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Design and Validation of Portable SPME Devicesfor Rapid Field Air Sampling and Diffusion-BasedCalibration

Fabio Augusto,† Jacek Koziel,‡ and Janusz Pawliszyn*

Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

TheuseofSPME fibers coated withporous polymer solid

phases for quantitative purposes is limited duetoeffects

such as interanalyte displacement and competitive ad-

sorption. For air analysis, theseproblemscan beaverted

byemployingshort exposuretimes toair samples flowing

around the fiber. In these conditions, a simple math-

ematical model allows quantification without the need of

calibration curves. This work describes two portable

dynamic air sampling (PDAS) devices designed for ap-plication ofthis approach to nonequilibrium SPME sam-

pling and determination of airborne volatile organic

compounds (VOCs). The use of a PDAS device resulted

in greater adsorbed VOC mass compared to the conven-

tional SPME extraction in static air for qualitative screen-

ingof live plant aromas and contaminants in indoor air.

For all studied air samples, an increasein thenumber of

detected compounds and sensitivity was also observed.

Quantification of aromatic VOCs in indoor air was also

carried out using this approach and the PDAS/SPME

device. Measured VOC concentrations were in lowparts-

per-billion byvolume range usingonly 30-s SPME fiber

exposure and werecomparable to those obtained with a

standard NIOSH method 1501. The useofPDAS/ SPME

devices reduced the total air samplingand analysis time

byseveral orders of magnitude compared to the NIOSH

1501 method.

Sampling of air and related gas mixtures for chromatographic

analysis of contaminants has been performed using a broad range

of techniques. Sorbent adsorpti on, cryotr apping, and canister

sampling, followed by thermal desorpti on/ cryofocusing or solvent

desorption are the most employed procedures for air analysis.1

However, most of these procedures have several serious draw-

backs, such as production of arti facts2 and retention of large

amounts of water.3 Techniques such as membrane extraction with

sorbent interface(M ESI) ,4 where the analytespresent in a sample

selectively permeate through a polymeric membrane and are

trapped in a sorbent interface for further desorption into a

chromatographic system, also had been suggested.5

SPM E is an attractive alternative to the aforementioned

techniques, considering features such as accuracy, cost, simplicity,

and speed,6 and has been widely used in analysis of several

contaminants in air.7-10 Many of these SPME methods reported

in the literature employ fibers coated with li quid polymeric phases,

such as poly(dimethylsiloxane) (PDMS) and polyacrylate. How-ever, the use of fibers covered with mixed porous solid adsorptive

coatings, such as Carboxen/ PDMS and PDMS/ divinylbenzene

(PDMS/ DVB), seems to be especially interesting for analysis of

air contaminants. They are more efficient than the liquid-coated

fibers,11 especially for extraction of analytes with low molecular

weight.12 Both quantitative and qualitative applications of solid-

phase coated fibers have been described for analysis of food

contaminants,13 fruit pulp volatiles,14 and flavor compounds in

milk.15

Adsorption is the physicochemical mechanism involved in

extractions using fibers coated with solid phases. Both the

theoretical foundations of the equilibrium16 and the kinetics17 of

adsorption by solid-phase coated fibers had already been ad-

dressed. These studies point to problems, e.g., competition

between the analytes for the adsorptive sites available in the fiber

and interanalyte displacement, as severe drawbacks to the ap-

plication of solid-phase coated fibers to quantitative analysis and

limiting the accuracy and precision of the results. However, in

recent work, Koziel et al.18 presented an alternate methodological

approach to overcome these deleterious effects. According to the

* Corresponding author : (fax) (519) 746-0435; (e-mail) [email protected].† Current address: Instituto de Quımica, Unicamp, CP 6154-13083-970

Campinas, SP, Brazil.‡ Current address: Texas Agricultural Experiment Station, Amaril lo, TX

79106.

(1) Dewulf, J.; Van Langenhove, H. J. Chromatogr., A 1999, 84 3 , 163-177.

(2) Clausen, P. A.; Wolkoff, P. Atmos. Environ. 1997, 31 , 715-725.

(3) Helmig, D.; Vierling, L. Anal. Chem. 1995, 67 , 4380-4386.

