FULL SHORT COMMUNICATION

Comparison of SPE-TD-GC-FID with UPLC-PDA and GC-MSMethods for Analysis of Benzene, Toluene and Xylene Isomersin Solid-Liquid Mixing Paints

Shuai Zhang • Tianbo Zhao • Haiwang Wang •

Jia Wang

Received: 21 December 2010 / Revised: 10 February 2011 / Accepted: 22 March 2011 / Published online: 22 April 2011

� Springer-Verlag 2011

Abstract Three methods were developed for analysis of

benzene, toluene, p-xylene, m-xylene and o-xylene (BTX)

in a solid-liquid mixing paint. These methods were based

on solid phase extraction-thermal desorption-gas chroma-

tography with a flame ionization detector (SPE-TD-GC-

FID), ultra performance liquid chromatography-photodiode

array detector (UPLC-PDA) and gas chromatography-mass

spectrometry (GC-MS). At their optimum conditions of

operation, the developed methods were compared in terms

of recovery, sensitivity, selectivity and universality.

Although the time required for GC-MS analysis was

shorter than for GC-FID and UPLC-PDA, it offered rela-

tively poorer recoveries and suffered from matrix inter-

ferences. All of the mentioned methods were proven to be

ideal for the analysis of targeted analytes; SPE-TD-GC-

FID was particularly fit for the determination of trace level

BTX residues present in the complex matrix. As one of the

sample pretreatment techniques, the novel SPE also

showed some selectivity towards BTX and was found to be

superior to the conventional SPE.

Keywords Gas chromatography-mass spectrometry �Solid phase extraction-thermal desorption � Gas

chromatographic-flame ionization detector � Ultra

performance liquid chromatography-photodiode array

detector � BTX in paint

Introduction

Chronic exposure to benzene, toluene, p-xylene, m-xylene

and o-xylene (collectively BTX) through vapor inhalation

causes disorders of the central nervous system and gas-

trointestinal tract. The most relevant consequences of

chronic poisoning are plastic anemia and leukemia [1].

BTX has already been confirmed to be a strong carcinogen

by the World Health Organization (WHO) and classified as

a priority pollutant by the US Environmental Protection

Agency (EPA) [2]. At present, the use of BTX is restricted

in the manufacturing of primers, top-finish paints, barrier

paints, fire-retardant paints, decoration adhesives and

diluents.

Widely used paints are known to contain a considerable

number of organic compounds and solid additives. For

example, BTX is present in complex matrices at a wide

range of concentrations [3]. From an analytical point of

view, the composition is responsible for the difficulties in

the analysis of trace level BTX residues present in solid-

liquid mixing paint. There are various options for chro-

matographic detection that depend upon the phase and/or

the concentration range of samples. For instance, direct

injection (DI) with a microsyringe can be adopted for

highly concentrated BTX samples [4]. However, in the

case of low concentration paint samples, i.e., trace level

BTX in solid-liquid mixing paint, the adoption of certain

preconcentration treatments is inevitable. The combination

of GC with the pretreatment stage (e.g., the use of SPE-TD)

is efficient for extending the detectability of complex

matrix samples [5]. In this work, we used Tenax as an

absorbent to accomplish selective pre-separation of BTX

and solvents.

Although there is a considerable amount of literature

[1, 6–14] on the analysis of BTX in different matrices

S. Zhang (&) � T. Zhao � H. Wang � J. Wang

Key Laboratory of Cluster Science of Ministry of Education,

Beijing Institute of Technology, Beijing 100081,

People’s Republic of China

e-mail: zs_4444666666@163.com

123

Chromatographia (2011) 74:163–169

DOI 10.1007/s10337-011-2029-z

(e.g., gaseous, aqueous and solid sediment), we could find

hardly any papers dealing with the application of UPLC-

PDA for the determination of BTX in solid-liquid mixing

paint samples. UPLC, as its first producer Waters claims,

means ‘speed, resolution and sensitivity’ [15], and it can be

regarded as a new direction for liquid chromatography.

Recent technological advances have resulted in the avail-

ability of reversed-phase chromatographic media of 1.7-lm

particle size and a liquid-handling system that can be

applied at much higher pressures. UPLC has significant

additional advantages in time saving and solvent con-

sumption as well [16–20].

