Development of a hydrophilic lipophilic balanced thin film solid phase

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Development of a hydrophilic lipophilic balanced thin film solid phase microextraction device for balanced determination of volatile organic compounds Jonathan James Grandy, Varoon Singh, Maryam Lashgari, Mario Gauthier, and Janusz Pawliszyn Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b04544 • Publication Date (Web): 29 Oct 2018 Downloaded from http://pubs.acs.org on October 29, 2018

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Analytical Chemistry

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Development of a hydrophilic lipophilic balanced thin film solid phase microextraction

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device for balanced determination of volatile organic compounds

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Jonathan J. Grandyϯ, Varoon Singhϯ, Maryam Lashgari, Mario Gauthier, Janusz Pawliszyn*

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Department of Chemistry, University of Waterloo, 200 University Avenue West, Waterloo,

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Ontario N2L3G1, Canada

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Ϯ Both authors claim equal contributions in the preparation of this manuscript

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*Corresponding author

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Phone number: 1-519-888-4567 ext. 84641

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E-mail: [email protected] (Janusz Pawliszyn)

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1 ACS Paragon Plus Environment

Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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ABSTRACT

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A novel hydrophilic-lipophilic balanced (HLB) thin film solid phase microextraction (TF-

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SPME) device is proposed for polarity-balanced determinations of volatile organic compounds.

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The proposed HLB particles used in the preparation of these membranes were prepared using a

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precipitation polymerization technique, and determined to have a specific surface area of 335 m2/g

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with an average pore diameter of 13 Å. Membranes prepared from these particles were found to

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extract 1.8, 2.2, 1.9, 1.7, 2.0, and 1.3 times more benzene, 2-pentanone, 1-nitropropane, pyridine,

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1-pentanol, and octane, respectively, than the established DVB/PDMS-based membranes.

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Furthermore, membranes prepared from these lab-made particles were shown to extract

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significantly (p = 0.00047) larger amounts of these analytes than membranes prepared from

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comparative commercial HLB particles. The inter-membrane extraction efficiency between 3

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membranes was determined to be reproducible at 95% confidence for 4 different coating

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chemistries tested, including the DVB/PDMS membranes, and those prepared with 3 different

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HLB compositions. Furthermore, method reliability was established by confirming that, once

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extracted, modified McReynolds standards were stable on the HLB/PDMS membranes stored in

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thermal desorption tubes on an autosampler rack for at least 120 hours, for 5 of the 6 standards,

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but only for 24 hours for pyridine at a 95% level of confidence. Finally, using a TF-SPME enabled,

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portable GC-MS instrument, an entirely on-site proof of concept application was performed for

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the determination and quantitation of chlorination by-products in a private hot tub, successfully

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identifying chloroform, bromodichloromethane, dichloroacetonitrile, chlorobenzene, benzonitrile,

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and benzyl chloride, while further quantifying chloroform and dichloroacetonitrile at levels of 270

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ppb and 79 ppb with %RSD values of 13% and 5%, respectively.

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INTRODUCTION

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Solid-phase microextraction (SPME) devices, particularly those used for gas

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chromatography-based determinations, have been well-published in the literature since the early

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90s.1–3 Among these, most sorbent chemistries and commercial devices have been tailored to target

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non-polar volatile and semi-volatile organic compounds (VOC’s, SVOC’s) via extraction

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facilitated by primarily hydrophobic sorbents.3–5 Notable exceptions include the more polar

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compound-oriented poly(ethylene glycol) (PEG) and polyacrylate (PA) SPME fibers which, much

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like polydimethylsiloxane (PDMS), may be considered liquid-like sorbents that rely on absorption

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as their primary mechanism of extraction.3,4,6–9 In fact, Naccarato et al. were able to demonstrate

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that for applications aimed at the extraction of polar VOCs and SVOCs from the benzothiazoles,

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benzotriazoles, and benzosulfonamides compound classes, polyacrylate-based fibers were able to

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provide broader coverage in comparison with the sorbents Carboxen (CAR/PDMS),

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divinylbenzene (DVB/PDMS), and DVB/CAR/PDMS fibers.9 However, these liquid-like fibers

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still lack the broad spectrum sorbent strength exhibited by solid sorbent particles due to the their

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lower affinity for lower boiling VOCs, and in particular for very volatile organic compounds

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(VVOCs).4,7 Moreover, polar absorptive coatings remain impractical for determinations of non-

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polar contaminants, in the same way that PDMS is unsuitable for determinations of polar

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compounds.4,7 This limitation may leave a little to be desired in terms of simultaneous polar and

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non-polar analyte determinations, as even DVB/PDMS has a moderately high hydrophobic

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character.10 Multi-polar Carboxen-based SPME fibers have their limitations as well; although

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shown to provide better coverage for both polar and non-polar compounds, they are known to

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exhibit poor desorption characteristics, making them only suitable for determinations of low

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boiling VVOCs.3,4,7



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These challenges can addressed with Hydrophilic-Lipophilic Balance (HLB) particles,

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which were specifically designed for the extraction of low-molecular-weight polar and non-polar

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compounds. HLB particles are second-generation mesoporous polymers characterized by a high

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surface area. They are synthesised with a poly(divinylbenzene-co-N-vinylpyrrolidone) skeleton

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structure that provides a balance between hydrophobic and hydrophilic interactions, due to the

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respective presence of aromatic rings in divinylbenzene and polar groups in the lactam ring of N-

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vinylpyrrolidone.11 In a study by Dias et al.12 on the sorption mechanism of HLB particles, N-

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vinylpyrrolidone was demonstrated to have strong electron lone-pair interactions leading to a high

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affinity for hydrogen-bonded compounds. Due to these interactions, compounds possessing

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electron-rich structures (aromatic rings) and hydrogen bonding capability (hydrogen bond donors)

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are well-retained on the surface of HLB particles.

