Kateřina Holadová

Matrix-induced effects: a critical point in the gas chromatographic analysis of pesticide residues

Abstract The influence of several experimental factors related to the enhanced gas chromatographic responses yielding apparent recoveries of pesticide residues greater than 100% was investigated. Optimisation of a gel permeation chromatographic clean-up step with respect to the trueness and precision of generated data was performed. An increase of relative detector response (100%=response of analyte in pure solvent solution) was evidenced to be dependent both on the concentration of the analyte and the character of the matrix: pronounced matrix-induced effects were observed particularly in orange and wheat extracts at low concentration levels of analytes (especially for GC–electron-capture detection analysis of certain pesticides). As soon as the splitless injector became contaminated after injection of large series of matrix-containing samples, a decrease of relative responses of pesticides, largely below 100%, was experienced. Although troublesome compounds tending to give matrix-induced effects can be identified, and increased recoveries may be tentatively predicted, poor accuracy of generated data can be presumed as long as quantitation is not based on a standard prepared in blank matrix extract to compensate for matrix-induced effects.

A Comparison of Different Ways of Sample Preparation for the Determination of Phthalic Acid Esters in Water and Plant Matrices

Abstract Different methods for the isolation of phthalates from water were tested and compared with the aim of evaluating the risk of secondary contamination of sample and to reach good values of recovery for six tested esters (i.e. dimethyl-, diethyl-, di-n-butyl-, benzylbutyl-, bis(2-ethylhexyl)- and di-n-octyl phthalates). Classic liquid-liquid extraction with hexane gave good recoveries for all six esters (70 - 100%, spiking level 20 μg/1), but the increased relative standard deviations document problems with cross contamination. Micro extraction with iso-octane is suitable for the determination of benzylbutyl-, bis(2-ethylhexyl)- and di-n-octyl phthalates even at low levels of contamination (1 μg/1) and also for di-n-butyl phthalate at higher levels (tens of μg/1). The detection limits for these esters ranged from 0.01 to 0.05 μg/1. The recovery of more polar phthalates (dimethyl-, diethyl phthalate) is very low. Solid phase extraction on octadecyl reverse phase with ethyl acetate as elution solvent ...

OCCURRENCE OF PERSISTENT ORGANOCHLORINE CONTAMINANTS IN HUMAN MILK COLLECTED IN SEVERAL REGIONS OF CZECH REPUBLIC

The concentrations of persistent organochlorine contaminants including polychlorinated biphenyls (PCBs), DDT (its isomers and metabolites), hexachlorobenzene (HCB) and isomers of hexachlorocyclohexane (HCH) have been determined in human milk samples from the three regions in the Czech Republic. Results were generated by the congener-specific analyses (two-dimensional high resolution gas chromatography). The results are compared with the similar studies from other industrial countries (Norway, Great Britain, the Netherlands and Germany). Typical patterns of major PCBs contained in analyzed breast milk samples are presented. PCB No.153 was the dominant congener in all the samples. A good correlation was found between the sum of PCBs and PCB No.:153 (r = 0.99), constitutes approx. 30% of calculated PCBs content.

Microwave-assisted solvent extraction — a new method for isolation of polynuclear aromatic hydrocarbons from plants

Abstract The efficiencies of polynuclear aromatic hydrocarbons (PAHs) transfer into various solvents from pollen and spruce needles by two alternative extraction techniques — sonication and a microwave enhanced process — were compared. The effects of extraction mixture composition, temperature, time and number of repeated extractions on the recoveries were studied. Microwave extraction — realised at 140°C for 20 min with n-hexane–acetone (3:2, v/v) as the extraction solvent — was identified as the most effective extraction procedure for isolation of PAHs from biotic matrices (pollen and spruce needles). Gel permeation chromatography on Bio-Beads S-X3 with chloroform as a mobile phase was used for clean-up of extracts. HPLC with programmable fluorescence detection was employed for identification and quantification of analytes.

Comparison of two clean-up principles for determination of trichothecenes in grain extract

Two clean-up principles for the multi-determination of seven trichothecene toxins, deoxynivalenol, nivalenol, diacetoxyscirpenol, fusarenon-X, T-2 tetraol, HT-2 toxin and T-2 toxin in wheat extract are described. For clean-up of acetonitrile–water (84:16, v/v) extract either gel permeation chromatography (Bio-Beads S-X3 gel) or solid-phase extraction (combination of Florisil and C18-silica gel SPE cartridges or a Romer Labs. MycoSep 225 column) were used. The MycoSep 225 column was chosen as the best alternative for clean-up of grain samples. Recovery of this procedure was tested on certified material. Derivatisation of analytes prior to the final determinative step was carried out by trifluoroacetic acid anhydride. Trifluoroacyl derivatives of the trichothecenes were separated by high-resolution capillary gas chromatography with electron-capture detection.

