Nickel determination in oily sludge leachates using isotope dilution inductively coupled plasma mass spectrometry following photochemical vapor generation: A feasibility study

The feasibility of photochemical vapor generation for the production of volatile Ni species was evaluated and applied to the analysis of acetic acid leachates obtained from oily sludge samples. Sludge samples originating from a petrochemical plant were submitted to extraction using standardized procedures with solutions adjusted to pH 2.88 or 4.93, with acetic acid. The leachate solutions were subsequently treated with a mixture of acetic and formic acid and exposed to UV radiation from a Hg discharge lamp; the irradiated solution was pumped to a gas-liquid separator and the volatile species were transported by a stream of argon for detection using inductively coupled plasma mass spectrometry. Experimental variables, including the nature and concentration of low molecular weight acids, irradiation interval, carrier gas flow rate and the effect of concomitant species on the efficiency of photochemical production of volatile Ni species were systematically evaluated. Oxygenated anions, particularly nitrate, were found to suppress the analytical signal, whereas the effect of cationic species depended on the nature of the cation. Lead was found to induce substantial signal suppression even at ppb levels. Considering the significant influence of concomitant species on the overall efficacy of the photochemical process, isotope dilution calibration was adopted as a strategy to overcome non-spectral interferences. Under optimized conditions, relative standard deviations better than 8.5% were achieved, along with detection limits better than 40 μg L−1. The accuracy was statistically attested upon comparison of the results to those obtained from the analysis of leachates using sample introduction via pneumatic nebulization. The proposed photochemical vapor generation setup was proven efficient to carry out the determination of Ni in the leachates, although the technique is highly sensitive to the presence of concomitants.