(4) Yang, M. J.; Harms, S.; Luo, Y. Z.; Pawliszyn, J. Anal. Chem. 1994, 6 6 ,

1339-1346.

(5) Luo, Y. Z.; Pawliszyn, J. Anal. Chem. 2000, 72 , 1064-1071.

(6) Pawliszyn, J. TrAC, Trends Anal. Chem. 1995, 14 , 113-122.

(7) Chai, M.; Pawliszyn, J. Envi ron. Sci. Technol. 1995, 29 , 693-701.

(8) Grote, C.; Pawliszyn, J. Anal. Chem. 1997, 69 , 587-597.

(9) Martos, P. A.; Pawliszyn, J. Anal. Chem. 1997, 69 , 206-215.

(10) Eisert, R.; Pawliszyn, J.; Barinshteyn, G.; Chambers, D. Anal. Commun.1998, 35 , 187-190.

(11) Mani, V. Propertiesof Commercial SPME Coatings.I n Applications of Soli d-

Phase Mi croextraction ; Pawliszyn, J., Ed.; RSC.: Cornwall, UK, 1999; Chapter

5, pp 63-67.

(12) Gorecki, T. Solid versus Liquid Coatings. In A pplications of Soli d-Phase

Microextraction ; Pawliszyn, J., Ed.; RSC.: Cornwall, UK, 1999; Chapter 7,

pp 92-108.

(13) Page, D. B.; Lacroix, G. J. Chromatogr., A 2000, 87 3 , 79-94.

(14) Augusto, F.; Valente, A. L. P.; Tada, E. S.; Rivellino, S. R. J. Chromatogr., A

2000, 87 3 , 117-127.

(15) Marsili, R. T. J. Chromatogr. Sci. 1999, 37 , 17-26.

(16) Gorecki , T.; Yu, X.; Pawliszyn, J. Analyst 1999, 12 4 , 643-649.

(17) Semenov, S.; Koziel, J.; Pawliszyn, J. J. Chromatogr., A 2000, 87 3 , 39-51.

Anal. Chem. 2001, 73, 481-486

10.1021/ac000629k CCC: $20.00 © 2001 American Chemical Society Analytical Chemistry, Vol. 73, No. 3, February 1, 2001 481Published on Web 12/30/2000

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authors, when a fiber is exposed to a gaseous sample moving

perpendicularly to the fiber axis for a period of time much smaller

than the equilibr ation time, the coating behaves as a perfect sink

and all analyte molecules r eaching the fiber surface are im-

mediately adsorbed. As a large number of nonoccupied adsorptive

sites are available in these conditions, interanalyte competition

and displacement are minimized and can be disregarded. It can

be demonstrated that the extracted amount of an analyte n

depends only on its concentration in the gaseous matrix C g, its

diffusion coefficient in air D g, the fi ber’s l ength and r adius L andb , respectively, the thickness of the effective static boundary l ayer

surrounding the fiber δ, and the sampling time t :

The extracted amount, n , can be calculated from the peak area

and from the detector response factor. Equation 1 holds true for

air speeds up to values between 4 and 10 cm s-1, depending on

the analyte. Further increase in the air velocity shows no effect

on the mass uptake rate, which becomes nearly constant and

limited by the diffusion of the analyte in the coating.18 For practical

reasons, devices that allow extractions using air speeds superiorto t his cri tical limit would be desirable because variations in air

velocity would not affect the mass uptake rate, ensuring better

analytical precision and accuracy.

Several models are available to estimate diffusion coefficients

in air needed for the use of eq 1 with the Fuller-Schettler-

Giddings19 model being the most adequate for a large number of

analytes in normal air sampling conditions:

where T is the absolute temperature, M air is the air apparent

molecular weight (i.e., the weighted average of the molecular

weights of the components of air), M voc is the molecular weight

of the analyte, p is the ambient pressure, and V air and V voc are

respectively the molar volumes of air and of the analyte.

The thickness δ of the effective static boundary layer sur-

rounding the fiber can be calculated from eq 3, where Re refers

to the Reynolds number (Re ) 2u b / νj; u is the linear velocity of the air and ν is the air kinematic viscosity) and Sc to the Schmidt

number (Sc ) ν / D g).

