Rapid analysis of aldehydes by simultaneous microextraction and derivatization followed by GC-MS

Short Communication

Rapid analysis of aldehydes by simultaneousmicroextraction and derivatization followedby GC-MS

Ultrasound-assisted dispersive liquid–liquid microextraction (UDLLME) and simulta-

neous derivatization followed by GC-MS was developed for the analysis of four aldehydes

including acetaldehyde (ACE), propionaldehyde (PRO), butyraldehyde (BUT) and valer-

aldehyde (VAL) in water samples. In the proposed method, the aldehydes were derivatized

with O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine (PFBHA) and extracted by UDLLME

in aqueous solution simultaneously; finally, the derivatives were analyzed by GC-MS. The

experimental parameters were investigated and the method validations were studied. The

optimal conditions were: aqueous sample of 5 mL, PFBHA of 50 mL, 1.0 mL ethanol

(disperser solvent) containing 20 mL chlorobenzene (extraction solvent), ultrasound time

of 2 min and centrifuging time of 3 min at 6000 rpm. The proposed method provided

satisfactory precision (RSD 1.8–10.2%), wide linear range (0.8–160 mg/L), good linearity

(R2 0.9983–0.9993), good relative recovery (85–105%) and low limit of detection

(0.16–0.23 mg/L). The proposed method was successfully applied for the analysis of

aldehydes in water samples. The experimental results showed that the proposed method

was a very simple, rapid, low-cost, sensitive and efficient analytical method for the

determination of trace amount of aldehydes in water samples.

Keywords: Aldehydes / Derivatization / DLLME / GC-MS / WaterDOI 10.1002/jssc.201100145

1 Introduction

The low-molecular mass aldehydes are widespread in air,

water, alcohol and industrial waste material, which is

harmful to the environment [1]. The toxicity of aldehydes

mainly has stimulation to the skin and mucosa, as well as

carcinogenicity [2]. The determination of low-molecular

mass aldehydes present in environmental liquids such as

wastewater is becoming an urgent task due to their toxic or

carcinogenic characteristics. GC is widely used in the

analysis of aldehydes owing to its simplicity, high resolving

power, good sensitivity, short analysis time and relatively

low cost [2–5]. However, GC analysis of low-molecular mass

aldehydes presents certain difficulties because of their high

volatility and polarity. Therefore, derivatization procedures

are usually required for GC analysis. Among the existing

derivatizing agents, O-2,3,4,5,6-(pentafluorobenzyl)hydroxyl-

amine (PFBHA) is widely used for aldehydes, and the

derivatizing reaction can proceed rapidly in aqueous

solution at room temperature and provides very good yield

[6–8]. After derivatization, the formed derivatives require

further extraction and concentration prior to GC analysis.

Liquid–liquid extraction (LLE) is among the oldest of the

preconcentration and matrix isolation techniques in analy-

tical chemistry. However, LLE is time-consuming and

requires large amounts of organic solvent. Solid-phase

extraction (SPE) uses much less solvent than LLE, but can

be relatively expensive. Supercritical fluid extraction (SFE)

can also be relatively expensive [9]. Because of these

disadvantages, microextraction techniques gain a growing

interest. Owing to its simple, solventless and flexible

properties, solid-phase microextraction (SPME) has become

an attractive alternative to the conventional sampling

techniques [10–13]. The SPME technique was used for

determination of aldehydes [3, 14]. However, SPME suffers

from some drawbacks: its fiber is fragile and has limited

lifetime and desorption temperature, and also sample carry-

over is a problem [15–17]. In the recent years, liquid-phase

microextraction (LPME) has been developed as a mini-

mized-solvent-based pretreatment method. Single-drop

microextraction (SDME) is one of the modalities of liquid-

Qing YeDagui ZhengLinhai LiuLiming Hong

Key Laboratory of AppliedOrganic Chemistry, HigherInstitutions of Jiangxi Province,Shangrao Normal University,Shangrao, P. R. China

Received February 19, 2011Revised March 20, 2011Accepted April 5, 2011

Abbreviations: ACE, acetaldehyde; BUT, butyraldehyde;

