Eva Matisová

Carbon sorbents and their utilization for the preconcentration of organic pollutants in environmental samples

Abstract This review deals with carbon sorbents and their utilisation to trace analysis of organic pollutants in environmental samples. The first sections are devoted to the general characteristics of various kinds of carbon sorbents, carbon formation, the structure of carbon, their classification and characterisation (activated charcoal, graphitized carbon black, carbon molecular sieves and porous carbon). Information is given on the development of carbonaceous adsorbents, their characteristics and properties, development of various preconcentration techniques, off-line or on-line combination with the analytical measuring system (GC and HPLC), and the application of carbon sorbents to the enrichment of analytes is evaluated. The main use of carbon materials as a preconcentration/preseparation step has been in the sampling and trapping of volatile organic compounds (VOCs) from air and water matrices. An other field of application is the trapping of semi-volatile and non-volatile compounds and/or their separation into subclasses. According to the characteristics of the sampled components, carbon sorbents have been utilised in single-bed or multi-bed arrangement (combination of various carbon sorbents or combinations of carbon sorbents with other non-carbonaceous materials) to achieve quantitative trapping of trace components from environmental samples, followed by their desorption for subsequent identification and quantitation. Various achievements and problems, particularly in multicomponent-mixture analysis, are discussed. The physico-chemical properties of recently developed carbon adsorbents are superior compared to those of the “traditional” sorbent materials. Over the recent years much attention has been paid to the application of carbon sorbents for the on-site automated analysis and monitoring of trace pollutants.

Fast gas chromatography and its use in trace analysis

There is revived interest in the development and implementation of methods of faster GC. The paper summarises the advantages of faster GC analysis, general approaches to faster GC method development and practical aspects of fast gas chromatography with the utilisation of open tubular capillary columns with the stress on trace analysis. There are a number of ways to take the advantage of the improved speed of analysis by faster GC. Numerous options exist for pushing the speed of capillary gas chromatography (CGC) analysis. The scope of this paper is also to give an overview of the present state of faster GC instrumentation which is already available for trace analysis. The practicality of fast CGC is a function of sample preparation and the matrix interferences and how they affect the resultant resolution that may be achieved. Researchers have demonstrated the applicability of fast GC to trace and ultratrace analysis of volatile and semivolatile compounds also with narrow bore columns and difficult sample matrices (such as food, and soil extract). The main development of faster GC methods has been observed in the field of environmental analysis. Practical applications are presented. Both optimised sample preparation and experimental conditions for faster GC are the future perspective of trace analysis.

Analysis of pesticide residues by fast gas chromatography in combination with negative chemical ionization mass spectrometry

A combination of fast GC with narrow-bore column and bench top quadrupole mass spectrometer (MS) detector in negative chemical ionization (NCI) mode (with methane as reagent gas) is set up and utilized for the ultratrace analysis of 25 selected pesticides. The observed pesticides, belonging to the endocrine disrupting chemicals (EDCs), were from different chemical classes. A comparative study with electron impact (EI) ionization was also carried out (both techniques in selected ion monitoring (SIM) mode). The programmed temperature vaporizer (PTV) injector in solvent vent mode and narrow-bore column (15mx0.15mm I.D.x0.15microm film of 5% diphenyl 95% dimethylsiloxane stationary phase) were used for effective and fast separation. Heptachlor (HPT) as internal standard (I.S.) was applied for the comparison of results obtained from absolute and normalized peak areas. Non-fatty food matrices were investigated. Fruit (apple - matrix-matched standards; orange, strawberry, plum - real samples) and vegetable (lettuce - real sample) extracts were prepared by a quick and effective QuEChERS sample preparation technique. Very good results were obtained for the characterization of fast GC-NCI-MS method analysing EDCs pesticides. Analyte response was linear from 0.01 to 150microgkg(-1) with the R(2) values in the range from 0.9936 to 1.0000 (calculated from absolute peak areas) and from 0.9956 to 1.0000 (calculated from peak areas normalized to HPT). Instrument limits of detection (LODs) and quantification (LOQs) were found at pgmL(-1) level and for the majority of analytes were up to three orders of magnitude lower for NCI compared to EI mode. In both ionization modes, repeatability of measurements expressed as relative standard deviation (RSDs) was less than 10% which is in very good agreement with the criterion of European Union.

Fast gas chromatography for pesticide residues analysis

The importance of method development in the area of pesticide residues analysis is apparent from legislative requirements continuously decreasing the maximum acceptable concentration levels in food and water. This covers also contribution in the science in the field of ultra-trace analysis of organic pollutants in complex mixtures. Analysis time is one of the most important aspects that should be considered in the choice of analytical methods for routine application. With this fact, fast gas chromatography (GC) has acquired a real importance in the pesticide residue analysis. This paper provides an overview of fast GC methods for analysis of pesticide residues in variety of matrices at ultra-trace concentration levels. Emphasis is put on the development in the last 6 years.

