ABSTRACT
ESI+ mode. e instrument conditions and the markers for qualitative identi cations and quanti cation for this group are shown in Tables 23.8 and 23.9, respectively.
Sample Preparation
If the sample is aqueous, take two aliquots of volume 1 L each and adjust the pH to 2 and 10, respectively, by adding an acid or a base. Isotopically stable labeled analogs of the selected analytes are then added into their respective acid and the base fractions. Such labeled analogs are employed in this method because many compounds are quanti ed by isotope dilution technique. e acid fraction of the sample is then stabilized by adding tetrasodium ethylenediamine tetraacetate dihydrate (Na4 · EDTA · 2H2O) into it. If the sample is a solid, biosolid, or a semisolid, use an amount of 1 g measured as dry weight or as dry solid ltered from an aqueous sample for the analysis. Take two aliquots of the sample 1 g each. While one aliquot of this solid sample is adjusted to an acidic pH with a phosphate bu er, the other aliquot is made basic with ammonium hydroxide. e acid fraction is stabilized with Na4 EDTA · 2H2O. e labeled compounds are then spiked into
their respective acid and base fractions. ey are then extracted ultrasonically. e acid fraction is mixed with 20 mL acetonitrile, sonicated for 30 min and centrifuged for about 5 min at 3000 rpm. Decant the supernatant extract and add 15 mL of phosphate bu er and adjust the pH between 1.95 and 2.05. Perform a second extraction of the solid residues repeating the above steps and a third extraction only with 15 mL of acetonitrile solution and combine all the extracts. e base fraction is similarly extracted thrice as outlined above, however, with the pH being adjusted between 9.95 and 10.05 by adding ammonium hydroxide
Sample Cleanup
e acid and the base fractions of the aqueous samples or the aqueous extracts of the solid samples prepared above are cleaned up separately by SPE with hydrophilic-lipophillic balance (HLB) cartridges. Assemble the SPE extraction apparatus and condition the HLB cartridges by eluting with 20 mL methanol and 6 mL reagent water. For acid fractions, the cartridges should be further eluted with 6 mL reagent water at pH 2. e sample fractions are loaded onto the cartridges and eluted at a ow rate of 5-10 mL per min. Acid fraction cartridge is washed with 10 mL reagent water to remove the EDTA. Base fraction cartridge need not be washed. Dry the cartridges for either fraction under vacuum for approximately 5 min. Acid fraction analytes are eluted from the cartridges with 12 mL methanol rst using vacuum and then under gravity. If triclosan and triclocarban that are to be analyzed elute these two compounds with 6 mL acetone-methanol (1:1). e base fraction is eluted with 6 mL methanol followed by 2% formic acid solution.
