Simultaneous ultratrace analysis of antimony, arsenic and germanium species by hydride generation–cryotrapping–ICP-MS/MS: Focus on antimony in freshwaters

Abstract

A method is presented for the ultratrace analysis of antimony (Sb) species in natural water samples, performed simultaneously with the analysis of arsenic (As) and germanium (Ge) species. Compromise conditions enable efficient generation of volatile inorganic and methyl-substituted hydrides, which are cryotrapped, separated in a semi-automated system and detected by inductively coupled plasma mass spectrometry with triple quadrupole (ICP-MS/MS). Selective hydride generation (HG) from a TRIS buffer at pH 6, with or without L-cysteine for prereduction, distinguishes between trivalent and pentavalent Sb and As species. Limits of detection are in the low ng L⁻¹ for inorganic As and Sb, low tenths of ng L⁻¹ for methylated As species and a few hundredths of ng L⁻¹ for methylated Sb and Ge species, making the method suitable for natural waters. Speciation of Sb, As and Ge in SLRS-6 and AQUA-1 reference materials is presented. Main analytical challenges and key considerations are discussed, supported by a one-year monitoring of Sb, As and Ge species at (sub)ng L⁻¹ concentrations in Czech drinking water reservoirs. Limitations in quantifying methylated Sb species due to the absence of analytical standards are addressed. Conservation by HNO₃ preserves speciation well, but the selectivity of trivalent iAs and iSb determination in the presence of pentavalent species is affected. EDTA is effective in maintaining the oxidation state of Sb and As species; however, inorganic Ge must be analyzed within days due to the slow formation of stable EDTA complexes, which are inaccessible for HG.