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Owing to the above, HLB particles have been increasingly employed as functional particles

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in applications targeting the simultaneous extraction of polar and non-polar compounds in SPE

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cartridges,13 in-line SPE columns,14,15 TF-SPME HPLC,

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applications,18,19 as well as in various direct-to-MS configurations.20–24 One recent approach,

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presented by Poole et al., demonstrated that when used in-lieu of C18, recessed SPME-needle

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devices prepared with HLB particles were able to extract 3-4 times more polyunsaturated fatty

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acids from salmon tissue.25 Moreover, in very recent work, Gionfriddo et al. introduced an

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HLB/Polytetrafluoroethylene SPME fiber capable of withstanding both thermal and solvent

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desorption, allowing parallel GC- and HPLC-based determinations.26 Prior to this, HLB particles

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had already been employed for the preparation of a GC-amenable TF-SPME device.27 A 2015

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study highlighted the use of HLB particles in the preparation of two distinct TF-SPME devices to

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be used in conjunction with GC/MS or HPLC/MS instrumentation for the in vivo determination of

16,17


and magnetic dispersive SPE

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prohibited substances in human saliva.27 Although innovative, the assembled HLB/PDMS

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membranes were not without their limitations. At only 6 mm diameter, the membranes were rather

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small as compared to those used in other work, which provided less surface area and coating

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volume, and hence higher detection limits.28–30 This small size membrane may have been selected

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in an attempt to reduce the high siloxane background associated with PDMS-based sorbents.

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However, more recent work by Grandy et al. demonstrated that the employment of higher (cross-

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link) density PDMS enabled the minimization of the siloxane background, without having to

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decrease the size of the membrane, thus enabling lower limits of detection.29 Furthermore, as the

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selected commercial HLB particles were intended for use in SPE cartridges, they were quite large

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at 60 µm diameter; 12 times larger than the DVB particles typically used in SPME devices. Given

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that HLB-based sorbents are considered solid sorbents, sorbent strength is directly related to their

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specific surface area, which increases as the particle size is decreased and/or as the pore volume is

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increased. Furthermore, depending on the molecular size of the targeted analytes, pore size may

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also play an important role in extraction. With these considerations in mind, ideal HLB-based

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sorbents aimed at simultaneous balanced determinations of both polar and non-polar analytes of

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varying volatility should be composed of smaller HLB particles, with micro- and/or meso-

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porosity, combined with the aforementioned high density PDMS.

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The present work aimed at exploring various membranes of this type. Using the carbon

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mesh-supported high-density PDMS-based membrane design,29 several HLB/PDMS/carbon mesh

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TF-SPME devices were prepared, using various types of lab-made and commercial HLB particles.

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These membranes were shown to extract substantially higher amounts of mixed polarity VOC

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standards than the comparative DVB/PDMS composition, while exhibiting a similar level of

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background bleed. Moreover, one of the lab-made HLB chemistries exhibited performance equal



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to or better than the top-tier 5 µm commercial HLB particles, making these newly developed

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HLB/PDMS/carbon mesh membranes an ideal choice for the untargeted determination of

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chlorination by-products in hot tub water.

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EXPERIMENTAL SECTION

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Chemical and materials

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Benzene, 2-pentanone, nitropropane, pyridine, 1-pentanol, octane, toluene, chloroform,

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dichloroacetonitrile, divinylbenzene, N-vinylpyrrolidone, and 2-azobisisobutyronitrile were

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purchased from Sigma-Aldrich (Mississauga, ON, Canada). HPLC-grade methanol, acetone, and

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acetonitrile were obtained from Caledon Laboratories Ltd. (Georgetown, ON, Canada). Ultrapure

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water was obtained using a Barnstead/Thermodyne NANO-pure ultrapure water system (Dubuque,

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IA). DVB particles (5 μm diameter) and high-density PDMS were provided by Supelco

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(Bellefonte, PA). The carbon fiber mesh weave (Panex 30) was provided by Zoltec Co.