Determination of tetracycline antibiotics in animal tissues of food-producing animals by high-performance liquid chromatography using solid-phase extraction

A high-performance liquid chromatographic (HPLC) method was developed for the determination of oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC) residues in bovine and porcine muscles. The method involved the homogenization of the sample in EDTA-McIlvaine buffer with added n-hexane and dichloromethane, centrifugation, precipitation of the supernatant using trichloroacetic acid and filtration. Preconcentration on Separcol SI C18 cartridges improved the clean-up and the recovery of tetracyclines that were separated by HPLC using the optimized mobile phase of 0.01 M oxalic acid-acetonitrile-methanol (45:35:20) on a Spherisorb ODS 2 column (250 x 4 mm I.D.). UV detection at 360 nm was applied with a detection limit of about 50 ng/g. The diode-array spectra confirmed the applicability of this method to the study of tetracycline residues in carcasses.

Comparison of negative chemical ionization and electron impact ionization in gas chromatography-mass spectrometry of endocrine disrupting pesticides.

The study of pesticide residues belonging to endocrine disrupting chemicals (EDCs) (23 analytes of different chemical classes--organochlorines, organophosphates, pyrethroids, dicarboximides, phtalamides, dinitroanilines, pyrazole, triazinone) in apple matrix with conventional capillary GC-NCI-MS (with methane as reagent gas) in comparison to EI ionization is presented. For sample preparation QuEChERS method was applied. The lowest calibration levels (LCLs) for all pesticides were determined in both modes. Calibration in the NCI mode was performed at the concentration levels from 0.1 to 500 microg kg(-1) (R(2) > 0.999) and for EI in the range from 5 to 500 microg kg(-1) (R(2) > 0.99). From LCLs the instrumental limits of detection (LODs) and quantification (LOQs) were calculated. Chemometric study of pesticide signals in two MS modes was performed. Repeatability of all measurements, expressed by the relative standard deviations of absolute peak areas was better than 10% for the majority of compounds. Significantly lower values were obtained for the NCI mode.

Application of porous carbon for solid-phase extraction of dicarboxyimide fungicide residues from wines in combination with high-resolution capillary gas chromatography and gas chromatography-mass spectrometry

Solid-phase extraction with a novel porous carbon sorbent CARB GR was used for the clean-up step of dicarboxyimide fungicides residues from variety of Slovak grape wines with subsequent capillary gas chromatography-flame ionization detection, -electron-capture detection (ECD) and -mass spectrometry-ion-trap detection (MS-ITD) analysis. Recovery was tested at various concentration levels of vinclozolin and iprodione in standard solutions (R = 80-97%, R.S.D. < or = 5). The value of recovery in spiked wines is dependent on concentration level (studied in the range of 5.9 micrograms/1-1.96 mg/l) and on the variety of wine (R = 80-96%; R.S.D. = 3-5%). Limits of quantitation (for sample volume 50 ml) were determined to be with GC-ECD for both fungicides in ppt range and with GC-MS-ITD in the multiple ion detection mode monitoring in ptt range for vinclozolin and ppb range for iprodione. Concentration levels of vinclozolin residues were determined in treated wines (with 0.1% Ronilan 50 WP) as well as iprodione residues (with 0.15% Rovral 50 WP) and a strong dependence on the protective term before the harvest is shown.

Liquid Phase Microextraction Techniques as a Sample Preparation Step for Analysis of Pesticide Residues in Food

Many conventional sample preparation methods are tedious, time-consuming, and use high volume of organic solvent. Minimized sample preparation methods, which use significantly smaller volume of organic solvent, represent an alternative to these methods. Three liquid phase microextraction (LPME) techniques: single drop microextraction, dispersive liquid-liquid microextraction, and hollow fiber liquid phase microextraction and a variety of its modifications are reviewed. Advantages and limitations are discussed. Extraction parameters influencing the extraction efficiency are evaluated. Applicability of LPME methods for pesticide residues analysis in various food matrices is overviewed. Determination of low-level pesticide residues was realized predominantly by chromatographic methods utilizing selective detectors. Powerful features of mass spectrometric detection for identification and determination of pesticide residues are pointed out.

Study on pesticide residues in apples, apple-based baby food, and their behaviour during processing using fast GC–MS multiresidue analysis

Food-processing experiments using apples were conducted to obtain more knowledge on the behaviour of pesticides during apple-based baby-food production. The residues were determined in raw material (apples), in intermediate products at different steps of the processing procedure (baby food production) and in final products (apple purée) using a rapid GC–MS method in combination with two different sample-preparation approaches. During 2 years of a monitoring programme, 84 analyses of apple samples and 102 of baby food sample apple purée intermediate and final product samples from baby food production were performed. A pesticide-residue search revealed that residues in fresh apples do not exceed the maximum residue limit for the adult population, but there were some positive findings concerning apples as baby food. The maximal pesticide concentration (fluquinconazole) found in apples was 0.099 mg kg−1. In the processed apple-based baby food the concentration of pesticide residues were mostly below 0.010 mg kg−1.

Use of a novel carbon sorbent for the adsorption of organic compounds from water

A porous carbon sorbent prepared by pyrolysis of cellulose in the presence of porogens was tested for the preconcentration of volatile organic pollutants (particularly hydrocarbons in the gasoline range) from water matrices by the purge-and-trap method. The trapped components were desorbed by carbon disulphide and measured by high-resolution capillary gas chromatography with on-column injection. The studied concentration range of individual hydrocarbons in water was 10 ppb-10 ppm. Drinking water, spring water and gasoline-contaminated water are given as examples of real sample analysis.