Journal of Pharmaceutical and Biomedical Analysis 54 (2011) 1040–1046 Contents lists available at ScienceDirect Journal of Pharmaceutical and Biomedical Analysis journal homepage: www.elsevier.com/locate/jpba A fast and accurate method for the determination of total and soluble fluorine in toothpaste using high-resolution graphite furnace molecular absorption spectrometry and its comparison with established techniques Heike Gleisner a,∗ , Jürgen W. Einax b , Silvane Morés c , Bernhard Welz c , Eduardo Carasek c a Analytik Jena AG, Konrad-Zuse-Str. 1, 07745 Jena, Germany b Department of Environmental Analysis, Institute of Inorganic und Analytical Chemistry, Friedrich Schiller University of Jena, Lessingstr. 8, 07743 Jena, Germany c Departamento de Química, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil article info Article history: Received 19 October 2010 Received in revised form 8 December 2010 Accepted 8 December 2010 Available online 16 December 2010 Keywords: Toothpaste High-resolution continuum source atomic absorption spectrometer Molecular absorption spectrometry (MAS) Total and dissolved fluorine Gallium mono-fluoride abstract A fast and reliable method has been developed for the determination of total and soluble fluorine in toothpaste, important quality control parameters in dentifrices. The method is based on the molecular absorption of gallium mono-fluoride, GaF, using a commercially available high-resolution continuum source atomic absorption spectrometer. Transversely heated platform tubes with zirconium as perma- nent chemical modifier were used throughout. Before each sample injection, a palladium and zirconium modifier solution and a gallium reagent were deposited onto the graphite platform and thermally pre- treated to transform them into their active forms. The samples were only diluted and introduced directly into the graphite tube together with additional gallium reagent. Under these conditions the fluoride was stable up to a pyrolysis temperature of 550 ◦ C, and the optimum vaporization (molecule formation) temperature was 1550 ◦ C. The GaF molecular absorption was measured at 211.248 nm, and the limits of detection and quantification were 5.2 pg and 17 pg, respectively, corresponding to a limit of quan- tification of about 30 gg -1 (ppm) F in the original toothpaste. The proposed method was used for the determination of total and soluble fluorine content in toothpaste samples from different manufactures. The samples contained different ionic fluoride species and sodium monofluorophosphate (MFP) with covalently bonded fluorine. The results for total fluorine were compared with those obtained with a modified conventional headspace gas chromatographic procedure. Accuracy and precision of the two procedures were comparable, but the proposed procedure was much less labor-intensive, and about five times faster than the latter one. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The benefits of fluorides in the prevention of dental caries have been discussed controversially for many years, but are generally accepted nowadays. Small quantities of fluorides are added to water, food and especially to toothpastes and dental gels [1–5]. Toothpastes are multi-component mixtures of different inorganic and organic components. They contain polishing, sweetening, and foaming agents, flavors, detergents, preservatives and different active ingredients. Among them are plaque inhibiting, antiphlo- gistic agents and fluorides as effective anti-caries agents. Today more than 95% of toothpastes contain fluorides for caries pre- vention. An effective toothpaste formula requires that fluoride is ∗ Corresponding author. Tel.: +49 3641 77 7201; fax: +49 3641 77 9279. E-mail address: H.Gleisner@analytik-jena.de (H. Gleisner). available to the enamel microenvironment in a bio-active form. Among the fluorides used are stannous fluoride (SnF 2 ), sodium flu- oride (NaF), sodium monofluorophosphate (Na 2 PO 3 F), and amine fluoride, which have different chemical and biological properties. SnF 2 was the first fluoride used in toothpastes in the USA since the end of the 1960s [6]. SnF 2 and NaF are highly soluble in water and supply the bio-active fluoride. Amine fluorides provide an effective bacterial protection reducing the bacteria-producing plaque; they dissociate in water to fluoride anions and an organic cation. It has been shown, however, that the abrasives used in tooth- paste can have a dramatic influence on the stability of available fluoride in the toothpaste formulas [7]. With aluminum and cal- cium containing abrasives the loss of added fluorides from NaF is about 60–90% after one-week storage at room temperature. Sodium bicarbonate and sodium metaphosphate are less harm- ful, but also inactivate about 20–25% of the added fluoride within nine months of storage. These stability problems due to a change of water soluble fluoride forms to insoluble ones are accompanied by 0731-7085/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jpba.2010.12.013