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(Bridgetown, MO). Liquid nitrogen and ultrahigh-purity helium were supplied by Praxair

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(Kitchener, ON, Canada). The 65 μm divinylbenzene/polydimethylsiloxane (DVB/PDMS) SPME

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fiber assemblies and polystyrene-DVB resin (XAD-4) were provided by Sigma-Aldrich. A 19-

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gauge Tenax/Car needle trap device was purchased from Perkin Elmer. Commercial 5 µm HLB

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particles were provided by Waters Inc. A Twister sorptive PDMS stir bar (SBSE) (2 cm long) and

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TF-SPME holding clips were supplied by GERSTEL Co. (Mülheim an der Ruhr, GE). A KJLC

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704 silicon pump fluid (tetramethyl tetraphenyl trisiloxane) was ordered from Kurt J. Lesker

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Company (Toronto, ON, Canada). The membrane conditioning unit used in this work was

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developed at the University of Waterloo Science Electronics Shop (Waterloo, ON, Canada). Cross-

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locking grip tweezers with stand were purchased from KW surplus store (Kitchener, ON, Canada).

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An Elcometer 4340 motorized automatic film applicator and coating bar (adjustable gap of 0−250


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μm) were acquired from Elcometer Ltd. (Rochester Hills, MI). HLB-TF-SPME and DVB-TF-

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SPME membranes were prepared according to a method reported in the literature.29 Overhead

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stirrers with regulated speed controls were purchased from Scilogex LLC (Rocky Hill,

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Connecticut, USA).

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Instrumental analysis method for the benchtop GC/MS

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An Agilent 6890 GC and a 5973n quadrupole MS (Agilent Technologies, CA U.S.A.) were

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used for separation and quantitation, respectively. Sample introduction was achieved with a

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Gerstel MPS2 autosampler, which was used to transfer TF-SPME devices to the thermal

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desorption unit (TDU1) cooling injection system (CIS4) (GERSTEL, Mülheim an der Ruhr, GE)

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for membrane desorption. Chromatographic separations on the Agilent 6890-5973n were

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performed on a 30 m × 0.25 mm I.D. × 0.25 μm SLB-5 fused silica column (Sigma-Aldrich,

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Mississauga, ON, CA). Helium served as carrier gas at a flow rate of 1.2 mL/min. The column

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temperature was initially held at 40 °C for 2 min, ramped to 140 °C at a rate of 8 °C min-1, then

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ramped to 250 oC at 40 oC min-1 and kept for 2 min. The MS detector transfer line temperature,

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MS quadrupole, and MS source temperature were set at 300, 150, and 230 °C, respectively. Gas

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phase ions were generated using electron impact ionization at 70 eV, and the quadrupole was

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operated in SIM mode, selecting ions 78, 86, 43, 79, 55, 85 m/z for benzene, 2-pentanone, 1-

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nitropropane, 1-pentanol, and octane, respectively.

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To facilitate desorption from the 20 mm x 4.75 mm x 400 µm (L × W × T) TF-SPME

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membranes, an inert glass bead was inserted into the tapered 5 mm I.D. glass desorption tube to

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prevent the membranes from slipping through the tapered bottom of the desorption tube, which

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was designed to hold a wider cylindrical PDMS stir bar rather than a flat thin film. Desorption was

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carried out at 250 oC with a helium stripping gas flow of 60 mL min-1 for 5 minutes. The desorbed



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analytes were cryo-focused at -130 oC within the CIS module. Following desorption, the CIS

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module was then ramped to a temperature of 270 oC at a rate of 10 oC s-1, so as to enable analyte

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transfer to the Agilent 6890 GC column for separation and quantitation.

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Instrumental analysis method for the portable GC/MS

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The on-site separation and quantitation of analytes extracted from a hot tub were performed

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using a Tridion-9 portable GC-MS equipped with a low thermal mass (LTM) MXT-5 (5 m × 0.1

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mm × 0.4 μm) Siltek-treated stainless-steel column (Restek Co. Bellefonte, PA). Helium served

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as carrier gas at a flow rate of approximately 0.3 mL min-1. The GC column was initially held at

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35 oC for 30 seconds, and then ramped to 250 oC at 2 oC s-1, where the temperature was held for

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an additional 30 s. Transfer of the compounds extracted by the TF-SPME membranes onto the 19-

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gauge Tenax/Carboxen NTD was performed using a previously validated method29 that employs

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a SPS-3 high volume desorption module (Perkin-Elmer American Fork, Utah) at a temperature of

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250 oC for 5 minutes, using a helium flow of 35 mL/min. To maximize sensitivity while

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maintaining an acceptable peak shape for early eluting compounds, desorption from the

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Tenax/CAR 19-gauge needle trap, used to transfer analytes from the TF-SPME membranes, was

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performed at 280 °C for 5 s in splitless mode, followed by opening of the 10:1 split for 5 s, and

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then further opening of the 50:1 split for a final 20 s. The ion-trap heater was operated at 155 °C,

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and the transfer-line was held at 250 °C during the analysis. Ionization was performed using a 70

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eV electron gun and an electron impact ion source, while the ion trap was operated in reduced scan

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mode set in a range of 43−325 m/z.

