Determination Of Aromatic Hydrocarbons In Bituminous Emulsion

Journal of Chromatography A, 1137 (2006) 15–21

Determination of aromatic hydrocarbons in bituminous emulsion sealants using headspace solid-phase microextraction and gas chromatography–mass spectrometry Bing Tang, Ulf Isacsson ∗ Division of Highway Engineering, Department of Civil and Architectural Engineering, Royal Institute of Technology, Brinellv¨agen 34, SE-100 44, Stockholm, Sweden Received 18 May 2006; received in revised form 3 October 2006; accepted 4 October 2006 Available online 27 October 2006

Abstract The possibility of quantitative determination of aromatic hydrocarbons in bituminous emulsion sealants was investigated using headspace solidphase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS). The target analytes studied were benzene, toluene, ethylbenzene, p-, m-, and o-xylene (BTEX) as well as 1,3,5- and 1,2,4-trimethylbenzene. Experimental factors influencing HS-SPME efficiency were studied (sample-headspace equilibration time, extraction time and sample matrix effects). A HS-SPME method using surrogate matrix was developed. The detection limit was estimated as approximately 0.1 ppmw for the target analytes investigated. Good linearity was observed (R2 > 0.997) for all calibration curves obtained. The repeatability of the method (RSD, relative standard deviation) was found less than 10%. The accuracy of the method given by recovery of spiked samples was between 99 and 116%. The HS-SPME method developed was applied to two commercially available bituminous emulsion sealants. External calibration and standard addition approaches were investigated, and statistical paired t-test was performed. The contents of target aromatic hydrocarbons in the sealants studied varied from approximately 0.4 to 150 ppmw. The method developed shows potential as a tool for the determination of aromatic hydrocarbons in emulsified bituminous materials. © 2006 Elsevier B.V. All rights reserved. Keywords: Bituminous emulsion sealants; Aromatic hydrocarbons; BTEX; Headspace; Solid-phase microextraction

1. Introduction Bituminous sealants are used for sealing cracks in asphalt pavements in order to delay road deterioration and extend pavement life [1]. Commercially available sealants essentially comprise three material families, i.e. cold- and hot-applied thermoplastic bituminous materials and chemically cured thermosetting materials [2,3]. Concerns of potential environmental and health aspects of bituminous materials have been discussed for a long time in the asphalt construction industry [4]. Based on the literature studied, it is concluded that current data available is insufficient for quantifying acute and chronic health risks of exposure to bituminous materials and their emissions, and therefore, potential health risks should not be precluded until further data are available.

∗

Corresponding author. Tel.: +46 8 7908700; fax: +46 8 4118432. E-mail address: [email protected] (U. Isacsson).

0021-9673/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2006.10.016

The composition of bituminous materials is very complex and varies greatly with origin, manufacturing process, additive, etc. Among the very great number of compounds in bituminous materials, polycyclic aromatic compounds (PACs) and volatile organic compounds (VOCs) are widely monitored due to health aspects. The chemical composition of bituminous emulsion sealants should be even more complex, as this type of materials generally also contains different additives [3], e.g. petroleum oils, wasted rubber and emulsifying agents. Health risks of bituminous emulsion sealants should be evaluated case by case. For cold-applied sealants, VOCs may be of primary concern, while both VOCs and semi-volatile organic compounds (e.g. PACs) should be monitored for hot-applied sealants. Bituminous emulsion sealants, which comprise both organic (e.g. bitumen) and aqueous phase, are difficult to analyze directly using conventional methods. Furthermore, traditional sample treatment (e.g. cleanup and fractionation) procedure may cause loss of target analytes. In this study, solid-phase microextraction (SPME) technique was explored. SPME is a solvent-free sample

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Table 1 Brief descriptions of bituminous emulsion sealants studied Sample

Description

Use and application

NM40

40 % cutback emulsion based on bitumen B 300, heavy mineral oils and solvent. Bitumen emulsion Mixture of bitumen emulsions consisting of three components, which are intermixed in-line.

