National Institute for Occupational Safety and Health

“ Whenever the identity of an analyte is uncertain, confirmation may be achieved by analysis on a column of different polarity. If primary analysis was performed using a nonpolar or weakly polar column e.g., ( DB-1 or DB-5) , confirmation should be accomplished by reanalyzing on a polar columne.g., ( DB-17 or DB-1701) . See Table 4 for approximate retention times for each column type. For positive identification of high-level analytes (1 to 10 μg/mL or greater) , GC/MS may be used. Table 5 gives notes on the analytical characteristics of the chlorinated and organonitrogen herbicides. ”

“ Among those observed are plasticizers (e.g., dibutyl phthalate) , methylated fatty acids (give negative responses) , phenols, and antioxidants and other additives (e.g., BHT) , any volatile or semivolatile halogenated or nitrated organic, organophosphorous compounds, and other pesticides. Agricultural spray additives can presentserious interferences. Such additives include solvents, emulsifiers, wetting agents, breakdown products, and fertilizers (e.g., fatty acids and urea) . ”

“ Inject sample aliquot manually using solvent flush technique or with autosampler. See Table 4 for retention times of selected analytes. NOTE: If peak height is greater than the range of the working standards, dilute the sample with isopropanol and reanalyze. Apply the appropriate dilution factor in calculations. 9. Measure peak height of analyte.
CALCULATIONS: 10. 11.
Determine the concentration, μg/mL, (corrected for DE) of the respective herbicide found on the patch sample (Cp) and in the media blank (Bb) from the calibration graph. ”