APPENDIX G: SOLID-PHASE CARTRIDGE EXTRACTION

TR02-1(ERDC-CRL)
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tration method for explosives in water (Jenkins et al. 1995a). Briefly, prepacked

cartridges of Porapak RDX Sep-Pak, 6 cc, 500 mg (Waters Corporation) are

cleaned by placing them on a Visiprep solid-phase extraction manifold (Supelco)

and passing 15 mL of acetonitrile through each cartridge at gravity flow. The

acetonitrile is then flushed from the cartridges using 30 mL of reagent-grade

water. Care is taken to ensure that the cartridges are never allowed to dry after

the initial cleaning. A connector is placed on the top of each cartridge and fitted

with a length of 0.635-cm (1/8-in.)-diameter Teflon tubing. The other end of the

tubing is placed in a 1-L flask containing 500 mL of the sample. The vacuum is

turned on and the flow rate through each cartridge is set at 10 mL/min. If the

flow rate declines significantly due to partial blocking from suspended material,

it is readjusted. After the sample is extracted, the top plug containing the fitted

tubing is removed from each cartridge, and 10 mL of reagent-grade water is

passed through the cartridge under gravity flow, unless the cartridges are suffi-

ciently blocked to require vacuum. A 5-mL aliquot of acetonitrile is used to elute

analytes from the cartridges under gravity flow. The volume of recovered aceto-

nitrile is measured and diluted (1:1) with reagent-grade water prior to analysis.

Solid-phase cartridge extraction (SPE) has several advantages over the

salting-out method, including the speed at which a sample can be concentrated

and extracted. It is a technique that brings excellent recovery and reproducibility

and requires less solvent than the salting-out method. Furthermore, it is inexpen-

sive and easy to use. However, this method does require that the extraction cart-

ridge be cleaned prior to use, and water samples with a lot of suspended solids

may need to be filtered. Recently, the SPE alternative has been given preliminary

approval for use by the US EPA Office of Solid Waste; it will be issued as

Method 3535 (A).