Comprehensive methodology for semi-volatile organic compound determination in ambient air with emphasis on polycyclic aromatic hydrocarbons analysis by GC–MS/MS
- Photo: Journal of Chromatography A 2024, 1730, 465086. Fig. 1. Recoveries (%) of the spiked PAHs in the SPE cartridges (triplicates) that were stored inside Kapac heat-sealable bags at room temperature (25 °C), in a fridge (4 °C) for 1 and 2 weeks, and in a freezer (−20 °C ) for 3 months. Control SPE were extracted on the day of spiking (Day 0). All quantified amounts were compared with the original standard used in the test.
In the research article published recently in the Journal of Chromatography A the researchers from the Institute for Environmental Assessment and Water Research (IDÆA-CSIC), and the Department of Analytical Chemistry, University of Barcelona, Barcelona, Spain, introduced a methodology for semi-volatile organic compound determination in ambient air with emphasis on polycyclic aromatic hydrocarbons analysis using GC–MS/MS.
This study introduces a method for sampling and analyzing polycyclic aromatic hydrocarbons (PAHs) in ambient air using low-volume pumps and solid-phase extraction (SPE) cartridges. This approach captures both gas and particulate phase PAHs in indoor and outdoor environments, while reducing the number of extraction steps and solvent use. PAHs were analyzed by GC–MS/MS, with recoveries ranging from 40% to 118% and no breakthrough detected during sampling. Storage tests showed stable PAH concentrations under various conditions for up to three months, except for naphthalene and acenaphthylene. The method proved effective in detecting PAHs at levels significantly above quantification limits in urban indoor air samples.
The original article
Comprehensive methodology for semi-volatile organic compound determination in ambient air with emphasis on polycyclic aromatic hydrocarbons analysis by GC–MS/MS
Maria A. Aretaki, Judith Desmet, Mar Viana, Barend L. van Drooge
Journal of Chromatography A 2024, 1730, 465086
https://doi.org/10.1016/j.chroma.2024.465086.
licensed under CC-BY 4.0
Selected sections from the article follow. Formats and hyperlinks were adapted from the original. Tables 1,2 and 4 were truncated.
Highlights
- A simplified on-site SPE sampling is proposed for analyzing PAHs in indoor air.
- Storage of SPE in heat-sealable bags for transport from sampling sites to laboratory.
- GC–MS/MS analysis enabled quantification of PAHs in background urban indoor air.
- PAH analysis can be combined with the analysis of other semi-volatile organic compounds.
Abstract
Polycyclic aromatic hydrocarbons are air pollutants that affect the human health and the environment, and their accurate determination in outdoor and indoor environments is important. This study presents a methodology for sampling and analysis of semi-volatile compounds in ambient air with emphasis on the polycyclic aromatic hydrocarbons, collected with low-volume pumps (4.8 m3) in unconditioned solid phase extraction cartridges (Isolute ENV+). Sampling in SPE cartridges with low-volume pumps allows the collection of both gas and particulate phase compounds in indoor as well as outdoor environments, and reduces the number of extraction steps required as well as the solvent volume used for extraction. Analysis of the 16 US-EPA priority PAHs after extraction was conducted by GC–MS/MS with recoveries of the PAHs 40–118 %. No breakthrough was detected during sampling. Moreover, the methodology includes storage test to assess the conservation of PAHs in the SPE cartridges in heat-sealable Kapac bags; simulating transport from sampling sites to laboratory, and storage under room, cold and frozen conditions at different time-intervals, up to 3 months after sampling. The results showed that concentration levels remained constant across various storage time intervals and temperatures, with naphthalene and acenaphthylene being the only exceptions, showing high blank levels for the first and losses at room temperature for the later. The method quantification limits, including sampling, storage and GC–MS/MS analysis ranged from 2000 pg m-3 for naphthalene and 300 pg m-3 for phenanthrene to less than 20.0 pg m-3 for higher molecular and less volatile PAHs, such as benzo[a]pyrene (LOQ = 8.0 pg m-3). The feasibility of the method was tested by sampling indoors under urban background air conditions, showing individual PAH concentrations 4 to 10 times higher than their method quantification limits.
