Trace ion analysis of seawater by capillary electrophoresis: Determination of iodide using transient isotachophoretic preconcentration

Abstract

An improved transient isotachophoresis (tITP) procedure for the preconcentration of iodide from highly saline matrices was developed with the objective to quantify iodide in seawater by capillary electrophoresis (CE). The procedure takes advantage of introducing cetyltrimethylammonium chloride into the high-sodium chloride background electrolyte, which due to a specific interaction with iodide amended placement of the analyte at a large distance from the matrix chloride (the latter performed the role of a leading anion). Computer simulation showed that 2-(N-morpholino)ethanesulfonate could be adopted as a suitable terminating ion to enable isotachophoretic focusing at the beginning of the CE run. Under optimized tITP conditions, the sensitivity response of iodide was improved by a factor of 140 over normal CE mode. This allowed for direct UV detection of as low as 0.6 microg/L iodide and made feasible CE analysis of undiluted surface seawater samples where iodide was found at a 30 microg/L level. The applicability of the proposed tITP-CE method could apparently be extended to the determination of other trace seawater anions (e.g., iodate).

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips

“…In the area of seawater analysis, Hirokawa and Timerbaev [62][63][64][65] and the group of Fukushi [66,67] have used tITP for the analysis of inorganic constituents. Seawater contains a high concentration of chloride which, combined with its high electrophoretic mobility, allows it to function perfectly as a leading ion to stack trace anionic components by tITP provided a suitable terminating ion is used.…”

Dynamic computer simulations of electrophoresis: A versatile research and teaching tool

“…In the area of environmental analysis, Hirokawa et al [202] used SIMUL to simulate the electrokinetic injection of cations with and without the hydrodynamic injection of potassium acetate. Following this, they presented simulation results for the tITP stacking of iodide in seawater [202,203]. Another report of note in the area of tITP is that by Schwer et al [47] who used SIMUL 4.0 to examine tITP stacking with a discrete pH difference between the leading and terminating electrolytes.…”

Determination of organic anions in atmospheric aerosol samples by capillary electrophoresis after reversed pre‐electrophoresis

“…Also, in the existing applications of ITP not more than three analytes are commonly concentrated and simultaneously measured [20]. The use of high-conductivity BGEs have been reported as a useful and easy way to achieve a field-amplified stacking effect for highsaline samples, and is frequently combined with ITP [14,15], but these BGEs can generate problems due to excessive Joule heating and the fact that the sample matrix is not eliminated but also concentrated.…”

“…These samples require an off-line sample cleanup [12,13] prior to the CE analysis. As an alternative, various online methodologies have been developed to overcome these limitations, including transient ITP [14][15][16] and the use of highconductivity electrolytes [17][18][19]. Transient ITP has been demonstrated to be useful for the determination of highly saline natural waters and biological samples [20], but this methodology can cause problems when samples with complex matrices are analyzed or the content of major sample components varies [21].…”