DLLME, dispersive liquid–liquid microextraction; LLE,liquid–liquid extraction; PFBHA, O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine; PRO, propionaldehyde;

SDME, single-drop microextraction; SPME, solid-phasemicroextraction; UDLLME, ultrasound-assisted dispersiveliquid–liquid microextraction; VAL, valeraldehyde

Correspondence: Dr. Qing Ye, Key Laboratory of AppliedOrganic Chemistry, Higher Institutions of Jiangxi Province,Shangrao Normal University, Shangrao 334001, P. R. ChinaE-mail: [email protected]: 186-7938150694

& 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com

J. Sep. Sci. 2011, 34, 1607–1612 1607

phase microextraction, which combines extraction, concen-

tration and sample introduction in a single step. The SDME

technique has been used for extraction and analysis of

different compounds in various samples [18–21]. Deng et al.

developed SDME technique for determination of aldehyde

in water samples [5]. However, there are some disadvan-

tages in this method; it is difficult to achieve a stable organic

drop, formation of air bubbles can occur and extraction is

time-consuming and in most cases equilibrium is not

attained even after a long time [22, 23]. In 2006, Assadi and

co-workers developed a new microextraction technique

that was named dispersive liquid–liquid microextraction

(DLLME) [9]. DLLME is a simple and fast microextraction

technique based on the use of an appropriate extractant, i.e.

a few microliters of an organic solvent such as chloroben-

zene, chloroform or carbon tetrachloride with high

density and a disperser solvent such as methanol,

ethanol, acetonitrile or acetone with high miscibility in

both extractant and aqueous phases. It is a ternary

component solvent system, in which extraction and

disperser solvents are rapidly introduced into the aqueous

sample to form a cloudy solution. Extraction equilibrium is

quickly achieved, due to the extensive surface contact

between the droplets of the extraction solvent and the

sample. After centrifugation, extraction solvents depending

on their densities are sedimented at the bottom of the tube

or collected on the top of it and taken with a microsyringe

for later chromatographic analysis. DLLME is fast, inexpen-

sive, easy to operate with a high enrichment factor and

consumes low volume of organic solvent [24–26]. Simulta-

neous DLLME and derivatization were studied for the

analysis of chlorophenols, anilines and fatty acids in water

samples [27–29].

In this work, for aldehyde determination, for the first

time, ultrasound-assisted dispersive liquid–liquid micro-

extraction (UDLLME) and simultaneous derivatization

followed by GC-MS was developed for the analysis of the

low-molecular mass aldehydes in water samples. In this

proposed method, the extraction, concentration and deriva-

tization of aldehydes in water was performed in one step,

and the obtained derivatives in the extraction solvent were

analyzed by GC-MS. The extraction and derivatization

conditions were studied, and the method validations were

also investigated.

2 Materials and methods

2.1 Reagents and materials

Acetaldehyde (ACE) (99%), propionaldehyde (PRO) (99%),

butyraldehyde (BUT) (97%), valeraldehyde (VAL) (98%) and

PFBHA (98%) were purchased from Sigma (St. Louis, MO,

USA). Methanol and ACN (HPLC-grade) were purchased

from Merck (Darmstadt, Germany). All of other chemicals

were of analytical grade, and were purchased from Shanghai

Chemical Reagent (Shanghai, China). Aldehyde stock

standards were prepared in methanol, with concentration

levels of 100 mg/L for each compound, and were stored in a

freezer at �41C. Working standard solutions were prepared

by dilution of an appropriate amount of the above stock

solution in double-distilled water. PFBHA solution (5 mg/

mL) was made by dissolving PFBHA into double-distilled

water. The water used was of MilliQ grade (Millipore,

Bedford, MA, USA).

Wastewater samples were obtained from Shangrao

Water Treatment, Shangrao, China. River water samples

were obtained from the Xin Jiang River, Shangrao, China.

2.2 Instrumentation

An HP 6890 GC system, coupled with an HP MD5973

quadrupole mass spectrometer was used.

The extracted compounds were separated using HP-

5MS capillary column (30 m� 0.25 mm id, 0.25 mm film).

