Polyaromatic hydrocarbons (PAHs) are of great environmental concern due to their carcinogenic impact. When water samples are
extracted and analyzed for the PAHs, many methods require the water sample to first be filtered, such that the particulate
matter is removed. Filtration is required when conventional solid-phase extraction (SPE) cartridges are used for extracting
the sample because SPE cartridges will plug easily when any particulate matter is present. With liquid–liquid extraction (LLE)
techniques, emulsions typically create problems that could impact the proper extraction of the suspended material adversely.
However, compounds such as polychlorinated biphenyls (PCBs) and PAHs will come out of the dissolved phase and adsorb onto
the surface of the suspended particulate matter in the water column. Therefore, to determine the actual concentration of PAHs
in the water sample, the "whole" water sample with the suspended particulate matter should be processed. As many water samples
extracted for PAHs are surface water, river water, ground water, waste water, or water with suspended material, it is desirable
to have an analytical method that can handle the "whole" water sample. SPE in a 47-mm disk format is a proven extraction method
for extracting particulate-laden water samples. SPE disks provide fast flow rates with no breakthrough of analtyes. Aqueous
samples of 1 L and greater can be processed quickly and effectively, providing excellent recoveries of PAH compounds at lower
detection limits.
The International Organization for Standardization (ISO), a worldwide federation of national standards solicited their technical
committees to develop a new ISO method for analyzing PAHs in particulate-laden water. The IWW Water Centre Institute, located
in Muelheim an der Ruhr, Germany, offered to participate in the development of a method to explore the possibilities of using
SPE disks for the analysis of 16 PAHs in drinking water, ground water, waste water, and surface water. The study conducted
by IWW had several goals:
- Develop an SPE disk method that could handle "whole" water samples (including particulates and suspended matter).
- Due to possible partitioning of PAHs between the dissolved and particulate phase of the water column, to determine the effectiveness
of the extraction technique for PAHs when the particulate matter and the SPE disk are both extracted and eluted with the SPE
extracting solvent.
- Determine the total amount of particulate matter that can be handled by the SPE disk.
- Determine the best nonhalogenated solvent to be used for extracting the SPE disk.
- Determine if a method could be developed that did not require a solvent concentration step.
- Develop a fully automated SPE disk method.
Experiments were carried out using both spiked drinking water and spiked surface water coming from natural water bodies (river
water). These experiments would examine the ability of "whole" water samples to be extracted and confirm if SPE would be sufficient
to extract the sediment particles properly and remove any PAHs adsorbed onto the sediment particles. The best recoveries for this work were achieved with reversed-phase SPE disks used with an automated extraction system. This
combination worked well for many surface water samples spiked with natural sediments up to a level of 1000 mg/L. Even with
this level of suspended material, 1000-mL samples could still be processed in less than 20 min, without ever plugging a disk.
Before starting the planned work on surface water samples spiked with natural sediments, the following preliminary work was
done:
- Calculate recoveries of PAH-spiked drinking water samples not containing any suspended particulate matter (without any solvent
concentration step).
- Explore potential adverse effects of solvent extract concentration, that is, potential losses of target compounds.
- Determine PAH recoveries from the extraction of certified dried natural sediments (not spiked to the water sample).
Instrumentation
An SPE-DEX 4790 automated extractor system (Horizon Technology, Salem, New Hampshire) was used with C18 Speedisk SPE disks
(JT Baker, Phillipsburg, New Jersey) and a model 6890 gas chromatography–mass spectrometry (GC–MS) system (Agilent Technologies,
Palo Alto, California).
