Single-residue methods

Pesticide Analytical Manual, Food and Dmg Administration, Rockville, Md., Vol. I, 1990, and Vol. II, 1989. Includes multiresidue methods used by U.S. FDA to routinely check foods for pesticide residues, and single residue methods for certain pesticides not detected by any of the multiresidue methods. 

The FDA coordinates the method trial process for non-NADA methods. The sample requirements are the same as for the NADA trials. Non-Federal laboratories such as contract laboratories and State laboratories can participate in the process. For a single-residue method, the minimum numbers of samples and laboratories are the same as for NADA method trials. 

On the other hand, single-residue methods developed by the applicants give basic information about appropriate cleanup steps and specific determination procedures. In addition, not many laboratories other than those from the applicants are able to test the real solvent extraction efficiency. The reason is that extraction studies need radio-labeled incurred residues instead of fortified samples. Hence enforcement methods provided by the manufacturers accelerate the development of methods which meet the needs of (official) food control laboratories. 

Occasionally, an additional derivatization step would allow the application of a multi-residue approach. Provided that this derivatization can be done after the standard cleanup, applicants are invited to present those methods. In most cases, for monitoring purposes a supplementary derivatization will be much simpler than a completely separate single-residue method. 

Most modern methods of analysis to determine pesticide residues in food commodities, whether a multi-residue method (MRM) or a single-residue method (SRM), can be broken down into three or four basic steps sample processing, sample extraction, extract cleanup (optional) and instrumental determination. 

The methods most frequently used to monitor for pesticides are high-performance liquid chromatography (HPLC) and gas chromatography (GC) (14,15). On the other hand, multiresidue analytical techniques are preferred to single-residue methods, because multiresidue methods provide the capability to determine different pesticide residues in a single analysis (12,16-18). As... 

Increasing demand for screening our environment for pesticide residues has generated a need for more efficient residue methods. Multiresidue methods, or those which measure several compounds at once, are generally more efficient than single residue methods in satisfying these needs. A mass spectrometer can be used as a universal selective detector for multiresidue analysis in different sample matrices, since it is generally blind to interferences present in the sample. In addition to selectivity, use of a mass spectrometer offers structure confirmation, and in many cases, can eliminate sample cleanup steps. 

Part 1 contains mass spectromctric El data for confirmation of results. Part 2 deals with the updated cleanup methods, including SPE with various types of sorbents. Part 3 describes some single residue methods (SRMs), The pertinent methods for OP.s and CMs arc method 261-378-370 for methomyl, carbendazim, and thiophenate-methyl method 378 for car-bendazim method 658-344 for cabosulfan and carbofuran method 522 for fonofus method 405 for glyphosate and method 441 for oxamyl. Part 4 deals with MRMs, and a pertinent method for OPs and CMs is method S8, an updated version of method S19. Method S25 is for methyl CMs. Thin-layer diromaiographic methods using the automated multiple development technique are described in part 6. 

EU-Community Reference Laboratory for Pesticide Analysis using Single Residue Methods hosted at the Chemisches und Veterinaruntersuchimgsamt Stuttgart Schaflandstr. 3/2 70736 Fellbach Germany... 

Single residue methods or SRMs, are used by FDA when no general or selective MRM is available. These methods are usually capable of determining the level and identity of the residue of only one pesticide from a limited number of commodities. SRMs are usually submitted during the registration process to meet EPA s requirement for an analytical method capable of determining compliance with the requested tolerance. 

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