The aim of this paper was to investigate and compare

the performance of SPE-TD-GC-FID with UPLC-PDA and

GC-MS. We tried to determine which method is the most

reliable solution for the determination of BTX compounds

in solid-liquid mixing paint.

Experimental

Chemicals and Reagents

Standards of benzene, toluene, p-xylene, m-xylene and

o-xylene were purchased from the State Center for Stan-

dard Matter (concentration levels: 0.97, 1.01, 0.98, 0.99

and 1.00 mg mL-1, respectively; Beijing, China). All of

the above standards were prepared in methanol. Methanol

of HPLC grade was obtained from Merck (Darmstadt,

Germany). Ultrapure water (18.2 MX cm, 25 �C, produced

by Millipore, USA) was used throughout the study. High-

purity nitrogen and helium (99.999%) were purchased from

South Asia Air Products (Beijing, China). The adsorption

tube was fabricated by filling Tenax 60–80 mesh (Beifen

Tianpu Instrument Technology Co. Ltd., Beijing, China)

into a silanized glass tube (150 9 6 mm o.d. 9 4 mm

I.D.). The Tenax adsorbent was kept in place by a piece of

stainless-steel wire.

Instrumentation

The Waters ACQUITYTM Ultra-Performance Liquid Chro-

matography system (UPLC, Waters, Milford, MA) is com-

posed of a photodiode array detector (PDA), sample manager,

column heater and binary solvent manager. The guard col-

umn (3.9 9 20 mm) was packed with Symmetry C18 (5-lm

particle size, Waters, USA), and the analytical column was

an ACQUITYTM BEH C18 column (100 9 2.1 mm I.D.,

1.7-lm particle size, Waters, Milford, MA).

The GC-MS (HP6890 N GC Series combined with the

5975I MS, Agilent, USA) was equipped with an Agilent

7863 autosampler (with an Agilent 10-lL syringe) and a

30-m HP-5MS capillary column with an I.D. of 0.25 mm

and a film thickness of 0.1 lm (J&W Scientific, Folsom,

CA).

Gas chromatographic analysis was performed by using

a GC1100, equipped with a flame ionization detector

(GC-FID, Purkinje General Instrument Co. Ltd., Beijing,

China). Hydrogen was supplied by a DH-500 high-purity

hydrogen generator (BCHP Analytical Technology Insti-

tute, Beijing, China). Chromatographic separation was

carried out on a stainless-steel packed column

(300 9 3 mm I.D.) containing 5% DNP ? 3.5% Ben-

tone34/Chromsorb WAW (80–100 mesh, Lanzhou Atech

Technologies Co. Ltd.). For the desorption of analytes from

the adsorption tube, a TP-2050 thermal desorption unit

(Beifen Tianpu Instrument Technology Co. Ltd., Beijing,

China) coupled to a GC-FID was adopted [3].

A glass insert for GC-MS was silane-treated by di-

chlorodimethylsilane in order to diminish adsorption of

compounds at the injection port. All of the glassware for

the preparation of samples and standard solutions was

cleaned with deionized water and acetone, and then dried at

room temperature.

Preparation of Standard Solutions

A stock solution containing benzene, toluene, p-, m- and

o-xylene standards was prepared by mixing the commercial

standards to a final concentration of 0.194, 0.202, 0.196,

0.198 and 0.200 mg mL-1, respectively. Later, the stock

solution mixture was diluted step by step with methanol to

appropriate concentrations for calibration curve construc-

tions and spiking tests. All these solutions were used for

peak identification and quantitative analysis as well and

stored at 4 �C in a refrigerator before use.

Preliminary Procedures for BTX Extraction from Paint

(1) A 0.01–0.1-g (accurate to 0.0001 g) commercial paint

sample was weighed into an extraction vessel;

(2) The analytes were extracted in 3 mL methanol

(ultrasonic-associated extraction, 40 kHz working

frequency and 100 W power, 40 �C, 3 min);

(3) The extract was collected in a 5-mL volumetric flask,

and the volume was made up to the mark with

methanol;

(4) The solution was filtered through a 0.45-lm micro-

syringe filter into 2-mL brown high-airtight vials and

stored at 4 �C in a refrigerator before analysis.

