Selective Sweeping Of Overloaded Zn(â…¡) And Transient Isotachophoresis Of Trace Metals In Highly Saline Samples

When trace metals such as Fe²⁺ and Ni²⁺ in a highly saline sample are analyzedby transient isotachophoresis (tITP), Masking of Zn²⁺ often overloaded in transient isotachophoresis (tITP) of trace metals in a highly saline physiological sample was achieved by using thioglycolic acid (TGA) in the background electrolyte (BGE).However, the trace amounts of Fe²⁺ and Ni²⁺ in the same samples as their anionic complexes with 4-(2-pyridylazo) resorcinol (PAR) could be successfully stacked by transient isotachophoresis and determined without interference from the excessiveamount of Zn²⁺ . tITP stacking of Fe-PAR and Ni-PAR was induced by the sample chloride acting as a leading electrolyte where free-PAR in the sample acted as a terminating electrolyte. A selective sweeping mechanism could be described as means of masking in CE which includes dynamic complexation and sweeping of a particular metal ion selectively from the sample. The optimized BGE was composed of 95 mM N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid and 0.1 mM PAR, 2 mM TGA and 0.02% FC-PN (a fluorocarbon neutral polymeric surfactant) and adjusted to pH 9.0 with triethylamine,. Using our method several hundred-fold enhancements in the absorbance response of Fe-PAR and Ni-PARpeaks was achieved in highly saline samples compared to the normal CE mode ofinjection even in the several thousand-fold excess of Zn²⁺ in the sample. The limitsof detection (S/N = 3) were in the sub-ppb range (Fe²⁺ 0.3 ppb, Ni²⁺ 0.2 ppb). Themethod was successfully applied to determine the trace amounts of Fe²⁺ and Ni²⁺ in the standard reference urine and human urine samples containing excessive amounts of Zn²⁺.