SECTION 501 Pesticide Analytical Manual Vol I Cleanup Solvent extraction of pesticide residues also extracts food constituents ("co-extrac tives")from the sample Cleanup steps are included in residue analytical method to remove co-extractives that can interfere in the determinative step of the analysi or cause damage to the column and/or detector. For many years, predominant use of the nonselective electron capture(EC)detec- tor caused justifiable concern about potential detector response to nonpesticidal co-extractives. In addition, documented cases in which sample co-extractives dam aged GLC columns and caused subsequent breakdown of injected residues sup ported the need for extensive cleanup prior to GlC determination [3] More recently, several factors have reduced emphasis on cleanup. The more selec tive glC detectors now in use have decreased the likelihood that sample or re- agent artifacts might be mistaken for pesticide residues. In addition, use of cap llary columns, which are more efficient than equivalent packed columns, result in increased peak height response for the same amount of analyte. The amount of extract injected can thus be reduced without changing the level of quantitation and this in turn reduces the likelihood of damage to the GlC system. Inlet liners and adapters used with capillary columns(Section 502 C)also provide the column with some degree of protection from damage caused by co-extractives. Finally, there are many incentives to perform more analyses with the same or fewer re- sources and to minimize the volume of solvents that must be purchased and disposed of. These factors contribute to a trend toward performing only minimal cleanup of sample extracts during routine surveillance analyses, with the intention of cleanup with applicable step(s)if an extract is found to contain interfering materials Despite these compelling reasons to reduce cleanup glc systems that are not protected from co-extractives deteriorate faster than those into which only cleaned up extracts are injected. The column and/or detector may be damaged by injec tion of insufficiently cleaned up samples, especially when the method and the chromatograph are used repeatedly. Such detrimental effects can occur even when the chromatogram appears to be clean enough for residue identification and measurement. Experience with a variety of sample types should make the analyst aware of these occurrences Detector response to sample co-extractives(artifacts)is still possible even with element-selective detectors. Although a selective detector is less likely to to chemically unrelated artifacts than the nonselective EC detector, artifacts con- analysis. This occurs most often with nitrogen-selective detectors because of the number of nitrogenous chemicals in foods, but it can occur with any detector Likelihood of interferences and potential for mistaken identity increase with de creasIng cleanup. Insufficiently clean extracts may also affect quantitative accuracy when determin- ing residues that are polar or otherwise subject to adsorption by active sites in a GLC column. Such chemicals usually exhibit poor chromatography when standard solutions are injected, because adsorption delays or inhibits the chemical during its passage through the column. Peak tailing and/or changes in retention times are caused by adsorption. The net effect is an apparently diminished detector 501-4 Transmittal No. 94-1(1/94]501–4 Transmittal No. 94-1 (1/94) Form FDA 2905a (6/92) SECTION 501 Pesticide Analytical Manual Vol. I Cleanup Solvent extraction of pesticide residues also extracts food constituents (“co-extrac￾tives”) from the sample. Cleanup steps are included in residue analytical methods to remove co-extractives that can interfere in the determinative step of the analysis or cause damage to the column and/or detector. For many years, predominant use of the nonselective electron capture (EC) detec￾tor caused justifiable concern about potential detector response to nonpesticidal co-extractives. In addition, documented cases in which sample co-extractives dam￾aged GLC columns and caused subsequent breakdown of injected residues sup￾ported the need for extensive cleanup prior to GLC determination [3]. More recently, several factors have reduced emphasis on cleanup. The more selec￾tive GLC detectors now in use have decreased the likelihood that sample or re￾agent artifacts might be mistaken for pesticide residues. In addition, use of cap￾illary columns, which are more efficient than equivalent packed columns, result in increased peak height response for the same amount of analyte. The amount of extract injected can thus be reduced without changing the level of quantitation, and this in turn reduces the likelihood of damage to the GLC system. Inlet liners and adapters used with capillary columns (Section 502 C) also provide the column with some degree of protection from damage caused by co-extractives. Finally, there are many incentives to perform more analyses with the same or fewer re￾sources and to minimize the volume of solvents that must be purchased and disposed of. These factors contribute to a trend toward performing only minimal cleanup of sample extracts during routine surveillance analyses, with the intention of cleanup with applicable step(s) if an extract is found to contain interfering materials. Despite these compelling reasons to reduce cleanup, GLC systems that are not protected from co-extractives deteriorate faster than those into which only cleaned up extracts are injected. The column and/or detector may be damaged by injec￾tion of insufficiently cleaned up samples, especially when the method and the chromatograph are used repeatedly. Such detrimental effects can occur even when the chromatogram appears to be clean enough for residue identification and measurement. Experience with a variety of sample types should make the analyst aware of these occurrences. Detector response to sample co-extractives (artifacts) is still possible even with element-selective detectors. Although a selective detector is less likely to respond to chemically unrelated artifacts than the nonselective EC detector, artifacts con￾taining an element to which the detector responds can still interfere with residue analysis. This occurs most often with nitrogen-selective detectors because of the number of nitrogenous chemicals in foods, but it can occur with any detector. Likelihood of interferences and potential for mistaken identity increase with de￾creasing cleanup. Insufficiently clean extracts may also affect quantitative accuracy when determin￾ing residues that are polar or otherwise subject to adsorption by active sites in a GLC column. Such chemicals usually exhibit poor chromatography when standard solutions are injected, because adsorption delays or inhibits the chemical during its passage through the column. Peak tailing and/or changes in retention times are caused by adsorption. The net effect is an apparently diminished detector