SPE-TD-GC-FID Analysis

To conduct a GC-FID-based analysis of standard solutions

and extracts, a GC system was equipped with a thermal

164 S. Zhang et al.

123

desorption (TD) unit as well as the solutions needed to be

further pretreated by the novel solid phase extraction (SPE)

technique.

SPE Procedures

As shown in the schematic diagram of Fig. 1, the SPE was

carried out in several steps as follows:

(1) Standard solution or extract (10–50 lL) was injected

through the head gasket seal into a Tenax adsorption

tube under 20 mL min-1 nitrogen flow. (One end

connected to the nitrogen flow while the other end

was exposed to the atmosphere.)

(2) Most of the solvents were eliminated by nitrogen

flow, and the BTX was selectively enriched in the

absorbent.

(3) Both ends of the Tenax adsorption tube were sealed

with silicone caps; the analytes were then desorbed

and analyzed as soon as possible after the preparation.

TD Operation

The TD unit was operated in the following sequences. At

the beginning, the Tenax adsorption tube was inserted into

the tube furnace, and the stainless-steel injection needle,

which was connected with the Tenax tube, directly pene-

trated through the septum for an injection port. Then, the

Tenax adsorption tube was rapidly heated up to 200 �C and

held for 5 min. Finally, the tube was purged by

30 mL min-1 nitrogen flow, and thermally desorbed ana-

lytes were subsequently delivered into the stainless-steel

packed column. The desorbed analytes were separated and

detected by GC-FID [3].

GC-FID Analysis

The GC-FID system was operated at a flow rate of

30 mL min-1 (high-purity nitrogen was used as carrier

gas). The flow rate of hydrogen was 55 mL min-1,

whereas the air flow rate was 400 mL min-1. The column

temperature was maintained at 110 �C. The injection port

temperature and the FID detector temperature were set at

250 and 260 �C, respectively.

UPLC-PDA Analysis

For UPLC-PDA analysis, all of the extracts were filtered

through a filtering cartridge with a 0.2-lm nylon mem-

brane. The injection (volume: 3.0 lL) was performed by an

autosampler with an injection needle. Other detail analyt-

ical conditions were as follows: needle wash, strong wash

(MeOH/H2O = 8/2): weak wash (MeOH/H2O = 1/9) =

600:300 lL; seal wash, MeOH/H2O = 1/10; re-equilibra-

tion time: 3 min; the mobile phase consisted of methanol

(A, 70%) and ultrapure water (B, 30%); the analysis were

achieved at a flow rate of 0.1 mL min-1 and the column

temperature fixed at 45.0 �C; the wavelength of PDA was

set at 203 nm for analysis; the data were collected and

processed by Waters Empower system.

GC-MS Analysis

For GC-MS analysis, the extract was dried with Na2SO4.

The temperature of the injection port, interface and qua-

druple as well as ion source was constantly maintained at

250, 260, 120 and 250 �C, respectively. The GC oven was

temperature programmed as follows: the column was ini-

tially maintained at 40 �C for 1 min. Subsequently, the

temperature was increased up to 120 �C at a rate of

40 �C min-1. Then, it was maintained at 120 �C for 2 min.

The total time for each GC run was 5 min. High-purity

helium (purity 5.0) was used as a carrier gas, and the

column flow rate was 1.2 mL min-1. Injection of 1 lL in

the splitless mode was performed by using an Agilent 7863

autosampler equipped with an Agilent 10-lL syringe. The

mass spectrometer setup was as follows: electron impact

mode, EI; ionization energy, 70 eV in the positive-ion

mode; repel voltage, 25 V; analytical mode, full scan

(mass range of m/z 50–150 a.m.u. with mass accuracy of

0.1 a.m.u.).

Fig. 1 Schematic diagram of the solid phase extraction device.

A assembled SPE device; B SPE decomposition diagram; a head

gasket seal, b three-way piece, c and d graphite seal, e tail pipe,

f cylinder, g stainless-steel injection needle, h nitrogen pipe, i silicon

rubber cap, j stainless-steel wire, k Tenax adsorbent

Comparison of SPE-TD-GC-FID with UPLC-PDA and GC-MS Methods 165

123

Results and Discussion

Conventional SPE and Novel SPE

SPE is a sample preparation method that is well adapted

especially to the handling of liquid samples. Trace ana-

lytes are trapped by a suitable sorbent packed in a car-

tridge through which the liquid is percolated and then

eluted with a small volume of organic solvent. Extraction

and concentration are performed simultaneously [21].

