Investigating the formation of an Sb(v)–citrate complex by HPLC-ICP-MS and HPLC-ES-MS(/MS)

Abstract

Complexation of Sb(V) with citrate has recently been shown to be of relevance in food chemistry. Here we characterize the products of the reaction of inorganic Sb(V) with citric acid by use of various chromatographic methods coupled on-line with inductively coupled plasma mass spectrometry (ICP-MS) and electrospray (ES)-MS(/MS). By use of HPLC-ICP-MS, estimates for the conditional formation constants are obtained for the main product of the reaction, the 1 ∶ 1 Sb(V)–citrate complex, present in reaction systems of pH 3, 5 and 7 (log K^cond = 4.6, 3.75 and 1.76, respectively). The physiological relevance of an Sb(V)–citrate complex was studied by use of HPLC-ICP-MS and ES-MS by evaluating: (1) the competition of Sb(V) and Al(III) for binding to citrate; (2) the competition of citrate and adenosine for binding to Sb(V); (3) the rate of reduction of inorganic Sb(V) and Sb(V)–citrate complex in the presence of L-cysteine; and (4) the formation of the Sb(V)–citrate complex in urine samples spiked with inorganic Sb(V). All results of this study suggest that the Sb(V)–citrate complex may be of physiological relevance, especially in the acidic cell compartments. A highly selective and sensitive detection method (SRM-ES-MS/MS) was developed for the screening of Sb(V)–citrate potentially present in biological samples.