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Development and Validation of a multistep derivatization method for the determination of polar species in organic aerosol

Secondary organic aerosol (SOA) is a significant constituent of airborne fine particles. A multistep derivatization method was developed, optimized, and fully validated for the determination of organic compounds in the atmospheric aerosol with mono- and multi-functional species, with GC/MS. The first step includes the alkylation of the carbonyl (C=O) moieties using o-methylhydroxylamine hydrochloride as the derivatization reagent. The second step refers to the conversion of carboxylic acids to their methyl esters derivatives using trimethylsilyldiazomethane (TMSD)/methanol or BF3/methanol. Finally, alcohols are converted to trimethylsilyl ethers with N,O-bis(TMS)-trifluoroacetamide. The use of TMSD/methanol as the derivatization reagent in step 2 is preferred over BF3/methanol due to the higher average MS responses of the derivates of the first reagent. Additionally, BF3/MeOH was ineffective at converting low molecular weight dicarboxylic acids and species with 2-OH moieties. The derivatization procedure in stages 1 and 3 was optimized yielding the appropriate reaction temperature and time, while in stage 2 yielding the appropriate amounts of the derivatization reagents. The method, was validated for twenty-two compounds which are possible SOA tracers. Detection limits ranged from 0.35 ng m-3 to 2.8 ng m-3 And recoveries from 73.5% to 108%. This method was applied to field samples from rural and industrial areas. Approximately 70 organic compounds were identified and quantified with concentration levels ranging from below limits of detection to 42 ng m-3 .