In-situ Ti-Ir and ammonium thiocyanate modifiers for improvement of sensitivity of Sc to sub parts per billion levels and its accurate quantification in coal fly ash and red mud by GFAAS.

A new analytical method for the determination of scandium at parts per billion levels in an industrial by products such as red mud and coal fly ash has been developed. Current technology developments demand for routine testing of Sc in various samples and for simple methods to use. Graphite furnace atomic absorption spectrometry (GFAAS) meets these requirements, but its detection limit is often too high due to Sc peak tailing problem, likely caused by carbide formation. This issue is resolved, and sensitivity is enhanced, by using permanent, conventional and sulfate-based modifiers and optimizing operational parameters. Maximum sensitivity and optimal peak shape are achieved using a mixed solution of 250 μg each of Ti and Ir, with 1 % ammonium thiocyanate as an in-situ modifier. Sensitivity is further enhanced by an in-situ furnace pre-concentration by multiple injection mode, yielding a detection limit of 0.2 ng mL and a characteristic mass of 11 pg. The method is validated using scandium-based NIST SRM 1633b coal fly ash and spiked recovery studies on coal fly ash and red mud. A rapid leaching procedure for Sc from coal fly ash is optimized. Scandium concentrations obtained via the proposed method are compared with ICP-OES results, showing good agreement. The trueness of the method expressed as the percentage deviation of the method value from the corresponding true value was found to be 4.3 % for determination of Sc in the coal fly ash and 2.1 % for red mud. The relative standard deviation (RSD) is found to be 5 %.