The Analysis of Pesticides & Related Compounds Using Mass Spectrometry
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APPENDICES The analysis of pesticides & related compounds using Mass Spectrometry John P. G. Wilkins 3 December 2015 Appendix I – Compilation of EI+ MS Data for Pesticides & related compounds Pesticides & Chemical Warfare (CW) agents .................................... 5 - 318 GC Contaminants & Artefacts ........................................................ 319 - 322 Supplementary accurate mass data for selected pesticides ........... 323 - 350 Appendix II – Eight Peak Index of MS Data in Appendix I ........................... 1 - 26 Appendix III – Comprehensive Pesticide MW Index ...................................... 1 - 30 Appendix - Page 1 Introduction to the Appendices The purpose of these data compilations is to provide a convenient source of data for analysts involved in the identification of pesticides using mass spectrometry. Data for related compounds, such as metabolites and degradation products produced during analysis, have been included when relevant. Where direct GC-MS techniques are unlikely to be of use, alternative analytical strategies are sometimes suggested. The MS data in Appendices I and II are presented in two ways: alphabetically by compound name in Appendix I (with data for commonly encountered GC contaminants at the end); and by most intense ion, in a style similar to that of The Eight Peak Index of Mass Spectra (MSDC, 1983), in Appendix II, in order to facilitate the identification of unknowns, without recourse to dedicated MS search software. Where possible, mass spectra were obtained following GC separation. When this was not possible, direct insertion (DI) introduction into the mass spectrometer was used. Most of the data are the averaged results of several acquisitions, generated at different times and (in many cases) on different mass spectrometers. Two magnetic sector instruments were used by the author to generate the data; a VG7070 (for packed column GC introduction) and a JEOL DX300 (for capillary GC introduction). An ion source temperature of 200°C and electron ionisation energy of 70eV was used throughout. Spectra were recorded from m/z 20 to beyond the expected molecular ion region. Although the mass spectra obtained for most compounds on different instruments are fairly consistent, some variation in the data, even when obtained under apparently similar conditions, is unavoidable. This fact must be borne in mind when using the data in this compilation. Many spectra reported elsewhere, especially those obtained using quadrupole instruments of early design, exhibit exaggerated intensities for low mass ions, at the expense of the more characteristic and diagnostically useful high mass ions. Comparison of the data obtained for many pesticides in this collection with those obtained using bench-top GC-MS instruments (a Finnigan-MAT ITD800 [ion-trap] and a Hewlett-Packard 5971A Mass Selective Detector quadrupole) demonstrated good overall agreement. Compounds prone to degradation reactions, such as dehydration or reduction, tend to be most susceptible to mass spectral irreproducibility. For these compounds, e.g. alcohols, epoxides, sulphoxides and nitro-compounds, the design, temperature and state of cleanliness of the ion source are critical factors in determining the appearance of their mass spectra. An interesting example is the behaviour of methiocarb sulphoxide. Data obtained on the two different GC-MS systems used are included in order to illustrate this effect. Poor reproducibility of mass spectra may also be observed Appendix - Page 2 with compounds that undergo many energetically similar MS fragmentations, e.g. endrin. These compounds produce many ionic species, none of which is particularly abundant, so the overall appearance of the mass spectrum can be particularly sensitive to factors which affect the fragmentation pathways. Appendix I has a supplement which contains accurate mass MS data for 25 pesticides, generated at Cardiff using GCT MS. These mass spectra had proved difficult to interpret. Appendix III contains mass-ordered, accurate mass, molecular weight information for nearly 2,000 pesticides, for use in the identification of unknown compounds. Appendix - Page 3 Appendix - Page 4 How to use the Appendices Data are presented in three sections: Appendix I Pesticides and chemical warfare agents are listed in alphabetical order of their common name, with related metabolites and significant degradation products. The name of the compound is followed by the empirical formula and the nominal molecular ion mass or masses (not the average molecular weight) and the observed EI+ MS relative intensity/intensities in brackets. On the next line are the theoretical molecular ion accurate masses and their