Internal-standard-normalized process efficiency

Internal-standard-normalized process efficiency compares the overall preparation-and-response efficiency of an analyte with that of an internal standard. With matched corresponding amounts, let ${\mathrm{PE}}_A$ and ${\mathrm{PE}}_{IS}$ be their mass spectrometry process efficiencies. The normalized quantity iswhere $r$ denotes extraction recovery and MF a mass spectrometry matrix factor. It combines recovery matching with the internal-standard-normalized matrix factor.

The underlying separation between recovery and matrix response is important in quantitative mass spectrometry.^[ref] A ratio near one can conceal substantial losses affecting both signals.

For original stipulated values, let analyte and standard each have recovery $0.6$ and matrix factor $0.5$. Their process efficiencies are both $0.3$, so the normalized value is 1 even though each observed response is only 30% of its matched neat reference. Now change only standard recovery to $0.9$. Its process efficiency becomes $0.45$ and the normalized value becomes $0.3/0.45=2/3$, despite identical matrix factors.

Addition timing changes the comparison. If the standard is added after the extraction stage, its recovery through that stage is effectively 1 by construction. Equal matrix responses can then cancel while the analyte's preparation loss remains. A standard added earlier can track more of the process, but equivalent behavior still requires evidence.

The desired property is a stable, appropriately calibrated analyte-to-standard response relationship. A constant nonunity normalized efficiency can be incorporated into a valid calibration; an unmodeled change across samples or levels can bias results. Report the reference, addition stage, quantities compared and blank correction rather than treating normalization as a guarantee of full material recovery.