Using these equations, the concentration of an analyte can be

directly estimated from the chromatographic peak area, given that

the sampling conditions (sampling time, air velocity, temperature,

and pressure) and constants (diffusion coefficient and fiber

dimensions) are known. For that reason, apart from the suppres-

sion of interanalyte effects, this methodology also allows quanti-

tation of analytes in air without construction of calibration curves.

Another benefit would be the increase of the extracted amounts

(and, therefore, of the sensitivity), when this approach is compared

to the traditional static SPME sampling (simple exposure of the

fiber to the air) . It can beproved, from eqs 1 and 3, that increasing

the air speed also increases the fiber’s mass uptake, due to the

decrease of the boundary layer thickness. Under static conditions,

the extraction would depend on transport of the mass through a

boundary layer which would turn progressively thicker during theprocess, due to the depletion of the analyte.20 This, in turn, would

limit the amount extracted in short periods of fiber exposure to

the sample.

This work describes several portable devices designed to apply

the dynamic nonequilibri um sampling concept to analysis of

airborne chemicals. The suitability of this approach both for

qualitative analysis of living plant aroma compounds and for

volatile organic contaminants in indoor air was examined. Also,

quantitation of air contaminants using dynamic SPME sampling

was compared to results obtained using a standard air analysis

method.

EXPERIMENTAL SECTIONMaterials. Chemi cals and Suppli es . All chemicals were of

analytical grade and used as supplied: benzene, toluene, ethyl-

benzene, o -xylene, p -xylene, and mesitylene (Sigma-Aldri ch, M is-

sissauga, ON, Canada) and carbon disulfide (BDH, Tor onto, ON,

Canada). The SPME holder and 65- µm PDMS/ DVB fibers were

obtained from Supelco (Oakville, ON, Canada); the fibers were

conditioned at 210 °C for 8 h prior to their use. Supelco ORBO-

32 charcoal tubes and a model I.H. portable air pump (A.P. Buck,

Orlando, FL) were employed for the validation quantitativeanalysis

according to NIOSH method 1501.21 All preparations involving CS2

(fl ammable and toxic) and benzene (suspect carcinogen) were

carried out in a ventilated hood.

Gas Chromatography . Qualitative chromatographic analyses of aromas were carr ied out in a Saturn IV GC-ITMSsystem (Varian

Associates, Sunnyvale, CA) fitted with a 30 m × 0.25 mm × 0.25

µm H P-5 column ( Hewlett-Packard, Avondale, PA) and a septum-

purged injector (SPI). The carrier gas was 1.5 mL min-1 helium

at 12 psi. The SPI was k ept at 210 °C, and the column oven

temperature was ramped fr om 60 to 280 °C at 5 °C/ min. Profiles

of indoor air contaminants and quantitative data were obtained

using a Varian Star 3400 GC-FID chromatograph equipped with

a30m × 0.25 mm × 0.25 µm Supelco SPB-5 column and SPI; 2.0

mL min-1 helium at 20 psi was used as carrier gas. The

temperatures were set at 250 °C for the FID and 210 °C for the

SPI, and the column oven program for all injections was as

follows: 1 min hold at 60 °C, followed by a 15 °C/ min r amp untilramped to 180 °C, and hold there for 3 min.

Plant Sample. Aroma from juniper bushes (Juni peru s commu-

ni s ) from the University of Waterloo campus gardens was used

as a sample for the qualitative application in this work.

Portable Dynamic Air Sampling Devices ( PDAS) for SPME . Two

devices to perform air sampling under dynamic conditions were

(18) Koziel, J.; Jia, M.; Pawliszyn, J. Anal. Chem. 2000, 72 , 5178-5186.

(19) Fuller, E. N.; Schettler, P. D.; Giddings, J. C. Ind. Eng. Chem. 1966, 5 8 ,

19-27.

(20) Pawliszyn, J. Solid-Phase M icroextraction : Theory an d Practice ; Wiley-VCH:

New York, 1997; pp 67-69.

(21) National Institute of Occupational Safety and Health. Manual of Analytical

M ethods , 4th ed.; U.S. Department of Health and Human Services: Cincin-

nati, OH . 1994; Vol . I (M ethod 1501 ( “Hydrocarbons, Aromatic”) .

