Speciation of aluminium in tea infusions by use of SEC and FPLC with ICP-OES and ES-MS-MS detection.
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.
Department of Environmental Sciences, Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
Blaz
B
Kralj
Igor
I
Krizaj
Peter
P
Bukovec
Simon
S
Slejko
Radmila
R
Milacic
D000535:Aluminum / Q000032:analysis* / Q000737:chemistry*; D000818:Animals; D002853:Chromatography, Liquid; D002957:Citrus / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008892:Milk / Q000737:chemistry; D008970:Molecular Weight; D021241:Spectrometry, Mass, Electrospray Ionization; D013662:Tea / Q000737:chemistry*
D013662:Tea; D000535:Aluminum