The extraction solvent after DLLME was injected directly in

the splitless mode. The oven temperature program was as

follows. The initial temperature was 801C, and held for

1 min, then increased to 2801C at a rate of 101C/min, and

was maintained at 2801C for 3 min. The injection

temperature was 2501C. Helium (99.999%) was used as the

carrier gas with a flow rate of 1.0 mL/min. The quadrupole

temperature, transfer line temperature and MS source

temperature were 150, 280 and 2301C, respectively. Electron

impact ionization (EI) with nominal electron energy of

70 eV was used. The quantitative analysis was carried out in

SIM mode. The retention time and ratio of mass-to-charge

(m/z) of the characteristic ions for each aldehyde derivatives

are presented in Table 1.

Table 1. The retention time and the characteristics (m/z) for aldehyde derivatives, linear dynamic ranges, estimation of coefficients (R2),

limits of detection (LODs) and precision (RSD%)

Compound tR (min) Characteristic ions (m/z) Range (mg/L) R2 LOD RSD%, n 5 5

10 mg/L 100 mg/L

ACE 5.28, 5.38 181, 195 0.8–120 0.9983 0.16 6.6 1.8

PRO 6.39, 6.47 181, 236 0.8–160 0.9993 0.20 8.7 2.8

BUT 7.56, 7.63 181, 239 0.8–160 0.9986 0.22 7.8 4.2

VAL 8.76, 8.83 181, 281 1.2–160 0.9990 0.23 10.2 6.4

J. Sep. Sci. 2011, 34, 1607–16121608 Q. Ye et al.


2.3 Simultaneous derivatization and UDLLME

procedure

About 5.00 mL of the aqueous standard solution with the

concentration of 100 mg/L for each aldehyde and 50 mL of

PFBHA were placed in a 10 mL screw cap glass test tube

with conic bottom. Next, ethanol (1.00 mL) as a disperser

containing 20 mL chlorobenzene (as an extraction solvent)

was rapidly injected into the solution using a 1.00 mL

gastight syringe. Then, the mixture sonicated for 2 min and

a cloudy solution was formed in the conic glass tube.

Further, the solution was centrifuged at 6000 rpm for 3 min

and chlorobenzene containing derivatized analytes was

sedimented in the bottom of the tube. One microlitre of

the extraction phase was taken using a 10 mL microsyringe

(Hamilton, Reno, NV, USA) and injected into the GC-MS

system for further analysis.

3 Result and discussion

3.1 Optimization of simultaneous derivatization and

UDLLME conditions

In order to obtain the maximal extraction efficiency, several

important parameters such as amount of derivatization

agent, type and volume of extraction solvent, volume of

disperser solvent, sonication time and centrifuging time

were studied and optimized. Analytes in aqueous matrix

were derivatized, extracted, concentrated and injected into

the GC-MS for analysis. For each aldehyde, after derivatiza-

tion with PFBHA, two isomers, namely (Z)-oxime and (E)-

oxime, can form [30]. Three analyses were done in replicate;

the total peak area of the two isomers for each aldehdye was

used for the determination of the optimal parameters.

3.1.1 Optimization of derivatization conditions

The derivatization of aldehydes with PFBHA proceeds

readily in weakly acidic to neutral media [6] that encom-

passes all excipient sample solutions studied, making the

use of a buffer solution unnecessary. In our previous study

[4], we have also noted that the condensation reaction was

complete in water in less than 10 min at room temperature.

In the work, the effect of the reaction time was studied at

0–10 min at room temperature. The results showed that the

time of the derivatization reaction is less than 2 min.

The amount of derivatization agent can affect the alde-

hyde derivatization efficiency. The five different volumes of

PFBHA (5 mg/mL) (20, 40, 50, 60 and 80 mL) were tested.

We found that peak areas of the derivatives of aldehyde

derivatization increased with the increase of PFBHA volume

in the range of 20–50 mL. However, the peak areas of alde-

hyde derivatives slow down when the volume of PFBHA is

up to 60 mL. The decrease occurs probably because at a high

volume of PFBHA the concentration of PFBHA in the

organic phase increases; therefore, the extraction efficiency

decreases. Hence, 50 mL PFBHA was selected in the

following experiments to ensure quantitative derivatization

of aldehydes.