Sealants for asphalt pavement maintenance. Normally applied without heating. Could be heated up to 40 ◦ C. Sealants for asphalt pavement maintenance. Applied at 50–80 ◦ C Sealants for asphalt pavement maintenance. Applied without heating.

NYBE PETK* *

Used as surrogate sample matrix.

preparation technique developed since the beginning of the 1990s [5,6], and represents a quick, sensitive and economical approach used in laboratory as well as field work. A great number of papers and a few books describing theoretical studies and applications of SPME have been published during the last decade [7–10]. Successful applications of SPME to complex and difficult environmental sample matrices have been reported in the literature, e.g. soils [11–14], sediment [15,16] and sludges [17]. In our own laboratory, SPME has been successfully applied to the determination of aromatic hydrocarbons in oil-based asphalt release agents [18,19]. In a recent publication [20], the possibility of using SPME technique for screening emission profiles of bituminous sealants has been described. In this paper, the development of a headspace (HS)-SPME method for extraction and analysis of aromatic hydrocarbons from bituminous emulsion sealants is presented. The target analytes includes BTEX (an acronym for benzene, toluene, ethylbenzene and xylene isomers) as well as 1,3,5and 1,2,4-trimethylbenzene. Experimental variables affecting the HS-SPME procedure, such as analyte equilibration between headspace and sample matrix, extraction time profiles of analytes as well as effects of sample matrix, were studied. The method developed was applied to two commercially available bituminous emulsion sealants (NM40 and NYBE, respectively, cf. Table 1). Two different calibration approaches, external calibration and standard addition, respectively, were statistically evaluated. Although this study only covers the subject of aromatic hydrocarbons, it is believed that, the methodology is applicable to characterization of other types of volatile organic compounds in bituminous emulsion sealants. Overall, the present investigation, together with the previous work [18–20], provides an interesting analytical approach to characterization of complex organic materials used by the asphalt construction industry. As far as the authors know, scientific studies in this specific field have not been reported by other researchers. 2. Experimental 2.1. Samples and chemicals The bituminous emulsion sealants studied were obtained from different contractors. In Table 1, general information of the sealants is given. The sealants studied are cold-applied thermoplastic bituminous materials (applied without heating or by slight heating).

Neat aromatic standards, benzene (Ben), toluene (Tol), m-, pand o-xylene (Xyl), ethylbenzene (Etb), 1,3,5-trimethylbenzene (1,3,5-T) and 1,2,4-trimethylbenzene (1,2,4-T) (Supelco, Sweden) were used to prepare stock solution (10 mg ml−1 ) in methanol (>99% by GC, Merck, Germany). The stock solutions were diluted into various calibration standards using methanol. Throughout the study, ethylbenzene-d10 (Supelco, Sweden) was chosen as an internal standard. 2.2. HS-SPME device The SPME device, consisting of a manual holder and a 100 ␮m polydimethylsiloxane (PDMS) fiber, was obtained from Supelco, Sweden. A crimp-top borosilicate glass vial (capacity about 24 ml, height 85 mm, diameter 23 mm, ScherfChroma, Germany), a 18 mm laminated Butyl-PTFE septum (ScherfChroma, Germany) and a plastic screw cap with a hole in the middle were used as head space set-up. When the sample was introduced into the vial, the top of the vial was sealed immediately with septum and screwed tightly with the cap. Before SPME sampling, the septum was pierced by a syringe needle to facilitate the passage of the SPME needle. After inserting the SPME needle into the HS vial through the precored septum, the fiber was exposed in the headspace above the sample. After sampling, the fiber was redrawn into the SPME needle and ready for GC–MS analysis. 2.3. Instrumentation of GC–MS All the analysis was performed using a Varian 3400 gas chromatograph coupled with a Finnigan SSQ 7000 mass spectrometer. The GC column used was a DB-WAX polar capillary column (J&W Scientific, Folsom, CA, USA, 30 m × 0.25 mm I.D. and a film thickness 0.25 ␮m). Carrier gas was helium at a pressure of 67 kPa. The injector temperature was 215 ◦ C (splitless injection for 45 s) and the transfer line was operated at 225 ◦ C. The GC column was programmed from 40 ◦ C (hold 3 min) to 80 ◦ C at 5 ◦ C min−1 (no hold) and then to 220 ◦ C at 20 ◦ C min−1 (hold 3 min). The mass spectrometer was operated at 70 eV EI mode. The source temperature was 150 ◦ C and the manifold temperature 70 ◦ C. MS full scan mode at a range of 45–400 m/z (2 scans/s) was used for qualitative screening analysis of the samples, whereas selected ion monitoring (SIM) mode was used for quantitative analysis. The ions monitored included m/z 78* for benzene; 91* for toluene; 91* and 106 for ethylbenzene and xylene isomers; 98* and 116 for