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Characterization of the sorbent particles and resulting membranes

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Infrared spectroscopic data were collected on a Bruker Tensor 27, Fourier-transform

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infrared spectroscopy (FT-IR) spectrometer (Madison, WI USA) in powder form between 4000


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and 450 cm−1. The shape and size of HLB particles, as well as the morphology of HLB thin film

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membranes were investigated with a Zeiss UltraPlus field emission scanning electron microscopy

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(FE-SEM) (Carl Zeiss, Germany). The HLB particles were also characterized by transmission

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electron microscopy (TEM; JEOL JEM-2010). The specific surface area of the HLB particles was

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determined using N2 adsorption-desorption isotherms at 77 K. The samples were degassed at 100

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°C for 24 h prior to the adsorption measurements. The speciﬁc surface area was calculated by the

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Brunauer-Emmett-Teller (BET) method. The thermal stability of the synthesized membranes was

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evaluated by running blank membrane analyses on the Agilent 6890-5973N GC-MS in the full

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scan mode. Desorption was performed on a Gerstel TDU at 250 oC for 5 minutes using 60 mL

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min-1 of stripping He gas and trapping the compounds in the CIS at -80oC. The preparation protocol

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for the lab-made HLB particles is provided in Section S1 of the Supplementary Information.

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Comparison of thin film extraction sensitivity for various sorbent particles

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To investigate the relative extraction efficiencies for the various TF-SPME sorbent

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chemistries, PDMS-Carbon mesh-supported membranes prepared with 5 µm DVB, 5 µm

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commercial HLB, 1.3 µm precipitation-polymerized HLB, and 2 µm suspension-polymerized

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HLB were compared in terms of extracted amounts. A 2 cm PDMS-coated stir bar and a 65 µm

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DVB/PDMS SPME fiber were also included for comparison in this study, so as to allow for a

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broader comparison of the extraction capabilities with respect to different geometries. These

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extractions were performed from a 250 mL McReynolds headspace generator jar (Figure S1),

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prepared in accordance with the methods described by Grandy et al.,31 Gomez et al.,32 and Poole33

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et al., with exact formulation described in the Supplementary Section S2. Headspace extractions

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were carried out at 55 oC for 10 minutes under static conditions. To account for intermembrane

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variability, 3 different membranes of each chemistry were analyzed 3 times each (n = 9 per



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membrane). All the results were calibrated and presented in terms of nanograms. This calibration

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was performed using a completely novel methodology coined “on-membrane liquid injection”

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which is fully described in Section S3 of the Supplementary Information. To avoid overloading of

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the MS detector while remaining well within the calibration range, 75:1 split, 10:1 split, and

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splitless injections were used for the TF-SPME, SBSE, and SPME injections, respectively. All the

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extractions were randomized to account for any undetected drift of the detector response. QC

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extractions were performed and analyzed throughout the experiment.

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Intermembrane analytical reproducibility of a modified McReynolds standard

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To ensure that the TF-SPME preparation procedure yielded statistically reproducible

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membranes, an intermembrane reproducibility study was carried out using the data obtained in the

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coating comparison experiments. As such, the results of this study are based on the same extraction

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protocols and membranes described in the aforementioned study. To confirm membrane

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reproducibility, 3 membranes of each coating chemistry type were compared through a one-way

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ANOVA test at a 95% confidence level for each of the 6 McReynolds analytes. Furthermore, the

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inter-batch reproducibility of lab-made HLB particles was also assessed by comparing two

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completely unique batches of HLB(P)/PDMS and DVB/PDMS thin film membranes.

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On-site thin film solid phase microextraction of chlorination by-products in a private hot tub

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As a proof of concept, thin film solid phase microextraction was performed at a private hot

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tub. Direct immersion extractions were performed using a custom TF-SPME sampling case (PAS

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technologies, Magdala, GE), which allowed 4 replicate extractions to be performed at 2000 rpm

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directly from the hot tub for 10 minutes (Figure 1A). It is worth noting that even though only 4

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replicate extractions were performed as part of this experiment, the sampling head of the sampling

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case could accommodate up to 6 TF-SPME membranes (Figure 1B). The temperature of the hot


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tub water was set to 103 oF (39.5 oC), but measured to vary between 38.5 oC and 40.5oC during

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sampling. The pH, free available chlorine, and alkalinity (concentration of sodium hydrogen

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carbonate buffer) were measured to be between 7.2-7.4, 3-5 ppm, and 120-160 ppm, respectively.

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Following extraction, the membranes were dried by dabbing with a Kimwipe, placed in 3.5-inch

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thermal desorption tubes, and then immediately submitted to on-site analysis on the portable

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GC/MS instrument. Extractions were also performed with a C7-C20 n-alkane standard gas

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generating vial to assist with retention time indexing, and hence with the identification of unknown

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compounds.29,31 Quality control injections of benzene, toluene, ethylbenzene, and o-xylene were

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also performed using a BTEX standard gas generating vial before and after on-site sampling, and

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as part of in-lab calibration so as to ensure stable response for the portable GC/MS instrument.

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Calibration for the quantitation of chloroform and dichloroacetonitrile was performed in

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the analytical laboratory, after sampling. To closely match the conditions of the hot tub water, a

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replicated matrix was prepared by spiking 3 L of deionized water with 150 µL of 6% residential

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grade sodium hypochlorite, 1 g of sodium hydrogen carbonate, and 55 µL of HCl. The obtained

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solution was then heated to 39.5 oC on a digital hotplate and stirrer (Scilogex, USA). After reaching

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that temperature, appropriate amounts of a methanolic chloroform and dichloroacetonitrile

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standard were spiked into the 3-L replicated hot tub water. Immediately thereafter, 3 replicate TF-

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SPME extractions were performed and analyzed by the same methodology described for the on-

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site experiments.

