Spectrophotometric determination of trace molybdenum in plants and seeds with 3,5-dibromo-4-hydroxyphenylflurone

A novel spectrophotometric method based on a new reagent, 3,5-dibromo-4-hyd roxyphenylflurone, was developed for the determination of molybdenum in pla nts and seeds. 3,5-Dibromo-4-hydroxyphenylflurone showed outstanding analyt ical characteristics for spectrophotometric determination of molybdenum. Th e reaction conditions are simple and stable. In 0.2 mol l(-1) phosphoric ac id medium (which can combine with iron and other metal ions and greatly imp roves the selectivity of the color system), molybdenum(vi) reacts with 3,5- dibromo-4-hydroxyphenylflurone to form a 1:2 red complex with an absorption maximum at 530 nm, the color reaction can completed in 2 min and the absor bance of the molybdenum complex remains stable for at least 72 h at room te mperature. Its stability constant is 1.21 x 10(28) at 25 degreesC. Beer's l aw is obeyed over the range 0-0.6 mug ml(-1) Mo(vi). The reagent has very h igh sensitivity and selectivity; the molar absorptivity of the complex is 1 .35 x 10(5) l mol(-1) cm(-1) and the limit of quantification, the limit of detection and relative standard deviation (n = 10) were found to be 6.7 ng ml(-1), 2.2 ng ml(-1) and 1.01%, respectively. Cu (50000-fold), Fe (20000-f old), K (20000-fold), NH4+ (20000-fold), Mg (15000-fold), Zn (10000-fold), Na (10000-fold), Al (4000-fold), Ca (25000-fold), Mn (2000-fold), Ce (500-f old), Cr (400-fold) and Bi (200-fold) do not interfere with the determinati on of trace levels of molybdenum up to the excesses indicated. The selectiv ity is much superior to that of other published methods. The proposed metho d was applied to the direct determination of molybdenum in plants and seeds with satisfactory results. The synthesis of the reagent and conditions of color reaction were studied in detail.