Keywords
Active air sampling; Solid phase extraction; Polycyclic aromatic hydrocarbons; GC–MS/MS
1. Introduction
The importance of Indoor Air Quality (IAQ) has become a focal point in numerous scientific studies due to the growing concerns within the scientific community about its impact on human health [1,2]. Among a variety of health-relevant air pollutants are Polycyclic Aromatic Hydrocarbons (PAHs), widely known for their toxicity, mutagenicity, and carcinogenicity [3,4]. These semi-volatile organic compounds (SVOCs) portion between vapor and particle phase in the atmosphere [3,5]. Regarding their origin, PAHs can derive from natural sources including volcanic eruptions and forest fires, but their primary source in urbanized areas are anthropogenic emission sources such as combustion of fossil fuel, biomass burning and residential heating and cooking [5,6]. While these compounds are mainly recognized as outdoor pollutants in modern urban areas, their infiltration into buildings makes them a noteworthy indoor pollutant [5].
While there are hundreds of known PAHs, the US Environmental Protection Agency (EPA) designated sixteen of them as priority pollutants including: naphthalene, acenapthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-c,d]pyrene, dibenz[a,h]anthracene, and benzo[g,h,i]perylene [7](Table S1). PAHs with higher molecular weight, indicating a greater number of aromatic rings, along with lower vapor pressure and solubility, are considered to be more carcinogenic according to the International Agency for Research on cancer (IARC). Numerous studies have established a connection between exposure to environmental PAHs and the onset of neurodegenerative disorders and diseases [8,9].
For all the reasons mentioned above, PAHs are a group of compounds which have been the subject of ongoing and extensive research. Regarding air sampling, the conventional collection of gas and particle-bound PAHs in ambient air is typically performed by low or high-volume samplers (12 or 24 h) by passing air through an adsorbent and collecting the aerosols on filters [7], and subsequently following established protocols, such as the US EPA method, to quantify compounds as PAHs from ambient air samples [10]. For atmospheric sample collection, the recommendation is to employ high-volume air samplers as these samplers allow the collection of both gaseous and particulate PAHs separately. In such sampling setups, a flow rate of approximately 0.1 to 1.0 m3 per minute is typically advised and therefore many studies focusing on the analysis of PAHs in the atmosphere follow this protocol and collect large volume air samples [[11], [12], [13], [14]].
Moreover, the sorbent selection plays a crucial role for PAH sampling and analysis. Many publications describe the collection of gas and particle phase PAHs in different sorbent materials. Volatile PAHs such as naphthalene and other volatile organic compounds are typically collected with Tenax in stainless steel tubs [12,15,16], XAD-2 sorbent tubes [17,18], and polyurethane foam (PUF) [[19], [20], [21]]. Particle phase PAHs or particle-bound PAHs are usually collected in filters such as glass fiber filters [22,23] or quartz filters [12,24] which before sampling are pre-baked in a muffle furnace to eliminate residual organic impurities and remove moisture. Simultaneous collection of both gas phase and particle phase PAHs, can be done using glass fiber filters for particle-bound PAHs, while the more volatile PAHs are adsorbed on plugs of polyurethane foam (PUF) placed behind the filter [11]. Nonetheless, many of the sorbents mentioned above, prior to deployment, require several, time-consuming steps for pre-treatment and often large solvent volumes which poses challenges concerning environmental disposal [19,25]. Regarding air sampling, SPE cartridges have also been deployed according to literature, but their application until now involves the collection of SVOCs such as organophosphate flame retardants (OPFRs) [26] and polyfluorinated alkyl substances (PFAs) [27].
