以解聚搭配極致液相層析/串聯式質譜術分析飲用水中塑膠微粒

Abstract

塑膠因重量輕、穩定和耐用的特性，廣泛應用於飲用水包裝。塑膠微粒主要源自於大型塑膠製品的分解，其可做為有機物和環境污染物的載體。動物攝取塑膠微粒後可能導致發炎、氧化壓力增加或代謝功能紊亂。飲用水中的塑膠微粒目前主要透過立體顯微鏡、傅立葉變換紅外線光譜和拉曼光譜儀檢測。然而，這些方法有其限制，例如誤判其他微粒為塑膠、無法檢測到奈米級顆粒、以及不易比較不同研究間所測定的不同顆粒大小和數量。本研究欲透過解聚和極致液相層析/串聯式質譜儀分析飲用水中聚對苯二甲酸乙二醇酯(PET)、聚碳酸酯(PC)、聚醯胺6 (PA 6)、聚醯胺66 (PA 66)和聚乳酸(PLA)的塑膠微粒。根據解聚單體(即對苯二甲酸(TPA)、六種雙酚類(BPs)、6-氨基己酸(6-ACA)、己二酸(AA)和乳酸(LA))的濃度個別計算五種塑膠微粒的濃度。 本研究完成極致液相層析/串聯式質譜儀分析10種待測物的質譜參數與層析條件優化。游離源為UniSpray，雙酚A二環氧甘油醚(BADGE)與6-ACA以正電模式分析，其餘五種雙酚類、TPA、LA與AA以負電模式分析。BADGE和6-ACA於Ascentis Express F5 (30 × 2.1 mm, 2.0 µm)管柱，使用5-mM醋酸銨/0.4%醋酸水溶液與甲醇的移動相組成，可產生良好峰形；五種BPs則於F5管柱，以Milli-Q水與甲醇為移動相，可產生尖銳峰型。此外，TPA、AA和LA無法在Atlantis Premier BEH C18 AX (50 × 2.1 mm, 1.7 μm)管柱上良好滯留，因而改用親水作用層析(HILIC)；TPA、AA 和LA於ACQUITY UPLC BEH Amide (50 × 2.1 mm, 1.7 μm)管柱，使用20-mM醋酸銨水溶液和20-mM醋酸銨於90%乙腈/10% Milli-Q水的移動相組成，可有良好的滯留與分離。 本研究測試五種塑膠微粒之解聚效率。PET、PC及PLA於1.0克氫氧化鉀和20毫升正戊醇於135°C反應45分鐘，可達99%以上最佳解聚效率；PA 6和PA 6因無法在鹼條件下進行解聚，另以回流酸水解之方式進行PA 6與PA 66解聚，與40%硫酸水溶液於115°C反應五小時之解聚效率分別為2.0%與14%；使用微波輔助酸水解法進行PA 6和PA 66的解聚，與2.76 M鹽酸水溶液於170°C反應30分鐘後解聚效率分別為2.4%和35%。PA 6和PA 66於微波酸水解系統中的解聚效率相較回流酸水解略有提升，且大幅縮短反應時間，但仍需進一步優化微波酸解聚參數，以提高PA 6和PA 66的解聚效率。 為了濃縮樣本中的待測物並減少干擾，本研究使用Waters Oasis HLB µElution plates (2 mg)優化固相萃取的淨化條件。當樣本為中性時，6種BPs的滯留率為100%，6-ACA、TPA、AA和LA無法被完全滯留。將樣本調整至pH 2.5時，除6-ACA (15%)和LA (-23%)外，其他待測物在吸附劑上的滯留率皆在90%以上；樣本經由酸化有助於提升分析物在固相萃取的吸附效果。另吸附劑換用Waters Oasis WAX (2 mg)時，調整樣本為pH 4.5與6.0，六種BPs、TPA和AA的滯留率均為100%；6-ACA和LA則仍無法被有效吸附，滯留率僅分別為15%與41%。未來需測試Oasis MAX的固相萃取條件，以提升對於6-ACA和LA的吸附效果。 本研究最適化10種塑膠單體的儀器分析方法以及可同時解聚PET、PC與PLA之反應條件。PA 6和PA 66之解聚及6-ACA和LA之固相萃取方法進一步優化後，將可應用於飲用水中五種塑膠微粒之分析。