C g ) n l n(b + δ

b ) / 2π D gL t (1)

D g )

0.001T 1.75

1

M air

+1

M voc

p [ (∑V air)1/ 3

+ (∑V voc)1/ 3

]2

(2)

δ ) 9.52b / Re 0.62

Sc 0.38 (3)

482 Analytical Chemistry, Vol. 73, No. 3, February 1, 2001

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projected and built; the design concepts for these apparatus are

discussed in Results and Discussion. Figure 1 shows the schemat-

ics of the fir st device, built using a VS-513F household hair-dryer

(Helen of Tr oy, El Paso, TX) modified to revert the air flow

direction and to disable the internal heating coil. An aluminum

tube was machined and adapted to the front part of the modified

hair-dryer. Two plain cardboard sheets fixed to the opposite side

of the aluminum tubing creating a 3-mm slit; the modified hair-

dryer suction forces the passage of the ambient air through this

slit. PDAS-SPME sampling is performed by exposing the fiber

to the flowing air in front of the slit. The average air speed in

front of the slit was measured to be 1.5 m s-1 with an HHF51

digital wire anemometer (Omega Engineering, Stamford, CT).

This value is greater than the critical air speeds mentioned in the

introduction. All datapresented in this work were collected using

this apparatus.

A different PDAS-SPME (“sandwich” design), shown in

Figure 2, was also pr ojected and assembled. A portable air

sampling pump was used to force ambient air through the

rectangular orifi ce of the device; a small hole (di ameter 0.6 mm)

in the Teflon spacer allowed exposure of the SPME fiber to the

ambient air flowing through the orifice. Using a Buck I.H. air

pump, it is possible to sample air flowing with controllable speeds

up to 1.38 m s-1. This device is presented here as an alternative

to that described above, and its use is currently being evaluated.

Methods. Screening of Li ving Plant Aromas . PDAS-SPME was

compared with conventional (static) SPME sampling for identifica-

tion of compounds found in the fragrance released by an aromatic

plant (juniper). Both for static SPME and for PDAS-SPME, the

SPME fiber was exposed to the air surrounding the livingspecimen for 30 s, and the approximate di stance between the

SPM E fiber and the specimen was 5 cm. The extracted materials

were separated and identified by GC-ITM S. The desorption time

was 5 min. The time between sampling and chromatographic

analysis was kept lower than 20 min for all extractions performed

here and in the subsequent essays; under these conditions, loss

of sorbed materials can be assumed as negligible.22,23

Qualitati ve Profiles of Contami nants in Indoor Air . Qualitative

profiles of the contaminants present i n the air of the Motor Vehicle

Maintenance Shop of the University of Waterloo were obtained

using PDAS-SPME and conventional SPME. Extractions with a

fiber exposure time of 30 s were carried out simultaneously by

both methods. The SPM E fibers were kept refrigerated under dry

ice and capped during their transportation to the laboratory and

storage. Several samples were collected during one workday to

show the variation of the air contamination profile during this time

span.

Quantitati ve Analysis of Ar omatic Hydrocarbons in Indoor Air .

PDAS-SPME was employed to quantify aromatic hydrocarbons

present in the air of several sites in the University of Waterloo.

These sites included two different l ocations in a chemical l abora-

tory (close to a solvent storage cabinet and in an analytical

instrument room), the Motor Vehicle Maintenance Shop, and in

the Engineering M echanical Shop. Replicate measurements

exposing the SPM E fiber to the flowing air for 30 s were made.Uncertainties were expressed as estimates of standard deviation

of r eplicates, i .e., vehicle and mechanical shop air analysis, thr ee

replicates, and laboratory air analysis, eight replicates. Concentra-

tions of the aromatic hydrocarbons were calculated using eq 1

for nonequilibr ium dynamic SPME extraction. It was assumed that

the thickness of the boundary layer did not significantly change

when air velocity was greater than 10 cm s-1. Thus, the threshold

air velocity of 10 cm s-1 was used to estimate the thickness of

the boundary layer in eq 3.

