European standardization of methods for pesticide residue analysis in foods--current status.

The aim of this paper is to inform all scientists working in pesticide residue analysis on the contents, size and background of European standards (ENs) in this area. These ENs were established by a Technical Committee (TC 275, of the European Committee for Standardization (CEN, and each CEN member country is obliged to implement them as national standards. EN 1528:1996 comprises eight methods for the multiresidue determination of organochlorine pesticides and polychlorinated biphenyls (PCBs) in fatty foods. For non-fatty foods such as fruits and vegetables, EN 12 393:1998 provides five multi-residue methods. In addition, three methods for dithiocarbamate fungicides in EN 12 396: 1998/2000 and two methods for bromide residues in EN 13 191:2000 are already available. In this way, a valuable harmonization of methods across Europe is achieved which is useful for quality control in the food industry as well as in official food inspection.

A new parameter for checking the suitability of alpha-tocopherol standards.

The quality of an alpha-tocopherol standard can be checked easily by measuring the UV absorbance at minimum (255 nm, Amin) and maximum (292 nm, Amax) wavelengths in n-hexane. If the quotient Amin/Amax exceeds 0.18, the standard contains less than 90% alpha-tocopherol and the determination at 292 nm will yield inaccurate results.

Solid phase extraction for the confirmation of results in polar pesticides residue analysis by HPTLC.

HPTLC is a convenient method for confirming the presence and identification of pesticide residues following gas chromatographic analysis of sample solutions obtained by clean-up according to the Deutsche Forschungsgemeinschaft multiresidue method S 19. For several crops, however, the polar eluates 4 and 5 obtained from the small silica gel column are abounding with co-extractives which interfere with HPTLC determination and also with GLC in some cases. They are effectively removed by solid phase extraction on a small aminopropyl cartridge, using a tertbutyl methyl ether/methanol (99 + 1) mixture as the eluant. The recoveries for 28 polar pesticides were not adversely affected.

Polychlorinated biphenyl residues in food and human milk: determination of co-planar and mono-ortho substituted congeners.

An analytical method is described for determining the residues of coplanar as well as mono-ortho substituted PCB congeners both exhibiting toxicological relevance, in foods of animal origin and in human milk. The unsophisticated procedure, convenient for routine analyses, includes the extraction of lipids, clean-up steps using liquid/liquid partition and column chromatography, fractionation of the congeners using HPLC on a special carbon column with an optimal gradient elution, and capillary column gas chromatography with electron capture or mass spectrometric detection. As preliminary results indicate, the low-chlorinated PCB technical products contribute more to the actual contamination of environment and foods than has been estimated so far. Obviously the co-planar congeners are accumulated during the food chain in a portion different from that found for the other congeners.

[HPTLC for the confirmation of results in the analysis of pesticide residues]. / HPTLC zur Befundsicherung bei der Rückstandsanalyse von Pflanzenschutzmitteln.

HPTLC is an effective method for confirming gas-chromatographic results for insecticide and fungicide residues in sample solutions obtained by clean-up of fruit and vegetable extracts according to the Deutsche Forschungsgemeinschaft multiresidue method S 19. This study describes the possible interference caused by co-extractives from some crops rich in typical components, and gives the best operating conditions for separating and detecting the residues by HPTLC on silica gel and C18 reversed-phase material. The routine limit of determination was 0.01-0.05 mg/kg in most cases.

Determination of coplanar polychlorinated biphenyl congener residues in food using HPLC fractionation.

An analytical method is described for determining the residues of coplanar PCB congeners exhibiting toxicological relevance, in foods of animal origin and human milk. The unsophisticated procedure, convenient for routine analyses, includes extraction and saponification of lipids, isolation of the unsaponifiable matter and its cleanup on a small silica gel column, fractionation using HPLC on a special carbon column and gas-chromatographic analysis with capillary columns and electron capture detection (ECD).

[Identification and quantitative determination of currently important plant protectants by HPTLC]. / Identifizierung und quantitative Bestimmung aktueller Pflanzenschutzmittel durch HPTLC.

This systematic study describes the determination of approximately 150 pesticides (mainly insecticides and fungicides) on high-performance thin-layer chromatography (HPTLC) layers, using modern techniques for spotting and evaluation. Standardized mobile phases and reagents for visualization form the basis for the confirmation of gas-chromatographic results by HPTLC. The very high sensitivity of cholinesterase inhibition can be utilized only on plates coated with silica gel. Several other currently important pesticides can be separated on C-18 reversed phase layers and detected using silver nitrate-UV irradiation or chlorine-o-tolidine. Computer-assisted densitometric evaluation allows direct quantitative determination of the pesticides.