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Figure 1. TF-SPME on-site sampling head while: A) performing 4 replicate extractions at 2000 rpm from hot-tub water, and B) fully loaded with 6 replicate TF-SPME membranes.

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Physical characteristics of lab-made sorbent particles and thermal stability of thin films

RESULTS AND DISCUSSION

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The synthesized HLB particles were characterized by FT-IR, SEM, TEM, and surface area

258

analyses. The FT-IR spectrum obtained for the 1.33 µm HLB particles is shown in Figure S7 as

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an example. The peaks in the ranges of 3084–3018, 1642–1446, 795–708 and 2848–2921 cm-1

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were respectively assigned to aromatic C=C-H stretching, C-C stretching, aromatic C-H bending,

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and methylene C-H stretching. Furthermore, the signal at 1687 cm−1 was assigned to the C=O

262

stretching vibration of N-vinylpyrrolidone. These characteristic absorption peaks confirmed the

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formation of the poly(divinylbenzene-co-N-vinylpyrrolidone) resin.

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Following this, the morphological features of the particles were visualized by SEM and

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TEM analysis. As can be seen in Figure 2, the particles obtained by precipitation polymerization

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were spherical, uniform and monodisperse. TEM analysis indicated that the particles had a

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diameter of approximately 1.33 µm. Conversely, the particles obtained by suspension

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polymerization were spherical but non-uniform in size (polydisperse), with diameters ranging from

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30-60 µm.


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Figure 2. HLB particles synthesized by precipitation polymerization: (a) STEM image recorded at 200 kV (scale 1 µm), (b) TEM image recorded at 200 kV (scale 500 nm).

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total porosity of said particles. As such, it may be expected that the smaller 1.33 µm precipitation-

276

polymerized particles would have a higher SSA in comparison to the other tested HLB particles.

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However, as can be seen in Table 1, this was not the case. The specific surface area of the HLB

278

particles synthesized by precipitation polymerization was approximately half that of all the other

279

tested particles. Meanwhile, the SSA of the other particles, including the commercial DVB,

280

commercial HLB, and the HLB prepared by suspension polymerization, were all similar. The SSA

281

difference observed for the precipitation-polymerized HLB is likely related to a lower pore volume

282

and smaller pore size for these particles. Although purely speculative, the observed variations

283

likely stem from the porogen chosen in the preparation of each particle type. For the precipitation-

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based HLB, acetonitrile was used in lieu of toluene as porogen, which was employed in the

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suspension polymerization methodology. Toluene was also likely used for the preparation of the

286

commercial HLB particles, as specified in the original HLB patent.34 Despite having a lower SSA,

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the precipitation particles remained much more microporous, with an average pore diameter of

The specific surface area (SSA) of sorbent particles generally depends on the diameter and



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only 13 Å. Such a microporous nature may be an inherent advantage for the extraction and

289

retention of low boiling VOCs and VVOCs, as these compounds generally have a much smaller

290

molecular radius.4,7

291

In terms of thermal stability, comparison of blank analytical runs performed on the

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benchtop TDU-CIS4 equipped GC/MS instrument indicated that a similar amount of background

293

could be observed whether a HLB/PDMS, DVB/PDMS TF-SPME membrane or the pure PDMS

294

SBSE device was used. These results are further discussed in supplementary Section S4. and

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shown graphically in Figure S3.

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Table 1. Comparison of physical characteristics of tested sorbent particles. Sorbent particles DVB (comm.) HLB (comm.) HLB Suspension HLB Precipitation

SSA (m2g-1) 750 800 727 335

Pore size (Å) 400 80 71 13

Pore volume (mL/g) 1.54 1.30 0.64 0.20

Particle size (µm) 5 5 30-60 1.33

297 298

Improvement of TF-SPME affinity for polar VOCs using HLB-loaded thin film membranes

299

As HLB-based sorbents are designed to provide balanced coverage between both polar and

300

non-polar analytes, a modified McReynolds standard comprised of benzene (log [P] = 2.13), 2-

301

pentanone (log [P] = 0.98), , 1-nitropropane (log [P] = 0.94), pyridine (log [P] = 0.84), 1-pentanol

302

(log [P] = 1.7), and octane (log [P] = 4.78) was selected as the most appropriate matrix for a

303

comparative study, to enable a comparison of the relative efficiency of extraction of volatiles on

304

broad-spectrum sorbents.35 As shown graphically in Figure 3 and numerically in Table S4, the 1.3

305

µm HLB particles prepared by the precipitation polymerisation method yielded the highest

306

extraction amounts, with extracting factors of 1.8, 2.2, 1.9, 1.7, 2.0 and 1.3 times more benzene,

307

2-pentanone, 1-nitropropane, pyridine, 1-pentanol, and octane, respectively, than the established

308

DVB/PDMS based membrane. In terms of the more established extraction devices, the

