Bisphenol S (BPS),4,4′-sulphonyl bisphenol,is a chemical material to manufacture engineering plastics,such as epoxy resins,polycarbonates and polyester[1].BPS is also an important intermediate of pesticide,dyestuff and accessory ingredient,and can be used as a colorfast agent,leather′s tanning agent,dyeing dispersant,fibre improver,developer of heat-sensitive material and so on.Therefore,the production and demand of BPS in China and Japan are increasing continuously[2].Because of its widespread application the potential contamination for human exposure to BPS is very high.

Environmental endocrine disruptors,a global focus problem,is capable of disrupting the normal functioning of the endocrine system,may pose abnormal development and diseases of immune and nervous system,and can produce a potential threat to human health[3].Animal experiments have proved that BPS,which can promote the lymphocytes proliferation,is a suspected environmental endocrine disruptor[4].So far,analysis of bisphenol S has been accomplished by gas chromatography-mass spectrometry (GC-MS)[5]and thin-layer chromatography method[6].Although GC-MS has been widely used for estrogenic bisphenol S quantification and shows excellent accuracy,chromatographic analysis requires troublesome sample preparation.Therefore,an inexpensive,fast and sensitive method is necessary for monitoring the level of BPS in environmental samples.

Recently,we explored that the BPS could strongly absorb ultraviolet light.In this work a rapid and sensitive method had been established in detail for determination of BPS by ultraviolet spectrophotometry.

1 Experiment

1.1 Reagents

A 4.0×10-4mol·L-1stock solution of BPS was prepared by dissolving 25.0 mg commercial BPS (purchased from Beijing Hengye Zhongyuan Chemical Co.,Ltd.) in 250.0 mL volumetric flask with 5 mL ethanol,and the volume was filled up to the scale with water.The solution was kept at about 4℃ in brown bottles.Working standard solutions were made daily by appropriate dilution of the stock solutions as required.Phosphate buffer solution (PBS) was prepared by titrating a stock solution containing 0.1 mol·L-1phosphate (produced by Guanghua Technology Co.,Ltd.Shanghai Chemical Reagents Branch) and adjusted to the desired pH value with 0.2 mol·L-1sodium hydroxide or 0.2 mol·L-1hydrochloric acid.

All the other reagents were of analytical grade,and twice-distilled water was used throughout.

1.2 Instruments

UV1102 Spectrophotometer with 1.0 cm quartz cells， Shanghai Techcomp Instrument Ltd.;Electron balance，Shanghai Yueping Instrument Co.,Ltd.;PHS-P Acidimeter， Shanghai Precision & Scientific Instrument Co.,Ltd.;HH-601 Super constant temperature water bath，Jintan Ronghua Instrument Co.,Ltd..

1.3 Procedures

The required amount of working standard solutions were pipetted into 10.0 mL volumetric flasks.Then,5.0 mL of PBS with pH value 6.0 was added to each volumetric flask and diluted to volume with distilled water.The solutions were shaken well for proper mixing and their absorbance values were measured at 258 nm after 10 min later.The absorption spectrum was recorded against a reagent blank.

1.4 Sample preparation

The sample solution was prepared based on reference[7].Six kinds of familiarly commercial samples,such as plastic bottle,plastic bag,fibre cloth,cotton cloth,heat-sensitive paper and leather,were chosen in this method.These samples were washed with distilled water,solarized at room temperature and cut into pieces of 2.0 cm2.An appropriate amount of each sample was taken,put in a conical flask and then 100 mL of water was added.The solutions were heated in a water bath at (70.0±0.2)℃ for 4 h,then cooled to room temperature.Finally,a portion of the prepared sample was diluted with distilled water directly or supplemented with BPS to test the recovery of the method.

2 Results and discussion

2.1 Absorption spectrum

Fig.1 The ultraviolet absorption spectrum of 4.0×10-5 mol·L-1 BPS(pH=6.0)

The ultraviolet absorption spectrum of BPS was showed in Fig.1.It could be seen that BPS had two absorption peaks at 234 nm and 258 nm.The intensity of the second peak at 258 nm was higher than the first one.On the other hand,the energy of ultraviolet ray at 258 nm was weaker than that at 234 nm,which was more favorable to keep the substance stable.So the wavelength 258 nm was decided as the determination wavelength in this method.

2.2 Optimization of experimental variables

The absorbance of BPS was strongly affected by pH value of the solution,and the result was presented in Fig.2.It was found that the values of absorbance were almost constant in the range of 2.0～7.0;however,they decreased rapidly with the increasing of pH value above 7.0.It was proposed that with a pH larger than 7.0,the active hydrogen in hydroxyl could react with OH-,which might change the wavelength of absorption peak.Therefore,the BPS solution was adjusted to pH value 6.0 with PBS for further study.

Fig.2 Effect of pH value on absorbance of 1.6×10-5 mol·L-1 BPS

The influence of determination time was also studied.A solution of 1.6×10-5mol·L-1BPS was prepared based on the above procedure,and its absorbance was measured at certain time intervals.It was showed that the absorbance reached a maximal value and kept constant after 10 min.Therefore,the absorbance value was determined after mixing for 10 min.

2.3 Analytical characteristics

Under optimum conditions,the absorbance of the solution had a good linear relationship with the concentration of BPS.The linear range was 4.8×10-7～4.0×10-5mol·L-1and the linear regression equation wasy=1.92×104x+0.0022 with a correlation coefficient of 0.9999.The relative standard deviation for 2.4×10-5mol·L-1BPS was 0.12% (n=11).The limit of detection was 4.0×10-7mol·L-1.This determination method offered potential advantages of simplicity,rapidity and sensitivity.

2.4 Interference

Tab.1 Tolerance to different substances in the determination of 1.6×10-5 mol·L-1 BPS

2.5 Application

The proposed method has been applied to the determination of BPS in samples.The samples were prepared and treated based on the procedure described in the above paragraph.The contents of BPS in samples were determined by standard addition method,and the results were listed in Tab.2.The recovery of 90.7%～103.9% indicated that no serious interference was observed in the samples.It can be seen the method is well applicable for real samples.

Tab.2DeterminationofmigratedBPSfromcommercialsamples

a:Average of three determinations

3 Conclusions

An ultraviolet spectrophotometric method for determination of BPS has been established based on the strong absorption of BPS to the ultraviolet light (λ=258 nm).This method is simple,rapid and sensitive and no sensitizers are needed.The results are satisfactory to detect BPS in some commercial samples.

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