Optimization study of suitable pre-reduction agents for selenium analysis in tomato samples by flow injection-hydride generation atomic absorption spectrometry

The pre-reducing agents for Se speciation analysis were subject to optimize under the online reduction conditions of flow injection-hydride generation atomic absorption spectrometry using 2 M HCl as a carrier solution and 0.3% (w/v) NaBH4 in 0.2% (w/v) NaOH as a reducing agent. For total Se, the pre-reduction of Se6+to Se4+must be completed when optimizing the prereducing conditions using (i) conc. HCl, (ii) 5% (w/v) KBr/conc. HCl, (iii) 15% (w/v) KBr/ dilute HCl and (iv) 10% (w/v) thiourea/conc. HCl, under heating for 30 min to overcome their matrix effects on the calibration curve using either Se4+ or Se6+ as standard compound. From the results, all of these pre-reducing agents, except that in the presence of thiourea interfered only the calibration curve using Se4+, could be used with both Se species as expressed in terms of their conversion factors of 98-116% and 81-103% for Se4+ and Se6+, respectively. The linear range was obtained between 5-25 μg/L with 0.5 μg/L LOD and 2 μg/L LOQ. The optimal prereducing agent was applied for real tomato varieties, resulting in almost satisfactory recoveries (75.6-115.9%). The Se contents in these samples were found to be 0.07-0.10 μg/g, 0.43-0.92 μg/g and 0.50-0.99 μg/g for Se4+, Se6+ and total Se, respectively.