Although SPE is an effective technique for the extraction

and pre-concentration of analytes from gaseous or aque-

ous matrices, it tends to use expensive and toxic elution

solvents and suffers from problems of cartridge plugging

and significant background interferences, which have an

adverse affect on repeatability [22]. In this study, we tried

to improve the conventional SPE technique by injecting

solutions onto the Tenax absorbent under nitrogen flow.

Most of the solvents were successfully purged by nitrogen

flow, whereas BTX was still retained in the absorbent.

The significant advantage of this novel SPE technique is

the replacement of expensive and toxic elution solvents

by nitrogen. The result has shown good reproducibility

with very little matrix dependency. The results of recov-

eries and limits of detection (LOD) would strengthen our

opinion.

K. Dettmer and W. Engewald [23] reported that Tenax is

a very hydrophobic material characterized by high thermal

stability. Because of its low specific surface area

(30 m2 g-1), it is not suitable for the sampling of highly

volatile organics. Referring to hydrocarbons, Tenax was

used for compounds with carbon numbers higher than four

[24]. However, because of the hydrophilic characteristic of

methanol with a carbon number of only one, it is not easily

adsorbed by Tenax, whereas the situation was the reverse

for BTX. Some studies on Tenax [25–28] have primarily

explained the reasons why BTX was still retained in the

absorbent while most of the solvents were removed by

nitrogen flow at room temperature. Our present study on a

novel SPE technique has exhibited good agreement with

the previous works.

Comparison of SPE-TD-GC-FID with UPLC-PDA

and GC-MS

Under optimum conditions, the SPE-TD-GC-FID, UPLC-

PDA and GC-MS methods were applied to standard solu-

tions and real commercial paint samples in order to

determine their recoveries and LOD. The results are sum-

marized in Table 1, and the advantages and drawbacks of

all three techniques are also presented in Table 1.

Time Demand

The sample preparations for UPLC-PDA and GC-MS were

more straightforward than what was required for SPE-TD-

GC-FID analysis, i.e., only dilution and filtration were

required after the ultrasonic-associated extraction. For

GC-FID analysis, the SPE procedure and TD operation

increased the sample preparation time significantly. The

analysis time of GC-MS was relatively shorter (twice as

fast as previous reports) compared with previous experi-

ments reported in the literature [29, 30]. Although the

GC-MS method was able to enhance the rapidity of

analysis, the injection volume limitation due to column

capacity presented a major problem. In addition, the

detection of a trace amount BTX in paint samples was

severely affected by the tailing area of the solvent (espe-

cially for benzene). In the case of GC-FID and UPLC, the

analysis time was commonly longer than 20 min. Never-

theless, it could be shortened when the flow rate of the

mobile phase was increased.

Table 1 Comparison of the

application of SPE-TD-GC-

FID, UPLC-PDA and GC-MS in

the analysis of benzene, toluene

and xylene isomers in solid-

liquid mixing paint

? Satisfactory; ?? normal;

??? good; ???? excellent

SPE-TD-GC-FID UPLC-PDA GC-MS

Solvent demand Little Too much Little

Time for sample preparation (min) 12–15 7–10 3–5

Analysis time (min) 20 15 5

Peak separation ???? ??? ??

Identification ??? ?? ????

Sensitivity ???? ??? ???

Ruggedness of the system ??? ???? ?

Recovery % 92.3–97.4 95.1–100.7 79.8–89.3

LOD range (lg mL-1) 0.021–0.16 0.23–0.79 5.6–13

Automation ?? ???? ????

Universality ???? ??? ???

Cost Low Expensive High

166 S. Zhang et al.

123

Peak Separation

Figures 2, 3 and 4 show the chromatograms corresponding

to GC-FID, UPLC-PDA and GC-MS. Simultaneous

determinations of p-xylene, m-xylene and o-xylene were

initially attempted, but they were successfully separated

only by using a Bentone34/Chromsorb column. The iden-

tification of xylene isomers was a great challenge with the

UPLC-PDA and GC-MS methods. For both methods,

standard solutions were used to qualitatively and quanti-

tatively analyze BTX in paint samples, while in GC-MS,

qualitative analysis was based on library spectra (NIST/

EPA/NIH Mass Spectral Database) and fragmentation

patterns.