relative abundances. The molecular structure is given. This is followed by pesticide chemical class (organophosphorus, carbamate, organochlorine etc.) and pesticide type (insecticide, acaricide, fungicide, herbicide etc.), plus typical applications (veterinary, public health, food production etc.). The online Compendium of Pesticide Common Names (Wood 2015) is a convenient source of information. The regulatory approval status is given, plus the acute oral LD50 (median lethal dose) for the rat, as an indication of acute mammalian toxicity. These data derive mainly from the online Pesticide Properties DataBase (PPDB 2015). Supplementary analytical information, concerning amenability to GC, isomerism or susceptibility to degradation etc., is included when relevant. Relative retention times on packed and/or capillary column GC are expressed, where determined, as n-alkane equivalent retention time: KI(SE-30/OV-17/OV-210) = n for packed column GC data and KI(CPSil5/19) = n for capillary GC data. The eight most intense ions in the electron impact mass spectrum are given (with the molecular ion(s), if present, underlined) and their relative intensities presented beneath (generally rounded to the nearest 5%, if >5%). Additional data for diagnostic or significant high mass ions are given, plus tentative empirical formula assignments and accurate mass data, in decreasing mass order. N.B. The empirical formula assignments are generally based on rational interpretation of the nominal mass data and isotope fingerprints. The ion formulae and accurate mass assignments are predictions, Appendix - Page 5 not experimental data (apart from the 25 pesticides described in the supplementary section, whose spectra were obtained using OA TOF MS at Cardiff School of Chemistry). Result of comparison with reported data, e.g. with the NIST WebBook (NIST 2015), is included when possible. Links to specific mass spectra, and critical appraisals, are provided. A collection of data for frequently encountered GC contaminants is included at the end of Part I, and these data are also included in Appendix II (in which contaminant names appear in italics to distinguish them from pesticides and related compounds). Supplementary accurate mass MS data for 25 selected pesticides are also included. These data were collected in order to investigate and confirm the empirical formula assignments. Appendix II - where the mass spectral data are sorted by most abundant ion, compiled in “Eight Peak Index” format, to facilitate the identification of unidentified spectra without resort to computerised systems. As such spectra will generally have been obtained following gas chromatographic separation, those compounds that are not readily amenable to GC are distinguished (by an asterisk). For spectra in which the base peak is at low mass, and which therefore may be difficult to observe (either because it is outside the acquired range or because it is obscured by solvent/co-extractive interference), a second entry has been made under the most intense ion in the spectrum observed at high mass (>m/z 100). Such entries are readily distinguished by the appearance in the relative intensity list of the 100% value in the second column rather than the first. Some spectra exhibit no ions of any significant intensity of m/z greater than 100 (particularly those whose molecular weight is less than 100), but the only pesticides in this category in this collection were 2-aminobutane, aminotriazole, binapacryl, dinocap, metaldehyde, methyl bromide, methyl isothiocyanate and thiodicarb. Appendix III - is intended to facilitate the identification of pesticides by their molecular weights. It contains mass-ordered, accurate mass, molecular weight information for pesticides described in the Pesticide Manual (Worthing 1990). Happy Hunting! John Wilkins Appendix - Page 6 Appendix I. The compilation of EI+ MS data Abamectin / Avermectin C48H72O14 M:872(0%) Theoretical molecular ion: m/z 872.4922 (100%), m/z 873.49556 (51.9%), m/z 874.49892 (13.2%), m/z 874.49645 (2.9%), m/z 875.50227 (2.2%), m/z 875.49981 (1.5%). Average MW: 873.077 Macrocyclic lactone disaccharide insecticide, acaricide and nematicide. Originally isolated from the Japanese soil bacterium Streptomyces avermitilis. Abamectin is a 4:1 mixture of avermectin B1a (C48H72O14, mw 872) and B1b (C47H70O14, mw 858). It is not amenable to GC analysis. Residues may be determined by HPLC/ESP+ MS/MS. See e.g. European Community Reference Laboratory method: http://www.crl-pesticides.eu/library/docs/srm/meth_Abamectin_CrlSrm.PDF Electrospray+ MS/MS ions: Avermectin B1a: m/z 890.5 567.4, m/z 890.5 305.1, m/z 891.5 568.1 Avermectin B1b: m/z876.6 553.3, m/z 876.6 291.2 For plant commodities, the total residue is defined as the sum of avermectin B1a + avermectin B1b, plus the photo-isomers 8,9-Z-avermectin