Depending on the environmental sample and the sorbent material used for the collection of PAHs, there are diverse extraction methodologies reported in literature such as Solid phase extraction, Soxhlet extraction, ultrasound assisted extraction (UAE), accelerated solvent extraction (ASE) and other separation methods [[20], [28], [29]]. Over the past decade, the majority of studies describe the performance of UAE and Soxhlet extraction protocols using solvents such as dichloromethane, toluene, hexane, acetone, methanol or acetonitrile as well as mixtures of these, due to the high solubility of PAHs in these solvents [[20], [28], [29]]. However, certain extraction procedures widely used such as the Soxhlet and the UAE require relatively large volume of solvent and are time-consuming, typically ranging from several hours to overnight depending on the sample type [20,30,31]. Moreover, although ASE is a fully automated extraction technique that can be used for routine analysis offering rapid extraction times, the need for specialized and expensive equipment can sometimes make its application less feasible an unpractical [31]. Additionally, this extraction method is not selective as the high temperature and pressure used, are affecting the selectivity [32]. Concerning the determination of ambient air PAHs, gas or liquid column chromatography coupled to mass spectrometry or fluorescence detection systems are suitable analytical techniques to detect the ambient air PAH concentration ranging between few pg m-3 and several ng m-3 [10].
The present study aimed to develop a simplified and cost effective SPE extraction methodology, designed for multi-compound analysis, with focus on the analysis of Polycyclic Aromatic Hydrocarbons (PAHs) in air samples. To this end, low-volume samples were collected in unconditioned SPE cartridges and analyzed by an optimized gas chromatography (GC)-tandem mass spectrometry (MS/MS) method for the determination of 16 PAHs. The results from this study are expected to provide useful information for future research concerning air sampling for the characterization of concentrations of both gas and particle phase PAHs, as well as other SVOCs even at conditions with low ambient air concentrations. The results pertaining to the other compounds, such as organophosphate flame retardants (OPFRs) and phthalate Esters (PEs), are addressed in separate publications. The proposed methodology will be applied for indoor and outdoor air sampling in schools in different cities from Central, Northern and Southern Europe, within the framework of the Horizon EU project InChildHealth [33]. Given that this project involves sample shipment across EU to a central laboratory in Barcelona, a secondary goal of this work was to examine sample transport and storage strategies to ensure the preservation of the quality of the air samples and prevent the loss or contamination of volatile compounds during shipment. For this purpose, the use of light weight heat- sealable silicon Kapac bags was tested.
2. Materials and methods
2.1. Sampling setup and sites
Sampling to determine concentrations of PAHs was conducted in May and June 2023 in different indoor locations (offices, IT workshop and warehouse of the Institute of Environmental Assessment and Water Research (IDAEA-CSIC)) in urban background area in Barcelona (Spain). For the collection of air samples, low- volume pumps (Leland Legacy SKC, Dorset,UK) were deployed with an air flow rate of 4.0 L min−1 and sampling time of 8 h during the day, for five days in each sampling site. The pumps operated inside soundproofed boxes to minimize the noise generated. Each pump was connected with two SPE cartridges (Isolute ENV+200 mg/6 mL, Biotage, Uppsala Sweden) with a flow splitter, for the joint collection of both gas and particulate phase PAHs in each cartridge. One cartridge was used for PAH analysis. The SPE cartridges were used directly from their commercial packages without any previous cleaning or conditioning step. The total collected air volume in each cartridge was approximately 4.8 m3. Breakthrough of PAHs in the sampling setup was tested by placing SPE cartridges in series and spiking the first SPE with 25.0 µL of 100 μg L−1 deuterated PAH, and measure them after the total sampling period in both cartridges.