Although we need further analysis to confirm the com-

position of the mixed peaks in UPLC chromatograms for

the assignments of p- and m-, p- and o-, or m- and o-xylene,

our preliminary study has readily shown that the total

quantitative analysis of xylene isomers could be achieved.

Recovery Test

The accuracies of all developed methods were confirmed

by the following recovery test. Toluene was chosen as the

spiked analyte for the recovery test because there were no

interfering peaks presented in its chromatogram. The

spiked samples were extracted and analyzed under the

conditions as described above. The overall average

recoveries for solid-liquid mixing paint spiked at levels of

0.1, 0.3 and 0.5 mg mL-1 ranging from 79.8 to 89.3% for

GC-MS, 92.3 to 97.4% for GC-FID and 95.1 to 100.7%

for UPLC-PDA, as listed in Table 1. The results indicated

that all methods were satisfyingly accurate for the deter-

mination of the targeted analytes in solid-liquid mixing

paint.

Apparently, the recovery of GC-MS was remarkably

lower than those of GC-FID and UPLC-PDA. One reason

for the bad values by GC/MS could be the condition of the

MS instrument (impurities in the ion source, calibration of

mass scales, etc.). In case of a low concentration solution,

quantitative analysis of GC-MS can be affected by the

tailing area of the solvent, and loss of targeted analytes was

possible during sample injection. The splitless injection

mode is not absolutely splitless in reality; only over 95% of

analytes could be ensured to enter the chromatographic

column. UPLC-PDA does not behave in this way, since its

mobile phase and solution are using the same solvent, and

methanol has no strong adsorption at 203 nm. It became

obvious that the recovery of UPLC appeared to be superior

to GC methods.

LOD

The LODs were calculated on the basis that concentration

gives a signal three times greater than background noise.

The GC-FID and UPLC-PDA method exhibited excellent

LOD. As shown in Table 1, it is obvious that the LODs for

GC-FID were 2–4 orders of magnitude lower than those for

Fig. 2 GC-FID chromatograms obtained from the analysis of stan-

dard solution and real commercial paint sample. a BTX standards in

methanol, the concentration levels (lg mL-1) of the solutions were:

1.94, 2.02, 1.96, 1.98 and 2.00 for benzene, toluene, p-xylene,

m-xylene and o-xylene, respectively; b real commercial sample,

injection volume: 15 lL

Fig. 3 GC-MS chromatograms obtained from the analysis of stan-

dard solution and real commercial paint sample. a BTX standards in

methanol, concentration levels (mg mL-1) of the solutions were:

0.194, 0.202, 0.196, 0.198 and 0.200 for benzene, toluene, p-xylene,

m-xylene and o-xylene, respectively; b real commercial sample,

injection volume: 1.0 lL; SD solvent delay

Comparison of SPE-TD-GC-FID with UPLC-PDA and GC-MS Methods 167

123

GC-MS. There are two possible reasons for this

phenomenon:

(1) The injection volume of GC-FID was dozens of times

larger than that of GC-MS. Meanwhile, drawbacks

like the tailing area of the solvent could be overcome

by the SPE-TD pretreatment technique and

(2) MS and PDA were much less sensitive than FID for

BTX analysis. This could also be seen in the

repeatability of the peak area: better results were

obtained in GC-FID analysis, even after more com-

plicated SPE-TD pretreatment. In case of GC/MS, the

sensitivity can be increased using the SIM technique.

Conclusions

A new SPE technique comprised by a stainless-steel tube

packed with Tenax adsorbent material has enabled highly

efficient and repeatable adsorption and desorption of trace

quantities of BTX from the solid-liquid mixing paint

sample. The main advantages of SPE-TD-GC-FID in

comparison with UPLC-PDA and GC-MS included an

excellent matrix effect elimination capacity, very low

detection limit, high reproducibility, simplicity and sol-

vent-free elution. It is also noteworthy that the excellent

lifetime of the Tenax adsorption tube enables at least 150

desorption operations at 200 �C to be carried out besides

maintaining excellent stability and reproducibility. It is

suitable to analyze BTX in complex matrix in an accurate

manner.

