dilutions of Paraquat&DiquatCalibrationMix (cat#32437) into the system, andmonitor for paraquat at 257nm and for diquat at
308nm.
Note that EPAMethod549.2 requires retestingof all samples if the response for the reference standards changes bymore than20%
over the timeof theanalysis.We findall reference standards showdegradationafteronly1hour inuntreatedglassware, and the low-
est concentrations are affectedmost. 30% losses in response are not uncommon; a reference standard of 6ppb diquat inwaterwas
undetectable. This makes non-reactive glassware critical; all volumetric ware and vials used for preparing and extracting samples
containing paraquat and diquat, or paraquat/diquat reference standards, must be deactivated. In our studies we use
dimethyldichlorosilane (DMDCS) todeactivate all glassware.
Toachieve the lowest detection levels, solidphase extraction (SPE) isused to extract, clean, and concentrate the samples.The extrac-
tionprocedure inEPAMethod 549.2 relies on the same ionpairing technique as theHPLCmethod, andwouldnot be compatible
withour simplified, chaotropic analyticalmethod.Using the new SPEprocedure detailed inTable II,we removedUV interferences
and concentrated theherbicide analytes 200-foldbefore analysis.The simple and ruggedprocedure,usinganoptimizedweak cation
exchanger (UltraQuat SPE), produced the quantitative and highly reproducible recovery results detailed inTable III. Sample vol-
umes of up to 1 liter can be extracted through this procedure. The water samples we used did not require pH adjustment, but all
samples shouldbe at pH 6-7 to assure that the analytes are fully chargedbefore extraction.Glassware used for extractionwas deac-
tivated using DMDCS, following label directions, and the extracted samples were stored and analyzed in Silcote CL7-deactivated
autosamplervials.Byconcentrating theSPEeluate toa smallervolume,or increasing the injectionvolume,quantificationanddetec-
tion limits canbe further reduced.
Our specially designedUltraQuatHPLC column,UltraQuat Reagent Solution,UltraQuat SPE tubes, and paraquat/diquat refer-
encematerials, used according to the conditions describedhere,will not only simplify your anlaysis, but will alsoprovide themost
accurate and consistent information about paraquat anddiquat.
a
An appropriate solvent, such as acetonitrile,must be used for this separation.Organic solvents that can formhydrogenbondswill
cause loss of retention.
b
Note that limitswill varywithdiffering systems and levels of optimization.Thedetectorwill detect a finite lower amount ofmate-
rial (e.g., 0.12ng), but as this amount is present in an increasingly larger volume, the detected
concentration
will be lower.
Reference
1.Pan,L.,R.LoBrutto,Y.V.Kazakevich,R.Thompson
Influenceof inorganicmobilephase additives on the retention, efficiency and
peak symmetryof protonatedbasic compounds in reversedphase liquid chromatography
; J.Chromatogr.A, 1049: 63-73 (2004).
PesticideStandards
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