Evaluation of capillary electrophoresis combined with a BCR sequential extraction for determining distribution of Fe, Zn, Cu, Mn, and Cd in airborne particulate matter Original Research Article

This work continues an evaluation of a previously developed capillary electrophoresis (CE) method to determine the distribution of Fe, Zn, Cu, Mn, and Cd in airborne particulate matter (PM) after sequential extraction. A three-stage extraction procedure following the BCR protocol was used to chemically fractionate metals between (F1) “exchangeable water and acid-extractable” (0.11 M acetic acid), (F2) “reducible” (0.1 M hydroxylamine hydrochloride acidified to pH 2.0 with nitric acid) and (F3) “oxidizable” (1.0 M ammonium acetate extraction after oxidation by 8.8 M hydrogen peroxide) PM fractions. The reliability and applicability of the developed procedure were tested using NIST 1648 Urban Air Particulate Matter. Small-scale extractions (10 mg mass in 1 ml extractant) have been used. The work has been focused on (i) the optimization of CE experimental conditions for sensitivity measuring trace metals in the BCR extractants and (ii) speeding up BCR extraction by finding a set of sonication conditions giving recoveries similar to conventional extraction for the metals of interest. The CE method was validated with respect to linearity, detection limits, precision, and accuracy. Detection limits were at low-μg/l (μg/g) and mid-μg/l (tens of μg/g) levels using electrokinetic and pressure injection modes, respectively. The efficiency of the accelerated BCR extraction method using an ultrasonic bath was evaluated, for each metal in each fraction, as a percent recovery of the conventional method. With the exception of iron (45.0 and 55.2%, respectively, in F1 and F2 fractions), the results attempted from ultrasonic extraction for all metals were reasonably comparable with those obtained using the conventional BCR procedure. The optimized procedure was found to be precise (typically R.S.D.<10%) for all metals in all fractions. Detailed fraction-specific concentration data are presented, based on six replicates, for Fe, Zn, Cu, Mn, and Cd in NIST 1648 PM using both accelerated and conventional BCR extraction. Taking into account that the overall extraction time was reduced from 48 to 2 h, the proposed analytical methodology provides a promising approach to obtain information about origin, mode of occurrence, and/or potential bioavailability of metals in airborne particulate matter with a much shorter operating time.