For comparison purposes, vehicle and mechanical shop samples

were simultaneously analyzed using the NIOSH method 1501 for

aromatic hydrocarbons.21 Air was pumped through ORBO-32

charcoal adsorption tubes with sampling times and flow ratesadjusted according to the level of contamination of each sample

(see Results below). Immediately after the sampling, both the

charcoal portion of the tube containing the extracted analytes and

the breakthrough control portion were transferred to separate

4-mL glass vials sealed with Teflon-coated silicone septa. Two

milliliters of CS2 was added to each vial. After 1 h, 1 µL of the

(22) Mu ller, L. Fi eld Analysis by SPME. In A pplications of Soli d-Phase M icro-

extraction ; Pawliszyn,J., Ed.; RSC.: Cornwall, UK, 1999; Chapter 20, pp 269-

283.

(23) Koziel, J.; Pawliszyn, J. J. A ir Waste Manag. A ssoc., in press.

Figure 1. Side view (A) and front view (B) of the portable dynamicair sampling device for SPME. (1) modified hair-dryer; (2) aluminum

tube; (3) 18 VDC power supply cable; (4) fixing brace; (5) cardboard

pieces; (6) 3-mm slit; (7) SPME holder and fiber.

Figure 2. “Sandwich” PDAS-SPME; (A) unassembled and (B)

assembled device. (1) 1-mm-thick stainless steel sheets; (2) 3-mm-thick Teflon spacer; (3) 0.6-mm hole; (4) ) SPME holder and fiber;

(5) silicone tube.

Analytical Chemistry, Vol. 73, No. 3, February 1, 2001 483

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CS2 phase in the vials was injected into the GC-FID system using

the same operational conditions employed for the PDAS-SPME

analysis.

RESULTS AND DISCUSSION

Design Aspects of the PDAS-SPME. The PDAS-SPME

complements previously described devices for field SPME sam-pling.22 These alr eady reported devices and the techniques used

extractions under analyte/ fiber equilibr ium conditions, which

demands the use of calibration curves or quantitation based on

chromatographic retention data.24 However, quantitation in pre-

equilibrium conditions, where the analyte uptake depends only

on its diffusion through the static boundary layer,18 has several

advantages for field use. Since no calibr ation procedures are

needed for well-defined flow rates, the analytical process is

simplified. Also, the sampling time is noticeably shorter when

compared to the typical equilibrium times for airborne analytes,

resulting i n faster analysis. The main design feature of the PDAS-

SPM E project is to ensure a constant and uniform air flow around

the fiber, consistent with the demands of diffusion-based extrac-tion. These devices should also provide flow rates high enough

to have air speeds higher than the critical values mentioned in

the i ntroduction, where the extraction r ate i s dependent mainly

on diffusion of the analyte through the adsorbent pores or through

the liquid coating film.

For the device shown in Figure 1, this was achieved by using

a modified dc-powered hair-dryer. The r eversion of the direction

of the air flow wasmade to avoid contact of the fiber with potential

artifacts originated from the dryer body and motor. The device

shown in Figure 2 was intended to use with industrial hygiene

air sampling pumps, a resource already existent in several

laboratories, as a source of air motion. In addition to these

features, characteristics such as weight, cost, and handiness of

use were taken in account. An alternate version of this device

without the two cardboard sheetsallowssampling of large volume

air samples, i.e., indoor air, under higher flow rates. In this case,

a special 1-in.-O.D. short tube is mounted perpendicularly to the

main aluminum tube to position the SPME holder and to allow

one-hand operation. A 1-mm hole was madein the aluminum tube

for insertion of the SPME needle and fiber in the sampled air

stream.

Screening of Living Plant Aroma. Figure 3 allows the

comparison of a selected section of GC-ITM S chromatograms

obtained with PDAS-SPME and conventional SPME for juniper

aroma. Three compoundsslimonene, 3-nonen-1-ol, and 2-decen-

1-olswere identified in this section of the PDAS-SPME chro-

matogram (Figure 3A). Peaks corresponding to the same com-

pounds in the static SPME chromatogram section were considerably

lower (Figur e 3B). In addition, the 3-nonen-1-ol peak is not distinct

from the baseline noise and not detected with static SPME

sampling.As shown by these results, the application of PDAS-SPME

produced a significant increase in the number of detectable

compounds in the analyzed samples, when compared to conven-

tional SPME. This observation agrees with the theory; i.e., the

air flow around the fiber increases the extracted amount of

analytes per unit of time due to the reduction of the effective

boundary layer thickness. The increase in the analyte uptake is

also reflected in the increase of the number of detected com-

pounds.

