Abstract: Phthalate esters are widely used as plasticizer. They can migrate from plastic materials to the environment. Some of these compounds may have risk to get cancer. Phthalate esters; dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) were extracted simultaneously using solid-phase and analyzed by gas chromatograph. The percentage recoveries were carried out on LC-18 and Florisil cartridge using various eluting solvent. The 6 mL Florisil (1 g) with 5 mL of ethyl acetate as eluting solvent showed good recoveries in the range of 98.2-110.0% and the limit of determination in the range of 0.025-00.05 mg L-1. This proposed method was successfully applied to analysis of phthalates in drinking water. The contamination of DMP, DEP and DBP in drinking water samples were in the safe levels, except DEHP concentration in three samples were found out of regulated maximum admissible concentration.
INTRODUCTION
Phthalate esters are widely use as additives in the manufacture of plastic, paint and cosmetics (Penalver et al., 2000; Cai et al., 2003) to increase their flexibility, transparency, durability and longevity. Most of phthalate esters are used in the manufacturing of Polyvinyl Chloride (PVC). Dibutyl Phthalate (DBP) is used in epoxy resins, dimethyl (DMP) and Diethyl Phthalate Esters (DEP) are typically used in cellulose ester-based plastics (Stales et al., 1997). Phthalate esters can migrate from plastic materials to the environment. They are often found in water, soil, air, food products and the human body (Castillo et al., 1998). The finding of some phthalates; DEP, DBP and bis (2-ethylhexyl phthalate (DEHP) show the ability to interfere in environmental samples. Some of these compounds are carcinogen and estrogenic (Holadova et al., 2007). The US environmental Protection Agency (EPA) has set the Maximum Admissible Concentration (MAC) or maximum contamination level (MCL) of DEHP at 6 μg L -1 (USEPA, 1991), the threshold limit value (TLV) of DEP, DBP, DMP and DEHP were 0.55, 0.45, 5.0 and 5.0 mg L-1, respectively. In order to detect phthalate esters at sub mg L-1 levels, preconcentration step is necessary before analysis. Various liquid-liquid extraction have been used for extraction of phthalate esters (Yasuhara et al., 1997). However, the conventional pretreatment method need large quantities of sample and organic solvents (Farahani et al., 2007). Solid-phase extraction (Carlo et al., 2008), solid-phase microextraction (Luks-Betlej et al., 2001; Penalver et al., 2001; Prokupkova et al., 2002; Feng et al., 2005; Holadova et al., 2007; Xu et al., 2007) and dispersive liquid-liquid microextraction (Liang et al., 2008; Farahani et al., 2007) have gained importance for determination of phthalate esters in water samples. Solid-Phase Extraction (SPE) is the most common technique for water sample pretreatment (Zhao et al., 2008). It has many advantages such as high recovery, solvent consumption, simplicity and easy operation. The aim of this study was to optimize the condition of solid-phase extraction and applied to determine phthalates esters in bottled drinking water.
MATERIALS AND METHODS
Instrumentation: Gas chromatograph model GC17 (Shimadzu, Japan) with a DB-5 fused silica capillary column (30 m, 0.25 mm id., 0.25 μm film thickness) was used. The injector and detector temperature were 270°C with flame ionization detector and nitrogen gas was used as carrier gas. The temperature program was started from 60°C held for 5 min then ramp to 270°C with the rate of 15°C min-1 and held for 11 min.
Chemicals: Dimethyl Phthalate (DMP), Diethyl Phthalate (DEP), Dibutyl Phthalate (DBP) and bis (2-ethylhexyl) phthalate (DEHP) were analytical reagent grade and obtained from Fluka (Switzerland). The individual standard stock solutions were prepared in methanol and stored at 4°C. All organic solvent were HPLC grade from Labscan (USA).
Solid-phase extraction (SPE): The 3.0 mL of LC-18 (500 mg) and 6.0 mL Florisil (1 g) column were obtained from Supelco (USA).
Optimization of solid-phase extraction: Prior to extraction, the SPE columns were conditioned with 5.0 mL methanol under vacuum, following by 5.0 mL with deionized water. The 100 mL deionized water was spiked with the standard solution of phthalate esters (20 mg L-1 of each) and subsequently passed through the column with the flow rate of 1.0 mL min-1. The phthalate esters were eluted with various kind of organic solvent. The percentage recovery was carried out by gas chromatography. The limit of detection of solid-phase extraction were taken as the lowest concentration of phthalate esters that could be extracted and yielding good recoveries.
