Technically, this is not a dilution factor, but a scaling-up factor. You take 0.5059 g of the solid and your analyte solution is 100 mL. But the AAS reading comes as mg/L. Whether you work with 100 mL or 1 L, the concentration is still the same. However, when you convert mg/L solution into mg/g (or kg) of solid sample (before digestion), then you factor in a 10 thus: 0.1 L*0.2887 mg/L = 0.02887 mg (of whatever metal you were analyzing, which was present in the 0.5059 g of solid sample you digested); 0.02887 mg(metal)/0.5059 g(sample) * (1000 g/1 kg sample) = 57.067 mg(metal)/kg(sample).

100 mL = 0.1 L, right?

Okay got it. Thanks a lot.

Concentration of sample and Concentration of blank are very critical to make μg/mL. dilution factor is important to calculate (if original solution is diluted) = dilution volume (mL /original aliquot volume (mL) used for dilution.

i think you are definitely right.