2.2. Solvents and analytical standards
High purity SupraSolv® acetone and n-hexane were purchased from Merck (KGaA, Darmstadt, Germany). The Standard Reference Material SRM2260 dissolved in toluene was from the National Institute of Standards and Technology (NIST; Gaithersburg, USA). Surrogate standards with sixteen deuterated PAH compounds dissolved in cyclohexane (d8-naphthalene, d8-acenaphthylene, d10-acenaphthene, d10-fluorene, d10-phenanthrene, d10-anthracene, d10-fluoranthene, d10-pyrene, d12-benz[a]anthracene, d12-chrysene, d12-benzo[b]fluoranthene, d12-benzo[k]fluoranthene, d12-benzo[a]pyrene, d12-indeno[123-cd]pyrene, d12-benzo[ghi]perylene, d14-dibenz[ah]anthracene) were from Dr. Ehrenstorfer (Augsburg,Germany). The PAH mix with native compounds (Table S1) of the sixteen EPA PAHs dissolved in cyclohexane were obtained from Dr. Ehrenstorfer (Augsburg,Germany).
2.3. Extraction and instrumental analysis
Before the extractions, 25 μL of a mixture (50 pg μL−1) of sixteen deuterated PAHs was injected inside each cartridge as surrogate standard. The cartridges were extracted in a mixture of n-Hexane and Acetone (1:1 v/v, 2×5 mL). This low solvent consumption method reduced the extraction times as the solvent mixture passed readily from the cartridges and the subsequent evaporation step occurred rapidly. More specifically, after the extraction step the extracts were evaporated under a gentle N2-gas stream in TurboVap (20 °C) to 1.5 mL. The remaining extracts were transferred to vials and evaporated to 1 mL. An aliquot of 0.5 mL was further concentrated to 25 μL for analysis by GC–MS/MS. The other half was used for the analysis of other semi-volatile organic compounds. Instrumental analyses were carried out by gas chromatography coupled with tandem mass spectrometer. Sample extracts were injected (1.0 μL; pulsed splitless) into an Agilent 7890A gas chromatography coupled with Agilent 7000B triple mass spectrometry (GC–MS/MS) and equipped with a HP-5MS 30 m capillary column (i.d. 0.250 mm; 0.25 µm film thickness; Agilent Technologies (USA)). The instrument operated under electron impact ionization (70 eV) while selected reaction monitoring (SRM) was used for acquisition. The oven temperature program started at 90 °C, held for 1 min, and was then heated to 120 °C at 10 °C min−1 and to 320 °C at 6 °Cmin−1, and held for 12 min. Hydrogen (99.9999 % purity) was used as carrier gas at 1.1 mL s−1, and nitrogen (99.9999 % purity) was used as collision gas. The transfer line temperature was 280 °C, and the ion source temperature was 230 °C.
2.4. Quantification
The PAHs and the deuterated PAHs were identified by comparing the retention time of the peaks generated with specific ions given in Table 1. Peak detection and integration were performed with Agilent Mass Hunter Workstation Software for Quantitative analysis (Version: B:08.00/Build 8.0.598.0) provided by Agilent Technologies (USA). The quantification of the compounds involved calculating the concentrations from the relationship between the chromatographic area of the product ion peaks of the compounds to those of the product ion peaks of the deuterated surrogate standards (given as area/area-D response) in the samples. This relationship was then compared to amount/amount-D responses in a six -point calibration curve for the accurate determination of concentrations. The concentration levels used for the calibration curves were 0.8, 4, 20, 100, 400, 2000 pg μL−1, while the deuterated PAH had a concentration of 50 pg µL−1. For the recovery test of the deuterated and targeted PAHs, the extracts and control vials were spike with 1-phenyldodecane, and their corresponding peak area ratios were compared and recovery % were calculated.
Journal of Chromatography A 2024, 1730, 465086: Table 1. (snippet) Parameter settings for studied PAHs and deuterated standard compound analyzed by GC–MS/MS.
