Hu Xialin, Liu Jingfu, Peng Jinfeng, Jiang Guibin * Woven Bag,PP Woven Bags,PP Woven Sacks,Woven Plastic Bags ZHEJIANG IMERIC ENVIRONMENTAL PROTECTION SCIENCE & TECHNOLOGY CO., LTD. , https://www.imeric-valvebags.com
(State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085)
Abstract: The freely soluble concentration of bisphenol A in environmental water samples was determined using negligible loss solid phase microextraction and high performance liquid chromatography. In order to obtain high sensitivity and reduce the influence of environmental factors (such as temperature and stirring, etc.), commercial solid phase microextraction fiber CW / TPR is used for balanced sampling. Under the common pH (5-8), buffer capacity (5-200 mmol / L) and salinity (0-500 mmol / L) of environmental water samples, 4
h Extraction equilibrium can be achieved. 100 mL of sample is sufficient to avoid sample wear. Formulated at 250 mmol / L
The standard solution of bisphenol A in NaCl and 125 mmol / L phosphate solution (pH 6.4) can be calibrated. The buffer (0 to 200 mmol / L), salinity (0 to 500 mmol / L) and pH can be adjusted. (5.7 to 8.5) The impact is controlled at
Within 15% deviation. For a more accurate measurement, the influence of the sample pH can also be corrected.
When the pH is 6.4, the linear range of the method is 0.1 to 250 μg / L, the detection limit is 0.03 μg / L, and the relative standard deviation (5 μg / L, n = 3) is 1.1%. This method was used to determine the free dissolved concentration of bisphenol A at the outlet of the sewage treatment plant.
Keywords: free dissolved concentration; bisphenol A; solid phase microextraction; high performance liquid chromatography
Freely Dissolved Concentration
It is the concentration of the substance that dissolves freely in the water phase without combining with any medium or system components. It is not only related to the total concentration of the analyte, but also to the concentration and capacity of the matrix medium and its affinity for the analyte [1]. Studies have shown that the freely soluble concentration of a compound is the driving force for its migration and distribution in the environment, as well as the accumulation in organisms [2], and is the key parameter that explains the availability of compounds [3]. Therefore, the determination of the concentration of freely dissolved state has been paid more and more attention by environmental scientists, and a variety of analytical methods have been developed. Heringa and Hermens [4] reviewed in detail the commonly used methods for determining the free dissolved state concentration. Liu Jingfu et al. [5] recently developed a method for determining the free dissolved state concentration of polar organic pollutants based on supported liquid membrane extraction technology. Negligible depletion SPME (nd-SPME) is a method of collecting free dissolved concentration in environmental media that has been studied more frequently. It integrates sampling, extraction and enrichment in one, simple operation, and sample The small amount is particularly important because it is easy to achieve micro-loss sampling-only a small amount (generally less than 5%) of the freely soluble target compound in the medium is collected, and the balance between its various forms is not destroyed. nd-SPME sampling is mostly carried out under non-equilibrium conditions [6-9], but due to its relatively short equilibrium time, nd-SPME has been successfully used as a balanced sampling device [10].
When measuring the concentration of the freely dissolved state, the integrity of the sample must be maintained, that is, no artificial chemical control can be performed on the sample.
The actual environment water sample matrix is ​​complex, with different buffer capacity, salinity and pH, these factors can affect the extraction effect. Therefore, the key to establishing relevant analysis methods is to choose appropriate standard solutions,
Use external standard method to calibrate the influence of environmental factors.
Bisphenol A (BPA) is an endocrine disruptor, and its long-term low-dose exposure to biological effects is one of the hot issues in environmental chemistry research today [11], measuring the freely soluble concentration of BPA in the environment, and its environment Chemical behavior research and risk assessment are of great significance. In this paper, the method of nd-SPME-HPLC technique was used to determine the free dissolved concentration of trace BPA in environmental water samples.
1 Experimental part
1.1 Instruments and reagents HPLC system (Agilent, USA), by Agilent
Model 1100 unit pump and Agilent 1100 fluorescence detector; SPME-HPLC interface, manual 57331 solid phase microextraction fiber handle, commercial solid phase microextraction fiber 50 μm CW / TPR (Supelco, USA) The SPME-HPLC interface consists of a Rheodyne
The six-way valve is composed of a 60 μL desorption chamber, which replaces the sampling loop in a general liquid chromatograph.
Bisphenol A standard (Acros Organics, Belgium); acetonitrile is chromatographically pure, and other reagents are analytically pure. The experimental water is double-distilled water.
1.2 Chromatographic conditions Column: Agilent Zorbax Eclipse XDB type C8
Column (5
μm, 150 mm × 4.6 mm i. d.). The wavelength of the detector: excitation wavelength 220 nm, emission wavelength 315 nm. Mobile phase: V (acetonitrile)
: V (water) = 75: 25, 2 min before flow rate is 0.2 mL / min, at 1
Increase to 1 mL / min within s, and keep 1 mL / min.
1.3 Experimental method Add stirring magnet and 100 mL to a 100 mL extraction bottle
Analytical solution, covered with a perforated lid with a Teflon diaphragm,
Insert the SPME stainless steel needle into the bottle, push out the extraction head, adjust the position of the extraction head so that the stirring magnet will not damage the extraction head during stirring, and the extraction head is completely immersed in the solution. After extraction for 4 h, the extraction head was retracted and taken out, inserted into the desorption chamber for dynamic desorption determination.