3.1.2 Selection of extraction solvent

Selection of an appropriate extracting solvent is the major

parameter for DLLME process. Organic solvents are selected

on the basis of their higher density rather than water,

extraction capability of interested compounds and good

chromatographic behavior. In this sense, chlorobenzene,

tetrachloroethylene and carbon tetrachloride were tested as

extraction solvents. About 50 mL aliquot of PFBHA solution

was added to 5 mL of the aqueous standard solution

containing the four target analytes at 100 mg/L. A 0.5 mL

aliquot of ethanol solution containing 30 mL of extraction

solvent was rapidly injected. Then, the mixture were

sonicated for 3 min and centrifuged for 3 min. As shown

in Fig. 1, tetrachloroethylene presented the lowest extraction

efficiency and chlorobenzene showed the highest extraction

efficiency. Therefore, the chlorobenzene was selected for

further experiments.

3.1.3 Selection of the volume of extraction solvent

When the extraction solvent volume is increased, the

amount of extracted analyte is expected to increase too,

but it should be taken into account that the dilution effect is

also increased. To investigate the effect of the extraction

solvent volume, 0.5 mL of ethanol as disperser solvent

containing different volumes of chlorobenzene, ranging

from 10 to 40 mL, were tested. As the extraction volume

increased, the volume of sedimented phase also increased

and peak areas of the analytes decreased because of the

bigger dilution of the analytes. However, it should be noted

that no sedimented phase appeared on using 10 mL of

chlorobenzene. Thus, 20 mL was selected as the best

extraction solvent volume.

Figure 1. Effect of different extraction solvents on extractionefficiency. Extraction conditions: water sample volume, 5 mL;PFBHA volume, 50 mL; disperser solvent (ethanol) volume,0.5 mL; extraction solvent volume, 30 mL; concentration of eachaldehyde, 100 mg/L; ultrasonic agitation time, 3 min.

J. Sep. Sci. 2011, 34, 1607–1612 Sample Preparation 1609


3.1.4 Selection of disperser solvent

Miscibility of disperser solvent in both extracting solvent

and aqueous phase is essential in selection of it. In this

experiment, methanol, ethanol and acetonitrile were

selected as disperser solvents. Their effect on the extraction

efficiency of aldehyde derivatives was studied and the results

are shown in Fig. 2. According to these results, and owing to

less toxicity and low cost, ethanol is selected as disperser

solvent.

3.1.5 Selection of the volume of disperser solvent

In order to study the effect of the disperser solvent volume, a

fixed amount of chlorobenzene (20 mL) was dissolved in an

increasing volume of ethanol in the range of 0.25–1.5 mL.

As can be seen in Fig. 3, with the volume increase of ethanol

peak areas initially increased. It seems, at a low volume of

ethanol, cloudy state is not formed well, thereby, the

extraction efficiency decreases. At the high volume of

ethanol, the solubility of aldehyde derivatives in water

increases, therefore, the extraction efficiency decreases.

Therefore, the ethanol volume of 1 mL was chosen as

optimum volume.

3.1.6 Selection of sonication time

Enough time made the extraction solvent well dispersed into

the aqueous solution and resulted in the excellent enrich-

ment. Ultrasonic agitation time of 0, 1, 2, 3 and 5 min, were

tested. The experimental result indicated that the best

extraction efficiency was achieved in a short time of 2 min.

3.2 Evaluation of the method performance

Figure 4 shows the chromatogram of a standard solution

containing 50 mg/L of aldehydes after UDLLME with

derivatization at the optimum working conditions. Under

the optimal experimental conditions, the linearity, precision,

detection limit and recovery of the proposed method were

studied.

