Sample introduction remains as a critical step in analytical methods associated to inductively coupled plasma mass spectrometry (ICP-MS). Hence, the search for a straightforward technique that would allow analyte/matrix separation prior to ICP-MS detection has lead to the development of photochemical vapor generation (PVG) systems that could be coupled to ICP-MS. Photochemical vapor generation relies on the formation of volatile species of ionic analytes prepared in low molecular weight carboxylic acids solutions (typically) upon UV irradiation. Our group has focused on the investigation of PVG using a simple photoreactor assembled using two 40 W UV lamps emitting at 257 nm, on top of which a quartz capillary with a capacity of 6.5 mL is positioned. Acetic and formic acids, either individually or mixed in concentrations that range up to 40%, have been evaluated as to its efficiency in forming volatile species of elements such as Ni, Co, Fe, Hg and Te and also Au, Pd, Pt, Rh and Ir. The former group of elements benefited from a mixture of acetic and formic acid at 15% v/v each, whereas the noble metals provided higher sensitivity using formic acid individually. The experimental parameters, which include irradiation period, RF power, carrier gas flow rate and sample flow rate have all been investigated and optimized aiming at higher sensitivity. The effect of concomitant species, particularly oxygenated anions, has been thoroughly investigated. As predicted, nitrate is the most critical species, as even relatively low concentrations (sub-ppm) result in significant signal suppression for all investigated analytes. Therefore, quantification has been carried out using standard addition calibration and, particularly for Ni, isotope dilution calibration has been the technique of choice. A set of (undigested) samples, consisting on oily sludge leachates, seawater and biodiesel, have been analyzed following the optimized conditions for PVG for each group of analytes. Recovery tests were satisfactory and the analytical results were also compared to those obtained using sample digestion and pneumatic nebulization ICP-MS. Detection limits ranging from 0.07 to 5.0 ng mL<sup>-1</sup> were obtained, attesting the good detection capability of the developed methods. Overall, PVG was proven effective for the formation of volatile species of the investigated analytes under the given conditions.

Photochemical vapor generation for the quantitative analysis of transition elements by ICP-MS: A feasibility investigation

256th National Meeting (2018)

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