309

DVB/PDMS SPME fiber was ubiquitously found to offer the lowest extraction amounts, followed 14 ACS Paragon Plus Environment

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310

by the 2 cm PDMS SBSE stir bar. The low extraction amounts observed for these two devices are

311

likely attributable to the limited sorbent volume of the SPME fiber, and to the lack of broad polarity

312

sorbent particles in the chemistry of the SBSE stir bar. In fact, the DVB/PDMS TF-SPME device

313

was found to extract, on average, 35-75 times more analyte than the comparative SPME fiber. This

314

is significantly more than the 20-fold factor reported in previous work, where a membrane twice

315

as large was used.29 Such variations are almost certainly owed to the near-equilibrium extractive

316

conditions adopted in the current study, which enabled use of the entire volume of the sorbent for

317

extraction. Conversely, pre-equilibrium conditions were selected in the previously reported

318

pesticide study, as the goal was to show the benefits of having a high surface area extraction device

319

for quick on-site analysis of semi-volatile water contaminants.29 As previously alluded to, the

320

improved extraction efficiency offered by the precipitation polymerisation-based sorbent particles

321

is thought to be related to the improved polarity range of the HLB particles, as well as their

322

microporous surface structure. Particularly, even though the commercial HLB obtained from

323

Waters had a specific surface area twice as large as the latter, the much more microporous

324

precipitation polymerisation-based particles, which used acetonitrile as a porogen, still provided

325

significantly higher extraction amounts (2-tailed T-test at 95% confidence) for all the analytes

326

tested, with a value p = 0.00047 for octane being the highest reported. At this stage, it is not known

327

with certainty whether this observation is solely due to the microporous nature of the sorbent;

328

another possibly could be a higher concentration of sorptive functional groups on the particle

329

surface. As such, further characterisation of these particles is still required to confirm these

330

possibilities.



65 um DVB/PDMS fibre

2 cm PDMS SBSE

2 cm DVB/PDMS TF

2 cm HLB(S)/PDMS TF

2 cm HLB(C)/PDMS TF

2 cm HLB(P)/PDMS TF

7000 Amount extracted (ng)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 27

6000 5000 4000 3000 2000 1000 0

331

Benzene

2-Pentanone Nitropropane

Pyridine

1-Pentanol

Octane

332 333 334 335 336 337 338

Figure 3. Relative extraction efficiencies of the studied McReynolds standards using: 65 µm DVB/PDMS fibers, 2 cm PDMS SBSE stir bars, DVB/PDMS TF, HLB(S)/PDMS TF (suspension HLB) membranes, HLB(C)/PDMS TF (commercial HLB) membranes, HLB(P)/PDMS TF (precipitation HLB) membranes. Extractions performed from the McReynolds standard headspace generating vial for 10 min at 55 oC.

339

To perform reliable sampling while using different TF-SPME membranes to represent

340

replicate analyses, it remains very important to confirm that they can be manufactured to be

341

statistically reproducible, or at least within 10% variation of each other. Initially, as shown in

342

supplementary Section S5 and Figure S4 it was demonstrated that once stored within a TDU

343

desorption tube on the auto sampler rack, these TF-SPME devices could retain all of the

344

McReynolds probes for at-least 24 hours and up to 120 hours for all probes except pyridine at a

345

95% level of confidence. For the membranes being discussed, ANOVA tests at 95% confidence

346

level confirmed that, for the most part, the prepared membranes were statistically similar when

347

grouped by their corresponding sorbent chemistries. These 1-way ANOVA tests are summarized

348

in Table 2, while their corresponding bar charts are shown in Figure 4. Among the 24 one-way

349

ANOVA tests performed, the only exceptions to this were 2-pentanone on the precipitation HLB-

Intermembrane analytical reproducibility for extraction of modified McReynolds standard


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350

based membranes, and 1-pentanol on the commercial HLB-based membranes, which exhibited F-

351

values of 8.82 and 8.97, respectively (F-critical = 5.14). Such results are not uncommon when

352

using ANOVA testing, as one set of replicates with uncharacteristically low %RSD values can

353

make even the smallest variations seem statistically significant. A review of the data confirmed

354

this to be the case, as the first and second membranes prepared using the precipitation-based HLB

355

had %RSD values for 2-pentanone of 2% and 3% RSD, respectively. Similarly, the second

356

membrane prepared with commercial HLB exhibited a minuscule %RSD of 1% for the 1-pentanol

357

standard, in contrast to the majority of other values ranging between 5-10% RSD. Even so,

358

supposing that these values are to be considered statistically different, the inter-membrane %RSD

359

values for said compounds were still 8% for both membranes. Moreover, it was further shown that

360

completely different batches of TF-SPME membranes, that were themselves prepared with

361

different batches of homemade HLB and commercial DVB particles, were also statistically

362

identical by means of the 2-tailed T-test at a 95% level of confidence. This inter-batch

363

reproducibility is further discussed, tabulated and graphically presented in Section S6 of the

364

supplementary information.

