In USP gravimetric methods, which procedure is explicitly listed as an assay method?

In USP gravimetric methods, which procedure is explicitly listed as an assay method?

• A. Direct ignition
• B. Sublimation
• C. Extraction
• D. Precipitation with ignition

Answer: (A)

In gravimetric analysis, you determine amount by weighing a residue that has been transformed into a stable, weighable form. The USP gravimetric assay procedures specify direct ignition as the official way to reach that weighable residue: you ignite the weighed sample until it reaches a constant weight, typically converting it to a stable oxide and removing any combustible material. This direct ignition step provides a reliable, known final mass that directly reflects the amount of analyte present, which is why it’s listed as the assay method.

The other techniques serve different roles in analysis. Sublimation is mainly a purification/separation step, extraction is used to separate components, and precipitation with ignition combines precipitation with ignition in some procedures but isn’t the standard assay method named in USP gravimetric methods.