Quantification of Trace Elements in Natural Samples by Electrospray Ionization Mass Spectrometry with a Size-Exclusion Column Based on the Formation of Metal−Aminopolycarboxylate Complexes

Abstract

Metal ions were determined by ESI-MS in the negative ion mode as monovalent negative ions of their aminopolycarboxylic acid (APC) complexes, e.g., [Al(cydta)](-), [Pb(Hcydta)](-), where excess amounts of the APC agents were added to sample solutions. Among several APCs studied, we chose trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CyDTA) as the best chelating agent because of higher stabilities and higher sensitivities of the complexes. The ionization efficiency of these metal complexes was strongly affected by the presence of matrix salts, e.g., NaCl, KNO(3), and etc. Thus, a size exclusion column (Sephadex G-10) was used for the online separation of the metal-APC complexes from other matrix salts. This method was successfully applied to the quantitative analyses for total amounts of Al, Ni, Cu, Zn, and Pb in the biological certified reference materials, olive leaves (BCR-062) and plankton (BCR-414). The detection limits of the present methods for these elements were several to several ten nanomolar levels. Moreover, this approach was extended to determine ultratraces of fluoride based on the formation of the ternary complex of aluminum, fluoride and nitrilotriacetic acid (NTA), i.e., [AlF(nta)](-). Its detection limit was 10 nM and was 2 orders of magnitude better than that of a fluoride ion selective electrode method. This method was applied to determine fluoride in tap water, river water, and green tea samples.

Electrospray Ionization Mass Spectrometry for the Quantification of Inorganic Cations and Anions

“…In this paper, we review progress made in our laboratory over the last decade concerning the sensitive determination of metal ions, 7,13 halides, 7,14 cyanide, 14 and chromium species 15 using a simple ESI-quadrupole MS system.…”

“…Based on Ternary Complex Formation 7,14 3·1 Determination of ternary complex of halides, metal and APC So far, several techniques have been reported for the determination of halide anions by ESI-MS. [30][31][32][33] A direct determination of halide anions with an LOD of about 1 ppb has been reported, but a strong interference was observed due to the matrix effect. 30 The determination of inorganic anions as well as halides as ion-pairs with organic dications was studied by Armstrong, Dasgupta, and coworkers.…”

Highly Selective Detection of Trace Copper(II) Using Bathocuproinesulfonate by Flow-Injection Electrospray Ionization Mass Spectrometry

“…It has also often been used as an analytical method to measure the speciation of metal complexes, based on their nature. [1][2][3][4] Typically, a heavy metal ion in a water sample that is softly ionized by ESI forms various metal-hydration complexes. 5 Therefore, the coordination of a target metal ion and a chelating agent can prevent this hydration, and can effectively separate the ion from coexisting-ionic species.…”

“…For example, several researchers have reported [2][3][4] the quantification and speciation of metal complexes with chelating agents, such as ethylenediaminetetraacetate (EDTA) or diethyldithiocarbamate (DDC).…”

New Determination Methods of Halides and Cyanide Ions by Electrospray Ionization Mass Spectrometry Based on Ternary Complex Formation

“…The limit of detection (LOD) of this method is 10 nmol dm -3 , and currently it is one of the most sensitive methods for F -. 8 In this study, we extended this approach to the determination of other halide ions (X -= Cl -, Br -and I -), where negative ions of the ternary complexes of group-13 elements, NTA, and halides were measured by ESIMS. In particular, these halides were simultaneously determined by measuring [InX(nta)] -.…”