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Table 2 Validation of the HS-SPME method for determination of aromatic hydrocarbons in spiked bituminous emulsion sealants using PETK as a surrogate sample matrix (concentration unit: ppmw) Analytes

Ben Tol Etb p-Xyl m-Xyl o-Xyl 1,3,5-T 1,2,4-T

Quantitation ion (m/z)

Concentration range studied

Linear range

78 91 91 91 91 91 105 105

0.05–4 0.05–4 0.5–40 1.0–80 1.0–80 1.0–80 2.5–200 10–800

0.25–4 0.25–4 0.5–40 1.0–80 1.0–80 1.0–80 2.5–200 10–800

Spiked conc.

1.0 1.1 10.0 19.8 21.1 20.8 50.4 202.5

No I.S.

I.S.

R2

Mean

RSD %

Rec.%

R2

Mean

RSD %

Rec.%

0.9991 0.9980 0.9999 0.9999 0.9995 0.9997 0.9982 0.9985

0.9 1.0 8.6 17.2 18.2 18.2 41.9 166.5

9.7 11.9 13.4 12.8 13.5 13.5 17.5 15.1

94 91 86 87 86 87 83 82

0.9999 0.9999 0.9995 0.9996 0.9997 0.9995 0.9973 0.9985

1.1 1.3 10.5 21.1 22.6 22.5 52.4 200.6

9.0 6.3 4.8 5.8 5.1 5.4 7.9 8.2

116 114 105 106 107 108 104 99

Note: The calculated mean was based on triplicate samples (n = 3). I.S.: internal standard.

ethylbenzene-d10 , 105* and 120 for 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene. If not mentioned in the text, all peak areas were integrated based on the primary ion (marked with star) in SIM mode. The computer-based MS spectrum library used was the NIST mass spectral search program, version 1.7.

different concentration ranges (cf. Table 2). All these standards were analyzed using the HS-SPME procedure developed (cf. Section 3.1). Triplicate samples (PETK spiked with aromatic standards) were tested, and linearity, detection limit, relative standard deviation (RSD) and percentage of recovery of analytes were calculated (cf. Table 2).