365 366 367 368 369

Table 2. F-values corresponding to intermembrane variability generated from one way ANOVA testing performed at a 95% confidence level. The tested chemistries include DVB/PDMS TF, HLB(S)/PDMS TF (suspension HLB), HLB(C)/PDMS TF (commercial HLB), and HLB(P)/PDMS TF (precipitation HLB). Extractions performed from the standard McReynolds headspace generating vial for 10 min at 55 oC. Coating DVB/PDMS TF HLB(S)/PDMS TF HLB(C)/PDMS TF HLB(P)/PDMS TF

Benzene 1.13 4.39 4.49 1.27

2-Pentanone 1.64 1.41 0.75 8.82

Nitropropane 1.27 1.23 1.11 0.48

Pyridine 1.39 1.13 0.54 2.90

370


1-Pentanol 1.72 2.70 8.97 0.35

Octane 0.42 0.87 1.53 2.69

F Crit 5.14 5.14 5.14 5.14


371 372 373 374 375 376

Figure 4. Intermembrane extraction amounts corresponding to the 4 TF-SPME chemistries tested including, A) DVB/PDMS TF, B) HLB(S)/PDMS TF (suspension polymerization), C) HLB(C)/PDMS TF (commercial HLB), and, D) HLB(P)/PDMS TF (precipitation polymerization). Extractions performed for 10 minutes at 55 oC from the McReynolds standard headspace generating vial.

377

On-site TF-SPME analysis of chlorination by-products from a private hot tub

378

To demonstrate that the developed HLB/PDMS TF-SPME membranes could be employed

379

entirely on-site, untargeted extractions of disinfection by-products (DBPs) were performed from a

380

private hot tub. Generally speaking, swimming pools and hot tubs use chlorine in the form of

381

hypochlorous acid to disinfect the water. This chlorine reacts with organic compounds originating

382

from decaying organic materials such as leaves and soil, as well as the bodily fluids of bathers,

383

particularly human sweat and urine. Because of the high levels of humic acids and/or amines found

384

in these contaminants (particularly urea), disinfection through chlorination may result in the

385

formation of trihalomethanes (THMs), chloramines, and other DBPs whose vapors are known to

386

cause eye irritation and lung damage at high enough concentrations.36 Such compounds are 18 ACS Paragon Plus Environment

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387

generally very volatile while exhibiting neither strongly polar, nor strongly non-polar

388

characteristics, making a microporous sorbent that gives balanced polarity coverage an ideal

389

choice for their extraction.

390

Appropriately, the highly microporous precipitation polymerization-based HLB/PDMS

391

TF-SPME membranes were employed in conjunction with a portable GC-MS instrument for an

392

entirely on-site determination of chlorination by-products from the hot tub of one of the authors.

393

In total, over 30 different compounds were identified from the hot tub water, 6 of them being

394

classified as chlorination by-products. The identity of these 6 compounds, shown in Table 3, was

395

determined by matching with the NIST 2011 mass spectral database, followed by confirmation

396

with either analytical standards or a standard n-alkanes linear retention index plot.37 As can be

397

seen in Table 3, the precision of the linear retention index matching was exceptional, with values

398

within +/- 4 points of those reported in the literature, all of which reported the use of a similar GC

399

stationary phase (95% PDMS, 5% polymethylphenylsiloxane).38–41 These compounds, including

400

chloroform, bromodichloromethane, dichloroacetonitrile, chlorobenzene, benzonitrile, and benzyl

401

chloride, have been reported in terms of their occurrence as DBTs, so their presence was not very

402

surprising.42–44

403

In terms of quantitative analysis, calibration was only performed for chloroform and

404

dichloroacetonitrile. This calibration had to be performed in a large volume (3 L) of water, to

405

ensure that depletion of the standard was negligible, as this would most certainly be the case in the

406

750 L hot tub. Remarkably, over a span of 5 calibration points, both compounds yielded R2 values

407

over 0.99, indicating very good correlation to response, especially considering that this experiment

408

was performed on hand portable instrumentation. This summarized calibration data can be viewed



409

in Table 4 below, while the corresponding calibration curves are presented in Figure S8 of the

410

Supporting Information.

411

Chloroform and dichloroacetonitrile were found to be present at concentrations of 270 µg

412

L-1 and 79 µg L-1, with %RSD values of 13% and 5%, respectively. After reviewing similar studies

413

in the literature, these levels were considered acceptable but still somewhat high, and were in fact

414

the most prevalent THM, in addition to chloramine in our study.43,44 With %RSDs of less than

415

13% and, according to the experimentally produced control chart, good inter-day stability of the

416

portable GC/MS instrument (Figure S9), the entirely on-site TF-SPME-GC/MS methodology was

417

considered to be sufficiently sensitive and quite repeatable. For comparison, in a meta-study of

418

disinfection by-products originating from drinking waters, swimming pool waters, and spa waters,

419

these 2 compounds were also found to be the most prevalent contaminants reported for chlorinated

420

drinking waters.44 Overall, chloroform and dichloroacetonitrile were found at very high levels at

421

most tested sites, approaching concentrations of 762 µg L-1 and 160 µg L-1, respectively, in waters

422

stemming from the most heavily used spa included in this study. As part of their drinking water

423

guidelines, the World Health Organization (WHO) considers chloroform levels up to 300 µg L-1

424

and dichloroacetonitrile levels up to 20 µg L-1 to be safe for human bathing and consumption.42

425

Although the goal of this study was to show the effectiveness of the new HLB/PDMS TF-SPME

426

membranes for a real world on-site sampling of moderately polar VVOCs, it will also result in the

427

water of the tested hot tub being changed much more frequently than twice a year in light of these

428

results.

