Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection for the determination of anabolic steroids and related compounds in nutritional supplements.

A simple and effective analytical method for the determination of anabolic steroids and related compounds in nutritional supplements is reported. Target compounds are extracted with ethyl acetate, crude extract is purified using dispersive solid-phase extraction (SPE) with primary secondary amine (PSA) as sorbent, and finally they are identified and quantified as underivatized compounds using two-dimensional gas chromatography with time-of-flight mass spectrometric detection (GCxGC-TOF MS). This method was validated for 25 steroids in two types of commercially available solid nutritional supplements: protein concentrate and creatine monohydrate. Repeatability expressed as the relative standard deviation of analyte concentration ranged from 4.1 to 20.5%. Recoveries between 70.0 and 122.6% were obtained for the target compounds except for oxymetholone in protein concentrate where the recovery was low as a result of strong interactions with PSA. Excellent linearity was obtained for six-point calibration with regression coefficients of 0.997-1.000 for all compounds. The limits of quantification ranged from 0.007 to 0.114 mg kg(-1). For a monitoring programme of 48 samples of nutritional supplements, three were positive. Nandrolone, testosterone, dehydroepiandrosterone (DHEA), 5alpha-androstan-3,17-dione, 19-norandrostendione and progesterone were found in positive samples at concentrations between 0.022 and 0.398 mg kg(-1).

Determination of polychlorinated biphenyls in biotic matrices using gas chromatography--microwave-induced plasma atomic emission spectrometry.

Basic parameters associated with practical application of gas chromatography coupled with microwave-induced plasma atomic emission spectrometric detection GC-MIP-AED in the determination of seven "indicator" polychlorinated biphenyls (PCBs) in biotic matrices were evaluated. The detection limit for chlorine (Cl-479) was found to be 0.54 pg/s. Under the conditions used for sample analysis (1 microliters of purified extract injected into the GC-MIP-AED system represented 2.5 mg of original fat), this value corresponded approximately to 0.15 mg/kg of the respective congeners in fat. The detector response was linear within the tested range of 0.5-10 ng of each injected PCB. The relative standard deviation of repeated injections for the lowest concentration level of 0.5 ng of PCB per injection ranged between 10.5 and 34.4% depending on the chlorine content of the individual analytes. The results demonstrate a high selectivity of chlorine detection. Carbon (C-496) chromatograms recorded simultaneously demonstrated the efficiency of the clean-up step used. Quantitative results (analytes at levels of 0.1-1 mg/kg) obtained with the atomic emission detector did not differ significantly from those recorded with a conventional electron-capture detector.

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

Difficulties 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.

Analysis of chlorophenoxy acids and other acidic contaminants in food crops.

Several chlorophenoxy acids and chlorinated phenols were determined by means of gas chromatography in contaminated samples of cereals. Extraction of plant matrix with acetone/water mixture followed by alkaline hydrolysis was proved to be suitable for isolation of both free and conjugated residues. The use of pentafluorobenzyl bromide for volatilization of analytes, despite of enhanced ECD response, cannot be recommended for routine analysis. Methylation with either methanol/sulphuric acid or methanol/BF3 reagent can substitute diazomethane-based esterification procedure. Mass fragmentography provided the highest selectivity of detection, moreover good sensitivity--5 ppb--was achieved in this way. Even methyl derivatives of monochlorinated analytes could be, contrary to GC/ECD analysis, quantitated at this level.

Gas chromatographic determination of diquat and paraquat in crops.

A sensitive and reproducible gas chromatographic procedure for the determination of diquat and paraquat in potatoes and rapeseed was developed. The volatilization of analytes was carried out via their hydrogenation with sodium borohydride-nickel(II) chloride. After their isolation from the reaction mixture, the derivatives of bipiperidine were separated on a column packed with Apiezon L plus potassium hydroxide. Comparable detection limits (0.005 mg/kg) were achieved with a nitrogen-phosphorus detector and by mass fragmentography, however, the latter method was preferred for analyses of rapeseed extracts owing to its higher selectivity.