2.5. Spiked cartridges and storage test
Storage tests were conducted to evaluate the recovery of PAHs under different storage conditions (temperatures) and varying storage time intervals (1 and 2 weeks). This test aimed to understand sample behavior at ambient and cool temperature conditions, simulating sample shipping and storage conditions. This need derived from the shipment of samples across EU to the central laboratory in Barcelona for analysis, as planned in the InChildHealth project. Ambient temperatures simulated were around 25 °C, while cold conditions were approximately 4 °C. Moreover, additional cartridges were stored for three months in a −20 °C freezer to simulate the maximum storage time of the samples before analysis. For this purpose, triplicates of SPE cartridges were spiked with 10 ng of a PAH mix with native compounds. The cartridges were wrapped in aluminum foil, placed within heat-sealable silicon Kapac bags and stored under different temperature conditions until extraction.
3. Results and discussion
3.1. Analytical quality control
Efficiencies of the method were determined by examining the recoveries of deuterated standards added to the cartridges before extraction, as well as from recoveries from target PAH compounds from quantitative data obtained by instrumental analysis. For this purpose, 1-phenyldodecane (25 µL of 100 pg μL−1) was introduced into the final extracts and controls before instrumental analysis in GC–MS/MS. Solvent volumes for the extraction process were tested for 4.5 mL and 10 mL. The extraction recoveries were significantly higher using 10 mL of solvent instead of 4.5 mL, particularly for the higher molecular PAHs and surrogate standards, and ranged between 40 - 118 % and 9 - 47 %, respectively. Lower recoveries for the more volatile PAHs were caused by evaporation losses, and not by solvent volumes. Due to these results, the selected extraction volume of the solvent was 10 mL of n-hexane - acetone (1:1 v/v), which also allowed analysis of other semi-volatile organic compounds.
Regarding the recoveries of parent PAHs obtained from extraction with 10 mL solvent, the results can be divided into 3 groups: volatile compounds (naphthalene, acenaphthylene and acenaphthene, fluorene) with the lowest recoveries 41–48 %, PAHs portioning between vapor and particulate phase (phenanthrene, anthracene, fluoranthene, pyrene) with recoveries between 52 and 68 %, and less volatile and more particle bound PAHs (benza[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[123 cd]pyrene, dizenz[ah]anthracene, and benzo[ghi]perylene) with recoveries 81–115 % (Table 2). Previous studies utilized different sorbent materials for collecting air samples and different solvent mixtures for extraction; parameters which can greatly influence recovery outcomes. SPE cartridges are usually used as an extraction and purification step of analytes from various environmental matrices [34]. Typical recoveries of PAHs from air samples range between 40 and 100 % [35,36], where lower recoveries refer to the more volatile PAHs as naphthalene, acenaphthylene and acenaphthene. Volatile compounds in general show lower recoveries, given the difficulty in preventing their evaporation during sample manipulation and specifically while performing the evaporation step under gentle N2-gas stream. However, other studies using the same solvent for the extraction of PAHs (n-hexane-acetone), mention high recoveries for particulate phase PAHs that range between 80 and 120 % [[36], [37], [38]]. Consequently, the recovery results obtained in this study using 10 mL solvent align with other results documented in the existing literature even though the sorbent material for the collection of the compounds differ.
Journal of Chromatography A 2024, 1730, 465086: Table 2. (snippet) Mean recoveries% (n = 3) and coefficient of variation (CV%) of studied PAHs using two different solvent volumes.
Gas chromatography-mass spectrometry (GC–MS) has been the predominant method utilized for the analysis of polycyclic aromatic hydrocarbons (PAHs) in air samples [3,7,20,39,40]. This method is associated with many advantages such as high selectivity and resolution, quantitative accuracy, low detection limits and requirement of relatively small sampling volumes [40]. In the recent years triple quadrupole (GC–MS/MS) has been employed for the analysis of PAHs providing even better results depending on the type of environmental sample [41,42]. The LOD values typically account for the presence of target compounds in blank samples, varying from around 0.001 to 100 ng m-3, depending on the sample volume and the specific compound being analyzed [43,44]. In the present study, the instrumental limits of detection (LOD; Table 3) are low and indicative for the sensitivity of the GC–MS/MS analytical method. Here, the LOD for each compound was defined by applying a factor of 3 to the compound amount of the lowest point in the calibration curve (in this study 0.8 μg L−1) and dividing this by the chromatographic peaks’ Signal-to-Noise (S/N) ratio, and the sample volume (4.8 m3), resulted in LODs between 2.0 and 10.0 pg m-3.