2.4. Optimization of testing parameters A few key experimental variables of the HS-SPME procedure were studied, namely time required for the target analytes to reach equilibrium between headspace and emulsion sample, extraction time profile for the target analytes as well as effects of sample matrix. In this study, a commercially available product (PETK, cf. Table 1) was used as surrogate sample matrix. The choice of PETK was based on the fact that this product did not contain detectable amount of target analytes studied. The equilibration time was investigated by performing HSSPME on 1 g PETK containing 100 ppmw of each of the aromatic standards at every 60 min up to 300 min, at 420 min and finally at 600 min. During the course of this study, the SPME extraction time was kept constant (5 min, cf. Section 3.1.3). The extraction time profile was obtained by performing HSSPME on 1 g PETK containing 50 ppmw of each of the aromatic standards. After introduction of the spiked samples, the HS vial was sealed and equilibrated for 240 min. SPME sampling was performed consecutively at extraction time 0.5, 1, 2, 5, 10 and 20 min, respectively. After each extraction, the sample was re-equilibrated for 60 min to make sure that the equilibrium between the sample and headspace was reached. Sample matrix effects were investigated by spiking ethylbenzene-d10 (50 ppmw) in 1 g PETK, NM40 and NYBE, respectively. Triplicate samples were analyzed by HS-SPME using the optimized procedure described above (equilibration time 120 min, and extraction time 5 min). The peak areas of ethylbenzene-d10 at m/z 98 were integrated. After studying the experimental parameters, the HS-SPME method was validated by determination of spiked target analytes in the surrogate sample matrix (PETK, cf. Table 1). Calibration standards were prepared in 1 g PETK samples. Based on the estimated content profile of individual aromatic hydrocarbons in the sealants studied, calibration standards were prepared covering

2.5. Determination of aromatic hydrocarbons in NM40 and NYBE Two different calibration approaches (external calibration and standard addition, respectively) were investigated for the determination of aromatic hydrocarbons in two bituminous emulsion sealants, NM40 and NYBE, respectively (cf. Table 1). The calibration standards prepared in PETK, as described in Section 2.4, were used to generate external calibration curves. For the standard addition approach, a series of calibration standards were added into 1 g of the sealant sample (cf. Table 2 for analytes and concentration ranges studied). All samples spiked with the calibration standards also contained 5 ppmw ethylbenzene-d10 . The linear regression curve was formed by interpolation (the response of target analyte in pure sample was deducted from the response in sample spiked with standards), and the concentration of target analyte was calculated from the interpolated regression curve. 3. Results and discussion 3.1. Optimization of HS-SPME procedure 3.1.1. Surrogate sample matrix In the course of development of the HS-SPME method for a given type of materials, selection of a standard sample matrix is of great importance. For example, for aqueous samples, pure water is often used as a standard matrix. However, no standard sample matrix for bituminous emulsion sealants was found in the literature. The requirements of such a standard matrix at least include: (1) having chemical and physical properties similar to the samples tested; (2) containing no or negligible amount of target analytes; (3) being not reactive with the target analytes; (4) containing negligible interfering compounds. In the screen-

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Fig. 2. Equilibration of spiked aromatic hydrocarbons (100 ppmw each) in PETK (1 g) between the headspace and the emulsion sample matrix (extraction time 5 min).

Fig. 1. Total ion chromatogram and selected ion chromatograms of PETK (m/z 78 for benzene, 91 for toluene, ethylbenzene and m-, p- and o-xylene, 105 for 1,3,5- and 1,2,4-trimethylbenzene; the arrows show where the target analytes should appear based on retention time).

ing test of emission profiles of different bituminous emulsion sealants obtained from the contractors, it was observed that one of the sealants studied, PETK, met the requirements [20]. As indicated in Fig. 1, although a lot of peaks were observed in the total ion chromatogram (most of the peaks were identified as aliphatic compounds and fatty acid methyl esters), no detectable peaks (signal/noise ratio < 3) were identified as target analytes in the selected ion chromatograms. Therefore, PETK should contain negligible amount of target analytes. Furthermore, the other peaks in the selected ion chromatograms are weak and may not lead to interference to target analytes. In conclusion, PETK is considered to be a suitable surrogate sample matrix in this study. 3.1.2. Equilibration of samples In order to obtain the proportional relationship between extracted amount of analytes by HS-SPME and initial concen-

