Cleanup foodstuffs

Multi-residue Method S19 of the DFG Manual,including Cieanup Procedure Xll-6 (gel-chromatographic cleanup), has been used successfully in many laboratories because of its broad applicability for the gas-chromatographic determination of pesticide residues in foodstuffs. DFG method S19 is also included in the respective European Standards. Subsequently, a modification of the extraction and partition step has been implemented. The modified method requires less experimental effort and eliminates the use of dichloromethane, which is an undesirable solvent for toxicological and ecological reasons. As the results from validation studies demonstrate,... 

Liquid-liquid extractions (13) permit the elimination of slightly polar molecules (phospholipids, fatty acids, etc) that may interfere in the HPLC determination of carbohydrates. Hence, for solid foodstuffs, some form of extraction will be required prior to the chromatographic procedure, and even in liquid food samples it may be necessary to modify the solvent composition of the liquid phase to make it compatible with the HPLC eluent. The major role of the extracting solvent is to obtain all of the carbohydrate present in the food sample dissolved in a liquid phase, be it for direct injection into the chromatograph or for subsequent cleanup stages prior to HPLC. 

B Zimmerli, R Dick. Determination of ochratoxin A at the ppt level in human blood, serum, milk and some foodstuffs by high-performance liquid chromatography with enhanced fluorescence detection and immunoaffinity column cleanup methodology and Swiss data. J Chrom B 666 85-99,1995. 

The Extrelut cleanup method is suitable for most foodstuffs, such as cheese, yogurt, and other samples that tend to form emulsions during extraction. The prepacked or refilled Extrelut column in a plastic tube consists of a wide-pore kieselgel column. A sample is homogenized in 0.5 N sulfuric acid, diluted with water, and applied onto the Extrelut column for at least 15 min. The absorbed preservatives are eluted with a chloroform - isopropanol (9 1) mixture, and the elu-ate is collected and evaporated carefully nearly to dryness. The last few milliliters of solvent are removed with a gentle flow of nitrogen to prevent substantial losses of BA and SA, which have relatively high vapor pressures. The residue is transferred with methanol into a 10-ml volumetric flask and diluted to volume with methanol. To speed up the dissolution, the use of an ultrasonic bath is recommended. The filtered extract is analyzed on a /zBondaPak Cl8 column, with a... 

OP), and carbamate pesticides are available as standard methods by the AO AC covering both nonfatty and fatty foods. These methods are based on solvent extraction and a variety of column chromatographic cleanup procedures with determination by GC using selective detectors. The International Dairy Federation has approved similar methods for OC and OP pesticide residues in milk and milk products. The AOAC have standard methods for specific pesticides or groups of pesticides that are approved for certain foodstuffs these methods involve colorimetric, spectrophotometric, or gas chromatographic determination. In the case of me-thylcarbamate pesticides, a liquid chromatographic method is approved. 

Spectroscopic, luminescence, turbidimetric, and electrochemical methods of detection have been combined with SIA for the successful determination of amino acids, sugars, and trace elements in matrices such as meats, vegetables, breads, wines, juices, and milks. Many of these methodologies required sample pretreatment and whilst most performed this in an offline manner there have been some reports of online sample cleanup. Microwave assisted digestion was performed in-line for the determination of phosphorous, calcium, magnesium, and iron in slurried foodstuffs, wine, milk, and soft drinks whilst gaseous diffusion allowed interference removal for the determination of urea in milk. 

The conventional trace analysis of pesticides involves extraction and cleanup steps (liquid-liquid partitioning and/or column cleanup). These time- and solvent-consuming procedures have been simplified lately (see Section II). The best methods take into account the nature of the samples to be analyzed e.g., fatty foods should be handled differently from nonfatty foodstuffs or plant matrices... 

Appropriate GLC procedures have also been used for the analysis of pure vitamins, their optical isomers, pharmaceuticals, and, rarely, even foods. The main disadvantage of this group of chromatographic methods seems to be the tedious and relatively time-consuming sample preparation (derivatization and/or cleanup procedures) prior to the GLC analysis. Nevertheless, the newly developed and introduced GC-MS techniques show that GLC is a sufficiently sensitive tool for the trace analysis of pantothenic acid, its higher homolog and other related compounds such as acyl-CoA, even in biological samples (serum, brain, foodstuffs). 

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