奈米銀微粒於水環境中量測技術開發研究

Abstract

工業用奈米微粒 (Engineered nanoparticle)已廣泛地應用於醫療用品、化妝品、紡織塗料及食品包裝添加物等。其中，奈米銀微粒 (silver nanoparticle, Ag NP)具有獨特的抗菌性質，因此成為用量最高的奈米材料之一。Ag NP釋出至環境中，其所造成的潛在風險則受自身在環境中的宿命及轉變主導。因此，近年來發展出許多新興的分析技術，用以偵測水體中的奈米微粒，例如流力層析技術(hydrodynamic chromatography, HDC)、場流分離技術(asymmetric flow field-flow fractionation, AF4)以及單顆粒感應耦合電漿質譜儀(single particle inductively coupled plasma-mass spectrometry, SP-ICP-MS)。然而，這些新興的技術目前多僅侷限於量測純水中的奈米微粒，對於量測環境水體中的奈米微粒，其適用性則尚未明瞭。另外，環境中的奈米微粒常受水體物化性質的不同而有不同的轉變，進而造成偵測上的困難。因此，本研究之目的在於建立水體環境中量測Ag NP大小尺寸與濃度之方法。 AgNP A與B以動態光散射儀(dynamic light scattering, DLS)量測平均粒徑，分別為79.9及122 nm。環境水體則使用三處廢水水樣及三處環境水樣，其所含顆粒之粒徑大小分布不均勻，含有不同的離子強度，pH介於6.9-8.4，導電度在375-11200 µS/cm之間。Ag NP於不同水質之穩定性試驗中，發現pH的調整對Ag NP的聚集行為並無顯著影響。然而，在含有電解質的水體中則會促進Ag NP的聚集現象，且CaCl2之影響較NaCl顯著，因Ca2+較能顯著壓縮Ag NP表面的電雙層(electrical double layer)，進而減少Ag NP表面的靜電排斥力；此外，較低的溫度能夠抑制Ag NP的聚集與溶解行為，因為低溫下會降低顆粒與顆粒之間的碰撞頻率。因此建議含有奈米顆粒之環境樣品應置於低溫且不調整pH值的條件下保存。Ag NP量測前處理結果顯示，以離心轉速2000×g離心2分鐘後，可較過濾方式有效去除水體中的干擾，所以有較佳的回收率。探討HDC之分析條件，發現以pH 10之純水作為移動相時，奈米銀微粒之水合半徑(hydrodynamic diameter)與滯留時間有最佳的相關性(R2>0.99)。分析結果與DLS之結果大致符合。AF4結合多角度靜態光散射偵測器(multi-angle light scattering)亦能用以分析不同水體中Ag NP半徑，但其測值與DLS結果差異較大，且AF4中濾膜可能造成回收率偏低。SP-ICP-MS則可同時量測不同水體中的Ag NP粒徑及進行定量分析，SP-ICP-MS分析的粒徑也與穿透式電子顯微鏡之結果相符(p>0.05)，Ag NP之整體回收率亦最佳。因此，HDC及SP-ICP-MS為較適合用以分析水體環境中Ag NP粒徑之技術。研究結果初步建立了量測水體環境中Ag NP之方法。

Engineered nanoparticle has widely used in medical products, cosmetics, textiles and food additives. In particular, silver nanoparticle (Ag NP) has become one of the most extensive used nanomaterials in the world. The potential risks of Ag NP were controlled by their fates and transformations once released into the environment. As a result, many emerging analytical techniques have been developed in recent years and used to detect the NPs in the water, including hydrodynamic chromatography (HDC), asymmetric flow field-flow fractionation (AF4) and single particle inductively coupled plasma-mass spectrometry (SP-ICP-MS). However, these techniques have just applied to detect NPs in pure water system so far. Therefore, this study aims to establish a methodology for determining the particle size and concentration of Ag NP in the aquatic environment. The average particle sizes of two types of commercial Ag NP solutions were 79.9 and 122 nm, respectively. In water samples, the pH values ranged from 6.9 to 8.4 and the conductivities were between 375 and 11200 μS/cm as well as various particles. The stability of Ag NP in different solutions showed that pH did not cause a lot of effects on the aggregation of Ag NPs. However, Ag NPs aggregated obviously in the electrolytic systems. CaCl2 caused a more significant effect than the NaCl since the divalent cations could compress the electrical double layer of Ag NP more easily. Besides, the aggregation and dissolution levels of Ag NP were reduced under low temperatures since the NP-NP collision frequency could be inhibited. Therefore, environmental samples containing NPs should be preserved under a low temperature without pH adjustment. The result of pretreatment indicated that centrifugation with centrifugal speed of 2000×g for 2 minutes has a better performance for the removal of interferences, thus obtaining a higher recovery of Ag NP than filtration. For the HDC, a good correlation coefficient (R2 >0.99) was achieved with pH 10 water as a mobile phase. The particle size of Ag NP by HDC was consistent with DLS analysis in different water samples. AF4 can also determine the size of Ag NPs well but with low recoveries, which could result from the interactions between Ag NP and working membrane. For the SP-ICP-MS, both particle size and concentrations can be determined with high overall recoveries. The size results from SP-ICP-MS also corresponded to the TEM (p>0.05). Therefore, HDC and SP-ICP-MS were recommended for the environmental samples after the established pretreatment process. Combined the transformation studies of NPs and these analytical methods; the methodology to quantify and qualify the NPs in the aquatic environment was proposed.