Plastics are widely used for drinking water bottles because of their low weight, high stability, and durability. Microplastics (MPs) are primarily caused by the breakdown of large plastic items and can carry organic matter and environmental pollutants. Ingestion of MPs would cause inflammation, increase oxidative stress, or disable animal metabolic function. MPs in drinking water are mainly detected using stereomicroscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy. However, these methods have several limitations, including false positives, the incapability to detect nanoparticles, and the difficulties in comparing particle sizes and numbers among different investigations. This study aimed to develop a method for determining polyethylene terephthalate (PET), polycarbonate (PC), polyamide 6 (PA 6), polyamide (PA 66), and polylactic acid (PLA) MPs in drinking water using depolymerization and ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS). Five categories of MPs in drinking water were quantified based on the concentrations of their depolymerized monomers: terephthalic acid (TPA), six bisphenols (BPs), 6-aminocaproic acid (6-ACA), adipic acid (AA), and lactic acid (LA). The chromatographic conditions and mass spectrometric parameters were optimized for the ten analytes using UPLC-MS/MS with UniSpray ionization; Bisphenol A diglycidyl ether (BADGE) and 6-ACA were ionized at the positive mode, and five BPs, TPA, LA, and AA were ionized at the negative mode. BADGE and 6-ACA formed good peak shapes on an Ascentis Express F5 column (30 × 2.1 mm, 2.0 µm) using the mobile phase compositions of 5-mM ammonium acetate/0.4% acetic acid(aq) and methanol. The five BPs produced sharp peaks on the F5 column using the mobile phase compositions of Milli-Q water and methanol. TPA, AA, and LA could not be retained effectively on an Atlantis Premier BEH C18 AX column (50 × 2.1 mm, 1.7 μm); therefore, hydrophilic interaction liquid chromatography (HILIC) was tested, and they were retained and separated well with an ACQUITY UPLC BEH Amide column (50 × 2.1 mm, 1.7 μm) using the mobile phase compositions of 20-mM ammonium acetate(aq) and 20-mM ammonium acetate in 90% acetonitrile/10% Milli-Q water. This study tested the efficiencies of chemical depolymerization into monomers on five targeted MPs. The optimal MP depolymerization conditions of PET, PC, and PLA were reacting with 1.0 g of potassium hydroxide in 20 mL of 1-pentanol at 135°C for 45 minutes, with the depolymerization efficiencies above 99%. In contrast, PA 6 and PA 66 could not be depolymerized under basic conditions. Furthermore, five hours of reflux acid hydrolysis was tested for the depolymerization of PA 6 and PA 66, reacting with 40% H2SO4(aq) at 115°C, resulting in depolymerization efficiencies of 2.0% and 29%, respectively. When microwave-assisted acid hydrolysis was performed with 2.76 M HCl(aq) at 170°C for 30 minutes, PA 6 and PA 66 depolymerization efficiencies were 2.4% and 35%, respectively. The depolymerization efficiencies of PA 6 and PA 66 in the microwave-assisted acid hydrolysis system were slightly higher than reflux acid hydrolysis, and the reaction time was much shorter. Further optimization of the parameters for microwave acid depolymerization is required to improve the depolymerization efficiency of PA 6 and PA 66. The solid-phase extraction (SPE) conditions for cleanup were tested using Oasis HLB µElution plates (2 mg, Waters Corporation) to concentrate the analytes and reduce interference in water samples. When water samples were neutral, the retention rates of six BPs were 100%, while 6-ACA, TPA, AA, and LA could not be retained. After acidification of the sample to pH 2.5, almost all analytes were retained above 90% on the adsorbent, except for 6-ACA (15%) and LA (-23%); acidification of samples improved the SPE retention of the analytes. Additionally, the retention of the analytes was tested using Oasis WAX (2 mg, Waters Corporation). At sample pH 4.5 and 6.0, the six BPs, TPA, and AA retentions were 100%; however, only 15% and 41% of 6-ACA and LA were retained, respectively. Further testing of the SPE conditions using Oasis MAX would be needed to improve the retention of 6-ACA and LA. This study optimized parameters of instrumental analysis on ten monomers of MPs and the conditions for simultaneous depolymerization of PET, PC, and PLA. After further optimizing the depolymerization of PA 6 and PA 66 and the SPE conditions for 6-ACA and LA, the validated method could be applied to analyze five categories of MPs in drinking water.