Detection and quantification of trace airborne transfluthrin concentrations via air sampling and thermal desorption gas chromatography-mass spectrometry

This efficient method allows for the remote collection of samples and rapid analysis of airborne transfluthrin from industrial applications, optimization studies of commercial products as well as domestic/household monitoring.

Journal of Chromatography A, 1573 (2018) 156–160 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Short communication Detection and quantification of trace airborne transfluthrin concentrations via air sampling and thermal desorption gas chromatography-mass spectrometry Michael W.C Kwan a , Jason P Weisenseel b , Nicholas Giel a , Alexander Bosak a , Christopher D Batich c,d , Bradley J Willenberg a,∗ a University of Central Florida College of Medicine, Department of Internal Medicine, 6900 Lake Nona Blvd, Orlando, FL, 32827, USA PerkinElmer Inc., 940 Winter St, Waltham, MA, 02451, USA c University of Florida, College of Engineering, Departments of Materials Science and Engineering, 549 Gale Lemerand Dr, Gainesville, FL, 32611, USA d University of Florida, J Crayton Pruitt Family Biomedical Engineering, 1275 Center Dr, Biomedical Sciences Building, JG-56, Gainesville, FL, 32611, USA b a r t i c l e i n f o Article history: Received July 2018 Received in revised form 29 August 2018 Accepted 31 August 2018 Available online September 2018 Keywords: Thermal desorption GC–MS Transfluthrin Pyrethroids Active air sampling Passive release a b s t r a c t A rapid thermal desorption-gas chromatography-electron ionization-mass spectrometry (TD-GC-EI-MS) method for airborne transfluthrin detection is studied Active air sampling of L over h at 23 ◦ C through a Tenax® -loaded tube resulted in efficient capture of airborne transfluthrin Subsequent thermal desorption was employed to achieve an LOD of 2.6 ppqv (parts per quadrillion by volume) A minimum primary desorption temperature of 300 ◦ C is necessary for optimal recovery of sample from the Tenax® adsorbent The matrix effects of indoor air lead to an error of 10.9% and 10.5% recovery of sample (10 pg and 100 pg loaded tubes, respectively) The linear range was 74–74,000 ppqv with a correlation coefficient of 0.9981 Active air sampling of a novel passive release device revealed a ∼150 pg/L airborne concentration gradient over m, providing spatial characterization of the device’s performance This efficient method allows for the remote collection of samples and rapid analysis of airborne transfluthrin from industrial applications, optimization studies of commercial products as well as domestic/household monitoring © 2018 The Author(s) Published by Elsevier B.V This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Introduction Transfluthrin ((1R,3S)-3-(2,2-Dichlorovinyl)-2,2-dimethyl-1cyclopropanecarboxylic acid (2,3,5,6-tetrafluorophenyl)methyl ester) is a semi-volatile organic compound of the pyrethroid class of insecticides that is routinely used as an indoor insecticide Transfluthrin (TF) works as a potent dipteran sodium channel agonist and can elicit effects such as repellency, restlessness, knockdown and death in mosquitoes [1] Commercial use of TF along with the inevitable exposure to humans has generated interest in quantifying low levels of airborne TF with the ultimate goal of understanding what constitutes an effective airborne concentration against mosquitoes without placing undue harm on people [2–4] Previously, our group has developed a passive release device that releases airborne TF at a constant rate into the air over several hundred hours [5, unpublished data] The precise quantification of airborne TF emanating from the device ∗ Corresponding author E-mail address: Bradley.Willenberg@ucf.edu (B.J Willenberg) will provide insight into device performance and may help guide optimization Furthermore, the lower limit of efficacy for each of TF’s effects towards mosquitoes (i.e confusion, excitation, knockdown and death) are currently unknown with a previous study suggesting that TF can effectively knockdown mosquitos at one parts per trillion by volume (1 pptv ) [6] Proper dissemination of TF is paramount as over and underexposure of insecticides have been linked to spurring resistance development [7–10] Gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) is