Journal of Chromatography A 2024, 1730, 465086: Table 3. Limits of detection (LOD) of the GC–MS/MS analytical method and limits of quantification (LOQ) of the complete methodology, obtained by field blank (n = 10) and the analytical procedure (average concentration plus 2 times the standard deviation).
For quantification of PAHs in air samples and blanks, the six-point power calibration curves were used ranging from 0.8 pg μL−1 to 2000 pg μL−1 ,Linear and power regression curves were tested for their homoscedasticity, and six point power curves showed better results than the linear curves, especially at the lowest concentration point, and was chosen to quantify the PAHs in the samples. The curves were also tested for a four point calibration curves at the lower concentration range (0.8 to 100 pg μL−1, but did not show any substantial improvements (see supplementary information Fig. S1 and Table S2). For the spiked cartridges for the storage test, the areas/area-D of the compounds in the extracts were directly compared to the area/area-D of the compound in the standard that was added to the cartridges (25.0 µL x 400 pg μL−1).
Lastly, for the validation of the sampling method with the SPE Isolute ENV+ cartridges, a breakthrough test was performed. Two cartridges were connected via an adaptor to the pump with the front cartridge being spiked with deuterated PAH standard. The breakthrough test was conducted for 8 h with an air flow of 4.0 L min−1 so as to test the actual sampling conditions foreseen. The results, after the extraction and analysis of the two cartridges, successfully showed no detectable levels of the deuterated compounds from the spiked SPE cartridge in the backup cartridge. Nevertheless, volatile parent PAH compounds, i.e. naphthalene to pyrene were detectable in both cartridges (see Sections 3.3 and 3.3).
3.2. PAH concentrations in indoor air
Indoor sampling was conducted in different sites in IDAEA-CSIC, including offices on the 5th and 3rd floor, as well as the IT workshop and the warehouse at ground level during months of May and June, when the PAH levels in the urban air are usually lowest [7,8]. Field blanks were collected in parallel at the sites by leaving the SPE cartridges in the room, but without passing air through them. After sampling the SPE cartridges were folded in aluminum foil and stored in heat-sealable bags at −20 °C overnight before they were extracted the next day and analyzed by GC–MS/MS.
Tabel 4 shows that naphthalene was the most abundant PAH compound in blanks and samples, followed by phenanthrene, fluorene and acenaphthene, while higher molecular weight and particle bounded PAHs (benz[a]anthracene to benzo[ghi]perylene), showed one to three orders of magnitude lower ambient air concentrations. The levels in the blanks were about four times lower than the cleanest sample (5th floor office) and >10 times lower than the more loaded sample at ground level. An exception was dibenzo[ah]anthracene, which showed levels in all blanks and samples below LOD. Field blanks are in the range of the levels observed in the analytical procedure blanks, indicating that PAH loadings in the blanks are mainly caused by solvent manipulation in the laboratory, and that SPE cartridges themselves and their passive exposure during sampling time do not affect the blanks substantially.
PAHs are byproducts of incomplete combustion of organic material and are primarily recognized as outdoor pollutants because of their prevalence in the ambient air. Nevertheless, their notable infiltration into buildings through openings like windows, doors, and ventilation systems makes them a noteworthy indoor pollutant [45,46]. In the vicinity of main sources in urban areas, such as emissions from industrial activities and transportation [46,47], these compounds can be detected in indoor environments such as schools and houses [5,12,14,46,48]. Therefore, the observation of higher concentrations of these compounds in the warehouse is not surprising, as it is located closest to parking lot with a significant number of car movements and truck discharges during the day. On the other hand, the office at the 5th floor is furthest away from these potential emission sources.
