Multivariate optimization for molybdenum determination in environmental solid samples by slurry extraction-ETAAS Original Research Article

A direct procedure to determine molybdenum in environmental solid samples (coal fly ash, sediment, soil and urban dust) by slurry extraction-electrothermal atomic absorption spectroscopy (SE-ETAAS) employing multivariate optimization is presented. Sample mass, ultrasonic power, HNO3 concentration and HCl concentration were the most important variables affecting the extraction of Mo, as Plackett–Burman designs put forward. Time of agitation revealed not significant (within the 10–100 s range), thanks to the focused ultrasonic agitation program employed throughout (using a USS-100 probe). Two Simplex, a regular and a modified one, were carried out to simultaneously optimize the HNO3 and HCl concentrations. Both Simplex converged to 14% (v/v) HCl and 10% (v/v) HNO3. Sample mass was studied by means of a univariate procedure (optimum at 50 mg). Furnace programs were studied using wall atomization with and without BaF2 as modifier, yielding similar results. Quantitative extraction was obtained, with good accuracy (ca. 90% recovery) and precision (R.S.D. < 9%), evaluated using five CRMs (coal fly ash SRM1633a, urban dust SRM1649a, marine sediments BCSS1 and PACS1, soil GBW07401). The limit of detection of the method was 0.1 μg g−1 (20 mg/1 mL slurry) and the characteristic mass was 9.5 ± 1.7 pg. Main advantages of the slurry extraction procedure are that it can be implemented directly on the autosampler cups, and that it is inexpensive and fast.