a powerful tool in separating, analyzing and quantifying the constituents of a complex mixture of volatiles Previous methods for monitoring TF airborne concentrations via GC-EIMS include air sampling followed by ultrasound-assisted solvent extraction [2], solid-phase microextraction [11] and direct air measurements using Proton-Transfer-Reaction Mass Spectrometry [4] These methods have reported airborne concentrations in the range of ␮g/m3 , pg/gram and single-digit ng/m3 , respectively The shift towards the reduction in extraction mass (aka microextractions), be it liquid or solid phase extraction, is attractive as the analyte can be concentrated from the adsorbent into microliters of solvent that can be injected into the column However, the handling https://doi.org/10.1016/j.chroma.2018.08.066 0021-9673/© 2018 The Author(s) Published by Elsevier B.V This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) M.W.C Kwan et al / J Chromatogr A 1573 (2018) 156–160 of micro-volumes can be cumbersome and sample loss is known to occur In this regard, thermal desorption (TD) is advantageous over microextractions as the lack of extraction matrix results in higher recovery of the sample, reduced potential contamination, and more rapid analysis [12] Additionally, this study used an automated TD system which helped to reduce human error Although previous works have utilized this method, no detailed methodology for the quantification of TF via TD-GC-EI-MS has been, to our knowledge, reported [6,13] Furthermore, the International Organization for Standardization (ISO) standard on indoor air sampling of volatile organic compounds (VOCs) with TD-GC-EI-MS (ISO 16000-6:2011) is broad in scope as the chemical and physical characteristics of VOCs encompass a wide range To this end, we report the quantification of indoor airborne TF via TD-GC-EI-MS and detail the instrumental and experimental conditions needed to obtain similar results This method was then used to characterize the emanations of a novel passive release device Materials and methods 2.1 Instrumentation and materials ® TD-GC-EI-MS was accomplished using a Perkin Elmer Clarus ® SQ 8C mass spectrometer, Clarus 580 gas chromatograph and TM TurboMatrix 650 automated thermal desorber (Waltham, MA, TM TC 220 conditioning oven USA) A Perkin Elmer TurboMatrix (Waltham, MA, USA) was used to condition thermal desorption tubes An SKC, Inc AirChek air sampler pump Model 224-44XR (Eighty Four, PA, USA) was used to collect air samples onto Markes International, Inc thermal desorption tubes (Sacramento, ® CA, USA) filled with the adsorbent Tenax 35/60 A MesaLabs Bios Defender 510 air flow calibrator was used to calibrate the SKC, Inc quad adjustable low flow holder (SKC, Inc., Eighty Four, PA, USA) TM Chromasolv methanol (HPLC Grade) was purchased from Fisher Scientific, Inc (Hampton, NH, USA) Ultra-high purity helium was provided by Airgas, Inc (Radnor, PA, USA) and nitrogen was generated in-house by a Parker Balston Model N2-35 nitrogen generator (Parker Hannifin Corporation, Lancaster, NY) 2.2 Standard preparation Standards of TF were prepared using Bayer TF obtained from United States Department of Agriculture-Agricultural Research Service-Center for Medical, Agricultural and Veterinary Entomology (USDA-ARS-CMAVE, Gainesville, FL Daniel L Kline, see 157 acknowledgements) A stock solution of 10 mg/mL of TF in isopropanol was prepared volumetrically and serial dilutions with isopropanol were used to prepare a set of 4–8 working standards ranging from 10 pg/␮L to 10 ng/␮L Standard tubes were spiked at the inlet with 0.5 ␮L of liquid working standard and transferred ® onto the Tenax bed with a flow of N2 at 100 mL/min for 15 All thermal desorption tubes were conditioned with N2 at a rate of 100 mL/min prior to spiking with working standards The conditioning cycle was 250 ◦ C for 20 min, followed by 300 ◦ C for 20 and then 335 ◦ C for 30 The heating rate for all ramp periods was 10 ◦ C/min 2.3 Parameters for quantitative analysis To recover the TF from the sample tubes, a two-stage thermal desorption method was used The primary desorption from the sample tube was performed at various temperatures ranging from 200 to 335 ◦ C for three minutes to assess the optimum desorption temperature Prior to secondary desorption, the samples ® were