from juice was particularly critical. Significant matrix effects were observed, but could be eliminated using matrix-matched standards. High recoveries (82–102%), good repeatability (RSD ≤ 12%) and low limits of detection (0.03 ng ml−1) and quantification (0.1 ng ml−1) were achieved with this method.

Pharmaceutical residues in the Danube River Basin in Serbia - a two-year survey.

Pharmaceuticals are emerging contaminants with damaging effects to the environment and human health. Their presence in surface and especially groundwaters is regarded as detrimental, as they can ultimately reach drinking water. The aim of this work was to monitor pharmaceutical contamination of the Danube River and its tributaries in Serbia, and to assess the potential of their passing through all natural filtrations and reaching the groundwater. A total of 70 surface and groundwater samples was collected at 38 sampling sites at the Danube in Serbia. They were taken in five sampling campaigns performed in summer and autumn of 2009 and winter, spring and autumn of 2010. Samples were analyzed using a previously developed method which includes solid-phase extraction followed by liquid chromatography-tandem mass spectrometry.

Methods for monitoring of pesticide residues in water: current status and recent trends

An overview of analytical methods currently used for the determination of pesticide residues in water samples is presented. As liquid chromatography and gas chromatography, coupled to mass spectrometry, are considered to be the most appropriate techniques for determination of pesticides in environmental waters, the most recent developments and applications in this field are discussed, as well as the extraction procedures employed for analyte isolation and preconcentration.

Formation of oxygen complexes in controlled atmosphere at surface of doped glassy carbon

The effects of boron and phosphorus incorporation in phenolic resin precursor to the oxidation resistance of glassy carbon have been studied. In order to reveal the nature and composition of the oxygen complexes formed at the surface of doped glassy carbon, under controlled atmosphere, the surface of the samples was cleaned under vacuum up to 1273 K. Specific functional groups, subsequently formed under dry CO2 or O2 atmosphere on the surface of boron-doped and phosphorus-doped glassy carbon samples, were examined using the temperature-programmed desorption method combined with mass spectrometric analysis. Characterization of surface properties of undoped and doped samples has shown that in the presence of either boron or phosphorus heteroatoms, a lower amount of oxygen complexes formed after CO2 exposure, while, typically, higher amount of oxygen complexes formed after O2 exposure. It has been concluded that the surface of undoped glassy carbon has a greater affinity towards CO2, while in the presence of either boron or phosphorus heteroatoms, the glassy carbon surface affinity becomes greater towards O2, under experimental conditions.