To obtain the method linearity, the standard solutions

from 0.8 to 160 mg/L were analyzed by simultaneous deri-

vatization and UDLLME followed by GC-MS. The linear

ranges and correlation coefficients (R2) obtained for each

aldehyde are given in Table 1. As seen from Table 1, the

method has good linearity. In order to assess the repeat-

ability, five repeated measurements at two different

concentrations of the analytes were carried out. Precision

was expressed by RSD values, reported in Table 1. Limit of

detections (LODs), which were calculated as three times the

SD of five replicated runs of spiked samples at lowest

concentration (0.8 mg/L) of calibration curve, reported in

Table 1.

Figure 2. Effect of different disperser solvents on extractionefficiency. Extraction conditions: water sample volume, 5 mL;PFBHA volume, 50 mL; extraction solvent (chlorobenzene)volume, 20 mL; disperser solvent volume, 0.5 mL; concentrationof each aldehyde, 100 mg/L; ultrasonic agitation time, 3 min.

Figure 3. Effect of ethanol volume on extraction efficiency.Extraction conditions: water sample volume, 5 mL; PFBHAvolume, 50 mL; extraction solvent(chlorobenzene) volume,20 mL; concentration of each aldehyde, 100 mg/L; ultrasonicagitation time, 3 min.

Figure 4. Typical SIM chromatogram of a standard solutioncontaining 50 mg/L of aldehydes obtained using UDLLME andsimultaneous derivatization combined GC-MS.

J. Sep. Sci. 2011, 34, 1607–16121610 Q. Ye et al.


3.3 Quantitative analysis of low-molecular mass

aldehydes in water sample

The optimum working conditions were applied to the

analyses of the aldehydes in real water samples. The water

samples were filtered through a 0.45-mm membrane filter

prior to analysis. The four aldehydes concentrations were

calculated by the external standard method and the results

are summarized in Table 2. The samples were spiked with

each target compound at the concentrations of 10 mg/L to

investigate the effect of sample matrices on extraction

efficiency, the relative recovery (RR) was obtained as the

following equation: The relative recovery (RR) 5 Cfounded�Creal/Cadded� 100%, where Cfounded, Creal and Cadded are the

concentrations of analyte after addition of known amount of

standard in the real sample, the concentration of analyte in

real sample and the concentration of known amount of

standard which was spiked to the real sample, respectively.

The relative recoveries of the four aldehydes ranged from 85

to 105%. The results showed that the method enabled the

precise and sensitive determination of standards and can be

applied to detect aldehydes in real samples.

4 Concluding remarks

In this work, we have demonstrated the feasibility of

aldehyde analysis by UDLLME and simultaneous derivatiza-

tion. It has been shown that extraction, concentration and

derivatization of analytes can be completed in a single step.

The proposed method had many practical advantages,

including simplicity of the extraction method, use of a

small volume of organic solvent for extraction, high

sensitivity, low cost, extreme rapidity, good repeatability

and high recovery. Therefore, it has the potential of practical

applications and could be either a complementary or a

parallel method for the analysis of aldehydes in aqueous

matrices.

This research was financially supported by the ResearchProgram of Science and Technology from Education Departmentof Jiangxi Province, China (No. GJJ10735).

The authors have declared no conflict of interest.

5 References

[1] Committee on Toxicology, Environmental Healthhazards. Formaldehydes and Other Aldehydes [M],National Academy Press, Washington DC 1981.

[2] Beranek, J., Kubatova, A., J. Chromatogr. A 2008, 1209,44–54.

[3] Schmarr, H. G., Sebastian GanX, W. S. S., Fischer, U.,Kopp, B., Schulz, C., Potouridis, T., J. Sep. Sci. 2008, 31,3458–3465.

[4] Lin, H. Q., Ye, Q., Deng, C. H., Zhang, X. M., J. Chro-matogr. A 2008, 1198– 1199, 34–37.

[5] Deng, C. H., Yao, N., Li, N., Zhang, X. M., J. Sep. Sci.2005, 28, 2301–2305.

[6] Kobayashi, K., Tanaka, M., Kawai, S., J. Chromatogr.1980, 187, 413–417.

[7] Schmarr, H. G., Potouridis, T., Gan, S., Sang, W., Kopp,B., Bokuz, U., Fischer, U., Anal. Chim. Acta 2008, 617,119–131.

