A HIGHLY SENSITIVE AND SELECTIVE SPECTROFLUORIMETRIC METHOD FOR THE DETERMINATION OF LITHIUM AT PICO-TRACE LEVELS IN SOME REAL, PHARMACEUTICAL FORMULATIONS, BIOLOGICAL FLUIDS, SOIL AND FOOD SAMPLES USING 5,7-DIBROMO-8-HYDROXYQUINOLINE

Ayesha Afrin, Tanjina Akhter and M. Jamaluddin Ahmed*

ABSTRACT

A very simple, rapid, ultra-sensitive, highly selective and non-extractive spectrofluorimetric method for the determination of lithium at pico-trace levels using 5,7-dibromo-8-hydroxyquinoline(DBHQ) has been developed. DBHQ reacts in a slightly acidic (0.0003-0.0015 M H2SO4) aqueous solution with lithium in 30% ethanolic media and to form intensely fluorescent chelate, which has high fluorescence intensity (ex =278 nm; em=342 nm). The reaction is instantaneous and the fluorescent intensely remain stable for the period between 1 min and 24 h. Linear calibration graphs were obtained for 0.001- 400-μg L-1 of Li, with a R2 = 0.99987, having a detection limit of 0.1-ng L-1; the quantification limit of the reaction system was found to be 1-ngL-1 and the RSD was 0-3%. The stoichiometric composition of the chelate is 1:1 (Li:DBHQ). A large excess of over 60 cations, anions and complexing agents (like, chloride, phosphate, azide, tartrate, oxalate, SCN- etc.) do not interfere in the determination. The developed method was successfully used in the determination of lithium in several Certified Reference Materials (alloys, steels, sediments, human hair, bovine liver, fresh water, and rice flour) as well as in some lithium in commercial pharmaceutical formulations (tablet, syrup, drop and capsule) and biological fluids (human blood, urine and milk), soil, food samples. The results of the proposed method for assessing biological, food and pharmaceutical samples were comparable with ICP-OES and were found to be in excellent agreement. The results of the proposed method for assessing pharmaceutical samples were also comparable with the Official method stated in the U. S. Pharmacopoeia and were found to be in an excellent agreement. The method has high precision and accuracy (s ±0.01for 0.5μgL-1).

Keywords: Spectrofluorimetry; lithium determination; pharmaceutical formulations; biological fluids; food and vegetables samples.