Determination of trichothecenes in cereals

An effective method for the determination of seven trichothecenes-deoxynivalenol (DON), nivalenol (NIV), T-2 tetraol (T-24), fusarenon-X (FUS-X), diacetoxyscirpenol (DAS), T-2 toxin (T-2), HT-2 toxin (HT-2) in cereals is presented. Gel permeation chromatography on Bio-Beads S-X3 was used for clean-up of acetonitrile-methanol extract. GC-ECD was used for identification and quantification of trifluoroacetylated trichothecenes. The limit of quantitation for the method was in the range 40-200 micrograms/kg. Recoveries at a spiking level of 2 mg/kg ranged from 76 to 100%.

Analysis of PCBs in Biotic Matrices by Two-Dimensional GC-ECD

The suitability of three GC-ECD systems for the separation of a model mixture containing various congeners of PCBs together with persistent chlorinated aromatics (pesticides and their metabolites, industrial chemicals) was tested. Analyses were performed on two parallel capillaries, the stationary phase of one of them was always in routine practice very common 5% phenyl-methylpolysiloxane, the second one was either 50% phenylmethylpolysiloxane or 7% phenyl-7% cyanopropyl-methylpolysiloxane. The number of unresolved (coeluted) analytes was significantly reduced in these systems and thus unbiased quantitation of PCBs and other components used for regulation was possible. The utilization of this type of multidimensional chromatography for rapid and reliable analysis of real samples (fish oil, human fat) was documented.

Application of Supercritical fluid Extraction For Analysis of Organophosphates in Cereals

Abstract Application of supercritical fluid extraction (SFE) utilizing pure carbon dioxide for selective isolation of organophosphates from contaminated cereals has been tested. At the beginning of the experiments the extractability of added standards from an empty extraction vessel (thimble) and from various materials such as filter paper, sand, Celite and anhydrous sodium sulfate was tested to estimate the behavior of organophosphates. Further method development was carried out using a spiked sample of flour, which was analyzed within the proficiency testing for organophosphorus pesticides analysis (round 7) organized by Food Analysis Performance Assessment Scheme (FAPAS, MAFF-UK). Comparison of the SFE method with a classical method currently employed for sample preparation (i.e. extraction with acetone/methanol mixture followed by gel permeation chromatographic clean up) showed advantages of the SFE technique such as simplification of the sample preparation step and thereby significant speeding up of ...

Determination of PCBs in fatty tissues by means of several detection techniques

ZusammenfassungDas Problem mit der Harmonisierung der analytischen Verfahren und der geringen Vergleichbarkeit der Angaben ist ein Hauptgrund der Verspätung in der neuen Legislative für PCB in Lebensmitteln in der Tschechischen Republik. Die Arbeit beschreibt die möglichen Fehler (Falsch-positive Fehler), die durch die routinierte Bestimmung von PCB-Rückständen in Fettanteilen der biologischen Materialien auftreten können. Es werden die gaschromatographischen Bedingungen beschrieben, unter denen die Interferenzen, wie z. B. Phthalaten und chlorierten Pesticiden, von Stoffen abgetrennt werden können. Die Vorteile und Nachteile der Methoden GC-ECD, GC-MS und GC-AED werden diskutiert. Die verschiedenen für die Kalkulation des PCB-Gehaltes angewendeten Annäherungen werden miteinander verglichen.AbstractDifficulties with harmonization of analytical procedures and consequently poor comparability of generated data represent in the Czech Republic the main reason for the delay in issuing of updated legislation for polychlorobiphenyls (PCBs) in foodstuffs. This study draws attention to possible errors (overestimations) that can occur during routine determination of these residues in the fat portion of biotic matrices. We demonstrate the gas Chromatographic (GC) conditions under which interfering contaminants such as phthalates and/or chlorinated pesticides can be separated from analytes. Discussion is focused on the advantages and drawbacks of GC with an electron capture detector, GC mass spectrometry and GC with an atomic emission detector. Various approaches used for calculation of PCBs contents are compared.

The comparison of elution profiles of polychlorinated biphenyls and fats in various gel permeation chromatographic systems

Abstract An optimisation of gel permeation chromatography (GPC) is presented for separation of polychlorinated biphenyls (PCBs) from fats. The results of testing of Bio Beads S-X3 gel eluted with different mobile phases (mixtures of chloroform and cyclohexane) are evaluated with respect to the use of GPC as a single, rapid and efficient clean-up technique suitable for routine analyses of PCBs. Relations between theoretical assumptions and achieved results are discussed. Although the elution profiles for individual PCB congeners differed, various tested fats eluted in similar volumes. Several of investigated systems can be used for isolation of PCBs from fats. Nevertheless, for practical reasons a system with chloroform as a single mobile phase, in which PCBs were eluted in the lowest volume as a narrow fraction, has been chosen.