tration of analytes in the sample, multiphase equilibrium should be reached. In this study, the equilibration process involves three phases: fiber coating, headspace and emulsion sample matrix. The equilibration of target analytes between headspace and emulsion sample matrix was investigated and the results were shown in Fig. 2. As can be seen, the equilibrium was not reached at 60 min, since the extracted amount of target analyte is significantly larger than that at longer equilibration time. From 120 up to 600 min, the equilibration curves are relatively flat, indicating nearness to equilibrium. In general, a trend of slight decrease in extracted amount was observed. This phenomenon could be caused by repeated extraction of target analytes, which leads to a slight decrease in the concentration level of target analyte in the sample matrix. However, this decrease was considered to be insignificant compared with the experimental precision (cf. Section 3.2.4). Since shorter equilibration time means shorter overall analysis time, an equilibration time of 120 min was used for all HS-SPME tests performed. For repeated SPME extractions of the same sample, a re-equilibration time of 60 min was used. 3.1.3. Extraction time profile The volatile aromatic hydrocarbons studied normally reach equilibrium between the SPME fiber and the headspace phase very fast (in a few minutes) [21]. As shown by extraction time profiles in Fig. 3, more volatile analytes (benzene and toluene) reach equilibrium faster (<1 min) than less volatile compounds as 1,3,5- and 1,2,4-trimethylbenzene (≈5 min). Based on Fig. 3, an extraction time of 5 min was chosen throughout this study. Based on regular checking of the cleanness of the SPME fiber by GC–MS, 5 min was also chosen as desorption time. No carryover effects were observed. 3.1.4. Effects of sample matrices As shown in Fig. 4, the total ion chromatograms of the three bituminous emulsion sealants studied differ from each other in extraction profile as well as intensity, indicating different chemical compositions of the three agents investigated.

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Fig. 3. Extraction time profiles of spiked aromatic hydrocarbons (50 ppmw each) in PETK (1 g).

The complexity of the sample matrix not only increases the difficulty of chromatographic separation but also causes competitive extraction of non-target compounds on the SPME fiber. Consequently, the SPME extraction efficiency may vary in different sample matrices. In Fig. 5, effects of sample matrices are illustrated. Even though ethylbenzene-d10 was spiked at the same concentration level (50 ppmw) in the three samples, the means of extracted amount of the spiked standard are different. In general, matrix effect may be attributed to competitive extraction of other organic compounds co-existing with the target analytes as well as physico-chemical properties of the sample matrix. In principle, it is impossible to find a standard matrix for all types of bituminous emulsion sealants as these products may vary considerably with regard to chemical compositions (cf. Fig. 4), and therefore, external calibration using a surrogate sample matrix may not be appropriate. Instead, a standard addition method could be an alternative approach. 3.2. Validation of the HS-SPME method based on PETK 3.2.1. Linearity In general, SPME methods show wide ranges of linearity. For example, for fuel-related hydrocarbons in water samples, linearity ranging between 3 and 6 orders of magnitude have been reported [22]. The linearity of the calibration curve covering different concentration levels of target analytes in PETK was investigated. As shown in Table 2, R2 -values greater than 0.997 were observed for all analytes at different concentration ranges with or without internal standard. 3.2.2. Detection limit The limit of detection (LOD) was estimated by analysis of a series of spiked PETK samples with diluted calibration standards. It was observed that, at approximately 0.1 ppmw, the signal/noise ratios (S/N) of calibration standards were approximately 3:1. Generally, the detection limit for all target analytes investigated was approximately 0.1 ppmw. However, it should be noted that the estimated detection limits are solely valid for PETK as a surrogate sample matrix. Severe background inter-

Fig. 4. Total ion chromatograms of bituminous emulsion sealants extracted by HS-SPME and analyzed using GC–MS full scan mode (m/z 45–400) (sample amount, 1 g; sample equilibration time, 120 min; extraction time, 5 min; desorption time, 5 min).

ference on target analytes in other bituminous emulsion sealants may cause substantially higher detection limit. 3.2.3. Accuracy The accuracy of the testing procedure was studied by analyzing a set of spiked samples and was estimated by determining the analyte recovery (amount of analyte measured divided by amount of analyte spiked in %). As shown in Table 2, the mean recovery was between 82 and 94% without internal standard

