Kralj Blaz, Krizaj Igor, Bukovec Peter, Slejko Simon, Milacic Radmila
Department of Environmental Sciences, Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
Anal Bioanal Chem. 2005 Oct;383(3):467-75. doi: 10.1007/s00216-005-3312-3. Epub 2005 Oct 19.
Speciation of Al in tea infusions was studied by size exclusion chromatography (SEC) and anion-exchange fast protein liquid chromatography (FPLC). Fractions were collected throughout the chromatographic separations and Al was determined "off line" by inductively coupled plasma optical emission spectroscopy (ICP-OES). Black, green, and red tea samples were investigated. The total concentration of Al in tea infusions was determined by ICP-OES and ranged between 0.5 and 4 mg dm(-3). The pH of tea infusions ranged between 5.3 and 5.5. Data from SEC-ICP-OES analysis indicated that 10-35% of total Al in tea infusions was eluted at a retention volume corresponding to a molecular mass of approximately 3800 Da. The remaining Al was adsorbed on the column resin. The same tea infusions were also analysed by anion-exchange FPLC-ICP-OES. It was found experimentally that the same percentage of total Al as from the SEC column was eluted at a retention volume that corresponded to negatively charged Al-citrate. The remaining Al was adsorbed on the column resin. Identification of Al-binding ligands eluting under the chromatographic peak was performed by electrospray ionisation tandem mass spectrometry (ES-MS-MS) analysis. It was proven that ionic Al species in tea infusions (10-35% of the total Al) corresponded to negatively charged Al-citrate. The remaining species that was adsorbed on the SEC or FPLC columns was most probably bound to phenolic compounds. Speciation of Al in tea with milk or lemon was also studied. Results for tea with milk indicated that Al-citrate was not transformed and that approximately 60% of total Al was transformed into high-molecular-mass Al species. This fraction was subjected to sodium dodecyl sulfonate polyacryl gel electrophoresis (SDS-PAGE). The results indicated that Al was occluded by milk proteins (mostly caseins). When citric acid was added to tea infusions the percentage of negatively charged Al-citrate remained either the same or increased to 40% of total Al.
采用尺寸排阻色谱法（SEC）和阴离子交换快速蛋白质液相色谱法（FPLC）研究了茶浸出液中铝的形态。在整个色谱分离过程中收集馏分，并通过电感耦合等离子体发射光谱法（ICP - OES）“离线”测定铝含量。对红茶、绿茶和红茶样品进行了研究。通过ICP - OES测定茶浸出液中铝的总浓度，范围在0.5至4 mg dm⁻³之间。茶浸出液的pH值在5.3至5.5之间。SEC - ICP - OES分析数据表明，茶浸出液中10 - 35%的总铝在对应于分子量约为3800 Da的保留体积处洗脱。其余的铝吸附在柱树脂上。同样的茶浸出液也通过阴离子交换FPLC - ICP - OES进行分析。实验发现，与SEC柱中总铝相同百分比的铝在对应于带负电荷的柠檬酸铝的保留体积处洗脱。其余的铝吸附在柱树脂上。通过电喷雾电离串联质谱（ES - MS - MS）分析对在色谱峰下洗脱的铝结合配体进行鉴定。已证明茶浸出液中的离子态铝物种（占总铝的10 - 35%）对应于带负电荷的柠檬酸铝。吸附在SEC或FPLC柱上的其余物种很可能与酚类化合物结合。还研究了加牛奶或柠檬的茶中铝的形态。加牛奶的茶的结果表明，柠檬酸铝未发生转化，并且约60%的总铝转化为高分子量铝物种。该部分进行了十二烷基磺酸钠聚丙烯酰胺凝胶电泳（SDS - PAGE）。结果表明铝被乳蛋白（主要是酪蛋白）包合。当向茶浸出液中加入柠檬酸时，带负电荷的柠檬酸铝的百分比保持不变或增加至总铝的40%。
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