SolidPhaseExtraction (EPA 549.2Modification)
Tomeet the requireddetection limits for theseherbicides, a concentration
step is necessary. Solidphaseextraction (SPE) canbeused toextract the
herbicides fromawatermatrix, beforeelutionwithanaqueous acidic
solution. Several types of phaseswere tested for this application, including
both strong (propyl andbenzyl- types) andweak ionexchangers. We found
that aweak cationexchanger gave thebest overall recoveries.
Themodifiedextractionmethoddoes not require theuseof anSPE alkyl
C8phasewith ionpairingagents. Ionpair agents havedetrimental effects
upon sensitivity and resolutionusing themodifiedHPLCmethod.
Analytical conditions aregiven inTable I, thedetails of theextraction
methodare summarized inTable III and recovery results are listed inTable
IV. Whenusinga1L sample sizeand6mL tube size, sampling rates of up
to25mL/minwerepossibleand still resulted inexcellent recovery
efficiency. The1L sample for these studies hada concentrationof 50ppb
eachherbicideand requirednopHadjustment beforeextraction (extracts
weredoneat neutral pH).