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analyte concentrations tested are comparably high (100 ppmw), and the amount of each analyte extracted is totally less than 1% for the six tests performed. Six consecutive extractions of target analytes will not lead to significant decrease in concentration level, and consequently, the change of multiphase equilibrium can be considered negligible. 3.3. Determination of aromatic hydrocarbons in NM40 and NYBE

Fig. 5. Sample matrices effects on extraction efficiency of ethylbenzene-d10 (50 ppm) in the bituminous emulsion sealants studied.

and between 99 and 116% with internal standard. These mean recovery ranges can be considered acceptable. In conclusion, the results presented in Table 2 indicate that the HS-SPME procedure developed can be used for accurate quantitative determination of aromatic hydrocarbons in bituminous emulsion sealants, at least in a concentration range of 0.2–800 ppmw. 3.2.4. Repeatability The repeatability of the HS-SPME method developed was evaluated in two different ways, namely by analyzing triplicate aliquots of spiked samples and consecutive testing of one and the same sample for several times, respectively. As shown in Table 2, the relative standard deviation (RSD) at triplicate tests for all target analytes are below 10%, when using internal standard, and below approximately 18% without internal standard. As calibration with internal standard gives higher repeatability, this approach is used. The repeatability of the HS-SPME method using one and the same sample (each target analyte at 100 ppmw in 1 g PETK) was estimated based on six consecutive tests performed within 10 h. Area accounts and area ratios (related to internal standard Etb-d10 ) were compared, and the results are presented in Table 3. As can be seen, all the RSD values of area accounts are below 10% and those of area ratios below 6%, indicating good repeatability. The results also suggest that the use of internal standard improves repeatability. It should be noted that the

Standard addition approach using internal standard (5 ppmw) was used for the determination of aromatic hydrocarbons in NM40 and NYBE samples. The results in form of mean concentration and relative standard deviation obtained from triplicate samples are shown in Table 4. In NM40, the content of the individual aromatic hydrocarbons varies greatly from <1 ppmw (toluene) up to approximately 150 ppmw (1,2,4trimethylbenzene), whereas in NYBE, the corresponding concentration levels are generally much lower (toluene was even not detectable). In both samples, benzene could not be detected. For comparison, the concentrations of aromatic hydrocarbons were also calculated by the external calibration approach, using PETK as a standard sample matrix. A paired t-test at a risk level of 0.05 was performed to compare the mean concentrations determined by standard addition and external calibration approach, respectively. As shown in Table 4, all p-values except that of ethylbenzene are less than 0.05, indicating significant difference in results obtained using the two calibration approaches. It is understandable that, due to matrices effects, the external calibration method may not be appropriate in the determination of aromatic hydrocarbons in complex bituminous emulsion sealant samples. However, it is interesting to note that, in both NM40 and NYBE, no significant difference in the mean concentrations of ethylbenzene is observed (p > 0.05). This fact could be due to the usage of the internal standard ethylbenzene-d10 , the chemical structure of which is closer to ethylbenzene than to any other target analytes studied. As a matter of fact, in selection of an internal standard for the determination of a specific compound, the corresponding deuterated counterpart is the best choice. It is a reasonable assumption that, if such deuterated standards were used for all the target analytes studied, probably no significant difference between the two calibration approaches would be observed. In other words, the matrices effects could, at least

Table 3 Six consecutive extractions on one and the same sample (100 ppmw of each analyte in PETK) by HS-SPME Analytes

Area accounts (×108 ) and area ratios (in parentheses, related to internal standard Etb-d10 ) at six consecutive extractions 1

Ben Tol Etb-d10 Etb p-Xyl m-Xyl o-Xyl 1.3.5-T 1.2.4-T

1.251 1.439 1.565 1.539 1.186 1.392 1.131 1.475 1.445

2 (0.800) (0.920) (1.000) (0.983) (0.758) (0.889) (0.723) (0.943) (0.923)

