Quantitative analysis of metal ions in pharmaceutical and cosmetic products can be done using direct and indirect complexometric titrations employing concepts of complex formation, masking, and blocking. For example, all Fe3+, Mg2+, Al3+ and Zn2+ can form a complex with EDTA at pH 10. However, at pH 5, Mg-EDTA complex formation is inhibited, whereas at pH 2, only Fe-EDTA complex formation is favored. Knowing these, an analyst tried to determine the % composition of a 0.1000 g sample containing soluble salts of Fe3+, Mg2+, and Al3+. The sample was initially dissolved in 250.0 mL of distilled water. To determine the total ion content of the sample, a 50.00 mL aliquot was buffered to pH 10.00 before adding 50.00 mL of 0.0500 M EDTA, and the excess EDTA was back titrated with 24.18 mL of 0.0750 M standard Zn2+ solution until the EBT endpoint. Another 50.00 mL aliquot was buffered to pH 2.00 and was added with small amount of SCN- producing blood-red Fe(SCN)2+ complex. This was titrated with 0.0500 M EDTA, requiring 1.79 mL to reach the endpoint signaled by the discoloration of the blood-red complex. The resulting solution was then buffered to pH 5 and 50.00 mL of 0.0500 M EDTA was added in excess. The excess EDTA was back titrated with 0.0750 M standard Fe3+ solution, requiring 30.86 mL to reach the endpoint signaled by the reappearance of the blood-red Fe(SCN)2+ complex.
Quantitative analysis of metal ions in pharmaceutical and cosmetic products can be done using direct and indirect complexometric titrations employing concepts of complex formation, masking, and blocking. For example, all Fe3+, Mg2+, Al3+ and Zn2+ can form a complex with EDTA at pH 10. However, at pH 5, Mg-EDTA complex formation is inhibited, whereas at pH 2, only Fe-EDTA complex formation is favored.
Knowing these, an analyst tried to determine the % composition of a 0.1000 g sample containing soluble salts of Fe3+, Mg2+, and Al3+. The sample was initially dissolved in 250.0 mL of distilled water. To determine the total ion content of the sample, a 50.00 mL aliquot was buffered to pH 10.00 before adding 50.00 mL of 0.0500 M EDTA, and the excess EDTA was back titrated with 24.18 mL of 0.0750 M standard Zn2+ solution until the EBT endpoint. Another 50.00 mL aliquot was buffered to pH 2.00 and was added with small amount of SCN- producing blood-red Fe(SCN)2+ complex. This was titrated with 0.0500 M EDTA, requiring 1.79 mL to reach the endpoint signaled by the discoloration of the blood-red complex. The resulting solution was then buffered to pH 5 and 50.00 mL of 0.0500 M EDTA was added in excess. The excess EDTA was back titrated with 0.0750 M standard Fe3+ solution, requiring 30.86 mL to reach the endpoint signaled by the reappearance of the blood-red Fe(SCN)2+ complex.
Calculate the the following:
1. Fe (%w/w) in the sample. %(w/w)
2. Mg (%w/w) in the sample. %(w/w)
3. Al (%w/w) in the sample. %(w/w)
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