Moreover, regarding the compositional pattern of PAHs observed from the results, low-molecular-weight (LMW) PAHs (2–3 rings) show higher concentrations compared to the high-molecular-weight (HMW) PAHs (5–6 rings). Notably, LMW PAHs display higher volatility, contributing to their increased presence in the atmosphere. According to a study by Qi et al., the concentrations of HMW PAHs in heavy traffic sites were 3 to 8 times higher than those in sites that were furthest away from this possible source [49]. The concentrations of HMW PAHs observed in the warehouse in this study are consistent with those reported in the aforementioned study, indicating higher levels compared to locations less affected by traffic emissions, like the office at the 5th floor. Additionally, other studies showed a correlation between PAH concentrations and traffic composition, as heavy-duty vehicles have been associated with LWM PAHs, whereas light-duty vehicles are linked to higher concentrations of HMW PAHs [50,51].
Among the 16 EPA-listed PAHs, benzo[a]pyrene is the only with a target value of 1.0 ng m-3, used as the primary carcinogenic risk indicator for PAHs in outdoor air [7]. In the present study, the results obtained from this sampling campaign in indoor air (16.0 to 57.0 pg m-3) did not exceed this value. Previous studies have shown a strong interest in determining concentrations of PAHs in indoor environments due to the impact of these compounds to the human health and the indoor air quality, with concentrations ranging from 0.03 to 62 ng m-3 [52]. Regarding concentrations of PAHs in indoor air in offices, particulate phase ∑PAH concentrations ranging from 300 to 1350 pg m-3 were found in Rome [48]. Comparing the results obtained in this study with existing literature on PAH concentrations in indoor locations, the results are consistent with previous studies. Specifically, concentrations range between 3 pg/m³ to 30,059 pg/m³ (Table 4).
Journal of Chromatography A 2024, 1730, 465086: Table 4. (snippet) Concentrations (pg/m3) of studied PAHs in different indoor sampling locations and blanks.
Concentrations of PAHs in the atmosphere are also affected by seasonal variations [53]. More specifically, several studies have highlighted the fact that during the winter period PAH concentrations are higher compared to summer, [7,46,48,53,54]. This variation can be attributed to a combination of meteorological factors influencing atmospheric stability, alongside physicochemical properties of PAHs, reactivity with oxidants, as well as the emergence of potential emission sources. Regarding the physicochemical properties of PAHs, their wide range of volatilities influences how temperature affects the equilibrium between particles and gases [55]. The relatively low indoor ambient air PAH concentrations in this study were in the range of those observed in former studies in summer indoor air in schools in the urban background in Barcelona [7,8,46]. These results evidence that the PAH sampling with SPE cartridges, and their chemical analysis by GC–MS/MS are suitable for the determination of PAHs in indoor air.
3.3. Storage test
The storage of samples with volatile and semi-volatile organic compounds has emerged as a topic of great interest as the preservation of samples plays a crucial role for the quality of the analysis. However, previous studies in the existing literature were primarily focused on the improvement of the analytical methodology and the treatment methods rather than the collection and proper storage of samples. Within the InChildHealth research project, SPE sampling will be performed in schools in different European cities, and samples will be shipped to a central laboratory for analysis on semi-volatile organic compounds and therefore it was necessary to develop a storage and transportation strategy.
The nature of the sample is important for storage capability because various environmental samples have specific characteristics that can affect storage efficiency. More specifically, a study by Rorst et al., regarding the changes in the profile of PAHs in cold storage temperatures(4 °C) from contaminated soil samples mentions that 3-ring PAHs were down to 29–73 % of the initial concentration and significant losses were observed as well for 5-ring compounds mostly due to biodegradation [56]. On the other hand, another study showed that the aromatic hydrocarbon VOCs in air samples with larger molecular weight had a lower recovery rate than the smaller molecular weights after storage in cold temperatures [57].
