A simple and high sensitive preconcentration method based on micelle-mediated extraction followed by high performance liquid chromatography (LC-UV) was developed for preconcentration and determination of trace amounts of bisphenol A (BPA) in aqueous samples. The BPA was quantitatively extracted from aqueous samples in the presence of Triton X-114 as a nonionic surfactant and preconcentrated into the small volume (about 30
The distribution and abundance of plastic particles in the environment have rapidly increased, and the adverse effects of chemicals that leach from the plastic debris on aquatic animals have been of great concern [
Micelle-mediated extraction is a simple and powerful extraction method that is based on the property of most non-ionic surfactants in the aqueous solutions to form micelles and to separate into a surfactant-rich phase with a small volume. Any component present in the solution that interacts with the micellar aggregates can thus be extracted in the surfactant-rich phase. Small volume of the surfactant-rich phase and its compatibility with hydroorganic mobile phases allow the extraction and preconcentration of organic compounds prior to high-performance liquid chromatography (LC) [
All chemicals used were of analytical reagent grade and were prepared from Merck (Darmstadt, Germany) and Fluka companies (Chemie AG, Switzerland). LC-grade solvents (water, methanol, and acetonitrile) were used throughout the experiments and were obtained from Merck. All solutions were prepared with doubly distilled water. A stock standard solution of BPA at a concentration of 1000 mg L−1 was prepared in methanol. This standard solution was diluted with distilled water to prepare stock solutions with the concentration of 5, 10, and 50 mg L−1 of BPA. The non-ionic surfactant, Triton X-114 from Fluka, was used without further purification. Nitric acid (1.0 mol L−1) and sodium hydroxide (1.0 mol L−1) were used to adjust the pH of solutions.
Chromatographic separations were carried out on a Knauer LC equipped with a K-1001 LC pump (Germany) and a K-2600 UV-Vis detector. Separations were carried out on a Zorbax Extend C18 column (250 mm × 4.6 mm i.d., 5
For the cloud point extraction, aliquots of the solution containing BPA (10 mL) were adjusted to the appropriate ionic strength and pH (sodium acetate: 0.25 mol L−1, pH 3.0). Triton X-114 at 0.2% (w/v) concentration was added to solutions and the solutions were kept at 50°C (the temperature above the cloud point temperature of the system) for 7 min in the thermostatic water bath to become cloudy. Since Triton X-114 is denser than water, the surfactant-rich phase typically settled through the aqueous phase. In order to accelerate the phase separation, the turbid solutions were centrifuged for 8 min at 3000 rpm. After that, the tubes were cooled in an ice bath for 5 min to reach a denser surfactant-rich phase that could facilitate the separation of aqueous phase by means of pipette. After the separation of aqueous phase, 100
In the proposed procedure, to achieve maximum extraction efficiency, various parameters affecting the extraction of BPA were studied using the Taguchi orthogonal array design (OAD). Taguchi method is a type of fractional factorial design in which orthogonal array is used to assign the selected factors to a serial of experimental combinations [
In this study, the effect of five experimental factors including solution pH and temperature, surfactant concentration, ionic strength, and organic solvent volume (acetone) on the micelle-mediated extraction of BPA was studied using Taguchi’s OA16 design. The used levels (four levels) of the main factors (A-E) and the OA16 (45) matrix employed to assign the considered factors are shown in Tables
Factors and levels for Taguchi orthogonal array design of proposed method (A–E are the respective codes for each factor).
Levels | Factors | ||||
---|---|---|---|---|---|
A (pH) | B (surfactant (%)) | C (ionic strength (mol L−1)) | D (temperature (°C)) | E (organic solvent volume (µL)) | |
1 | 3 | 0.05 | 0.01 | 30 | 50 |
2 | 4 | 0.1 | 0.1 | 40 | 75 |
3 | 5 | 0.2 | 0.25 | 50 | 100 |
4 | 6 | 0.3 | 0.5 | 60 | 125 |
OA16 (45) experimental design for the optimization of CPE of BPA.
Trial no. | pH | % Surfactant | Ionic strength (mol L−1) | Temperature (°C) | Organic solvent volume (µL) |
---|---|---|---|---|---|
1 | 6 | 0.3 | 0.01 | 50 | 75 |
2 | 5 | 0.1 | 0.5 | 50 | 50 |
3 | 4 | 0.05 | 0.1 | 50 | 125 |
4 | 3 | 0.3 | 0.5 | 60 | 125 |
5 | 3 | 0.1 | 0.1 | 40 | 75 |
6 | 5 | 0.3 | 0.1 | 30 | 100 |
7 | 3 | 0.2 | 0.25 | 50 | 100 |
8 | 5 | 0.05 | 0.25 | 60 | 75 |
9 | 4 | 0.2 | 0.5 | 30 | 75 |
10 | 5 | 0.2 | 0.01 | 40 | 125 |
11 | 6 | 0.1 | 0.25 | 30 | 125 |
12 | 3 | 0.05 | 0.01 | 30 | 50 |
13 | 4 | 0.3 | 0.25 | 40 | 50 |
14 | 6 | 0.05 | 0.5 | 40 | 100 |
15 | 6 | 0.2 | 0.1 | 60 | 50 |
16 | 4 | 0.1 | 0.01 | 60 | 100 |
The designing of the table was done via experimental design 7.0 software. For increasing the precision of the optimization process, each trial was repeated twice (
The mean values of the four levels of each factor revealed how the extraction efficiency changes with variation of the level of each factor. Figure
The response graph illustrating the variation of the mean area peak values plotted against various extraction parameters. pH (level 1 = 3.0, level 2 = 4.0, level 3 = 5.0, level 4 = 6.0). Surfactant (%) (level 1 = 0.05, level 2 = 0.1, level 3 = 0.2, level 4 = 0.3). Ionic strength (mol L−1) (level 1 = 0.01, level 2 = 0.1, level 3 = 0.25, level 4 = 0.5). Temperature (°C) (level 1 = 30, level 2 = 40, level 3 = 50, level 4=60). Acetone volume (
The ANOVA results (Table
ANOVA results for experimental responses in the OA16 (45) matrix.
