National Institute of Standards and Technology, Gaithersburg, Maryland GC-MS determination of environmentally important phenols and their thio-analogs as chemical modification products Levan A. Megutnishvili, Nino G. Todua, Stephen E. Stein, Anzor I. Mikaia National Institute of Standards and Technology, Gaithersburg, Maryland OVERVIEW RESULTS AND DISCUSSION Novelty Initial compound Derivative [M-R] + [M-R-CH3] + Guaiacol TMS 181 (26) 166 (100) TBDMS 181 (78) 5-Methylguaiacol 195 (27) 180 (100) 195 (76) 4-Fluoroguaiacol 199 (24) 184 (100) 199 (49) 4-Bromoguaiacol 259/261 (32/32) 244/246 (100/100) 259/261 (63/63) Syringol 211 (41) 196 (100) 211 (83) 2,5-Dimethoxyphenol 211 (11) 211 (39) Isovanillyl alcohol 1-TMS 209 (22) 194 (100) 2-TMS 283 (23) 268 (41) 1-TBDMS 209 (90) 2-TBDMS 325 (100) 310 (3) Vanillol 211 (33) 283 (43) 268 (58) 211 (70) 310 (.2) Isovanillin o-Vanillin 209 (100) 194 (32) 5-Aminoguaiacol O-TMS 196 (15) 181 (100) 268 (40) 253 (100) O-TBDMS 196 (11) 310 (15) 295 (100) 5-Nitroguaiacol 226 (75) 211 (100) 226 (100) 211 (91) Normetadrenaline O,O’-TMS 312 (3) 297 (100) 3-TMS 384 (5) 369 (.1) 4-TMS 456 (5) 441 (.4) 3-TBDMS 468 (3) 453 (0) 2-Methoxy-3-methyl-1,4-benzenediol 283 (3) 268 (100) 325 (36) 310 (100) A GC-MS method for the determination of substituted phenols is developed. It includes an employment of preliminary derivatization procedures. Trifluoroacetates Introduction. Phenols are largely present in plants and agro industrial byproducts, and they represent secondary metabolites in foods and natural health products. The food processing industries generate considerable quantities of various phenolic byproducts and the oil industry uses various phenols for production of oil field additives, fragrances, stabilizers and antioxidants for fuels and plastics. Identification of alkylphenols and differentiation of isomers in this series by GC-MS can be achieved with an employment of suitable chemical modification methods. A comparative study of trialkylsilyl and perfluoroacyl derivatives of tert-butylphenols has been conducted. EXPERIMENTAL Methods Chemicals. Trialkylsilyl and perfluoroacyl derivatives were prepared for poly-substituted phenols (I-III). The initial chemicals, derivatization agents and solvents were commercially available. Micro-synthesis. Well established reactions of the phenolic oxygen with bis(tert-butyldimethylsilyl) and bis(trimethylsilyl)trifluoroacetamides are employed for the synthesis of corresponding ethers. For micro- synthesis of perfluoroacyl phenol derivatives the reactions with trifluoroacetic, pentafluoropropionic and heptafluorobutyric anhydrides are utilized. The reactions of phenolic hydroxyls with methyl, ethyl, n-propyl and isopropyl chloroformates are used for the acquisition of corresponding alkoxycarbonyl derivatives. Instrumentation. EI mass spectra were recorded on GC/MS systems with quadrupole analyzers (ionization energy 70 eV and ion source temperature 230 oC). Separation was achieved on a fused silica capillary columns (15m, 0.25mm i.d.; non-polar stationary liquid phase: polymethylsiloxane + 5% phenyl groups) and (60m, 0.25mm i.d.; non-polar stationary liquid phase: 100% dimethyl polysiloxane) with programming oven temperatures from 60 oC to 270 oC (40 min) at a rate of 10 oC/min and 60 oC to 270 oC (20 min) at a rate of 15 oC/min ; the injection temperature was 270oC. The loss of water molecule from [M-CH3]+ ions is characteristic for trifluoroacetates of phenols containing tert-butyl at position 2. This decomposition direction is also typical for pentafluoropropionates and heptafluorobutyrates of ortho-substituted isopropyl-, sec-butyl- and neopentyl-phenols. Fig. 1 Mass spectra of ortho (A) and para (B) isomers of trifluoroacetyl derivatives of 4-tert-butylbenzenethiol Trialkylsilyl esters CONCLUSIONS Trialkylsilylation and perfluoroacylation of phenols yield corresponding derivatization products with unique mass spectral characteristics. The spectra of derivatives allow reliable differentiation of ortho- phenols due to the presence of dominant peaks of diagnostically important ions. Consecutive elimination of an alkyl radical and a water molecule is characteristic for trifluoroacetyl, pentafluoropropionyl and heptafluorobutyryl phenols containing branched alkyl substituents at ortho position. Successive loss of two alkyl radicals in violation of the ‘even electron rule‘ is specific for the vicinal trimethylsilyl and tert-butyldimethylsilyl esters of methoxyphenols. This process appears universal for TMS and TBDMS derivatives of 2-methoxyphenols, and results in the formation of dominant peaks in the spectra. The exceptions are tri- and tetra-trialkylsilyl derivatives of normetadrenaline , and dialkylsilyl derivatives of isovanillyl and vanillyl alcohols due to more favorable fragmentation processes. Fig. 2 Mass spectra of trimethylsilyl derivatives of 2,6-dimethoxyphenol (A), 2,6-dimethoxyphenol (B), 3,4-dimethoxyphenol (C), 2,5-dimethoxyphenol (D)