Studies in the past have mentioned the use of specific storage containers, Tedlar bags and PAE sampling bags, so as to overcome the barriers associated with gas-sample transfer and storage [57,58]. However, the majority of studies deal with the issue of the storage of various volatile compounds, and few refer to the storage of samples containing semi-volatile PAHs [58]. In addition to the type of storage container, the sorbent material for the collection of air samples is of great importance as well. According to previous studies, the use of Tenax for the recovery of VOCs from contaminated air was found to be significantly influenced by variation in storage time and storage temperatures [44]. Air sample PAHs on Teflon filters and PUF plugs and subsequent storage of the samples in aluminum foil and glass bottles, maintained their chemical composition at room temperature for periods from 35 to 118 days [59]. In the present study the use of heat-sealable silicon Kapac bags was tested, as a substitute for fragile glass bottles. These bags were successfully used in the past for the storage and transport of filter and PUF samples containing PCBs and PAHs [60].
After the spiking of the SPE cartridges with 10 ng PAH mix, they were wrapped into aluminum foil and stored in the heat-sealable bags at different temperatures and periods of time (Section 2.5), in triplicates. After storage they were spiked with deuterated PAHs, extracted, concentrated and analyzed by GC–MS/MS. Based on an ANOVA Tukey test, there no were no significant differences (p > 0.05) between the PAH levels quantified in the SPE extracts compared to the standard for most of the PAHs at any tested condition, except for the most volatile PAHs, naphthalene and acenaphthylene. Naphthalene levels increased in the SPE cartridges over time and showed more than twice the spiked amount (recoveries > 200 %; Fig. 1) to levels that were expected based on the blank levels observed for this compound in this methodology. On the other hand, acenaphthylene showed lower recoveries (70 %) in the SPE extracts than were stored at room temperature, compared to the control SPE and SPEs that were stored at lower temperatures. These results indicate that storage in Kapac heat-sealable bags may be a suitable method for storage and transport of the samples.
Journal of Chromatography A 2024, 1730, 465086: Fig. 1. Recoveries (%) of the spiked PAHs in the SPE cartridges (triplicates) that were stored inside Kapac heat-sealable bags at room temperature (25 °C), in a fridge (4 °C) for 1 and 2 weeks, and in a freezer (−20 °C ) for 3 months. Control SPE were extracted on the day of spiking (Day 0). All quantified amounts were compared with the original standard used in the test.
4. Conclusions
An efficient approach for the sampling, extraction procedure and analysis of polycyclic aromatic hydrocarbons (PAHs) in air samples was established, using SPE cartridges for sampling and gas chromatography tandem mass spectrometry (GC–MS/MS) for PAHs analysis.
SPE Isolute ENV+ cartridges were successfully used as a sorbent material for the collection of both gas-phase and particulate-phase PAHs from air samples employing low-volume pumps. A decrease in extraction times and analytical costs (concerning extra cleaning steps) was achieved. Additionally, the heat-sealable silicon Kapac bags were successfully used for sample storage and the results demonstrated that the concentration levels did not show any significant variation among the different storage time intervals and temperatures, in the range of weeks and −20 °C to room temperature, respectively. Exceptions were only detected for the most volatile compounds. Long-term storage is recommended at −20 °C, based on the sample stability evidenced during the storage tests.
The analysis of collected air samples from different indoor locations showed that this method allows for the detection of the 16 EPA-designated PAHs even in low concentration settings. The analysis of PAHs using GC–MS/MS provides low LOD and the recoveries of the compounds that are satisfactory for the purpose of methodology in indoor air in schools. In these settings, the method can be applied for PAH analysis in combination with the analysis of other organic compounds, such as organophosphate and phthalate esters.
- Comprehensive methodology for semi-volatile organic compound determination in ambient air with emphasis on polycyclic aromatic hydrocarbons analysis by GC–MS/MS. Maria A. Aretaki, Judith Desmet, Mar Viana, Barend L. van Drooge. Journal of Chromatography A 2024, 1730, 465086. https://doi.org/10.1016/j.chroma.2024.465086.
