Determination of oxoanions in river water by capillary electrophoresis

Abstract

A new capillary electrophoresis (CE) procedure was developed for simultaneous determination of ten oxoanions (CrO4(2-), SeO4(2-), MoO4(2-), WO4(2-), VO4(3-), SeO3(2-), As04(3-), TeO3(2-), TeO4(2-), and AsO3(3-)) which were baseline-separated from each other and from the interfering UV absorbing anions (NO3- and NO2-) commonly found in environmental water samples. The new background electrolyte system developed contained 5 mM potassium phosphate and 0.007 mM octadecyltrimethylammonium hydroxide, pH 11.2. The optimized working conditions were electrokinetic sampling at -5 kV for 10 s, running voltage at -15 kV with 5 microA current, and detection wavelength at 205 nm. No interference was observed for non-UV-absorbing anions and UV-absorbing anions up to 20 and 10 times higher concentrations respectively. The speed of analysis was fast, with a complete CE run within 6 min. Wide linear ranges (1-2,000 microg/L), good repeatability in migration time (relative standard deviation RSD 0.55-2.8%), satisfactory precision in peak area (RSD 3.8-5.6%) and peak height (RSD 3.9-5.3%) measurement, and detection limits (1-25 microg/L) sufficiently sensitive to detect oxoanions found in environmental water samples were obtained. The reliability of the CE procedure developed had been established by recovery test and parallel method determination using atomic absoprtion spectrophotometry for real river water sample.

Speciation of oxidation states of elements by capillary electrophoresis

“…The CE system with phosphate BGE showed a higher efficiency than ion-chromatography with common conductivity detection with regard to separation, detection limits, and reproducibility in the separation of thio-and oxothioarsenates [54] (Figure 2). Arsenite and arsenate were also determined with detection limits 2 and 15 ppb, respectively, in the presence of 8 other oxoanions of Cr, Se, Mo, W, V, and Te [51], and good recovery and determination were presented for river water spiked with 50 ppb of both forms. The electrolyte contained 5 mM potassium phosphate, 0.007 mM octadecylammonium hydroxide, pH 11.2, and direct UV detection at 205 nm was used.…”

“…The separation was achieved with 5 mM chromate BGE of pH 11.2 containing 0.5 mM trimethyltetradecylammonium hydroxide. Much better limits of detections were recently obtained in a CE system with direct UV (k = 205 nm) detection, i. e. 5 to 10 ppb for tellurite and tellurate [51]. Excellent fast and effective baseline separation of 12 oxoanions was obtained with 5 mM phosphate buffer of pH 11.2, containing 0.007 mM octadecyltrimethylammonium hydroxide.…”

“…However, the limit of detection was twice as high as for selenite with UV detection. The CE systems with direct UV detection were developed for studying the depletion of both selenium oxoanions in bacterial suspensions with successful resolution from matrix peaks [67] and for determination of selenium oxoanions in water [51]. The baseline separation from oxoanions of other trace elements such as As, Cr, Mo, Te, W, and V was obtained using 5 mM potassium phosphate of pH 11.2 with 0.007 mM octadecyltrimethyl ammonium hydroxide as BGE.…”

“…Typical examples are the determination of these oxoanions in rainwater samples [96], and a procedure had even been developed for their determination in individual and size-classified rain drops [97]. Direct UV detection was employed, for instance, in determination of nitrate and nitrite with polymer-coated capillaries [98,99] and in a recently reported sensitive procedure developed for determination of oxoanions with phosphate BGE [51]. A very sensitive determination was reported with suppressed conductivity detection [85,86], where the determination of another nitrogen species, azide, was also included [85].…”