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2.3. ProcedureMatrix-free standard solutions of fluorine, waste water reference standard and blanks were mixed with aluminum 3000 mg L−1 as the molecule forming element and aspirate to the flame at optimized conditions. Blank solution was 3000 g mL−1 aluminum as the nitrate. In order to prepare the toothpaste solution (or suspension), 1 g of sample was precisely weighed, dispersed in ultra pure water and completed to 50 mL again with ultra pure water. The mixture was homogenized in ultrasonic bath at 50 ◦C for 30 min and an aliquot of 5 mL was then immediately made up to 10 mL with 6000 g mL−1 of aluminum as the nitrate. In spite of an effective ultrasonic homogenization, the samples slowly precipitated upon waiting. Therefore, the mixture was vortexed for about 1 min prior to aspiration in to the flame. The samples were introduced as their suspensions (or dilute slurriy). The slurry was diluted to a certain level that it was aspirated like a solution without any problem (e.g. without clogging or deposition in the burner head and aspiration capillar tube). The results were given as the mean of 3 repetitive aspiration of each sample.
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