429 430 431


Page 20 of 27

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432 433 434


Table 3. Identification of chlorination by-products from hot tub water using a precipitation-polymerized HLB/PDMS TF-SPME device. Extractions performed directly from hot tub water at 39.5 oC at 2000 rpm for 10 minutes. Compound

RT(s)

RTIExp*

Chloroform 31.07 NA Bromodichloromethane 43.49 711 Dichloroacetonitrile 45.16 725 Chlorobenzene 59.57 847 Benzonitrile 74.03 989 Benzyl chloride 76.78 1019 *Retention time index values calculated by experiments **Retention time index values from literatures ***Identity confirmed by standards

RTI lit. **

Conc. (µgL-1)

SD

%RSD

Std.***

270 79 -

35 4 -

13 5 -

709(38) Std.*** 844(39) 989(40) 1023(41)

435 436 437 438

Table 4. Summarized portable GC/MS calibration data for chloroform and dichloroacetonitrile. The calibration of TFSPME extractions was carried out from 3 L of matrix-matched water at 39.5 oC for 10 minutes at 2000rpm. Compound

Range (µgL-1)

Slope

Y-Intercept

R2

Chloroform

125-1000

773.16

4453.7

0.9906

Dichloroacetonitrile

50-250

56.21

32.8

0.9957

439 440

CONCLUSION AND FUTURE DIRECTION

441

A new chemistry of TF-SPME, involving the use of lab-made HLB particles for the

442

balanced detection of both polar and non-polar volatile organic compounds, is proposed in this

443

study. Considerably improved sensitivity, as compared with membranes prepared from DVB

444

particles, was also demonstrated for the studied compounds. The microporous, custom-made HLB

445

particles, which were prepared by a precipitation-based polymerization technique, were shown to

446

significantly outperform comparable commercial mesoporous HLB particles with respect to the

447

studied volatile analytes. The background thermal stability of the prepared membranes for GC

448

desorption was also determined to be comparable to that exhibited by the previous DVB/PDMS-

449

based TF-SPME chemistry. Furthermore, the inter-membrane reproducibility was confidently

450

validated within four different batches of membranes using varying sorbent chemistries at a 95%

451

level of confidence, indicating that the herein proposed membranes could be prepared reliably. 21 ACS Paragon Plus Environment


452

The reliability of the membranes for the presented method was further substantiated with the

453

results of an on-membrane stability study, demonstrating that, provided that membranes are stored

454

properly, even compounds as volatile as benzene remain stable on the membrane for at least 120

455

hours. Finally, the concept was proven to be effective for real-world applications via a proof-of-

456

concept study involving on-site analytical sampling and instrumental analysis, the results of which

457

showed that the developed method enabled the precise determination of various halogenated

458

compounds from a private hot tub.

459

It is hoped that soon, the research completed in the development of these lab-made HLB

460

particles and the corresponding HLB/PDMS TF-SPME may offer a new and superior sorbent

461

phase for balanced coverage of volatile analytes.

462

ASSOCIATED CONTENT

463

Supplementary Information

464 465 466 467 468 469 470 471 472 473

The Supporting Information is available free of charge on the ACS Publications website at DOI:

474

AUTHOR INFORMATION

475

*CORRESPONDING AUTHOR

476

Phone: +1 519 888 4641. Fax: +1 519 746 0435. E-mail:

477

[email protected].

478

NOTES

Section S1. Preparation of in-house HLB particles; Section S2. Preparation of the large volume McReynolds headspace generating jar; Section S3. Calibration of the amount extracted by onmembrane liquid injection; Section S4. Comparison of the thermal stability of TF-SPME and SBSE devices; Section S5. Validation of analyte stability on thin films stored in TDU tubes postextraction; Section S6. Inter-batch reproducibility of the TF-SPME membranes; Supplementary Figures and Tables are as discussed in the manuscript text.


Page 22 of 27

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479

The authors declare the following competing financial interest(s): The authors of this

480

manuscript herein declare that although they have received financial support from Gerstel

481

Incorporated, they maintain their independence as a third-party academic body, resulting in an

482

unbiased representation of the results with no competing conflict of interest, financial or otherwise. The equal authorship is in accordance to alphabetical order.

483 484

ACKNOWLEDGMENT

485

The authors would like to acknowledge Supelco Co., and the analytical division of

486

MilliporeSigma Corp. for their contribution of raw materials for the preparation of the membranes,

487

Waters Inc. for their contribution of HLB particles, and Gerstel Inc. for continued financial and

488

instrument support. The authors would also like to thank the Natural Sciences and Engineering

489

Research Council of Canada (NSERC) for financial support.

490 491

REFERENCES

492 493 494

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Development of a hydrophilic lipophilic balanced thin film solid phase

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