Pesticide Analytical Manual Vol. I SECTION 301 301: MULTICLASS MRMS: CONCEPT AND APPLICATION Pesticide multiresidue methods (MRMs) are capable of simultaneously determin- ing more than one residue in a single analysis; this multiresidue capability is provided by a glC or HPLC determinative step that separates residues from one another before detection. The mRM concept is raised to a higher dimension when a single extract is examined with more than one chromatographic determinative step, each provid overage of residues in a different class, e. g, chlorinated hydrocarbons, organophosphates, and carbamates, PAM I refers to these broad scope methods as"multiclass MRMs. A multiclass MRM is potentially capable of determining any residue extracted by its extraction step; PAM I multiclass MRMs extract residues with organic solvents known to remove most nonionic residues from food commodities. each determi- native step in a multiclass MRM provides coverage for a particular group of resi- dues in the extract, and each cleanup step is designed to purify the extract suffi- ciently to permit accurate determination. A multiclass MRM scheme can be ex- panded continually as new technologies are developed and adapted This introductory section presents a recommended approach to application of multiclass MRMs and background information with which any analyst using such methods should be familiar 301 A: RECOMMENDED APPLICATON OF MULTICLASS MRMS Whenever a sample of unknown pesticide treatment history is analyzed, and no residue(s)is targeted, a multiclass MRM should be used to provide the broadest coverage of potential residues; Figure 301-a displays the recommended multiclass MRM for each commodity category. The more detailed scheme provided with each method(Figures 302-a, 303-a, 304-adirects the user to recommended module(s) for particular commodities. The user may choose as many or as few of these modules as time and resources permit; once residues are extracted, each determinative step extends coverage of the analysis to additional compounds Follow these directions to maximize coverage of residues without sacrificing quan- titative accuracy For broadest coverage of potential residues, examine the uncleaned extract by determinative steps that are sufficiently selective to permit residue identification and quantitation in the presence of co-extractives Following determination by selective determinative steps, clean up the extract as needed to permit additional determinations; these may in- clude determinative steps designed for specific groups of residues(e.g from Chapter 4 methods) When a peak appears in the chromatogram of the extract, use the fol- owing PAM I tables to tentatively identify the residue and to choose the additional analyses needed for optimum identification, quantitation, and/ or confirmation: 1)PESTDATA (Appendix I). Compare GLC relative retention time(rrt of the residue to lists of rrts on several common glc columns 301-1Pesticide Analytical Manual Vol. I SECTION 301 301–1 Transmittal No. 94-1 (1/94) Form FDA 2905a (6/92) 301: MULTICLASS MRMS: CONCEPT AND APPLICATION Pesticide multiresidue methods (MRMs) are capable of simultaneously determin￾ing more than one residue in a single analysis; this multiresidue capability is provided by a GLC or HPLC determinative step that separates residues from one another before detection. The MRM concept is raised to a higher dimension when a single extract is examined with more than one chromatographic determinative step, each providing coverage of residues in a different class, e.g., chlorinated hydrocarbons, organophosphates, and carbamates. PAM I refers to these broad scope methods as “multiclass MRMs.” A multiclass MRM is potentially capable of determining any residue extracted by its extraction step; PAM I multiclass MRMs extract residues with organic solvents known to remove most nonionic residues from food commodities. Each determi￾native step in a multiclass MRM provides coverage for a particular group of resi￾dues in the extract, and each cleanup step is designed to purify the extract suffi￾ciently to permit accurate determination. A multiclass MRM scheme can be ex￾panded continually as new technologies are developed and adapted. This introductory section presents a recommended approach to application of multiclass MRMs and background information with which any analyst using such methods should be familiar. 301 A: RECOMMENDED APPLICATION OF MULTICLASS MRMS Whenever a sample of unknown pesticide treatment history is analyzed, and no residue(s) is targeted, a multiclass MRM should be used to provide the broadest coverage of potential residues; Figure 301-a displays the recommended multiclass MRM for each commodity category. The more detailed scheme provided with each method (Figures 302-a, 303-a, 304-a) directs the user to recommended module(s) for particular commodities. The user may choose as many or as few of these modules as time and resources permit; once residues are extracted, each determinative step extends coverage of the analysis to additional compounds. Follow these directions to maximize coverage of residues without sacrificing quan￾titative accuracy: • For broadest coverage of potential residues, examine the uncleaned extract by determinative steps that are sufficiently selective to permit residue identification and quantitation in the presence of co-extractives. • Following determination by selective determinative steps, clean up the extract as needed to permit additional determinations; these may in￾clude determinative steps designed for specific groups of residues (e.g., from Chapter 4 methods). • When a peak appears in the chromatogram of the extract, use the fol￾lowing PAM I tables to tentatively identify the residue and to choose the additional analyses needed for optimum identification, quantitation, and/ or confirmation: 1) PESTDATA (Appendix I). Compare GLC relative retention time (rrt) of the residue to lists of rrts on several common GLC columns