[8] Deng, C. H., Zhang, X. M., Rapid Commun. MassSpectrom. 2004, 18, 1715–1720.

[9] Rezaee, M., Assadi, Y., Milani Hosseini, M. R., Aghaee,E., Ahmadi, F., Berijani, S., J. Chromatogr. A 2006, 1116,1–9.

[10] Deng, C. H., Zhang, J., Yu, X. F., Zhang, W., Zhang, X.M., J. Chromatogr. B 2004, 810, 269–275.

[11] Lin, H. Q., Deng, C. H., Zhang, X. M., J. Sep. Sci. 2008,31, 3225–3230.

[12] Li, N., Deng, C. H., Zhang, X. M., J. Sep. Sci. 2007, 30,266–271.

[13] Deng, C. H., Li, N., Ji, J., Zhang, X. M., Rapid Commun.Mass Spectrom. 2006, 20, 1281–1287.

[14] Deng, C. H., Li, N., Zhu, W. M., Qian, J., Yang, X. F.,Zhang, X. M., J. Sep. Sci. 2005, 28, 172–176.

[15] Helena, P., Locita, I. K., Trends Anal. Chem. 1999, 18,272–282.

[16] Hou, L., Lee, H. K., J. Chromatogr. A 2004, 1038,37–42.

[17] Farajzadeh, M. A., Seyedi, S. E., Shalamzari, M. S.,Bamorowat, M., J. Sep. Sci. 2009, 32, 3191–3200.

[18] Sha, Y. F., Meng, J. R., Lin, H. Q., Deng, C. H., Liu, B. Z.,J. Sep. Sci. 2010, 33, 1283–1287.

[19] Deng, C. H., Li, N., Wang, L., J. Chromatogr. A2006,1131, 45–52.

[20] Dong, L., Shen, X. Z., Deng, C. H., Anal. Chim. Acta2006, 569, 91–96.

[21] Li, N., Deng, C. H., Yao, N., Shen, X. Z., Zhang, X. M.,Anal. Chim. Acta 2005, 540, 317–323.

[22] Ahmadi, F., Assadi, Y., Milani Hosseini, M. R., Rezaee,M., J. Chromatogr. A 2006, 1101, 307–312.

[23] Shen, G., Lee, H. K., Anal. Chem. 2002, 74, 648–654.

[24] Rezaee, M., Yamini, Y., Faraji, M., J. Chromatogr. A2010, 1217, 2342–2357.

Table 2. Analytical results for the four aldehydes in water

samples (n 5 3)

Compound Concentrations (mg/L)

mean7SD

Relative recovery (RR) %

Waste water River water Waste water River water

ACE 11.270.48 1.870.17 85 90

PRO 4.670.25 ND 86 95

BUT 3.670.28 ND 93 105

VAL 4.270.31 ND 91 97

ND, no detection.

J. Sep. Sci. 2011, 34, 1607–1612 Sample Preparation 1611


[25] Herrera-Herrera, A. V., Asensio-Ramos, M., Hernandez-Borges, J., Rodrıguez-Delgado, M. A., Trends Anal.Chem. 2010, 29, 728–751.

[26] Anthemidis, A. N., Ioannou, K. I. G., Talanta 2009, 80,413–421.

[27] Kozani, R. R., Assadi, Y., Shemirani, F., Hosseini, M. R.M., Jamali, M. R., Talanta 2007, 72, 387–393.

[28] Chiang, J. S., Huang, S. D., Talanta 2008, 75,70–75.

[29] Pusvaskiene, E., Januskevic, B., Prichodko, A.,Vickackaite, V., Chromatographia 2009, 69,271–276.

[30] Cancilla, D. A., Hee, S. S. Q., J. Chromatogr. 1992, 627,1–16.

J. Sep. Sci. 2011, 34, 1607–16121612 Q. Ye et al.


Rapid analysis of aldehydes by simultaneous microextraction and derivatization followed by GC-MS

Documents

Transcript of Rapid analysis of aldehydes by simultaneous microextraction and derivatization followed by GC-MS