Graphitized carbon black (GCB) is a widely used solid phase extraction (SPE) sorbent. GCB is considered both a reverse phase and anion exchange sorbent due to its structure and somewhat positively charged surface (1). The major advantage of GCB is that it can retain nonpolar compounds, such as organochlorine pesticides, as well as some very polar compounds, such as surfactants, which are difficult to retain by reverse phase sorbents. This application presents a simple SPE method using UCT's proprietary, treated GCB for the determination of pesticides in water.
a) Transfer 100 mL of aqueous sample into a glass container; adjust pH to less than 2 with 6 N HCl. Spike as necessary.
b) Connect the 75 mL reservoirs to the top of the GCB cartridges using cartridge adaptors.
c) Wash the cartridges with 10 mL dichloromethane (DCM). Condition the cartridges with 10 mL methanol and 10 mL of reagent water.
d) Apply the samples to the reservoirs, adjust vacuum to give a drop-wise flow (about 10 mL/min).
e) Rinse the sample containers with 10 mL reagent water; apply the rinsates to the cartridges.
f) Dry the cartridges under full vacuum for 10 min.
g) Insert test tubes in the manifold; elute the cartridges with 5 mL ethyl acetate and 5 mL DCM.
h) Dehydrate the eluents with sodium sulfate; rinsing the test tubes and sodium sulfate with DCM.
i) Concentrate the extracts to 1 mL under a gentle stream of nitrogen at 35 °C. Add internal standard prior to GC–MS analysis.
GC–MS: Agilent 6890N GC coupled with 5975C MSD
Injector: 1 μL splitless injection at 250 °C
Liner: 4 mm splitless gooseneck liner with deactivated glass wool (UCT: GCLGN4MM)
GC column: Restek Rxi® -5sil MS 30 m × 0.25 mm × 0.25 μm with 10 m guard column
Carrier gas: He at a constant flow of 1.2 mL/min
Temperature program: Initial temperature of 55 °C, hold for 1 min; ramp at 10 °C/min to 200 °C; ramp at 7° C/min to 300 °C and hold for 0.21 min
Full Scan: 45–500 amu
Table I: Accuracy and precision data
Excellent analyte recoveries, intra- and inter-day precision were achieved using GCB in the solid phase extraction of OC pesticides in water samples.
(1) M.C. Hennion, J. Chromatogr. A 885, 73–95 (2000).
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