Contact
Janusz Pawliszyn, Department of Chemistry
The study proposed a new approach involving low cost, drone-based TF-SPME water sampling devices and methodologies. The device was shown to successfully extract, store and stabilize volatile compounds while preventing outside atmospheric contamination. After successful proof-of-concept testing, in-field use of the drone-based sampler, combined with the portable GC–MS, demonstrated the capability of determining a likely cause of surface water contamination in real time. The study method could prove especially useful for hard-to-reach or dangerous waters such as pit lakes and tailing pond waters.
Introduction
In recent years, drones have seen increasing use in analytical chemistry. Most studies, unsurprisingly, have focused on drone use for air measurements. More recent works have used heavy-lift drones to collect water samples, specifically in the mining industry for the sampling of pit lakes. In these cases, heavy-lift drones are required as pump operated grab samplers pull water up into onboard tanks, which are then flown back to the operator to be analyzed. When only used for water collection, these drones are costly as they need large lift capacity.
This study aimed to demonstrate the use of drones with lighter sampling payloads that maintain analytical sensitivity while not requiring heavy pumping systems. More specifically, we developed a drone-based thin-film solid-phase microextraction (TF-SPME) water sampler incorporating hydrophobic–lipophilic balance (HLB) pure poly(dimethylsiloxane) (PDMS) membranes to remotely extract pollutants present in environmental waters and screen for them using appropriate analytical instrumentation. To improve portability, the approach was coupled with portable gas chromatography–mass spectrometry (GC–MS) instrumentation, which, in combination with the drone-based water sampler, allowed for sampling, extraction, and analyte identification to be performed entirely on-site.
Methodology
A relatively cheap commercial drone was outfitted with lightweight pontoons, while a gravity-buoyancy manipulated TF-SPME sampler was constructed primarily out of fishing supplies. The sampler functioned by using split cotter pins, fishing swivels, and fishing lines to connect a TF-SPME membrane to two differently massed sinkers, one of which was made buoyant using floaters (Figure 1). As shown in Figure 2, this allowed the heavier sinker to pull the TF-SPME membrane into the tubing via gravity during flight, while allowing the lighter sinker to drop out of the tube and into the water for sampling. The total mass of a single sampling package was just under 12 g allowing for use with “toy” drones.
Figure 1: Schematic of a gravity and buoyancy operated TF-SPME drone water sampler
Figure 2. Deployment of a TF-SPME drone water sampler showing (A) membrane sealing in tubing when in flight and (B) the drone water sampler floating on hot tub water with the sealing tubes, floating heavy sinker, and a deployed membrane encircled in red.
To evaluate the effectiveness of the sampling method, handling blanks were run in-lab to prove that the membranes were sealed from the atmosphere and that moving the membranes in and out of the tubing would not add significantly to a potential background signal. The analyte storage capabilities of the drone sampler were evaluated using modified McReynolds standards. To determine whether the TF-SPME drone-enabled water sampler would properly function for real drone-based deployment, a trial run was performed on the surface of hot tub water.
Real on-site sampling was performed from a suspected landfill impacted watercourse south of London, Ontario, Canada. One 4 cm and one 2 cm HLB/PDMS TF-SPME membranes were attached to the drone to allow for immediate on-site analysis using portable GC–MS instrumentation and the ability to perform a comparative analysis on benchtop instrumentation once returned to the lab. Once on the surface of the stream, the drone TF-SPME sampler performed the extractions for 10 min prior to retrieval. In addition to the actual drone sampling, four replicate mock extractions were also performed with 2 cm HLB/PDMS TF-SPME membranes for laboratory analysis.
Outcomes
There was no observable difference between the blank desorption of unused membranes and those at various stages of handling. This indicates that the samplers were not at risk of being contaminated by the atmosphere when they were placed on the drone for flight and confirmed the feasibility of the sampler’s ability to protect them from the atmosphere until they need to be used for water sampling. Seal tests proved the drone sampler was capable of preventing sample loss, important as many aqueous environmental contaminants are volatile.
The hot tub testing validated that the drone-based TF-SPME sampler would operate as designed mechanically. The samplers also performed reasonably analytically during validation with the percent relative standard deviations for the six chlorination by-products identified ranging between 5 and 16 per cent.
Analytical results from on-site sampling were surprising. Despite expecting high levels of compounds indicative of landfill leaching, only a small amount of phthalates were observed. Instead, various alkyl-benzenes were identified consistent with hydrocarbon contamination originating from a nearby major highway. The fact that these components could be immediately identified on-site using portable GC–MS instrumentation following drone TF-SPME sampling is a good indicator of the potential impact of this methodology. Moreover, it was encouraging to see that the membranes brought back to the laboratory for determinations generated comparable results, whether they were deployed by drone, conventionally, or by using an in-bottle TF-SPME method.
Conclusions
The study proposed a new approach involving low cost, drone-based TF-SPME water sampling devices and methodologies. The device was shown to successfully extract, store and stabilize volatile compounds while preventing outside atmospheric contamination. After successful proof-of-concept testing, in-field use of the drone-based sampler, combined with the portable GC–MS, demonstrated the capability of determining a likely cause of surface water contamination in real time. The study method could prove especially useful for hard-to-reach or dangerous waters such as pit lakes and tailing pond waters.
The study showed that drones could be used to transport SPME and TF-SPME devices containing extracted chemicals taken from a variety of samples, potentially even clinical samples, as these SPME-based approaches have been demonstrated to be useful not only for extraction but also for convenient introduction to analytical instrumentation. The practical advantages of drone-based transportation of lightweight passive sampling devices could provide an opportunity to improve various services or emergency responses to small or remote communities.
Although the experiment was successful in demonstrating the applicability of the method for quick on-site screening, winter conditions were not favourable for further validation. It is also worth noting that the proposed design would not be suitable for fast-flowing rivers and is instead most appropriate for lakes, ponds, mining pools, and tailing ponds where high winds would be the only concern. Work continues on developing new extraction media and sampling devices suitable for drone deployment.
Grandy, J.J., Galpin, V., Singh, V. & Pawliszyn, J. (2020). Development of a Drone-Based Thin-Film Solid-Phase Microextraction Water Sampler to Facilitate On-Site Screening of Environmental Pollutants. Analytical Chemistry. 92, 19. https://doi.org/10.1021/acs.analchem.0c01490
For more information about WaterResearch, contact Julie Grant.
UAV Listing Photo by Aaron Burden on Unsplash.
