Speciation studies by capillary electrophoresis ? simultaneous determination of iodide and iodate in seawater

Abstract

A capillary electrophoresis (CE) method was developed for the simple and highly-sensitive determination of iodine species in seawater. The proposed method is based on the on-capillary preconcentration of iodide and iodate using the principle of transient isotachophoresis (tITP) stacking, and direct UV detection of the separated species at 226 and 210 nm, respectively. The preconcentration procedure takes advantage of the electrokinetic introduction of the terminating ion [2-( N-morpholino)ethanesulfonate (MES)] into the capillary, that enables a longer tITP state. The appropriate conditions for the tITP step were optimized by varying the MES and sample injection time and the concentration of cetyltrimethylammonium chloride (CTAC). The latter component of the separation electrolyte (SE) was shown to strongly affect the migration and therefore the enrichment of iodide due to specific ion-association. The optimized separations were performed in 12.5 mM CTAC, 0.5 M NaCl (pH 2.4). Valid calibration is demonstrated in the range 3-60 microg x L(-1) iodide ( R=0.9992) and 40-800 microg x L(-1) iodate ( R=0.9994). The detection limits achieved were 0.23 microg x L(-1) (2 nM) for iodide and 10 microg x L(-1) (57 nM) for iodate. Such sensitivity and linearity thresholds allowed the reported tITP-CE system to be applied to direct speciation analysis of surface and seabed seawater. The comparison of CE results with those of an ion-chromatography (IC) technique proved that the method has acceptable accuracy.

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.…”

Determination of Iodine and Bromine Compounds by Ion Chromatography/Dynamic Reaction Cell Inductively Coupled Plasma Mass Spectrometry

“…It is important to have highly sensitive analytical methods available for their determination. Several methods of ion chromatography (IC), liquid chromatography (LC), size-exclusion chromatography (SEC) and capillary electrophoresis (CE) coupled with different detection methods for iodine and bromine speciation have appeared, including UV detection, 2,6,7 inductively coupled plasma optical emission spectrometry (ICP-OES), 8,9 and inductively coupled plasma mass spectrometry (ICP-MS). 2,[9][10][11][12][13][14][15][16] However, all four species, namely Br − , BrO3 − , I − and IO3 − , have not been reported using a single procedure.…”

Determination of phosphate in seawater by CZE with on‐line transient ITP

“…We have developed CZE methods for simultaneous determination of nitrite and nitrate [25], and iodide and iodate [26] in seawater using artificial seawater as the BGE to eliminate the high salt interference and transient ITP as an on-line concentration procedure. Huang et al [27] have also established a transient ITP-CZE method for the determination of iodide and iodate in seawater. In addition, Okamoto et al [28] have developed a similar procedure for the determination of strontium and lithium in seawater.…”