Comparison of Different Fibers in the Solid Phase Microextraction of

Phthalate Esters from Water Samples

A. Peñalver

1

, E. Pocurull, C. Aguilar, F. Borrull, and R.M. Marcé

Departament de Química Analítica i Química Orgànica, Universitat Rovira i Virgili,

Imperial Tarraco 1, 43005 Tarragona, Spain;

1

e-mail address:

[e-mail]

Key Words: SPME; phthalate esters; water analysis; gas chromatography-mass spectrometry

1 Introduction

Phthalate esters have long been used as additives in the plastics industry. They are often found in

environmental matrices such as waters and soils [1-3]. As these compounds are thought to be

endocrine disrupting [4], the interest in determining them at low concentration levels has recently

grown. For example, the Environmental Protection Agency (EPA) has set the maximum admissible

concentration (MAC) for bis(2 ethylhexyl) phthalate ester at 6 µ g l

-1

[5]. This compound is one of

most common plasticizers.used today.

Gas chromatography (GC) [2,6] and high performance liquid chromatography (HPLC) [1-3],

preceded by preconcentration techniques such as solid phase extraction (SPE) [1,4] or liquid-liquid

extraction (LLE) [6], are the usual techniques for determining these compounds in environmental

samples. Solid phase microextraction (SPME), first introduced in 1990 by Pawliszyn and co-

workers [7], has successfully been applied to determine a wide variety of organic compounds from

environmental matrices [8-11]. SPME can be used with gas chromatography (GC) [8-10], high

performance liquid chromatography (HPLC) [11] and capillary electrophoresis (CE). In SPME, a

coated fiber is used to extract the analytes from the sample matrix. The first commercially available

SPME fibers were polydimethylsyloxane (PDMS) of different thicknesses (7, 30 and 100 µm) for

relatively apolar compounds, and 85µm-polyacrylate (PA) for more polar compounds. Other fiber

coatings have recently been developed to extend the range of application of SPME to a wider range

of compounds. At present, more specific coatings that contain polymers such as Carbowax (CWX),

divinylbenzene (DVB) and Carboxen have been developed. Selecting the most suitable fiber

coating for each application is a very important factor in SPME.

The main aim of this study is to develop a rapid method based on solid phase microextraction for

the most commonly used phthalates (dimethyl-, diethyl-, di-n-butyl-, butylbenzyl-, bis(2

ethylhexyl)- and di-n-octyl phthalate esters) and one adipate, the bis(2-ethylhexyl) adipate ester, in

water samples. The SPME experimental conditions for various commercially available fibers

(65µm carbowax-divinylbenzene, 65µm-polydimethylsiloxane-divinylbenzene, 85µm-polyacrylate,

75µm carboxen-divinylbenzene and 30µm-polydimethylsiloxane) have been optimized and the area

responses of phthalates and adipate have been compared under optimal conditions for each fiber.

The SPME-GC-MS method with the optimum fiber has been validated with different real water

samples.

2 Results and Discussion

The main parameters affecting the absorption and the desorption process in SPME were optimized

for each fiber: the time and temperature of the absorption step and the addition of salt to the sample,

and the time and temperature of the desorption process. Milli-Q water samples spiked with 2 µg l

-1

of each compound were used to evaluate the effect of these parameters.

Desorption conditions, time and temperature, were optimized for each fiber. Fibers remained in the

injector for different times at 250 ºC, from 2 to 16 min (total run time), and blanks were run to

confirm the absence of carryover. Absorption time was also optimized and its effect on the amount

of analyte extracted was studied by monitoring the peak area obtained for each compound when the

absorption time increased. Absorption temperature was mantained at 45 ºC and salt was not added

to the sample. The absorption temperature was the next parameter to be optimized and the

absorption time was set at the optimum value obtained for each fiber in the previous experiments.

Finally, the amount of salt added to the sample was also optimized. The time and temperature of

absorption were set at the optimum values previously obtained in these experiments for each fiber.

Table 1 shows the optimum values obtained for absorption time and temperature, and salt addition,

for each type of fiber. First experiments achieved by Carboxen-PDMS fiber showed that it was not

suitable for extracting phthalate or adipate esters and is therefore not included in Table 1.

Table 1. Optimum SPME extraction conditions for each fiber.

The four fibers were compared by extracting Milli-Q and river water samples containing the

compounds studied at a concentration of 2 µg l

-1

at the optimum SPME conditions for each fiber

coating. Figure 1 shows the areas obtained for phthalate and adipate esters extracted under optimum

conditions. As it can be observed, responses were better with the PDMS-DVB fiber.. However, with

PA and PDMS chromatograms were cleaner with real water samples. The responses from river

water samples were similar to those from Milli-Q.

Absorption process

Desorption process

Time

(min)

Temperature

(ºC)

Salt addition

(g/L)

Time

(min)

Temperature

(ºC)

30µm-Polydimethylsyloxane

30

60

25

10

250

65µm-Polydimethylsyloxane-divinylbenzene

30

80

360

3

250

85µm-Polyacrylate

90

45

180

16*

250

65µm-Carbowax-divinylbenzene

60

45

100

3

250

* total run time

Figure 1. Peak areas obtained for the compounds studied in optimum

extraction conditions for each fiber coating.

From the results obtained, 65 µm-polydimethylsiloxane divinylbenzene fiber has been selected to

perform the subsequent experiments in real water samples, since it provided the best results for the

compounds studied. The SPME-GC-MS method developed has been validated with river and

coastal real water samples.

References

[1]

M. Castillo, A. Oubiña, D. Barceló, Environ. Sci. Technol. 1998, 32, 2180-2184.

[2]

T. Hyötyläinen, K. Grob, M. Biedermann, M.-L. Riekkola, J. High Resol. Chromatogr.
1997, 20, 410 416.

[3]

M. Möder, P. Popp, J. Pawliszyn1, J. Microcol. Sep. 1998, 20, 225-234.

[4]

S. Jobling, T. Reynolds, R. White, M.G. Parker, J.P. Sumpter, Env. Health. Pers. 1995, 103,
582-587.

[5]

National Primary Drinking Water Regulations, Federal Register; Part 12, 40 CFR Part 141,
pp. 395; US Environmental Protect Agency, Jly 1

st

1991, Washington DC, USA.

[6]

K. Holadová, J. Hajslová, Int. J. Environ. Anal. Chem. 1995, 59, 43-57.

[7]

J. Pawliszyn in: Solid Phase Microextraction: Theory and Practice, Wiley-VCH , New
York 1997.

[8]

A. Peñalver, E. Pocurull, F. Borrull, R.M. Marcé, J. Chromagr. A 2000, 872, 191-201.

[9]

I. Valor, J.C. Moltó, D. Apraiz, J. Chromatogr. A 1997, 797, 195-203.

[10]

A. Peñalver, E. Pocurull, F. Borrull, R.M. Marcé, J. Chromatogr. A 1999, 839, 253-260.

[11]

H. Katakoa, J. Pawliszyn, Chromatographia 1999, 50, 532-538.

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