Factor | DOFa | Sum of squares | Variance |
|
Pure sum of squares | % PCc |
---|---|---|---|---|---|---|
pH (A) | 3 |
|
|
0.21 |
|
5.99 |
% surfactant (B) | 3 |
|
|
0.514 |
|
16.3 |
Ionic strength (C) | 3 |
|
|
0.343 |
|
10.49 |
Temperature (D) | 3 |
|
|
0.353 |
|
10.85 |
Organic solvent volume (µL) | 3 |
|
|
1.333 |
|
44.21 |
Error | 16 |
|
|
12.16 | ||
| ||||||
Total | 31 |
|
100 |
BPA with
In CPE, the theoretical preconcentration factors depend on the volume of the surfactant-rich phase, which at the same time varies with the surfactant concentration in the solution [
The addition of salt to solution can influence the phase separation process. To study the influence of the ionic strength on the extraction performance, the concentration of sodium acetate was changed in the range of 0.01–0.5 mol L−1. The results showed that the addition of the sodium acetate facilitates the phase separation since it increases the density of the aqueous phase [
It was desirable to employ the lowest possible equilibration temperature, which compromises completion of the reaction and efficient separation of the phases.
For Triton X-114, an increase in the cloud point temperature leads to a slight decrease in the volume of the surfactant-rich phase. This can be interpreted in terms of the fact that as temperature increases, hydrogen bonds are disrupted and dehydration occurs. Thus, by increasing of temperature, the amount of water in the surfactant-rich phase and consequently the volume of the surfactant-rich phase decrease [
After extraction and separation of the surfactant-rich phase from aqueous phase, it is necessary to decrease its viscosity before injection to LC. Acetone, acetonitrile, and methanol were studied as an organic solvents. In order to investigate the effect of solvent type on extraction performance a series of extracted samples of BPA (100
The quantitative parameters of the proposed method were calculated under the optimized conditions (pH 3, 0.2% (w/v) surfactant, 0.25 mol L−1 ionic strength, temperature 50°C, and 100
A comparison between the figures of merit of the proposed method and some of the recently published methods for extraction and determination of BPA is summarized in Table
Comparison of the characteristic data between recently published extraction methods and the developed method.
Methods | LOD (µg L−1) | LRa (µg L−1) | RSD (%) | SVb (mL) | Reference |
---|---|---|---|---|---|
LPMEc-GC-MS | 5.0 | 1–1000 | 15 | 10 | [ |
SBSEd-GC-MS | 0.5 | 2–100 | <10 | 2 | [ |
SPMEe-LC | 3.25 | 10–500 | 4.4 | 10 | [ |
ELISAf | 0.3 | 0.3–100 | — | 10 | [ |
ELISA | 0.1 | 1–10000 | — | 10 | [ |
DLLMEg-LC | 0.07 | 0.5–100 | 6 | 10 | [ |
CPE-LC | 0.13 | 0.5–150 | 6.6 | 10 | Proposed method |
The extraction method applied in the present work has some advantages in comparison with the other extraction methods including low consumption of organic solvents and reagents, ease of operation, simplicity, minimum carry over, and cross-contamination as well as producing a clean extracting phase for the analysis.
The applicability of the proposed method to real samples was studied by analyzing the lagoon water collected from Bojagh lagoon (Kiashahr, Gilan, Iran) and the leachate (BPA) from the solution of the baby feeding bottle and transfusion distilled water (preservation in plastic bottle). The leachate of baby feeding bottle was collected from the containers filled with 150 mL of boiling water. A 150 mL of boiling water (100°C) was transferred into a commercially available baby feeding bottle, which was tightly capped and kept in an oven at 95°C for 30 min and cooled to room temperature. Another leachate sample from baby feeding bottle was tested without thermal processing. Figure
LC chromatograms of BPA leached BPA from baby feeding bottle (a) nonspiked and without being kept in oven, (b) spiked (10
Results (Table
Analytical results for determination of BPA in real ware samples.
Sample | Concentration (mean, |
||
---|---|---|---|
BPA added | BPA found | Recovery (%) | |
S1 | 0.0 |
|
103 |
10.0 |
|
||
S2 | 0.0 |
|
98 |
10.0 |
|
||
S3 | 0.0 |
|
97 |
10.0 |
|
||
S4 | 0.0 |
|
97 |
10.0 |
|
S1: transfusion distilled water (preservation in plastic bottle).
S2: leachate from baby feeding bottle.
S3: leachate from baby feeding bottle kept in oven (95°C-30 min).
S4: lagoon water collected from Bojagh lagoon (Gilan, Iran).
The use of micellar systems as an alternative to other methods of separation and preconcentration offers several advantages including experimental convenience, safety and being an inexpensive method. Also, in this method, the consumption of organic solvent is low. In the present study, the results of ANOVA showed that the pH has low significant effect on the extraction efficiency. The proposed method gives low limit of detection as well as good RSD and linearity that results detection of low concentration of BPA in samples.