Application to real water samples: Phthalate esters in drinking water which contained in Polyethylene Terephthalate (PET) bottled were analyzed by using the optimum conditions.
RESULTS AND DISCUSSION
Figure 1 showed the chromatogram of DMP, DEP, DBP and DEHP with the retention times of 14.48, 15.76, 18.72 and 24.41 min, respectively. The linearity ranges were 0-100 mg L-1 with the correlation coefficient in the range of 0.9935-0.9972, as summarized in Table 1. The percentage recoveries were achieved by spiked sample (20 mg L-1 of each) using LC-18 and Florisil cartridge with various eluting solvent. Florisil showed suitable for extraction of phthalate esters, since Florisil form is a powdered magnesium-silica gel and used as normal phase.
| Table 1: | Linearity range, calibration data of phthalate ester using DB-5 fused silica capillary column (30 mx0.25 mm id., 0.25 μm film thickness) |
| Fig. 1: | Chromatogram of DMP, DEP, DBP and DEHP with the retention times of 14.48, 15.76, 18.72 and 24.41 min, respectively, by gas chromatograph using DB-5 fused silica capillary column (30 mx0.25 mm id., 0.25 μm film thickness) |
| Fig. 2: | Chromatogram of mineral water no 1 by solid-phase extraction and gas chromatograph using DB-5 fused silica capillary column (30 mx0.25 mm id., 0.25 μm film thickness) |
The interaction is adsorption, elution step is usually carried out with a polar solvent. The 5 mL of ethyl acetate showed good recoveries in the range of 98.2-110.0%, as shown in Table 2. The limit of determination (LOD) and Limit of Quantitation (LOQ) for extraction of phthalate esters by solid-phase were in the range of 0.025-0.050, 0.08-0.17 mg L-1, respectively. The repeatabilities were in the range of 1.20-2.20% RSD, as shown in Table 3.
To achieve the optimum SPE procedure, the technique was applied to determination of phthalate esters in drinking water samples, purchase from supermarket in Maha-Sarakham Province, Thailand. Figure 2 showed the chromatogram of mineral water samples No. 1, the results found DMP, DBP and DEHP. Table 4 showed the phthalate esters concentration in drinking waters and mineral waters from different brands (PET bottle), phthalate esters content were found depend on the sample brand. The DMP was found in drinking water sample No. 2, mineral water sample No. 1, 2 and 4 in the ranges of 0.16-0.53 mg L-1, DEP found only in sample No. 5 with the value of 0.54 mg L-1 (TLV 0.55 mg L-1), DBP in sample no. 1, mineral water sample No. 1 and 3 in the range of 0.13-0.33 mg L-1 (TLV 0.45 mg L-1). The DEHP content in drinking water sample No. 1, 4 and mineral water sample No. 1 were found in the ranges of 0.28-0.49 mg L-1, the results showed out of regulating maximum admissible concentration at 6 μg L-1. The results are agreed with the previous studies, DEP, DBP and DEHP were found in the water samples from PET bottles (Penalver et al., 2000).
| Table 2: | The percentage recoveries of phthalate ester by solid-phase extraction with various eluting solvent (Mean±RD, n = 3) |
| Table 3: | The detection limits of Florisil solid-phase extraction using 5 mL ethyl acetate eluting solvent and reproducibility |
| Table 4: | Phthalate esters concentration (mg L-1) in drinking water sample (Mean±SD, n = 3) |
*Nd: Not detected, lower than LOD | |
Prokupkova et al. (2002) reported that DBP and DEHP were found in mineral water higherthan in the other water samples. Phthalate esters may migration from the plastic bottle and the cap into the content of bottle. People who drink water containing DEHP in excess of the maximum contamination level for many years may have problems with liver and may have an increased risk to getting cancer (Holadova et al., 2007).
CONCLUSION
The DMP, DEP, DBP and DEHP can be extracted simultaneously by solid-phase Florisil using 5 mL ethyl acetate as eluting solvent. The results showed good recoveries in the range of 98.2-110%. Application of this proposed method was successful to determination of phthalate esters in PET bottled drinking water samples. The DMP, DEP and DBP contents in drinking water samples were found in the safe levels, while DEHP concentration in three samples were found higher than the regulated maximum admissible concentration.
ACKNOWLEDGMENT
This research has been financially support from Center of Excellence for Innovation in Chemistry (PERCH-CIC), Commission on Higher Education, Ministry of Education, Thailand.