Carrier element-free coprecipitation and speciation of inorganic tin in beverage samples and total tin in food samples using N-Benzoyl-N,N-diisobutylthiourea and its determination by graphite furnace atomic absorption spectrometry

A new, simple, rapid and selective separation, preconcentration and speciation of Sn(II) and Sn(IV) has been developed. The procedure is based on coprecipitation of Sn(II) on N-Benzoyl-N,N-diisobutylthiourea without carrier element. While Sn(II) can be quantitatively precipitated on N-Benzoyl-N,N-diisobutylthiourea in the pH range of 8.0-9.0, recovery of Sn(IV) was below 10%. Total tin was determined after the reduction of Sn(IV) to Sn(II) with 0.1M NaBH₄ in 1M NaOH solution. Sn(IV) concentrations were calculated as difference between total tin and Sn(II). Determination of tin concentrations was performed by graphite furnace atomic absorption spectrometry (GFAAS). Various analytical parameters including pH, amount of precipitant, sample volume, etc. were optimized. The effects of matrix ions were also examined. Enrichment factor was found as 50. The relative standard deviation was 5%. The detection limit was found 0.013μgL^-1 for Sn(II). The validation of this method was performed by using certificate reference materials (NIST SRM 1568a Rice flour and NRCC DORM-2 Dogfish muscle). Optimized method was applied to bottled mineral water, soda and ice tea samples for tin speciation. This procedure was also applied to microwave digested food samples for the determination of total tin.