SolidPhaseExtraction
Tomeet requireddetection limits for theseherbicides, a concentration step
is necessary. Solidphaseextraction (SPE) canbeused toextract the
herbicides as freeacids fromawatermatrix, beforeelutionwith suitable
solvents. Several types of bedswerepreviously tested for this application,
includingC18, andgraphitized carbon. Wehave confirmed that a specialty
divinylbenzenematerial, theResprepAHSPE6mL/500mg tube, gave the
best overall recoveries.
Analytical conditions are the sameas inTable II. TheSPEpreparation
method is detailed inTable IV.Water sample volumes from500milliliters to
1litermust beadjusted toapHof 2 for best recovery results. Results of a
final study for all 16herbicides, internal and surrogate standards are
summarized inTablesVandVI.Whenusinga1L sample size, recoveries
of theherbicideswere92-100%, with theexceptionof the internal standard
1,4dichlorobenzene. This analyte is not well retainedon thepackingand
reduced recovery is due tobreakthroughduring the sampleextraction step.
The1L sampleswere spikedwith10ppbof eachherbicideand theSPE
methodoverall produceda200-fold concentrationof theanalytes. Theuse
ofMTBEduringelution is optional.Most recoveries improvedonly slightly,
but it is required for quantitative recovery of pentachlorophenol.
