Flow injection electrochemical hydride generation inductively coupled plasma time-of-flight mass spectrometry for the simultaneous determination of hydride forming elements and its application to the analysis of fresh water samples

Abstract

A flow injection (FI) method was developed using electrochemical hydride generation (EcHG) as a sample introduction system, coupled to an inductively coupled plasma time-of-flight mass spectrometer (ICP–TOFMS) for rapid and simultaneous determination of six elements forming hydrides (As, Bi, Ge, Hg, Sb and Se). A novel low volume electrolysis cell, especially suited for FI experiments was designed and the conditions for simultaneous electrochemical hydride generation (EcHG; electrolyte concentrations and flow rates, electrolysis voltage and current) as well as the ICP–TOFMS operational parameters (carrier gas flow rate, modulation pulse width (MPW)) for the simultaneous determination of 12 isotopes were optimized. The compromise operation parameters of the electrolysis were found to be 1.4 and 3 ml min −1 for the anolyte and catholyte flow rates, respectively, using 2 M sulphuric acid. An optimum electrolysis current of 0.7 A (16 V) and an argon carrier gas flow rate of 0.91 l min −1 were chosen. A modulation pulse width of 5 μs, which influences the sensitivity through the amount of ions being collected by the MS per single analytical cycle, provided optimum results for the detection of transient signals. The achieved detection limits were compared with those obtained by using FI in combination with conventional nebulization (FI–ICP–TOFMS); values for chemical hydride generation (FI–CHG–ICP–TOFMS) were taken from the literature. By using a 200 μl sample loop absolute detection limits (3 σ) in the range of 10–160 pg for As, Bi, Ge, Hg, Sb and 1.1 ng for Se and a precision of 4–8% for seven replicate injections of 20–100 ng ml −1 multielemental sample solutions were achieved. The analysis of a standard reference material (SRM) 1643d (NIST, “Trace Elements in Water”) showed good agreement with the certified values for As and Sb. Se showed a drastic difference, which is probably due to the presence of hydride-inactive Se species in the sample. Recoveries better than 93% for Ge and Hg and 83.9% for Se were achieved on a spiked SRM sample. The developed method was successfully applied to the simultaneous multielemental determination of hydride forming elements in spring water samples originating from two different regions in Hungary.