In calcium determination, which method's interference from phosphate is mitigated by adding lanthanum chloride?

In calcium determination, which method's interference from phosphate is mitigated by adding lanthanum chloride?

• A. O-Cresolphthalein complexone
• B. Precipitation with chloranilic acid
• C. Chelation with EDTA
• D. Atomic absorption spectrophotometry

Answer: (D)

Phosphate can interfere with calcium measurements by either forming insoluble calcium phosphate or by creating interfering species in the measurement system, which can skew results. Lanthanum chloride is added as a masking agent because La3+ binds phosphate strongly to form insoluble LaPO4, effectively removing phosphate from participating in interference with the calcium signal. This masking is a common practice in atomic absorption spectrophotometry for calcium, where the presence of phosphate would otherwise distort the reading. The other methods rely on different chemistries (colorimetric complex formation, precipitation, or chelation) and do not use lanthanum chloride to suppress phosphate interference, so they aren’t aided by this masking approach.

Phosphate can interfere with calcium measurements by either forming insoluble calcium phosphate or by creating interfering species in the measurement system, which can skew results. Lanthanum chloride is added as a masking agent because La3+ binds phosphate strongly to form insoluble LaPO4, effectively removing phosphate from participating in interference with the calcium signal. This masking is a common practice in atomic absorption spectrophotometry for calcium, where the presence of phosphate would otherwise distort the reading. The other methods rely on different chemistries (colorimetric complex formation, precipitation, or chelation) and do not use lanthanum chloride to suppress phosphate interference, so they aren’t aided by this masking approach.