電噴灑質譜法對難溶性有機金屬沒食子酸-鐵錯合物離子的分析與研究

Abstract

本實驗改良紙片電噴灑質譜法，成功測量到難溶性有機金屬的質譜訊號。首先在離子源的部分，使用長度約為5 mm的有縫竹筆取代三角形濾紙，如此可以使反應溶液短暫儲存在竹筆狹縫之間，並隨著竹筆表面的天然多孔洞性質，在極短的時間內被揮發噴灑出去，並且被離子化。本實驗選用不溶於水也不溶於有機溶液的鐵-沒食子酸錯合物作為樣品。由於這樣的性質，造成該錯合物截至目前為止，還沒有任何文獻曾經發表過質譜的實驗結果。事實上，來自於硫酸亞鐵的鐵離子，一旦與沒食子酸水溶液接觸，兩者會在短時間內反應形成藍黑色的溶液。溶液中有機錯合物離子還會沉降為中性沉澱物(大顆粒沉澱，小顆粒懸浮)，容易造成質譜儀管線堵塞，並不適合使用電噴灑質譜法來進行測量。為了克服這樣的困難，本實驗先將沒食子酸溶液 (0.01 M) 裝在進樣注射針裡面，以低流速 (8 µL/min) 緩慢推送到竹筆電噴灑尖端。此時質譜儀使用負電模式，在負五千伏特之下可以清楚觀測到沒食子酸的特徵質譜峰，分別在m/z = 125、169。隨後將負電模式改成正電模式，此時雖然沒有觀測到任何特殊訊號，但是知道此時竹筆尖端已經調在最佳離子化位置。在此同時，將硫酸亞鐵溶液 (0.05M, 3 µL) 點在竹筆上。使兩者的生成物快速地被噴灑出去，期望測量到中間物，或者在反應物尚未沉澱物前，被質譜偵測到訊號。實驗結果發現，m/z = 153、225、243、431 的幾個訊號是加了鐵離子以後才出現的。可以確定這些訊號一定與鐵有關。參考 Lutui 等人過去以理論計算研究結果，可以推測出m/z = 153、225、243、431 的這些有機錯合金屬，可能分子式分別為：m/z = 153 → [C7H5O4]+; m/z = 225 → [C7H5O5IIFe]+ ; m/z = 243 → [C7H5O5IIFe‧H2O]+。鐵-沒食子酸錯合物的結構為 [(C6H3O3)2Fe2‧4H2O]；在電噴灑游離之下會帶上一個 H+ ，因此觀測到了 m/z = 431的譜峰。本實驗首度實證電噴灑質譜法可成功測量到難溶性有機金屬沒食子酸-鐵錯合物，今後可當作有機金屬錯合物的質譜分析模型，用以分析更多不同種的有機金屬錯合物。In this experiment, nib spray was used to instead of paper spray to measure insoluble organic metals samples - Iron Gallate ink (IGI) which results from a reaction of aqueous Iron(II) sulfate and gallic acid. Because the property of IGI are insoluble in solvents, neutral and high boiling point, it is difficult to measure by electrospray mass spectrometry (ESI-MS). So Professor Lin Cheng-Huang came up with new idea：bamboo pen nib which made by our laboratory connected to ESI ion source then syringe pump load gallic acid solution and flow rate was 8 µL/min. When a high voltage is applied to the nib, - 5000 V, gallic acid solution (0.01 M) is rapidly ionized towards the mass inlet. Make sure the resulting stream of charged droplets is stable and get the optimized parameter, then turn to positive mode, + 5000 V. Iron sulfate solution (0.05 M, 3 µL) was dropped onto the bamboo pen nib surface and reacted with gallic acid. A reactions of aqueous Iron(II) sulfate and gallic acid will be ionized and into the mass inlet. The result shows several special peaks, m/z 153, 225, 243, 431. Those peaks can conform Lutui et al.'s IGI theoretical m/z paper and Krekel Proposed IGI structure paper, the possible molecular formulae are : m/z = 153 → [C7H5O4]+, m/z = 225 → [C7H5O5IIFe]+, m/z = 243 → [C7H5O5IIFe‧H2O]+, m/z = 431 → [(C6H3O3) (C6H4O3)Fe2‧4H2O]+. We propose a new method to detect the organic metal-ligand complexes, and wish this method have more applications in the future.