[Residue analysis of pyrethroid insecticides in cereal grains, milled fractions and bread]. / Rückstandsanalyse von Pyrethroid-Insecticiden in Getreide, Mahlerzeugnissen und Brot.

A procedure is described for the residual analysis of eight pyrethroid insecticides at levels of 2-5 micrograms/kg. Residues are extracted from cereal grains, flour or bread with a mixture of acetonitrile/water (2 + 1) and are partitioned into petroleum ether. Clean-up is performed by gel permeation chromatography on Bio-Beads S-X3 and an additional Florisil column. Electron capture gas liquid chromatography on a non-polar SE-30 capillary column separates the isomers of the compounds. Under the conditions used in the experiments with cyfluthrin, cypermethrin, deltamethrin, fenvalerate, and permethrin, the compound levels in rye and wheat did not decrease significantly. Losses during milling and baking were small. Consequently, pyrethroid insecticides remain effective in grain stored over a long period of time. However, considerable residues result in the milled fractions as well as in different types of bread.

[Analytical method for residues of methylcarbamate insecticides in plant foods]. / Analysenmethode für Rückstände von Methylcarbamat-Insecticiden in pflanzlichen Lebensmitteln.

An analytical procedure is described for identification and quantitative determination of 15 methylcarbamate insecticides and 4 metabolites in fruits and vegetables. Clean-up includes ethyl acetate extraction, isolation of residues by a Sep-pak C18 disposable cartridge, elution with acetonitrile-water 1 + 1, and partitioning into dichloromethane. GLC is performed by using a well deactivated non-polar capillary column (e.g. SE-52, DB-1), splitless injection, and nitrogen-selective thermionic detection. Derivatisation with 2,4-dinitrofluorobenzene is suitable for confirmation. The limits of determination according to DFG criteria were in most cases as low as 0.005-0.01 mg/kg.

[Pesticide residues in foods ready for consumption]. / Beiträge zur Untersuchung verzehrsfertiger Nahrung auf Pesticidrückstände.

The well proven Specht cleanup procedure was miniaturized as far as possible and combined with glass capillary gas chromatography using on-column injection and ECD and thermionic detection (dual column gas chromatograph). The analysis of more than 50 consumption ready foods showed that detection and determination of relevant organochlorine and organophosphorous pesticide residues will be nearly always possible even in the low concentration range to be expected (1 micrograms/kg and less). Exceptions are only those foods exhibiting interfering peaks from coextractives already in the uncooked form. Cooking, frying, baking etc. often reduces the interfering components effectively.

[Quantitative determination of some thickeners in dairy products (author's transl)]. / Quantitative Bestimmung einiger Dickungsmittel in Milchprodukten.

An analytical method is described, by which nine polysaccharides used as thickeners for dairy products (locust bean gum, guar, gum arabic, tragacanth, arabinogalactan, carrageenan, furcellaran, agar, xanthan) can be identified in foods relatively rapidly and at the same time determined quantitatively. In this procedure interfering substances like fat, starch, proteins, sugars and salts are removed, the isolated polysaccharides are hydrolysed by trifluoroacetic acid and the monosaccharides resulting are measured by g.l.c. as aldonitrileacetates. The quantitative evaluation of the gas chromatograms is made by means of an internal standard and the content of thickener in the sample is calculated from one of the sugars. Recoveries of 80--90% with relative standard deviations of 5--10% were obtained when adding 0,05% of the thickeners to skim milk or 1--2% to mixtures of ice cream or pudding constituents.

[Residue analysis of plant material for organophosphorus pesticides with thioether groups including their sulphoxides and sulphones (author's transl)]. / Analysenmethode für Rückstände der Thioäther, Sulfoxide und Sulfone von Organophosphor-Pesticiden in Pflanzenmaterial.

Residue analysis of food of plant origin for organophosphorus pesticides containing thioether groups should include the corresponding sulphoxide and sulphone metabolites. A method is proposed, consisting of a simple clean-up step for extracts from plant material and subsequent oxidation with potassium permanganate. The sulphones formed are detected and determined by gas-liquid chromatography with alkali flame thermionic detection.