Study On Determination Of Plasticizer Content In Bottled Water By Isotope Dilution Mass Spectrometry

The synthesis of plastics is considered to be the alchemy of the last century,in which an indispensable additive,plasticizer,is used to improve the performance and processing properties of polymers.Phthalate esters（PAEs）are most frequently used plasticizers.They can enter the human body through water,food,skin contact and respiratory tract.They are essentially environmental hormones and are likely to cause reproductive toxicity and genotoxicity to the body.A few departments therefore issued restrictions.This topic selects water as the medium and uses gas chromatography-isotope dilution mass spectrometry to study the pollution of Dimethyl phthalate（DMP）,Diethyl phthalate（DEP）,Dibutyl phthalate（DBP）,Butyl Benzyl phthalate（BBP）,Dioctyl phthalate（DEHP）and n-Dioctyl phthalate（DNOP）in natural mineral water and purified drinking water.The specific content includes the use of external standard method and internal standard method to quantitatively analyze the phthalate compounds in water,compare the accuracy of the two methods,established an optimized internal standard method to quickly determine the pollution level of 6 plasticizers in commercially available bottled water.First,use the external standard method with GC/MS to analyze DMP,DEP,DBP,BBP,DEHP and DNOP in bottled water,draw a standard curve with a standard product of known purity,obtain its content and investigate the linear relationship of the method and the recovery rate of standard addition.The results show that the most suitable extraction solvent is 25 m L of n-hexane.The linear relationship of the external standard method is good;the correlation coefficients are all greater than 0.998;the limit of detection is 0.50～4.93μg/L and the limit of quantitation is1.67～16.10μg/L;the average recoveries of the 6 PAEs are between 10.8 and 82.7%and the relative standard deviations obtained in parallel experiments are between 2.30 and 7.96%.The external standard method cannot avoid the loss of the target in the experiment;the recovery rate is low and the difference is large and it cannot meet the precise trace analysis required by the experiment.Then switch to the internal standard method with gas chromatography-triple quadrupole mass spectrometry to analyze DMP,DEP,DBP,BBP,DEHP and DNOP in bottled water and synthesize DMP-D₄,DEP-D₄,DBP-D₄,BBP-D₄,DEHP-D₄and DNOP-D₄which are used as internal standard reagents by utilizing extra-ring labeling of phthalic anhydride.Its content is obtained by drawing a standard curve and the linear relationship of the method and the recovery rate of standard addition are investigated.In the synthesis process,the results show the best feed ratio（alcohol）:（phthalic anhydride-D₄）,reaction temperature and reaction time are 2.5:1,25℃and 5 h and the optimal collision voltage of the triple quadrupole multi-reaction monitoring scan mode（MRM）is 20 e V and the best qualitative and quantitative ion pairs are determined.When the concentration ratio is in the range of 0.001 to 1.127,the correlation coefficients are all greater than0.9992.The linear relationship is better than the external standard method;the limit of detection is0.06 to 0.33μg/L;the limit of quantitation is 0.20～1.11μg/L;the average recovery rate of 6 PAEs is between 85.22～103.92%and the RSD is 1.26～2.99%at the high spike level and 1.66～5.59%at the middle spike level and 4.48～7.79%at low spiked level.It shows that this method solves the problems of low recovery rate and large difference in results of the external standard method and further lowers the detection limit and quantification limit and has excellent reproducibility and precision.Finally,the optimized internal standard method is used to analyze the pollution level of DMP,DEP,DBP,BBP,DEHP and DNOP in 8 kinds of commercially available bottled water and bring the peak area ratio into the established standard curve and get its content is characterized by SD and RSD to show the discreteness and reproducibility of the data obtained by this method.The results show that the peak shape and peak separation of natural mineral water and purified drinking water are good under the optimized chromatographic-mass spectrometry method.DBP and DNOP are generally detected in 8 brands of bottled water and the content is 2.58～6.03μg/L and 16.08～47.48μg/L respectively;DEP is only detected in purified drinking water and the content is 2.26～6.57μg/L;Only two samples of DMP,BBP and DEHP are detected with the content ranging from 3.90 to 15.58μg/L.Among them,the excess rate of C brand DEP and D brand DBP exceeds 100%.The SD of the sample measurement data is between 0.0001～0.0029and the RSD is between 2.68%and 5.52%,indicating that this method has the advantages of low detection limit,excellent precision,accurate data and can quickly determine the pollution level of6 plasticizers in commercially available bottled water and can be extended to the detection of all plasticizers.