On‐line preconcentration of perfluorooctanoic acid and perfluorooctanesulfonic acid by nonaqueous capillary electrophoresis

Abstract

Separation of major environmental pollutants as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) by capillary electrophoresis is reported for the first time. It is not possible to resolve the solutes in an aqueous media. However, the use of methanol and acetonitrile as the background electrolyte (BGE) solvents allowed their rapid separation in an uncoated capillary. A major effort was put into BGE optimization in respect to both separation efficiency and detection for further on-line preconcentration. 5 mmol.L⁻¹ naphthalene-1-sulfonic acid and 10 mmol.L⁻¹ triethylamine dissolved in ACN/MeOH (50:50 v/v) provided best separation and detection conditions. Next, the large-volume sample stacking and the field-amplified sample injection were applied and compared. Large-volume sample stacking improved limits of detection (LODs) with regard to the standard injection by 69 times for PFOA and 143 times for PFOS with LODs of 280 and 230 nmol.L⁻¹, respectively. Field-amplified sample injection improved LODs 624 times for PFOAand 806 times for PFOS with LODs 31 and 40 nmol.L⁻¹, respectively. Both preconcentration methods showed repeatabilities of migration times less than 1.2% RSD intraday and 6.6% RSD interday. The method was applied on PFOA and PFOS analysis in a sample of river water treated with solid-phase extraction, which further improved LOD toward 5.6 × 10⁻¹⁰ mol.L⁻¹ for PFOS and 6.4 × 10⁻¹⁰ mol.L⁻¹ for PFOA and allows the method to be used for river water contamination screening or decomposition studies.

Recent developments in methods for analysis of perfluorinated persistent pollutants

“…Further improvement of sensitivity of such determination can be expected by employing a special design of flow-cells with longer pathway, or with the application of laser induced fluorescence (LIF) detection with appropriate derivatization, as it was discussed above for HPLC methods. A substantial improvement of the detection limit in CE determination with indirect UV detection of PFOA, where also PFOS was determined, was recently reported with the use of non-aqueous BGE [77] (see example recording in Fig. 9b).…”

“…a Electropherogram recorded in for mixture of C6 to C12 PFCAs 0.1 mmol · L −1 each using as background electrolyte 50 mmol · L −1 Tris buffer of pH 9.0 with 7 mmol · L −1 2,4-dinitrobenzoic acid and 50 % methanol [74]. b Electropherogram recorded employing a large-volume sample stacking for mixture containing PFOA and PFOS 0.5 μmol · L −1 each using as background electrolyte solution of 5 mmol · L −1 NSA and 10 mmol · L −1 TEA in ACN/MeOH (50:50 v/v) [77]…”

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2012–2014)

“…The first is switch the polarity just before the stacked zone exits the capillary, and is typically done when the current reaches 90–95% of the BGE current. This approach was recently employed for the analysis of plant hormones , salidroside, caffeic acid, and gallic acid in leaf ; secobarbital, amobarbital, barbital, and phenobarbital in cosmetic products ; flavonoids , perfluorooctanoic acid, and perfluorooctanesulfonic acid in river water ; degradation products of alkyl alkylphosphonic acids in chemical warfare agent ; cephalosporins residue in environment water ; androgenic steroids drugs in urine ; antiepileptic drug in serum ; and metformine in human urine and serum .…”

Contemporary sample stacking in analytical electrophoresis

“…The separation of two major environmental pollutants, perfluorooctanoic and perfluorooctanesulfonic acid, by CE with UV detection at 214 nm was reported for the first time by Knob et al. . Because the solutes were insoluble in an aqueous medium, a BGE consisting of 5 mM naphthalene‐1‐sulfonic acid and 10 mM triethylamine in 50:50 ACN/methanol at pH 9.2 was used.…”