QualitativeProfiles ofContaminants in Indoor Air. Figure

4 shows the chromatographic data profiles obtained after extr ac-

tion of the indoor air at the UW Vehicle M aintenance Shop, using

both PDAS-SPM E and static conventional SPM E sampling,

respectively. The signal scale for the chromatograms in both sets

was adjusted to the same value. Both the number of detectable

peaks and the peak intensities are considerably greater in the

chromatograms in the PDAS-SPM E profile (Figure 4B), allowing

easier visual assessment of the correlation between the pattern

of air contamination in this environment and the activities taking

place there. For example, it can be seen that the intensity of the

peak attributed to toluene (large peak with t R ) 2.6 min) decays

during the period between 9:15 a.m. (just after the beginning of

the work shift) and 12:15 p.m., becoming roughly constant after(24) Martos, P.; Pawliszyn, J. Anal. Chem. 1997, 69 , 206-215.

Figure 3. Section of GC-ITMS chromatogram of living juniper

aroma. (A) PDAS-SPME; (B) static SPME; (C) fiber blank). Peakidentification: (1) limonene; (2) 3-nonen-1-ol; (3) 2-decen-1-ol.

Figure 4. Variation of the GC-FID chromatographic profiles ofcontaminants in the UW Vehicle Maintenance Shop monitored in a

workday using conventional SPME (A) and PDAS-SPME (B) col-lected during a work shift. Chromatograms: (1) 9:15 a.m.; (2) 9:55

a.m.; (3) 10:20 a.m.; (4) 11:10 a.m.; (5) 12:15 p.m.; (6) 12:55 p.m.;(7) 1:55 p.m.; (8) 3:05 p.m. For peak identification see Results and

Discussion.

484 Analytical Chemistry, Vol. 73, No. 3, February 1, 2001

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this time. This was credited to the residues of degreasing solvents

containing toluene that were left for overnight cleanup of motor

parts. The group of peaks with retention times between 4 and 8

min were found to be volatile hydrocarbons present in gasoline

and diesel fuels. The intensity of these peaks was found to be at

maximum around 12:55 p.m., which correlated to the admission

of several vehicles to the shop.

QuantitativeAnalysis ofAromatic Hydrocarbonsin IndoorAir. Table 1 compares concentrations of several aromatic hydro-

carbons found after PDAS-SPM E sampling, combined with

nonequilibrium diffusion-based quantification, with concentrations

obtained after simultaneous application of NIOSH 1501 standard

method to the same samples. For PDAS-SPME calculations, the

values for the needed constants were as follows: b ) 0.0120 cm;

L ) 1 cm (both previously measured in the laboratory); M air )

28.97 g mol-1; V air ) 20.1 mL, and ν ) 0.15 cm2 s-1.25 Values for

V voc needed for estimation of D g (eq 2) were calculated accordi ng

to the literature.25 The sampling time and air fl ow rate for NIOSH

analysis was adjusted according to the expected concentrations

of contaminants in each sample, based on preliminary exploratory

extractions: 91 min for the vehicle shop air and 215 min for themechanical shop air, with a flow rate of 138 mL min-1 (sampled

air volumes: 12.6 L for vehicle shop and 29.7 L for mechanical

shop). Under these conditions, no analyte breakthr ough was

observed when the NIOSH method was applied. I t should be

emphasized that the sampling time for the NIOSH-based sampling

was a few orders of magnitude greater than the sampling time

associated wi th PDAS-SPM E. However, none of the existing

standard methods could be compared with the 30-s PDAS-SPME

sampling time.

The PDAS-SPME results obtained for the vehicle and me-

chanical shops were similar to those from NIOSH analysis, except

for the hydrocarbons with higher molecular weight in the set ( o -

xylene and mesitylene), which are underestimated by the NIOSH

method. A possible cause for this could be associated with the

incomplete desorption of these analytes from the charcoal tubes

employed in the NIOSH method, when the recommended de-

sorption procedure was used. Another reason for the observed

discrepancies in measured concentrations could be due to the

widely different sampling times used in both methods. The

NIOSH-based concentration can be considered as a time-weighted

average sample over a l ong sampling period. In contrast, the

PDAS-SPME concentrations can be associated wit h spot or grab

30-s sampling. In addition, it was not possible to measure benzene

concentration in the evaluated samples using this method.

