| dc.description.abstract | Since being introduced in 1989 solid phase microextraction (SPME) techniques have continually evolved from within the analytical chemistry community due in large part to their clean, portable and easy to handle design. It is no surprise then that these devices lend themselves well to on-site sampling approaches making their use in conjunction with field portable instrumentation a growing trend. However, as with any emerging analytical methodology, it is important that these entirely on-site approaches are developed such that they deliver comparably reliable and sensitive results to accepted techniques. As such, presented herein, various novel morphologies and analytical methodologies based on the principles of solid phase microextraction were developed and validated as a means to improve the reliability and sensitivity of on-site environmental analysis.
As an opening project, a portable in-vial standard analyte generator capable of delivering a highly reproducible gaseous headspace is proposed. The vial is comprised of a silicone diffusion pump fluid spiked with appropriate calibration or derivatization compounds, such as modified McReynolds probes (benzene, 2-pentanone, pyridine, 1-nitropropane, 1-pentanol, and n-octane) or pentafluorophenyl hydrazine (PFPH), respectively. The spiked silicone oil is then mixed with polystyrene/divinylbenzene (PS/DVB) particles and enclosed in a 20 mL headspace vial. Using the McReynolds calibration mixture, headspace concentrations were found to be substantially decreased in comparison to prior hydrocarbon pump oil based vials hence, the amount of standard loaded onto SPME fibers was at most, half that of the previous vial design. Appropriately, depletion for all compounds after 208 successive extractions was shown to be less than 3.5%. Smaller proportions of standards being used at each extraction resulted in a vial that depleted slower while remaining statistically repeatable over a wider number of runs. Indeed, it was found that this depletion could be predicted using a theoretical, mass-balance model. At a 95 % level of confidence, the ANOVA test demonstrated that prepared vials were statistically identical, with no significant intra- or inter-batch variations. Storage stability in varying conditions such as light exposure and temperature was also validated over 10 weeks for vials prepared with the reactive and unstable, pentafluorophenyl hydrazine in addition to the McReynolds probes. To demonstrate amenability for on-site environmental applications, a battery operated vial oven was constructed and employed in tandem with portable GC/MS instrumentation for the on-site PFPH derivatization and quantitation of formaldehyde from car exhaust. By using a combination of SPME fibers and needle trap devices (NTD’s) the concentration of this formaldehyde in aerosol particles could be determined and differentiated from the free gaseous concentration. Following these validatory experiments, varying standard headspace generating mixtures were continuously used to evaluate the portable GC/MS instrument while providing a means for on-site quality control.
As the main accomplishment of this thesis a durable, high surface area, and easy to handle thin film microextraction (TFME) device is proposed. The membrane is comprised of poly-divinylbenzene resin particles suspended in a high-density polydimethylsiloxane glue spread onto a carbon mesh support. This novel design was shown to exhibit a substantially lesser amount of siloxane bleed during thermal desorption while providing a statistically similar extraction efficiency towards a broad spectrum of compounds when compared to an unsupported DVB/PDMS membrane of similar size that had been prepared with former methods. At a 95 % level of confidence, the ANOVA test demonstrated that these membranes were also statistically similar, with no significant intra- or inter-batch variations. In an initial validation, membranes cut to 4 cm long, 4.85 mm wide and coated 30-40 μm thick (per side), were shown to extract 21.2, 19.8, 18.5, 18,4, 26.8, and 23.7 times the amount of 2,4-dichlorophenol 2,4,6-trichlorophenol, phorate-D10, fonofos, chlorpyrifos, and parathion respectively, from a 10 ppb aqueous solution than a comparable 65 μm DVB/PDMS SPME fiber.
Following these initial developments, these carbon mesh supported DVB/PDMS membranes were established as highly sensitive, accurate and green alternative to classical liquid-liquid extraction (LLE) for the determination of 23 multi-class pesticides from surface water samples. This signal improvement was made evident by method limits of detections (MLOD’s) in the low ng L -1 range for most of the pesticides studied while only requiring 30 mL of sample. Furthermore, these MLOD’s were shown to be at least 10 times lower than those achieved using an EPA certified, LLE method performed at an accredited analytical laboratory participating in the study. Moreover, the method accuracy was validated through double-blind split analyses of 18 surface water samples. Good agreement between the two methods was achieved with accuracy values between 70-130% for the majority of analytes tested. This methodology was further explored on-site with the design and deployment of a portable TFME sampling case to be used in conjunction with the portable GC/MS instrumentation. Although the chosen pesticides were found to be more-or-less absent from the 4 riparian sampling locations, a wide variety of untargeted compounds could still be detected and identified using the portable TFME-GC-TMS method. As such, the on-site method repeatability was still deemed acceptable with %RSD’s for the untargeted compounds around 20% (n=5). Moreover, by use of a BTEX standard headspace generating vial, the portable GC/MS was shown to remain stable over the entire 1-month sampling period.
Furthering the development of carbon mesh supported TFME, a highly sensitive HLB-PDMS thin film microextraction device for the balanced determination of VOC compounds of varying polarity was prepared. In addition to exhibiting a 50+ fold increase in sensitivity when compared to a 65 µm DVB/PDMS SPME fiber, these membranes extracted approximately double the amount of McReynolds probes versus a more comparable DVB/PDMS TF-SPME device of identical size. Inter-membrane extraction efficiencies for these compounds were determined to be reproducible at 95% confidence for all 4 of the coating chemistries tested including the DVB/PDMS membranes, and those prepared with 3 different HLB compositions. Further method reliability was established by confirming that, once extracted, the McReynolds standards were stable on the HLB/PDMS membranes stored in the thermal desorption tubes on the autosampler rack for at least 120 hours for 5 of the 6 standards and only 24 hours for pyridine at 95% confidence. Finally, a real-world proof of concept application determining chlorination by-products from a private hot tub was performed, successfully identifying, 2-chloroethylamine 3-chloro-1-propanamine, and dichloroacetonitrile with %RSD’s less than 10%.
Finally, as a side project, the goal of pushing on-site sampler design to its fullest was explored by means of the construction of a self-sealing coated bolt sampler for the analysis of deep ocean environments via divers and ROV submersibles. These samplers employ HLB particles which have been coated onto recessed stainless steel bolts by use of polyacrylonitrile (PAN) glue. 6 coated bolts are then inserted into a self-sealing, polytetrafluoroethylene (PFTE) bodied sampler designed to preserve extracted compounds for extended periods. To verify this stability, 3 samplers were deployed on-site at a waste-water treatment facility outflow pipe via kayak. Post-sampling, the samplers were stored using 3 storage conditions including A: immediate desorption, B: 3 days at 23 oC), C: 12 days at 23 oC and D: 12 days in a -80 oC freezer. All bolts tested were statistically indistinguishable when analyzed using principal component analysis (PCA). Furthermore, 10 randomly selected, volatile, features were also demonstrated to give a statistically identical response at a 95% level of confidence using the ANOVA test. Finally, in a cutting-edge application, these samplers were tailored for use on an ROV submersible and employed for the on-site sampling of hydrothermal vents at 2 locations along the Pacific Rim with 2 corresponding control extractions also performed from ambient waters away from these vents such that significant features could be differentiated. Separation and analysis of all samples were performed using an HPLC equipped orbit-trap mass spectrometer and 100’s of statistically unique features could be determined from the vents by use of multivariate statistical analysis. | en |
