Plasticizers are industrial additives whose main components are phthalic acid ester compounds(PAEs). Studies have shown that plasticizers can reduce fertility, increase the risk of cardiovascular disease, and damage the liver and urinary systems. Plasticizers are widely used in plastics, rubber, adhesives, cellulose, resins, medical equipment, cables and other products. These products enter the water environment directly or indirectly during manufacturing, use and consumption. Water is the source of life, which directly enters the human body after drinking, and has a vital impact on human health. Therefore, it is vital to test the plasticizer in water.

As the transport of phthalic acid ester compounds in water is very small, the sample should be pre-enriched and pre-treated before the plasticizer is tested. The common methods of sample pre-treatment include liquid-liquid extraction, solid-phase extraction, solid-phase microextraction, solid-phase membrane extraction, gel chromatography, etc. The methods of quantitative and qualitative analysis mainly include gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography-mass spectrometry (HPLC-MS) and micellar electrodynamic capillary chromatography (MEKC).

The plasticizer in water (http//: unsplash.com)

Pretreatment Methods

Liquid-liquid extraction (LLE) is a traditional pretreatment method for the analysis of organic pollutants in liquid samples. It uses organic solvent to extract organics PAEs from liquid samples one or more times, and to conduct concentration, volume determination and analysis. Although this technology has a wide range of applications and has a good extraction effect for a large number of PAEs, it is not easy to operate automatically, and it takes a long time, consumes a large amount of organic extraction and causes secondary pollution to the environment.

Solid Phase Extraction (SPE) is the most common way to purify PAEs in water. Although the traditional solid-phase extraction method has high selectivity and good purification effect, it has some deficiencies such as high cost of solid-phase extraction and long purification time caused by activation, elution and other processes. Khedr et al. pretreated the sample (drinking water and soft drink) with SPE method, and the average extraction rate of 2-ethylhexyl phthalate in the sample is 83-102.5%. The results showed that SPE has a good purification effect.

Analysis Methods

Gas chromatography-mass spectrometry (GC-MS) is currently widely used in the qualitative and quantitative of plasticizers. However, the component loss and cross contamination in the sample during the transfer process may lead to the deviation of test results. At the same time, when using EI ionization mode, multiple ion fragments may be formed, which will result in complex mass spectra and great difficulty in analysis.

High performance liquid chromatography-mass spectrometry (HPLC-MS) has the advantages of high sensitivity and good selectivity. The multiple reaction monitoring (MRM) mode in HPLC-MS is adopted, and the PAEs are qualitatively and quantitatively analyzed with liquid phase retention time and MRM characteristic ions, which greatly reduce the interference caused by different ions under test due to the same retention time, and greatly improve the detection sensitivity.

Micellar electrodynamic capillary chromatography (MEKC) is the product of the capillary electrophoresis (CE) and micellar liquid chromatography. Its column efficiency is up to hundreds of thousands, which is a good method to separate electroneutral samples. Yue et al. determined five phthalate esters in running water and milk by micellar electrokinetic capillary chromatography. They found that the separation efficiency of MEKC is very well and its work efficiency is also relatively high.

References

• Yue M E, Xu J, Hou W G. (2015) ‘Determination of Five Phthalate Esters in Running Water and Milk by Micellar Electrokinetic Capillary Chromatography’, Journal of Analytical Chemistry,70(9):1147-1152.

• Khedr, Alaa. (2013) ‘Optimized extraction method for LC–MS determination of bisphenol A, melamine and di(2-ethylhexyl) phthalate in selected soft drinks, syringes, and milk powder’, Journal of Chromatography B Analytical Technologies in the Biomedical & Life Sciences,930(6):98-103.

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