Benzene is a common and significant contaminant in the CS2

solvent recommended for the desorption step in the NIOSH

method.

The method precision can be estimated from the uncertainties

presented in Table 1. VOC concentration levels can be consideredtypical of indoor air in occupational environments. Expressed as

estimates of relative standard deviations ( s R), the precision of

PDAS-SPME results r anged from 13 to 28%, with an average

value of 20%. These results can be compared to those presented

in an extensive study of NIOSH charcoal tube collection methods

for airborne organics.26 The s R values calculated from the data

presented in t his study ranged from 0.4%to as much as 69%, with

an average of 15%(for xylene s R ranged fr om 5.2 to 22%, with an

average of 10%, and for benzene, fr om 4.3%to as much as 43%,

with an 15%average). Therefore, precision for the PDAS-SPME

method can be considered in the same order of magnitude (if

not better for some analytes) to the range of precision reported

for the NIOSH standard method.An estimate of the detection limits of PDAS-SPME was

provided by the laboratory air samples analysis. For sampling close

to the solvent cabinet 18 ( 6 ppbv benzene, 6 ( 3 ppbv toluene,

and 2 ( 1 ppbv p -xylene were detected, and for the air in the

instrument room, 3 ( 1 ppbv toluene and 2 ( 1 ppbv p -xylene;

other analytes were not detected. Those results show that the

detection l imits for PDAS-SPM E are in the low-ppbv range.

Comparison with the NIOSH method was not considered valid

here, since for the same samples no aromatic hydrocarbons were

detected with this method even extending the sampling volumes

to values up to 50 L, except for toluene in one of the samples.

For the sampling volumes employed in the vehicle and mechanical

shops analysis, the detection limits calculated according to data

provided i n method 1501 would be in the r ange between 6 and

100 ppbv for mechanical shop air sampling and 15-230 ppbv for

vehicle shop air sampling, depending on the analyte in consider-

ation. Therefore, PDAS-SPME can be considered as more

sensitive than the standard NIOSH 1501 method.

CONCLUSIONS

This work demonstrated that the combination of SPME and

the simple and inexpensive (∼U.S. $10) PDAS-SPME device was

a powerful tool for both qualitative screening and quantitative

analysis of varied samples as aromas from living plants to

occupational air. When compared to SPME extraction with simplestatic exposure of the fiber to the air, the application of PDAS-

SPME increased signifi cantly the number of detectable analytes,

the adsorbed amounts, and the method sensitivities. Findings in

this work suggest that PDAS-SPME can provide more accurate

qualitative profiles of extremely diluted samples such as natural

aromas.

A few remarks should be made on the herein proposed

methodology. As it involves short sampling times, the assessment(25) Tucker, W. A.; Nelken, L. H. Diffusion Coefficients in Air and Water. In

Handbook of Chemi cal Property Estimati on M ethods: Envi ronmental B ehaviour

of Organic Compounds ; Lyman, W. J., Reehl, W. F., Rosenblatt, D. H. Eds.;

M cGraw-Hill : New York, 1982; Chapter 17, pp 17-1-17-25.

(26) Larkin, R. L.;Crable,J. V.; Catlett, L. R.; Seymour, M. J. Am. In d. H yg. Assoc.

J. 1977, 38 , 543-554.

Table 1. Concentrations in ppb v/v of Some Aromatic

Hydrocarbons in Indoor Air Measured by PDAS-SPME

and NIOSH Standard Method 1501

vehicleshop mechanical shop

SPME NIOSH SPM E NIOSH

benzene 48 ( 10a b 17( 4 b

toluene 212 ( 43 215 62 ( 9 73ethylbenzene 60 ( 8 48 ndc ndp -xylene 189 ( 43 222 25 ( 5 ndo -xylene 249 ( 35 137 18 ( 5 ndmesitylene 202 ( 28 75 nd nd

a Uncertainties expressed as estimates of standard deviation of triplicates. b Not quantifiable (see text). c nd, not detected.

Analytical Chemistry, Vol. 73, No. 3, February 1, 2001 485

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