Graphitized Carbon Black for Solid Phase Extraction of Pesticides in Water

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.

SPE Materials

SPE Procedure

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.

Instrumental

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

Results

Table I: Accuracy and precision data

Conclusion

Excellent analyte recoveries, intra- and inter-day precision were achieved using GCB in the solid phase extraction of OC pesticides in water samples.

Reference

(1) M.C. Hennion, J. Chromatogr. A 885, 73–95 (2000).

UCT, LLC

2731 Bartram Road, Bristol, PA 19007, USA

tel. (800) 385-3153; Email: methods@unitedchem.com

Website: www.unitedchem.com