Following our feature on recent advances in oil spill analysis—highlighting studies that demonstrated the power of hydrophobic paper sampling paired with DART-ToF MS and GC/MS workflows—we spoke with one of the lead investigators, Dr. Dayue Shang of Environment and Climate Change Canada. In this conversation, Dr. Shang provides deeper insight into the motivation behind these methods, their practical applications, and how this work could transform field response, regulatory enforcement, and citizen science in spill forensics.
What was the primary motivation behind exploring the use of hydrophobic paper sampling combined with DART-ToF MS and GC-MS for oil spill analysis, given the existence of established methods like the CEN standard?
I have been working on oil spill forensics for the last 20 years and have noticed that there are two types of requirements for the lab: a) Rapid confirmation of spilled oils in the water systems to determine the scale and impact, and b) thorough investigations of the spill to match its source for legal actions. In my view, a thorough investigation requires the use of the CEN method, which is a gold standard for oil spill forensics. However, in the majority of oil spill cases, a simple GC/FID oil profile is sufficient. Nevertheless, even simple GC/FID analysis can be time-consuming, with each sample taking approximately 2 to 3 hours for extraction, clean-up, and run. In addition, for many oil spill incidents, sampling is a challenge because of the inaccessibility of remote locations, non-ideal weather during operations, and the need to transport collected samples in large and fragile glass containers. In this case, DART-ToF has some unique advantages, such as a 30-second instrument run time and minimal sample preparation. Additionally, DART-ToF is particularly suitable for analyzing ‘solid’ samples (as demonstrated in wood species identification work pioneered by Dr. Ed Espinoza of the US Fish and Wildlife lab in Ashland, Oregon). The ECCC North Vancouver lab in Canada has been working closely with Dr. Espinoza on wood species identification using DART-ToF and routine oil spill analysis. The idea of using hydrophobic paper for oil spill investigation was from the combination of these two areas of our routine work and expertise to achieve better efficiency and support enforcement and regulatory activities in dealing with oil spill situations.
Based on your findings across the three studies, what are the key strengths and weaknesses of using hydrophobic paper sampling in conjunction with DART-ToF MS compared to using it with GC-MS for oil spill identification?
The key advantages of this method are convenience in sampling, rapidity of analysis, and flexibility of the method in terms of further study using the CEN methodology. The weaknesses of this approach include the relatively small number of DART-ToF instruments available worldwide despite the introduction of this powerful tool over 20 years ago, and the shortage of collaborators due to concurrent unfamiliarity for many trace organic chemists. As for the hydrophobic paper for sample collection, the main shortcoming is the potential biased extraction related to the chemical characteristics of the paper’s coating, which is worth further investigation. Unlike the classic water-in-bottle sample, which could be used for additional polyaromatic hydrocarbon (PAH) analysis if needed, the current hydrophobic paper samples are not suitable for PAH determination. Again, much more research could tackle this issue, considering that this particular sampling method is similar to solid-phase microextraction (SPME), which has been used routinely for PAH analysis.
The CEN method is described as time-consuming but thorough. How does the level of detail and information obtained from the hydrophobic paper sampling with DART-ToF MS or GC-MS compare to the comprehensive biomarker analysis offered by the standard CEN GC-MS method?
The CEN method is based on the comparison of ion ratios of biomarkers, which are chemical compounds resistant to weathering. In our study, the hydrophobic paper samples can be further analyzed by GC/MS, followed by the CEN ion ratio comparison data processing. Note that for most oil spill cases, only the surface oil in the collected samples is used with either the CEN method or the paper sampling approach. Therefore, it is expected that no real difference should be noticed between the two methods. However, when dealing with dissolved components of the spilled oil, the difference may be significant, as the classic method uses multiple exhaustive solvent extractions, while only specific compounds from the dissolved portion of the spilled oil are selectively retained by the hydrophobic paper.
You've demonstrated the applicability of hydrophobic paper sampling for both petroleum-based oils and plant-based oils. Could you discuss any significant challenges encountered when applying this sampling technique to these two distinct types of oils?
We have demonstrated that this paper sampling with DART-ToF analysis is applicable to most petroleum-based and plant-based oils. Unlike petroleum oils, which contain a complex mixture of aromatics, alkylated hydrocarbons, and hetero-aromatics, plant-based oils consist mainly of fatty acids and their esters, mono-, di-, and triglycerides. Based on the abundance of the observed key mass ions of the fatty acids and their esters and the absence of ions related to petroleum oils, the plant-based oils are suitable for DART-ToFMS analysis, which is remarkable as the classic GC/MS analysis of plant-based oils is quite challenging.
What are the anticipated practical benefits for first responders and environmental agencies of adopting the hydrophobic paper sampling method for initial oil spill assessment, even if further analysis using traditional methods is required?
This particular analysis method may have the potential to change the way that oil spill investigation is conducted. For example, if widely adopted, enforcement officers, the general public, and regulatory personnel may be informed of the reach and impact of an oil spill within a day with DART-ToF analysis instead of a few days with the classic GC/MS procedure. Cost saving is another benefit which should not be overlooked, as there is no risk of glass bottle breakage, high transportation costs, or biodegradation of water-based samples. Perhaps more importantly, this handy paper-based sampling allows First Nations and the general public to participate in sampling of oil spills, as it is very convenient to send the sampling kits to remote areas. A salient point of this method is the use of plastic bags (such as Ziploc-type bags) for sample storage and transportation, which greatly reduces costs and encourages citizen participation in the process. Clearly, it is counterintuitive to store oil-paper samples in plastic bags due to the potential for cross-contamination. Nevertheless, our extensive tests provided convincing evidence that the oiled paper samples could be kept in the plastic bags for up to 50 days in most cases without losing the biomarkers and their ratios. Just imagine first responders heading to the site with paper sampling kits in their pockets instead of dragging heavy coolers with dozens of 1-liter glass bottles! Perhaps the emergency preparedness officers could use drones to drop sampling kits to remote locations for indigenous communities to collect samples and then retrieve them using the same unmanned aircraft. It seems that the potential applications are endless with such easy tools.
Considering the limitations identified in these studies, what are the key areas of ongoing or future research that could further enhance the reliability and applicability of hydrophobic paper sampling in oil spill forensics and environmental monitoring?
Currently, we are using a commercial product (Whatman® phase separator filter paper) and have not investigated other chemical coating formulations. I believe that, similar to the SPME technique, which has been widely accepted by trace organic chemical analysis labs, there are many ways to either increase the efficiency of the oil absorption or selectively extract particular fractions of the spilled oils. Moving forward, more research is needed to investigate the long-term stability of the paper collected samples, as well as degradation factors such as temperature, UV exposure, and agitation. Further studies on various desorption solvent combinations to selectively "wash off" the collected oils (fractioning) could help reduce matrix effects. Additionally, it is worth noting that further research may determine that the samples collected with this paper sampling method are suitable for PAH analysis by GC/MS.