collected on a Tenax concentrating trap held at -20 ◦ C via a flow of high purity helium at a rate of 75 mL/min The heated valve in the thermal desorption instrument was maintained at 300 ◦ C and transfer line to the GC was maintained at 280 ◦ C at all times to prevent condensation of the analytes in either the valve or transfer line To deliver the sample to the GC column for analysis, secondary desorption of the sample from the concentrating trap was performed by heating the trap to 335 ◦ C at a rate of 40 ◦ C/sec with a helium flow rate of mL/min The temperature program for the GC was two minutes at 55 ◦ C followed by a 20 ◦ C/min ramp to 290 ◦ C and then a hold at 290 ◦ C for 4.25 Helium was used as the carrier gas and the flow rate was mL/min The column utilized was a Perkin Elmer Elite 624 (Cat No N9315068) mid polar column (6% cyanopropyl phenyl – 94% dimethyl polysiloxane) with dimensions 30 m length, 0.25 mm ID and 1.4 ␮m film thickness The transfer line from the GC column to the MS source was maintained at 250 ◦ C and the electron ionization (EI) source was maintained at 280 ◦ C The mass spectrum of TF was identified (positive ion mode – 70 eV) for TF by identifying the target ion at m/z 163 and its fragmentation qualifying peak at m/z 91 (Fig 1), which is consistent with previously observed mass spectra of TF [14–19] For quantitative analysis, the mass spectrometer was set to selected ion recording (SIR) mode at 163 m/z with the resulting SIR chromatograph integrated and the peak area of the TF peak used for quantification Fig Mass spectrum of transfluthrin via EI at 70 eV with target ion 163 m/z and the qualifier 91 m/z The chemical structure of transfluthrin and the hypothesized 163 m/z fragment is shown above Background subtraction of the column was applied 158 M.W.C Kwan et al / J Chromatogr A 1573 (2018) 156–160 2.4 Statistical determination of limit of detection (LOD) and limit of quantification (LOQ) The LOD and LOQ were determined experimentally by signal to noise ratio (SNR) as well as the standard error of estimates (SEE) approach For the SNR measurement, the LOD must have an SNR of at least three while the LOQ was determined at the SNR of 10 [20] The calculation for the LOD following the SEE approach is shown in Eq (1) where sy/x is the standard error of the estimate, m is the slope of the fitted regression line and k-factor is 3.3 and 10 for the LOD and LOQ as noted by previous authors [21,22] LOD = k · sy/x /m (1) Eq (2) shows the calculation for the standard error of estimates where yi is the sample data and yF is the value of the fitted regression line from matrix spiked samples that corresponds to the concentration of TF used to achieve value yi Concentrations near the low end of the linear range was used for SEE calculations sy/x = (yi − yF )2 (2) Due to the large background drift (column bleed), the European Pharmacopoiea chromatographic method of selecting a large background region to sample the noise is not achievable without potentially misleading baseline correction techniques [20] Thus, the background noise was taken 0.1 away from the analyte peak in each direction Data was compiled from three different experiments over different days with samples collected in triplicate 2.5 Air sampling Air sampling of airborne TF was accomplished using a novel passive release device created with the same TF source used to create the standards in Section 2.2 This device was composed of a cotton wick with an interior reservoir of isopropanol and TF using the same Bayer TF from Section 2.2 [5] The device was activated and subsequently allowed to release volatiles in the center of a room of 5.2 × × 2.7 m The air sampling occurred within cm of the device, referred to here as the point of generation (POG), as well as one meter from the device at the same height (1 m) above the floor Both the air supply (∼0.17 m3 /s) and exhaust (∼0.21 m3 /s) were continuously running and located on the ceiling of the room Thermal desorption tubes were placed onto adjustable low flow holder suspended one meter off the ground at both POG and one meter Flow rate for each flow port was adjusted to 150 mL/min and validated using the air flow calibrator Air sampling without a passive release device present was accomplished to establish the background signal Afterwards, a device was activated and