Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab Towards the abatement of nitrate interference on selenium determination by photochemical vapor generation ☆ Alicia Mollo ⁎ , Moisés Knochen Química Analítica, Facultad de Química, Universidad de la República, Montevideo, Uruguay ARTICLE INFO Keywords: Photochemical vapor generation Nitrate interference abatement Selenium determination Trace analysis ABSTRACT A flow injection photochemical vapor generation atomic absorption spectrometry (FI-PVG-AAS) system was developed for selenium determination. The variables of influence of the photochemical generation process were evaluated and optimized. Sample already reduced to the Se(IV) state and mixed with the photochemical reagent (1.5% w/w HCOOH) was irradiated for 3 s. Selenium derivatives were transferred to an externally heated atomization cell by an argon-hydrogen mixture and selenium determined at 196.0 nm. Nitrogen was used as the carrier of the flow injection system. Nitrate is one of the most relevant interferents for the photochemical generation process; it is a very frequent concomitant as nitric acid is added for sample digestion or preservation. Hence, its removal before the vapor generation stage was studied. It was found that up to 3.0% w/w HNO 3 , it can be eliminated in the reduction stage of Se(VI) to Se(IV) with hydrochloric acid. For higher concentrations (up to 21% w/w HNO 3 ), prior to the reduction step, the addition of 40% w/w H 2 CO and evaporation almost to dryness was successful for the abatement of the interference. The performance of the method was studied and its ap- plicability evaluated with a Trace Element in Water Certified Reference Material (24.3 μgL -1 – Se, 2.8% w/w HNO 3 ) and a spiked rice-flour microwave-assisted digest (103.1 μgL -1 – Se, 18.5% w/w HNO 3 ). 1. Introduction Chemical vapor generation (CVG) is a well-established sample in- troduction technique for, among others, atomic absorption spectro- metry. The analyte metal ions in solution are transferred to the gaseous phase by means of a chemical reaction and driven by an inert gas to an externally heated quartz atomization cell for its determination. Sodium tetrahydroborate in strong acidic medium is the most extended redu- cing agent, and, the hydride, the volatile species released [1,2]. Photochemical vapor generation (PVG) is an alternative to CVG; the ultraviolet (UV) radiation interacts with the reaction medium creating a reducing environment where the volatile species of the analyte are generated. The analyte ion is reduced by radicals produced by the photolysis of a short chain aliphatic alcohol or carboxylic acid present in solution. According to the organic compound, the corresponding hydro- genated, carbonylated, alkylated analyte volatile species or their mix- ture are generated. The concentration of the organic compound should be optimized in order to allow adequate penetration of the photons so as to provide sufficient radicals to form the volatile species. The irradiation time as well, must be enough for the radical species gen- eration to promote the derivatization and to prevent its decomposition [3–6]. The acidity of the medium, the identity of the organic compound and its concentration, and the chemical species of the analyte determine the success of the photochemical vapor generation [3,4,7,8]. All these parameters must be optimized. Not every species of the element are able to generate volatile derivatives; Se(VI) oxidation state is not able to yield volatile species neither by CVG [1,2] nor by PVG [4].The most commonly used method for chemical reduction of Se(VI) to Se(IV) is by hot hydrochloric acid. The reduction rate has been found to be strongly dependent on the temperature and hydrochloric acid concentration; at higher acid concentration, lower temperatures are needed. Boiling is not recommended as selenium can be lost as SeCl 4 or SeOCl 2 [9–11]. An issue of concern in PVG is the presence of strong oxidants in the reaction medium. In the case of nitrate, it reacts with the reductant radicals decreasing its availability and yielding oxidizing species; the medium is no longer reductant and the formation of the volatile species is quenched. Furthermore the photo-induced reduction of nitrate leads to nitrite which in turn is a more severe interferent for the volatile species generation [12–16]. The permanence of the nitrogen oxides https://doi.org/10.1016/j.sab.2020.105875 Received 10 November 2019; Received in revised form 27 April 2020; Accepted 1 May 2020 ☆ Selected Paper from the Colloquium Spectroscopicum Internationale XLI & I Latin American Meeting on Laser Induced Breakdown Spectroscopy (CSI XLI - I LAMLIBS) held in Mexico City, Mexico, June 9–14, 2019. ⁎ Corresponding author. E-mail address: amollo@fq.edu.uy (A. Mollo). Spectrochimica Acta Part B 169 (2020) 105875 Available online 05 May 2020 0584-8547/ © 2020 Published by Elsevier B.V. T