1.305 1.422 1.586 1.500 1.183 1.378 1.124 1.353 1.324

3 (0.823) (0.897) (1.000) (0.946) (0.746) (0.869) (0.709) (0.853) (0.835)

1.240 1.350 1.505 1.455 1.121 1.269 1.076 1.258 1.261

4 (0.824) (0.897) (1.000) (0.967) (0.745) (0.843) (0.715) (0.836) (0.838)

1.217 1.326 1.483 1.431 1.112 1.244 1.056 1.227 1.240

5 (0.821) (0.894) (1.000) (0.965) (0.750) (0.839) (0.712) (0.828) (0.836)

1.182 1.282 1.433 1.344 1.073 1.159 1.028 1.192 1.178

6 (0.824) (0.894) (1.000) (0.938) (0.749) (0.809) (0.717) (0.832) (0.822)

1.203 1.281 1.436 1.318 1.127 1.166 1.012 1.162 1.149

Mean (0.838) (0.892) (1.000) (0.918) (0.785) (0.812) (0.705) (0.809) (0.800)

1.233 1.350 1.501 1.431 1.134 1.268 1.071 1.278 1.266

RSD% (0.822) (0.899) (1.000) (0.953) (0.755) (0.843) (0.713) (0.850) (0.842)

3.5 5.1 4.3 6.0 3.8 7.9 4.6 9.2 8.5

(1.5) (1.1) (0.0) (2.5) (2.0) (3.7) (0.9) (5.6) (5.0)

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Table 4 HS-SPME determination of aromatic hydrocarbons in NM40 and NYBE Analytes

Paired t-test*

Concentration determined by HS-SPME (ppmw) External calibration (I.S.)

Standard addition (I.S.)

p-value

Mean

RSD%

Mean

NM40 Ben Tol Etb p-Xyl m-Xyl o-Xyl 1,3,5-T 1,2,4-T

– 0.37 5.2 4.4 12.3 18.6 39.9 164.1

– 0.8 3.6 2.4 2.3 2.3 3.2 3.5

– 0.45 5.0 3.1 11.4 17.1 34.4 148.0

– 0.6 5.8 6.9 4.5 4.2 6.4 6.8

– <0.0001 0.072 0.002 0.020 0.013 0.010 0.023

NYBE Ben Tol Etb p-Xyl m-Xyl o-Xyl 1,3,5-T 1,2,4-T

– – 0.62 0.41 1.4 1.3 4.4 15.2

– – 7.6 7.7 7.4 7.2 3.7 3.7

– – 0.64 0.35 1.6 1.6 2.5 13.1

– – 9.7 12.2 8.8 9.7 10.5 6.4

– – 0.080 0.012 0.013 0.014 0.001 0.006

RSD %

(–) Not determined; I.S. internal standard; * two-sided paired t-test at 0.05 level, n = 3.

partly, be eliminated by use of deuterated analyte counterparts. Consequently, the external calibration approach, not being timeconsuming compared to the standard addition approach, could be utilized. However, further research is needed to prove this assumption.

4. Conclusions Based on the results presented in this paper, the following conclusions could be drawn: - HS-SPME technique is a valuable tool for the determination of volatile aromatic hydrocarbons (and probably also for other types of volatile organic compounds) in complex samples such as bituminous emulsion sealants. - Use of a surrogate sample matrix is important in order to facilitate optimization of the HS-SPME parameters as well as to validate the developed method. - The HS-SPME method developed was successfully applied to simultaneous determination of aromatic hydrocarbons in a broad concentration range (approximately 0.4 ppmw up to at least 150 ppmw) in two commercially available bituminous emulsion sealants. - In general, due to matrices effects, standard addition approach instead of external calibration, should be applied to complex samples like bituminous emulsion sealants. However, statistical analysis indicates that, selection of a deuterated analogue as an internal standard to the target analyte may reduce or even eliminate matrices effects. - The developed HS-SPME method can be a valuable tool for ranking of sealants with regard to health aspects.

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