Acknowledgments The authors would like to thank the China 111

project no. B07012 and the National Natural Science Funds no.

20973022 for supporting the research.

References

1. Mangani F, Lattanzi L, Rezai MA, Cecchetti G (2000) Chro-

matographia 52:217–220

2. Florez Menendez JC, Fernandez Sanchez ML, Sanchez Urıa JE,

Fernandez Martınez EF, Sanz-Medel A (2000) Anal Chim Acta

415:9–20

3. Zhang S, Zhao TB, Xu X, Wang HW, Miao C (2010) Chroma-

tographia 71:1131–1135

4. Pandey SK, Kim KH (2007) J Chromatogr A 1216:5436–5444

5. Kim KH, Pal R (2010) Environ Monit Assess 161:295–299

6. Campos-Candel A, Llobat-Estelles M, Mauri-Aucejo A (2009)

Talanta 78:1286–1292

7. Djozan D, Assadi Y (1997) Chromatographia 45:183–189

8. Mangani G, Berloni A, Maione M (2003) Chromatographia

58:115–117

9. Prikryl P, Kubinec R, Jurdakova H, Sevcık J, Ostrovsky I, Sliak

L, Berezkin V (2006) Chromatographia 64:65–70

10. Wang ST, Wang Y, You H, Yao J (2006) Chromatographia

63:365–371

11. Sarafraz-Yazdi A, Amiri AH, Es’haghi Z (2008) Chemosphere

71:671–676

12. Sarafraz-Yazdi A, Amiri AH, Es’haghi Z (2009) Talanta

78:936–941

Fig. 4 UPLC-PDA

chromatograms obtained from

the analysis of standard solution

and real commercial paint

sample. a Real commercial

sample, b BTX standards in

methanol (same standard

solution as for GC-MS was

used); injection volume: 3.0 lL

168 S. Zhang et al.

123

13. Sieg K, Fries E, Puttmann W (2008) J Chromatogr A

1178:178–186

14. Godoi AFL, Sawada EY, Marchi MRR, Grieken RV, Godoi

RHM (2009) Water Air Soil Pollut Focus 9:163–169

15. Waters Corporation (2004) Ultra performance LC by design.

Waters Corporation USA, 720000880EN:LL. &LW-UL

16. Wu T, Wang C, Wang X, Xiao HQ, Ma Q, Zhang Q (2008)

Chromatographia 68:803–806

17. Guvenc A, Satir E, Coskum M (2007) Chromatographia

68:S141–S145

18. Li X, Xiong Z, Ying X, Cui L, Zhu W, Li F (2006) Anal Chem

Acta 580:170–180

19. Guan J, Lai CM, Li SP (2007) J Pharm Biomed Anal

44:996–1000

20. Qin LX, Chao J, Wei Y, Yum L, Li YM, Gang CX (2008)

Chromatographia 68:57–63

21. Rivasseau C, Caude M (1995) Chromatographia 41:462–470

22. Magdic S, Pawliszyn J (1996) J Chromatogr A 723:111–122

23. Dettmer K, Engewald W (2002) Anal Bioanal Chem

373:490–500

24. Yang KL, Lo JG (1997) Chromatographia 44:405–410

25. Sakodynskii K, Panina L, Klinskaya N (1974) Chromatographia

7:339–344

26. Agelopoulos NY, Pickett JA (1998) J Chemical Ecology

24:1161–1172

27. Briand O, Millet M, Bertrand F, Clement M, Seux R (2002) Anal

Bioanal Chem 374:848–857

28. Zhao DY, Pignatello JJ (2004) Environ Toxicol Chem

23:1592–1599

29. Liu JF, Li N, Jiang GB, Liu JM, Jonsson JA, Wen MJ (2005) J

Chromatogr A 1066:27–32

30. Carrion CC, Lucena R, Cardenas S, Valcarcel M (2007) J

Chromatogr A 1171:1–7

Comparison of SPE-TD-GC-FID with UPLC-PDA and GC-MS Methods 169

123