Ni speciation in tea infusions by monolithic chromatography—ICP-MS and Q-TOF-MS
- 472 Downloads
For humans, Ni is not considered to be an essential trace element. Its compounds, at levels present in foodstuffs and drinks, are generally considered to be safe for consumption, but for individuals who already suffer from contact allergy to Ni and may be subject to develop systemic reactions from its dietary ingestion, dietary exposure to Ni must be kept under control. Being the second most popular beverage, tea is a potential source of dietary Ni. Present knowledge on its speciation in tea infusions is poor. Therefore, complete speciation analysis, consisting of separation by liquid chromatography using a weak CIM DEAE-1 monolithic column, “on-line” detection by inductively coupled plasma mass spectrometry (ICP-MS) and “off-line” identification of ligands by hybrid quadrupole time-of-flight mass spectrometry (Q-TOF MS), was implemented for the first time to study Ni speciation in tea infusions. Total concentrations of Ni in dry leaves of white, green, oolong and black tea (Camellia sinensis) and flowers of herbal chamomile (Matricaria chamomilla) and hibiscus (Hibiscus sabdariffa) tea were determined after microwave digestion by ICP-MS. They lay between 1.21 and 14.4 mg kg−1. Good agreement between the determined and the certified values of the Ni content in the standard reference material SRM 1573a tomato leaves confirmed the accuracy of the total Ni determination. During the infusion process, up to 85 % of Ni was extracted from tea leaves or flowers. Separation of Ni species was completed in 10 min by applying aqueous linear gradient elution with 0.6 mol L−1 NH4NO3. Ni was found to be present in the chromatographic fraction in which quinic acid was identified by Q-TOF in all the tea infusions analysed, which had pH values between 5.6 and 6.0. The only exception was the infusion of hibiscus tea with a pH of 2.7, where results of speciation analysis showed that Ni is present in its divalent ionic form.
KeywordsNickel speciation Monolithic chromatography Inductively coupled plasma mass spectrometry Time-of-flight mass spectrometry Tea infusions Quinic acid
This work was supported by the Ministry of Higher Education, Science and Technology of the Republic of Slovenia (Programme group P1-0143) and Project J1-4131. The authors would like to thank Dr. A. R. Byrne for linguistic corrections and valuable suggestions.
- 1.Williams RJP, da Silva JJR F (2001) The biological chemistry of the elements, the inorganic chemistry of life, 2nd edn. Oxford University Press Inc, New York, pp 436–449, Chapter 16Google Scholar
- 6.Klein C, Costa M (2007) Nickel. In: Nordberg G, Fowler B, Nordberg M, Friberg L (eds) Handbook on the toxicology of metals. Academic Press, London, pp 743–758, Chapter 35Google Scholar
- 9.Kalafova A, Kovacik J, Capcarova M, Lukac N, Chrenek P, Chrastinova L, Schneidgenova M, Cupka P, Jurcik R, Massanyi P (2008) The effect of single nickel and combined nickel and zinc peroral administration on growth, total protein and cholesterol concentrations in rabbit females. Slovak J Animal Sci 41:179–183Google Scholar
- 12.Ysart G, Miller P, Crews H, Robb P, Baxter M, De L’Argy C, Lofthouse S, Sargent C, Harrison N (1999) Dietary exposure estimates of 30 elements from the UK Total Diet Study. Food Add Cont 16:39–403Google Scholar
- 13.Dabeka RW, McKenzie AD (1995) Survey of lead, cadmium, fluoride, nickel and cobalt in food composites and estimation of dietary intakes of these elements by Canadians in 1986–1988. J AOAC Int 78:897–909Google Scholar
- 17.Zuliani T, Kralj B, Stibilj V, Milačič R (2005) Minerals and trace elements in food commonly consumed in Slovenia. It J Food Sci 17:155–166Google Scholar
- 25.Templeton DM, Ariese F, Cornelis R, Danielsson L-G, Muntau H, Van Leeuwen HP, Łobiński R (2000) Guidelines for terms related to chemical speciation and fractionation of elements, definitions, structural aspects, and methodological approaches (IUPAC Recommendations 2000). Pure App Chem 72:1453–1470CrossRefGoogle Scholar
- 30.Murko S, Milacic R, Kralj B, Scancar J (2009) Convective interaction media monolithic chromatography with ICPMS and ultraperformance liquid chromatography-electrospray ionization MS detection: a powerful tool for speciation of aluminium in human serum at normal concentration levels. Anal Chem 81:4929–4936CrossRefGoogle Scholar
- 36.Menelaou M, Mateescu C, Zhao H, Lalioti N, Salifoglou A (2009) The pH-specific synthesis, spectroscopic, structural, and magnetic properties of a new Ni(II) species containing the plat physiological binder D-(−)-quinic acid: association with the aqueous speciation of the binary Ni(II)-quinate system. Polyhedron 28:883–890CrossRefGoogle Scholar
- 38.Martell E, Smith RM (1977) Critical stability constants, volume 3: other organic ligands. Plenum Press, New York, p 163Google Scholar