placed in the room and allowed to emanate for 60 after which air samples ® were collected on Tenax 35/60 providing an average of L of sample volume passing through each tube Brass caps equipped with polytetrafluoroethylene ferrules were secured onto these air sample tubes to protect the sample from contamination and potential sample loss between collection and analysis Airborne concentration of TF was recorded in parts per quadrillion by volume (ppqv ) using the following equation: ppqv = 1015 · molTF · 24.6 /V (3) Where ppqv is the parts per quadrillion by volume of TF, molTF is the moles of TF quantified by TD-GC-EI-MS, 24.6 is the ratio of liters to moles according to the ideal gas law at 23 ◦ C and 101,325 Pa and V is the average volume (9 L) of air sampled in liters The matrix effect of indoor air on the recovery of TF was studied by exposing TF-spiked tubes to indoor air at 150 mL/min for one (1) hour or the nitrogen generator for one (1) hour at 100 mL/min Fig Effect of primary desorption temperature on transfluthrin recovery from spiked tubes At temperatures below 300 ◦ C, there is carryover transfluthrin remaining on the tube Samples were normalized to the highest intensity within each experimental repeat Error bars represent sample standard deviation Results and discussion 3.1 Optimization of parameters and methods To assess the retention of TF on the column, blank tubes were analyzed between each spiked tube The measured instrumental transfluthrin carry over was typically less than 1% of the signal intensity of the spiked sample TF The small mass of TF on the column (90% recovery of spiked samples 160 M.W.C Kwan et al / J Chromatogr A 1573 (2018) 156–160 At different airborne concentrations of TF, the insecticide displays unique effects; at extremely low airborne concentrations TF has been shown to be an attractant to mosquitos while increasing concentrations eventually leads to death [1] Currently, the concentrations at which these unique behaviors arise are not known but a previous study has suggested that a concentration of pptv may be enough to repel mosquitos [6] With the LOD and LOQ reported in this method, the airborne concentrations on the order of single digit pptv can be quantified This level of detection makes it possible to study the various behavioral effects of low concentrations of TF on mosquito behavior The method was tested by measuring the airborne concentration of TF emanating from a novel passive release device, demonstrating that low levels of airborne TF can reliably be quantified Disclaimer Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and not necessarily reflect the position or policy of the Government and no official endorsement should be inferred Conflict of interest statement BJW has minor ownership interests in Sustained Release Technologies, Inc and Pest Natural, Inc («5%); these entities did not contribute to the support of this study Acknowledgements This project was sponsored in part by the Department of the Army, U.S Army Contracting Command, Aberdeen Proving Ground, Natick Contracting Division, Ft Detrick MD via a grant to CDB from the Armed Forces Pest Management Board (AFPMB) Deployed Warfighter Protection Research Program (DWFP- Grant No.: W911QY-15-1-0003) and by UCF Preeminent Postdoctoral (P3) Program award to MWCK The authors would also like to thank Jedidiah Kline (University of Florida) for assistance in creating the novel passive release devices Transfluthrin (TF) utilized in this project was supplied to USDA-ARS-CMAVE (Gainesville, FL) by Bayer through a Material Transfer and Research Agreement (MTRa) The MTRa allows transfer of TF to a third party participating in research associated with DWFP References [1] T.G.E Davies, L.M Fields, P.N.R Usherwood, M.S Williamson, DDT, pyrethrins, pyrethroids and insect sodium channels, IUBMB Life 59 (2007) 151–162, http://dx.doi.org/10.1080/15216540701352042 [2] R Barro, C Garcia-Jares, M Llompart, M.H Bollain, R Cela, Rapid and sensitive determination of 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possible to study the various behavioral effects of low concentrations of TF... collected in triplicate 2.5 Air sampling Air sampling of airborne TF was accomplished using a novel passive release device created with the same TF source used to create the standards in Section 2.2