2 Results and discussion
2.1 Determination of extraction equilibrium time In order to obtain high sensitivity and reduce the influence of environmental factors,
In this experiment, balanced sampling is used, that is, extraction is stopped after the analyte reaches the distribution equilibrium between the sampling phase and the sample. The environmental factors that may affect the equilibrium time, such as pH, buffer solution concentration, and salinity, were investigated, and the results showed that common environmental water samples
pH (5 ~ 8), buffer capacity (5 ~ 200 mmol / L) and salinity (0
~ 500 mmol / L) [6], the extraction equilibrium can be reached within 4 h. Therefore, this experiment selected 4 h as the extraction time.
2.2 Selection of sample volume To obtain a reliable free dissolved state concentration value, it must be ensured that the loss of sampling is less than 5% of the total amount of dissolved substances, so as not to destroy the balance between its free dissolved state and bound state [10] . When the volume of the sampling phase (SPME fiber coating) is constant, a sufficiently large sample volume needs to be used to avoid sample wear. This experiment investigated the pH
When the concentration is 7.0 and the concentration of phosphate buffer solution is 30 mmol / L, the effect of sample volume on the extraction of 50 μg / L BPA is shown in Figure 1.
As can be seen from Figure 1, when the sample volume increases to 100 mL,
The signal (the area formed by the baseline is called the peak area. A = × σ × h = 2.507σh = 1.064 Wh / 2h> peak area) is constant, indicating that the selected sample volume is 100 mL
It is possible to ignore the effect of sample wear.
Figure 1 Effect of sample volume on extraction
Fig .1 Effect of sample volume on the nd-SPME of BPA
2.3 Calibration by environmental factors
2.3.1 Effect of buffer solution concentration Figure 2 shows a pH of 7.0
The impact of the buffer solution on the extraction effect of 50 μg / L BPA, as can be seen from Figure 2, the impact of the buffer solution is very small. In the common buffer capacity range of environmental water samples (0 ~ 200 mmol / L), use 125
mmol / L NaH2 PO4
The buffer can control the extraction deviation of the sampling within 15%. Therefore, it should be formulated at 125 mmol / L
NaH2 PO4
Calibrate the standard solution in the buffer.
Figure 2 Effect of buffer solution concentration on extraction
Fig. 2 Effect of buffer concentration on the nd-SPME of
BPA
2.3.2 The influence of salinity is 125 mmol / L NaH2 PO4
0。 Add different amounts of NaCl to the solution and adjust its final pH to 7.0,
The effect of salinity on 50 μg / L BPA extraction was investigated. It can be seen from the results in Figure 3 that due to the salting-out effect, the extraction effect is improved with the increase of salinity, but when using 250 mmol / L
The standard solution of NaCl can control the influence of salinity (0 ~ 500 mmol / L) in common environmental water samples within 15% deviation.
Therefore, add 250 mmol / L NaCl solution to the standard solution.
Figure 3 Effect of salinity on extraction
Fig .3 Effect of salinity on the nd-SPME of BPA
2 .3 .3 pH Impact The pH range of environmental water samples is 5 to 8,
This experiment examined the pH of 5.7, 6.4, 7.0, 7.7, 8.5 respectively
50 μg / L BPA standard solution (contains 125 mmol / L
NaH2 PO4
Buffer, 250 mmol / L NaCl).
It can be seen from the results shown in Figure 4 that when a standard solution of pH 6.4 is used, the pH of an environmental water sample with a pH of 5.7 to 8.5
The deviation caused by the difference can be controlled within 15%. Therefore, a standard solution of pH 6.4 is used for calibration. For a more accurate determination of the free dissolved concentration, the pH of the sample and Figure 4 can also be used
The regression curve shown corrects the effect of pH.
Figure 4 Effect of pH on extraction
Fig .4 Effect of pH on the nd-SPME of BPA
2.4 The linear range, detection limit and precision of the method under optimized conditions, the mass concentration is 0.1, 0.5, 1,
5, 25, 50, 100, 150, 200 and 250μg / L BPA standard series (contains 125 mmol / L NaH2 PO4
, 250 mmol / L NaCl,
pH 6.4) Sample analysis after extraction. The results show that the chromatographic peak area of ​​BPA has a good linear relationship with the concentration within the measured mass concentration range, the regression equation is y = 71.37Ï + 41.28, the correlation coefficient r = 0.9991; the detection limit of the method is 0.03μg / L (S / N = 3,
n = 5); the relative standard deviation (RSD) is 1.1% (5μg / L BPA
Standard solution, n = 3).
2.5 Analysis of actual water samples Sewage was collected from the outlet of Beijing Gaobeidian Wastewater Treatment Plant (pH
7.2), take 100 mL directly for nd-SPME, and measure BPA
The free dissolved concentration is 0.28 μg / L and the RSD is 10.8%
(N = 4); add 1μg / L to the sample, and the recovery rate is 68.5%. This is because the added BPA combined with the matrix in the sample (such as dissolved organic carbon and particulate matter), only 68.5% Exist in a freely dissolved state.
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Determination of environmental water samples by solid phase microextraction coupled with high performance liquid chromatography