Aluminium in tea: SEC-ICP-MS speciation studies of infusions and simulated gastrointestinal digests

Elemental characterisation of the medical plant Alchemilla velebitica

Alchemilla, commonly called "lady's mantle", is a genus of herbaceous perennial plants belonging to the family Rosaceae. The species Alchemilla velebitica is found only in Southern Europe, like in the Croatian National Park Northern Velebit. Its benefits, such as a astringent and emmenagogue activity as well as wound healing are correlated to the organic compounds found in the plant, but also certain trace elements are known to reduce skin lesions, such as zinc, selenium, copper, manganese, silicon and lithium. Thus the objective of the present study was the elemental characterization of leaves, blossoms and roots of A. velebitica. After acidic microwave assisted digestion the concentrations of selected essential and trace elements were determined by inductively coupled plasma--atomic emission spectrometry and inductively coupled plasma--mass spectrometry. Other minor elements, such as Al, B, Cu, Fe, Mn, Sr and Zn are also found in leaves, blossoms and roots with contents in μg/kg range. The preparation of decoctions and the extraction yields of the elements of interest are calculated.

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.

Selective Determination of Aluminum Bound with Tannin in Tea Infusion

In this study, an analytical method for indirect measurement of Al bound with tannin in tea infusion was studied. This method utilizes the ability of the tannins to precipitate with protein. Separation conditions were investigated using model solutions. This method is uncomplicated, inexpensive and suitable for real samples. About 34% of the total Al in brew extracted from commercially available teas was bound to condensed and hydrolyzable tannins.

Multielement determination and speciation of major-to-trace elements in black tea leaves by ICP-AES and ICP-MS with the aid of size exclusion chromatography

A multielement determination of major-to-trace elements in black tea leaves and their tea infusions was carried out by ICP-AES (inductively coupled plasma atomic emission spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry). Tea infusions were prepared as usual tea beverage by brewing black tea leaves in boiling water for 5 min. About 40 elements in tea leaves and tea infusions could be determined over the wide concentration range in 8 orders of magnitude. The extraction efficiency of each element was estimated as the ratio of its concentration in tea infusions to that in tea leaves. From the experimental results for the extraction efficiencies, the elements in black tea leaves were classified into three characteristic groups: (i) highly-extractable elements (>55%): Na, K, Co, Ni, Rb, Cs and Tl, (ii) moderately-extractable elements (20-55%): Mg, Al, P, Mn and Zn, and (iii) poorly-extractable elements (<20%): Ca, Fe, Cu, Sr, Y, Zr, Mo, Sn, Ba and lanthanoid elements. Furthermore, speciation of major-to-trace elements in tea infusions was performed by using a combined system of size exclusion chromatography (SEC) and ICP-MS (or ICP-AES). As a result, many diverse elements were found to be present as complexes associated with large organic molecules in tea infusions.

Speciation of aluminium in tea infusions studied by size exclusion chromatography with detection by post-column reaction

Aluminium-organic species in tea infusions were studied by size exclusion chromatography, using a Superose 12 HR column, a mobile phase of 0.12 mol l-1 tris(hydroxymethyl)aminomethane adjusted to pH 5.5 and detection by UV-visible spectrophotometry. Aluminium was detected after post-column reaction with pyrocatechol violet at 585 nm and the organic material was detected at 280 nm. Teas of different origin were analyzed; the results indicate that aluminium is bound to the same relatively narrow size-range of large organic molecules in the tea infusions, irrespective of the origin of the tea.

Urine levels of aluminum after drinking tea

A microwave-assisted acid digestion procedure coupled with a graphite furnace atomic absorption method has been applied in the determination of aluminum (Al) in urine to verify the correlation of free forms of Al in tea infusions and urinary excretion of Al. Significant urinary Al excretion has been found in 24-h urine of four volunteers after tea drinking. However, the difference in amount of Al excretion in urine between the consumption of Oolong (black tea) and Long-Jin (green tea), each of them with unique Al contents and species, was not significant. These findings indicated that the high levels of free Al species in tea infusions did not result in significant change in urinary excretion of the metal, possibly owing to the transformation by ligands present in food and the gastrointestinal tract (GIT). However, it could not be assumed that there was no big difference in absorption of the metal in the human body if fractions of consumed Al retained in the body or excreted by bile or feces were considered.

Bioavailability of labile aluminium in acidic drinking water: a study in the rat

The bioavailability of labile Al (Allab; Al3+, and monomeric hydroxo and sulfato complexes) in drinking water was studied in the rat. The hypothesis was that Allab in drinking water is more available for absorption in the gastro-intestinal tract than Al complexed in the rat feed. Male Sprague-Dawley rats were exposed to 4 mg Al/litre in acidic drinking water (pH 4-5) and 5 mg Al/kg in the feed for 10 wk. The Al intake of these rats was about twice that in a control group of rats that received Al only in the feed. Both a theoretical speciation calculation and a speciation analysis of the water in a flow injection system showed that more than 98% of the Al in the water was present as Allab. However, intake of this water did not result in increased levels of Al in the bone, liver or brain tissue of the rats. Al speciation in a simulated rat stomach indicated that Allab in drinking water is rapidly complexed by feed constituents as the water enters the acidic milieu of the stomach, resulting in a very low concentration of Allab. The concentration of dissolved Al was also low in comparison to the added amount of labile Al. The possibility of complex formation between Allab and feed components in the gastro-intestinal tract should be taken into account in further studies of the bioavailability of drinking water Al in experimental animals and in humans.

Aluminium fractionation in a simulated rat stomach: an in vitro study

This study is part of a project dealing with the absorption of aluminium in rats from acidified drinking water. The hypothesis of the project was that 'labile' forms of aluminium in water might be more available for absorption than aluminium in food. To investigate this hypothesis, the distribution of species of the metal within the rat stomach must be considered. So far, few attempts in this direction have been made. The distribution of aluminium forms in vitro was studied, simulating the conditions present in a rat stomach. The in vitro set-up is based on methods used for drug release studies. The results show that only part of the aluminium (29-54%) added in 'labile' forms at a concentration of 4.0 mg l-1 Al was detected as total dissolved aluminium (Altot) after incubation in a simulated rat stomach. The levels of 'quickly reacting aluminium' (Alqr) (approximately the sum of Al and its monomeric hydroxo and sulfato complexes) were very low (< 0.2 mg l-1), but difficult to quantify precisely in this matrix. The pattern of the in vitro results was confirmed by measurements in pooled rat stomachs from in vivo experiments. There are obviously considerable amounts of ligands present in rat feed that bind strongly to aluminium and thereby affect the distribution of metal species inside the rat stomach. It is believed that phosphoserine, present in the protein casein, is an important ligand for aluminium complexation in this case. The results show that studies of Al absorption should be accompanied by fractionation measurements within simulated or real gastric systems.

Aluminium uptake from some foods by guinea pigs and the characterization of aluminium in in vivo intestinal digesta by SEC-ICP-MS

The uptake of ingested aluminium (Al) from food items commonly consumed in a normal human diet was investigated by feeding five test diets to guinea pigs. Al concentrations were measured in the femur, brain, kidney and upper intestinal contents. Consumption of these diets did not lead to elevated Al levels in brain. Levels of Al in the bone were elevated in animals fed sponge cake with a permitted Al-containing additive, and the presence of citrate as orange juice enhanced bone deposition and increased kidney Al levels. Less than 1% of Al in the upper intestinal contents was found in the soluble fraction, and characterization by SEC-ICP-MS indicated that this Al was not present as Al-citrate.