Testing for semi-volatile organic compounds
Maintaining water quality in compliance with EPA 3511
What are semi-volatile organic compounds (SVOCs)?
Semi-volatile organic compounds (SVOCs) are organic molecules that are partially volatile, and encompass subgroups such as polycyclic aromatic hydrocarbons (PAHs) and phenols. They can arise from a range of sources, including car exhausts, industrial and chemical processes, general pollutants, and even naturally occurring compounds that become toxic through chemical reactions. SVOCs may dissolve into water, leach from soil or persist in the environment, which is why strict regulatory limits are in place – particularly for drinking water and wastewater – to prevent harmful discharges. A wide range of organisations need to carry out SVOC testing, including environmental contract laboratories, construction companies assessing environmental impact, agricultural labs monitoring soil and water runoff, pharmaceutical manufacturers tracking effluent, academic institutions conducting environmental research, and regulated industries that interact with the environment.
Traditional semi-volatile organic compounds testing methods
SVOCs are routinely measured in water quality monitoring applications – such as drinking water, wastewater and leachates – using gas chromatography (GC) combined with mass spectrometry (MS) being the traditional analytical method. Sample preparation typically involves liquid-liquid extraction (LLE), a widely used technique for isolating pollutants from various water sources. However, conventional LLE workflows are far from straightforward. The US EPA 3510C method requires a one litre water sample for LLE, which poses challenges in terms of collection, transport and handling. This method also requires the use of significant volumes of an organic extraction solvent, typically dichloromethane (DCM), along with multiple manual steps including shaking, phase separation, blowdown and solvent reconstitution. These manual processes are time consuming, difficult to reproduce, and pose health and safety risks due to regular solvent exposure. They also introduce variability, particularly when dealing with complex matrices or working to meet stringent regulatory detection limits.
An automated workflow for efficient water sample prep
The introduction of the US EPA 3511 method is a significant advance, allowing extraction using only 35 ml of sample water and 2 ml of DCM. This gives a suitable concentration factor, with no evaporation/reconstitution step. This approach aligns with the environmental laboratories’ goals of cost reduction and greener practices. ePrep has developed a workflow based on, and compliant with, EPA 3511, which supports safer, more reproducible and more efficient analyses.
Benefits of automating EPA 3511 SVOC testing
The ePrep® ONE fully automates every step of sample preparation for the EPA 3511 LLE SVOC-water method, enabling field samples to be prepared directly from collection bottles to sealed autosampler vials ready for chromatographic analysis. This eliminates the need for manual sample transfer and bottle washes to remove targets absorbed on the container wall, freeing up skilled analysts for higher value tasks and protecting them from solvent exposure. ePrep’s ALLEx (automated liquid-liquid extraction) provides fast, consistent mixing without manual shaking, ensuring method compliance. It uses analytical syringes to create micron-sized droplets of the organic phase in the aqueous phase. This dramatically improves kinetics and extraction efficiency, with only a single extraction step necessary.
The ability to automate manual tasks means the ePrep ONE increases throughput without additional staffing, supporting large-scale, routine testing with high reproducibility and reduced manual labour. The platform can be used with any analytical instrument type, and is adaptable to both GC and LC workflows for added flexibility. Combining automated sample preparation on the ePrep ONE using the EPA 3511 method with modern GC/MS instruments therefore represents an ideal solution for busy environmental labs, with dramatic labour savings and improved data reliability.
Case study
Optimising the EPA 3511 workflows with the ePrep ONE
This case study presents comparative extractable internal standard (EIS) and non-extractable internal standard (NIS) results from drinking water and synthetic wastewater samples prepared on the ePrep ONE and analysed using GC/TQ.
Sample prep
Synthetic wastewater was prepared using ASTM D5905 method. Water samples were spiked with EPA 8270 MegaMix at 2.86 ppb, giving 50 ppb in the final DCM extract. For the EIS quantitation method, internal standards were spiked directly into water samples. For the NIS method, internal standards were added exclusively to the final DCM extract.
Extraction
To improve phenol recovery, HCl was added to adjust the pH of the water samples, followed by a saturated salt solution. Two 1 ml aliquots of DCM were dispensed rapidly into the sample water. The DCM was syringe nebulised to micron-size droplets, which partition at least 1,000 times more effectively than the millimetre-size drops created by conventional shaking or vortexing. This enabled highly efficient liquid-liquid extraction. The workflow included drying the extract with sodium sulphate. A universal indicator can be added to check the solution pH after extraction.
Results
Results demonstrated acceptable recovery rates and relative standard deviations for the range of 8270 SVOCs. Phenolic compounds exhibited recovery patterns typical of 8270 methods due to chromatography instrument and matrix effects. Basic compounds were excluded from the analysis because they require separate basic extraction to achieve acceptable analytical performance – this can be incorporated into the ePrep workflow if desired. In synthetic wastewater analysis, high molecular weight compounds exhibited lower recoveries, which is consistent with emulsion binding effects. A centrifugation step can be implemented to improve recoveries of these compounds.
Conclusion
The ePrep EPA 3511 workflow using the ePrep ONE achieves limits of detection of 0.29-0.57 ppb, and limits of quantitation of 0.57-5.7 ppb in water. It also demonstrated excellent recoveries and reproducibility across the range of 8270 SVOCs analytes, showing that the ePrep method meets the performance criteria requirements of EPA method 3511.
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